The document summarizes key concepts about elimination reactions, including the E1 and E2 mechanisms. It discusses how the identity of the base, leaving group, and substrate affect the reactivity and selectivity of elimination reactions. Stereochemistry is also addressed, including the E2 reaction's preference for the anti-periplanar orientation and consequences for cyclic substrates. The Zaitsev rule is explained for regioselectivity. Strong bases generally favor the concerted E2 mechanism while weaker bases favor the stepwise E1 mechanism.
The document discusses elimination reactions, which involve the loss of elements from a starting material to form a new π bond in the product. There are two main mechanisms for elimination reactions - E1 and E2. The E1 mechanism is unimolecular and involves the leaving group departing before π bond formation. The E2 mechanism is bimolecular and concerted, with both bond cleavages and formations occurring simultaneously. Strong bases promote the E2 mechanism, while weaker bases favor E1. The type of reaction also depends on the nucleophilicity and size of the reactants.
The document summarizes the E2 elimination reaction.
1) The E2 reaction involves the concerted removal of a β-proton by a base and loss of a halide ion in a single step with no intermediate.
2) It is a second-order reaction that depends on both the base and substrate concentrations. The reaction proceeds through a transition state in which the β-proton and halide leave simultaneously to form an alkene.
3) Factors that increase the rate of the E2 reaction include stronger bases, better leaving groups, more substituted substrates, polar aprotic solvents, and bulky or conjugated substrates. The reaction favors antiperiplanar elimination to form the
1. The document outlines different elimination reaction mechanisms including E2, E1, and E1cb.
2. It discusses the regiochemistry and stereochemistry of elimination reactions and how Zaytzeff's rule and Hofmann's rule apply.
3. The key differences between the E2, E1, and E1cb mechanisms are described along with factors that determine whether substitution or elimination will occur for a given reaction.
1) Elimination reactions occur when two atoms or groups are removed from two adjacent carbon atoms of a substrate molecule to form a multiple bond.
2) Elimination occurs when a nucleophile attacks a hydrogen instead of a carbon.
3) In an E1 elimination reaction, the leaving group leaves in the rate-determining unimolecular step, and the proton is removed in a separate second step.
E1 elimination reactions proceed by a unimolecular mechanism involving the formation of a carbocation intermediate. The rate depends on the concentration of the reactant. There are two steps: 1) formation of the carbocation and 2) removal of a proton from an adjacent carbon by the base to form the alkene product. The orientation and stereochemistry of product formation is influenced by stability factors. The rate is affected by the stability of the carbocation, the leaving group ability, the base strength, and the solvent polarity. E1 reactions are useful for converting monoenes to dienes and trienes, and in vitamin interconversions.
1) Alkyl halides can undergo elimination reactions (E1 and E2) in addition to substitution reactions. E2 reactions involve a concerted removal of the halide leaving group and a proton, while E1 reactions proceed through a carbocation intermediate.
2) The rate and mechanism of elimination reactions depend on factors like the structure of the substrate, the base used, and solvent. E2 favors less substituted alkene products following Zaitsev's rule, while E1 can form either stereoisomer and favors more substituted alkenes.
3) Conditions like strong base, aprotic solvent, and high temperature promote elimination over substitution. Tertiary alkyl halides undergo only elimination
The E1 reaction involves the slow loss of a leaving group to form a carbocation intermediate. This allows rearrangements to occur. A base is not required for the rate determining step. The E2 reaction is an elimination reaction that results in a product with one more degree of unsaturation. The SN1 reaction involves the formation of a carbocation intermediate through a unimolecular rate determining step. This can allow for nucleophilic attack from either side and possible racemization. The SN2 reaction involves synchronous breaking of one bond and formation of another in one step, leading to inversion of configuration.
Elimination reactions can occur by either E1 or E2 mechanisms. In an E1 reaction, the rate-determining step is the unimolecular formation of a carbocation intermediate. In an E2 reaction, the rate depends on both the substrate and base concentrations, and it involves a single concerted step without an intermediate. The E1 pathway favors more stable carbocation intermediates and products, while the E2 transition state leads directly from starting material to product.
The document discusses elimination reactions, which involve the loss of elements from a starting material to form a new π bond in the product. There are two main mechanisms for elimination reactions - E1 and E2. The E1 mechanism is unimolecular and involves the leaving group departing before π bond formation. The E2 mechanism is bimolecular and concerted, with both bond cleavages and formations occurring simultaneously. Strong bases promote the E2 mechanism, while weaker bases favor E1. The type of reaction also depends on the nucleophilicity and size of the reactants.
The document summarizes the E2 elimination reaction.
1) The E2 reaction involves the concerted removal of a β-proton by a base and loss of a halide ion in a single step with no intermediate.
2) It is a second-order reaction that depends on both the base and substrate concentrations. The reaction proceeds through a transition state in which the β-proton and halide leave simultaneously to form an alkene.
3) Factors that increase the rate of the E2 reaction include stronger bases, better leaving groups, more substituted substrates, polar aprotic solvents, and bulky or conjugated substrates. The reaction favors antiperiplanar elimination to form the
1. The document outlines different elimination reaction mechanisms including E2, E1, and E1cb.
2. It discusses the regiochemistry and stereochemistry of elimination reactions and how Zaytzeff's rule and Hofmann's rule apply.
3. The key differences between the E2, E1, and E1cb mechanisms are described along with factors that determine whether substitution or elimination will occur for a given reaction.
1) Elimination reactions occur when two atoms or groups are removed from two adjacent carbon atoms of a substrate molecule to form a multiple bond.
2) Elimination occurs when a nucleophile attacks a hydrogen instead of a carbon.
3) In an E1 elimination reaction, the leaving group leaves in the rate-determining unimolecular step, and the proton is removed in a separate second step.
E1 elimination reactions proceed by a unimolecular mechanism involving the formation of a carbocation intermediate. The rate depends on the concentration of the reactant. There are two steps: 1) formation of the carbocation and 2) removal of a proton from an adjacent carbon by the base to form the alkene product. The orientation and stereochemistry of product formation is influenced by stability factors. The rate is affected by the stability of the carbocation, the leaving group ability, the base strength, and the solvent polarity. E1 reactions are useful for converting monoenes to dienes and trienes, and in vitamin interconversions.
1) Alkyl halides can undergo elimination reactions (E1 and E2) in addition to substitution reactions. E2 reactions involve a concerted removal of the halide leaving group and a proton, while E1 reactions proceed through a carbocation intermediate.
2) The rate and mechanism of elimination reactions depend on factors like the structure of the substrate, the base used, and solvent. E2 favors less substituted alkene products following Zaitsev's rule, while E1 can form either stereoisomer and favors more substituted alkenes.
3) Conditions like strong base, aprotic solvent, and high temperature promote elimination over substitution. Tertiary alkyl halides undergo only elimination
The E1 reaction involves the slow loss of a leaving group to form a carbocation intermediate. This allows rearrangements to occur. A base is not required for the rate determining step. The E2 reaction is an elimination reaction that results in a product with one more degree of unsaturation. The SN1 reaction involves the formation of a carbocation intermediate through a unimolecular rate determining step. This can allow for nucleophilic attack from either side and possible racemization. The SN2 reaction involves synchronous breaking of one bond and formation of another in one step, leading to inversion of configuration.
Elimination reactions can occur by either E1 or E2 mechanisms. In an E1 reaction, the rate-determining step is the unimolecular formation of a carbocation intermediate. In an E2 reaction, the rate depends on both the substrate and base concentrations, and it involves a single concerted step without an intermediate. The E1 pathway favors more stable carbocation intermediates and products, while the E2 transition state leads directly from starting material to product.
Factors that affect the rate of elimination reactions include the attacking base, leaving group, and reaction medium. A strong base is required for an E2 reaction to remove a weakly acidic hydrogen. A good leaving group is stable and weakly binds electrons, making it easier to form the carbocation intermediate. A polar solvent can stabilize charged carbocation intermediates in E1 reactions, making it the preferred medium, while a non-polar solvent favors the uncharged transition state of E2 reactions.
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The document discusses elimination reactions of alkyl halides. It begins by defining elimination reactions as those that involve the loss of elements from a starting material to form a new pi bond in the product. Specifically, it focuses on dehydrohalogenation reactions, where removal of HX occurs. The most common mechanism is E2 elimination, which is a bimolecular reaction promoted by a strong base. It follows second-order kinetics and has a single transition state. The document discusses characteristics of E2 reactions like Saytzeff's rule, Markovnikov's rule, anti-Markovnikov reactions, stereochemistry and stereoselectivity.
The E2 reaction mechanism involves the base-induced elimination of a hydrogen and halide atom from an alkyl halide, forming an alkene product. The reaction proceeds through a concerted bimolecular transition state where the C-H bond breaks as the C-X bond forms. Stereoselectivity is determined by whether the anti or syn orientation is preferred. Cyclic compounds exhibit varying degrees of stereoselectivity depending on ring size. The orientation of the double bond in the product can be predicted by either Hofmann or Saytzev rules based on the stability of the carbocation intermediate.
1) The document discusses different types of elimination reactions, including E1, E2, and E1cB mechanisms.
2) E1 reactions involve the generation of a carbocation intermediate, while E2 reactions occur in one step without intermediates. E1cB reactions first form a carbanion intermediate before the leaving group departs.
3) The mechanism depends on factors like the substrate, leaving group, solvent, and strength of the base used. Zaitsev's, Hofmann, and Bredt's rules also influence the regiochemistry of double bond formation.
The overall rate equation for this reaction is:
Rate = k[R-R-OH][H2O]
Where k is the rate constant and [R-R-OH] and [H2O] are the concentrations of the reactants R-R-OH and H2O, respectively.
Elimination reactions proceed by either an E1 or E2 mechanism. E1 reactions are favored with weak nucleophiles and follow Zaitsev's rule, while E2 reactions occur with strong nucleophiles and favor the formation of trans alkenes. E2 reactions follow both Zaitsev's and Hofmann's rules in determining the most stable alkene product. The choice between substitution and elimination depends on factors like the strength of the base/nucleophile and steric effects. Addition reactions allow for functionalizing alkenes and alkynes through hydration, halogenation, oxidation, hydroboration, conjugate addition and reduction reactions. Industrial processes exploit specific addition reactions, like the synthesis
1. Alkyl halides can undergo nucleophilic substitution or elimination reactions. Nucleophilic substitution reactions include SN2 and SN1 mechanisms, while elimination reactions include E1 and E2 mechanisms.
2. The type of reaction depends on factors like the structure of the alkyl halide, the nucleophile, the base, and the solvent. Primary alkyl halides favor SN2, while tertiary alkyl halides favor SN1 or E1/E2 in protic solvents.
3. The chapter examines these reaction mechanisms in detail to understand how they occur and how their characteristics can be used to predict and control reaction outcomes.
Pyrolytic elimination reactions involve the application of heat to induce an elimination reaction in an organic substrate without the need for an external base or solvent. This type of elimination proceeds through a concerted, syn-elimination via a cyclic transition state that allows for an intramolecular proton transfer and the formation of a new carbon-carbon double bond. Specific examples of pyrolytic eliminations discussed in the document include the conversion of esters to carboxylic acids and alkenes, eliminations in alicyclic systems, Cope eliminations, sulfoxide eliminations, xanthate pyrolysis, and selenoxide eliminations.
This document discusses elimination reactions where a small molecule is removed from a reactant. It describes the elimination of HBr from bromoalkanes using a dilute NaOH solution, which can cause either a substitution or elimination reaction depending on conditions. The two types of elimination reactions are E2, a bimolecular process without intermediates typical of primary/secondary halides, and E1, a unimolecular reaction with a carbocation intermediate typical of tertiary halides. Hydroxide acts as a base by accepting a proton from the alkyl halide, initiating electron movement that forms a C=C double bond and removes the halide.
This document discusses elimination reactions, specifically E1 and E2 reactions. It explains that E1 reactions proceed through a carbocation intermediate and involve a two-step mechanism, while E2 reactions are concerted and involve both the alkyl halide and base in a single step. It also describes factors that influence the reactivity and selectivity of elimination reactions, such as substrate structure, the nature of the leaving group and base, and conformational effects.
This document discusses various types of organic reactions including ionic reactions, radical reactions, and nucleophilic substitution reactions. It provides details on:
1) The mechanisms of SN1 and SN2 reactions including rate laws, stereochemistry, substrate structure effects, and effects of nucleophiles, leaving groups, and solvents. SN1 reactions proceed through a carbocation intermediate and follow first-order kinetics while SN2 reactions are bimolecular.
2) Substrate structures that favor SN1 or SN2 reactions. Tertiary substrates favor SN1 while primary and secondary favor SN2. Allylic and benzylic compounds are more reactive in both SN1 and SN2 reactions.
3)
The document summarizes key aspects of SN2 reactions including reaction mechanism, kinetics, stereochemistry, and factors that affect the rate of the reaction. It describes the SN2 reaction as a bimolecular nucleophilic substitution where the nucleophile attacks the substrate simultaneously as the leaving group departs, resulting in an inversion of configuration. Rate depends on both the nucleophile and substrate concentrations. The stability of the transition state is affected by substrate structure, nucleophilicity, leaving group ability, solvent properties, and conjugation effects in allylic and benzylic systems. Cyclic substrates and those without available orbital overlap do not undergo SN2 reactions as easily.
1) Heterolytic and homolytic bond fission can result in the formation of short-lived reaction intermediates called carbocations.
2) Carbocations are positively charged carbon ions that are electrophilic and undergo three reaction types: capture a nucleophile, lose a proton to form a pi bond, or rearrange.
3) Carbocation stability increases with increased substitution and the presence of electron donating groups, double bonds, or heteroatoms which delocalize the positive charge. Carbocations are key intermediates in SN1, E1, and rearrangement reactions.
1. The document discusses alkyl halide reactions including SN1 and SN2 mechanisms. It describes factors that affect the rates of these reactions such as the substrate, leaving group, nucleophile, and solvent.
2. SN1 is a two-step reaction involving a carbocation intermediate. SN2 is a single-step reaction without an intermediate. SN1 reactions result in racemization while SN2 reactions cause inversion of configuration.
3. Tertiary alkyl halides undergo SN1 reactions most readily due to stable carbocation intermediates. Polar protic solvents favor SN1 while polar aprotic solvents favor SN2.
This document discusses nucleophilic substitution reactions, specifically SN1 and SN2 reactions. It defines nucleophiles and explains that they are usually anions or neutral species that can donate an electron pair. The document then covers several factors that affect the rates and mechanisms of SN1 and SN2 reactions, including the leaving group, the nucleophile, the solvent, and steric effects. It describes the single-step SN2 mechanism and stepwise SN1 mechanism involving a carbocation intermediate. Several examples of nucleophilic substitution reactions are also provided.
Addition reactions occur when two reactants combine to form a new product with no leftover atoms. In an addition reaction, new groups are added to the starting material, breaking a pi bond and forming two sigma bonds. Addition reactions involve the addition of electrophiles, radicals, or nucleophiles across multiple bonds such as carbon-carbon double or triple bonds.
Reaction of alkyl halides: Nucleophilic substition Reaction 03313090492
The document discusses SN1 and SN2 nucleophilic substitution reactions of alkyl halides. SN1 is a two-step reaction that proceeds through a carbocation intermediate, while SN2 is a single-step bimolecular reaction. SN1 reactions give a mixture of products and occur more readily with tertiary alkyl halides. SN2 reactions result in inversion of configuration and are favored by primary alkyl halides and strong nucleophiles. Solvent effects and stability of carbocation intermediates also influence which reaction pathway occurs.
- Elimination reactions occur by either an E1 or E2 mechanism. E1 is a one-step reaction involving a carbocation intermediate, while E2 is a concerted, single-step reaction.
- The E1 mechanism is favored by good leaving groups, stable carbocations, and weak bases. It is non-stereospecific and does not occur with primary alkyl halides. The E2 mechanism is favored by strong bases and polar aprotic solvents. It is stereospecific and proceeds through an anti-periplanar transition state.
- Key factors that determine the mechanism include the stability of carbocation intermediates, the strength of the leaving group and base, and steric
1) The document discusses different types of nucleophilic substitution reactions including SN1, SN2, and SNi.
2) The SN1 reaction involves the formation of a carbocation intermediate and follows a two-step mechanism. The rate determining step is the formation of the carbocation.
3) The SN2 reaction is a concerted bimolecular nucleophilic substitution that occurs in one step without an intermediate. It follows second-order kinetics.
This document discusses elimination reactions, specifically E1 and E2 reactions. It explains that E1 reactions proceed through a carbocation intermediate and involve a two-step mechanism, while E2 reactions are concerted and involve both the alkyl halide and base in a single step. It also describes factors that influence the reactivity and selectivity of elimination reactions, such as substrate structure, the nature of the leaving group and base, and conformational effects.
1) Three types of elimination reactions are α-, β-, and γ-elimination which involve the loss of atoms or groups from the 1st, 2nd, and 1st/3rd positions respectively of an organic molecule.
2) The mechanisms of elimination reactions can be E1 or E2. E1 involves carbocation intermediate while E2 is concerted. Kinetic studies can determine the mechanism.
3) Factors like nature of alkyl halide, base, and solvent determine if the reaction follows E1 or E2. E2 is favored with strong base and polar aprotic solvent.
Factors that affect the rate of elimination reactions include the attacking base, leaving group, and reaction medium. A strong base is required for an E2 reaction to remove a weakly acidic hydrogen. A good leaving group is stable and weakly binds electrons, making it easier to form the carbocation intermediate. A polar solvent can stabilize charged carbocation intermediates in E1 reactions, making it the preferred medium, while a non-polar solvent favors the uncharged transition state of E2 reactions.
A fully interactive version of this presentation with functioning navigation buttons can be found by clicking on the link below:
https://connect.csupomona.edu/eliminations
The document discusses elimination reactions of alkyl halides. It begins by defining elimination reactions as those that involve the loss of elements from a starting material to form a new pi bond in the product. Specifically, it focuses on dehydrohalogenation reactions, where removal of HX occurs. The most common mechanism is E2 elimination, which is a bimolecular reaction promoted by a strong base. It follows second-order kinetics and has a single transition state. The document discusses characteristics of E2 reactions like Saytzeff's rule, Markovnikov's rule, anti-Markovnikov reactions, stereochemistry and stereoselectivity.
The E2 reaction mechanism involves the base-induced elimination of a hydrogen and halide atom from an alkyl halide, forming an alkene product. The reaction proceeds through a concerted bimolecular transition state where the C-H bond breaks as the C-X bond forms. Stereoselectivity is determined by whether the anti or syn orientation is preferred. Cyclic compounds exhibit varying degrees of stereoselectivity depending on ring size. The orientation of the double bond in the product can be predicted by either Hofmann or Saytzev rules based on the stability of the carbocation intermediate.
1) The document discusses different types of elimination reactions, including E1, E2, and E1cB mechanisms.
2) E1 reactions involve the generation of a carbocation intermediate, while E2 reactions occur in one step without intermediates. E1cB reactions first form a carbanion intermediate before the leaving group departs.
3) The mechanism depends on factors like the substrate, leaving group, solvent, and strength of the base used. Zaitsev's, Hofmann, and Bredt's rules also influence the regiochemistry of double bond formation.
The overall rate equation for this reaction is:
Rate = k[R-R-OH][H2O]
Where k is the rate constant and [R-R-OH] and [H2O] are the concentrations of the reactants R-R-OH and H2O, respectively.
Elimination reactions proceed by either an E1 or E2 mechanism. E1 reactions are favored with weak nucleophiles and follow Zaitsev's rule, while E2 reactions occur with strong nucleophiles and favor the formation of trans alkenes. E2 reactions follow both Zaitsev's and Hofmann's rules in determining the most stable alkene product. The choice between substitution and elimination depends on factors like the strength of the base/nucleophile and steric effects. Addition reactions allow for functionalizing alkenes and alkynes through hydration, halogenation, oxidation, hydroboration, conjugate addition and reduction reactions. Industrial processes exploit specific addition reactions, like the synthesis
1. Alkyl halides can undergo nucleophilic substitution or elimination reactions. Nucleophilic substitution reactions include SN2 and SN1 mechanisms, while elimination reactions include E1 and E2 mechanisms.
2. The type of reaction depends on factors like the structure of the alkyl halide, the nucleophile, the base, and the solvent. Primary alkyl halides favor SN2, while tertiary alkyl halides favor SN1 or E1/E2 in protic solvents.
3. The chapter examines these reaction mechanisms in detail to understand how they occur and how their characteristics can be used to predict and control reaction outcomes.
Pyrolytic elimination reactions involve the application of heat to induce an elimination reaction in an organic substrate without the need for an external base or solvent. This type of elimination proceeds through a concerted, syn-elimination via a cyclic transition state that allows for an intramolecular proton transfer and the formation of a new carbon-carbon double bond. Specific examples of pyrolytic eliminations discussed in the document include the conversion of esters to carboxylic acids and alkenes, eliminations in alicyclic systems, Cope eliminations, sulfoxide eliminations, xanthate pyrolysis, and selenoxide eliminations.
This document discusses elimination reactions where a small molecule is removed from a reactant. It describes the elimination of HBr from bromoalkanes using a dilute NaOH solution, which can cause either a substitution or elimination reaction depending on conditions. The two types of elimination reactions are E2, a bimolecular process without intermediates typical of primary/secondary halides, and E1, a unimolecular reaction with a carbocation intermediate typical of tertiary halides. Hydroxide acts as a base by accepting a proton from the alkyl halide, initiating electron movement that forms a C=C double bond and removes the halide.
This document discusses elimination reactions, specifically E1 and E2 reactions. It explains that E1 reactions proceed through a carbocation intermediate and involve a two-step mechanism, while E2 reactions are concerted and involve both the alkyl halide and base in a single step. It also describes factors that influence the reactivity and selectivity of elimination reactions, such as substrate structure, the nature of the leaving group and base, and conformational effects.
This document discusses various types of organic reactions including ionic reactions, radical reactions, and nucleophilic substitution reactions. It provides details on:
1) The mechanisms of SN1 and SN2 reactions including rate laws, stereochemistry, substrate structure effects, and effects of nucleophiles, leaving groups, and solvents. SN1 reactions proceed through a carbocation intermediate and follow first-order kinetics while SN2 reactions are bimolecular.
2) Substrate structures that favor SN1 or SN2 reactions. Tertiary substrates favor SN1 while primary and secondary favor SN2. Allylic and benzylic compounds are more reactive in both SN1 and SN2 reactions.
3)
The document summarizes key aspects of SN2 reactions including reaction mechanism, kinetics, stereochemistry, and factors that affect the rate of the reaction. It describes the SN2 reaction as a bimolecular nucleophilic substitution where the nucleophile attacks the substrate simultaneously as the leaving group departs, resulting in an inversion of configuration. Rate depends on both the nucleophile and substrate concentrations. The stability of the transition state is affected by substrate structure, nucleophilicity, leaving group ability, solvent properties, and conjugation effects in allylic and benzylic systems. Cyclic substrates and those without available orbital overlap do not undergo SN2 reactions as easily.
1) Heterolytic and homolytic bond fission can result in the formation of short-lived reaction intermediates called carbocations.
2) Carbocations are positively charged carbon ions that are electrophilic and undergo three reaction types: capture a nucleophile, lose a proton to form a pi bond, or rearrange.
3) Carbocation stability increases with increased substitution and the presence of electron donating groups, double bonds, or heteroatoms which delocalize the positive charge. Carbocations are key intermediates in SN1, E1, and rearrangement reactions.
1. The document discusses alkyl halide reactions including SN1 and SN2 mechanisms. It describes factors that affect the rates of these reactions such as the substrate, leaving group, nucleophile, and solvent.
2. SN1 is a two-step reaction involving a carbocation intermediate. SN2 is a single-step reaction without an intermediate. SN1 reactions result in racemization while SN2 reactions cause inversion of configuration.
3. Tertiary alkyl halides undergo SN1 reactions most readily due to stable carbocation intermediates. Polar protic solvents favor SN1 while polar aprotic solvents favor SN2.
This document discusses nucleophilic substitution reactions, specifically SN1 and SN2 reactions. It defines nucleophiles and explains that they are usually anions or neutral species that can donate an electron pair. The document then covers several factors that affect the rates and mechanisms of SN1 and SN2 reactions, including the leaving group, the nucleophile, the solvent, and steric effects. It describes the single-step SN2 mechanism and stepwise SN1 mechanism involving a carbocation intermediate. Several examples of nucleophilic substitution reactions are also provided.
Addition reactions occur when two reactants combine to form a new product with no leftover atoms. In an addition reaction, new groups are added to the starting material, breaking a pi bond and forming two sigma bonds. Addition reactions involve the addition of electrophiles, radicals, or nucleophiles across multiple bonds such as carbon-carbon double or triple bonds.
Reaction of alkyl halides: Nucleophilic substition Reaction 03313090492
The document discusses SN1 and SN2 nucleophilic substitution reactions of alkyl halides. SN1 is a two-step reaction that proceeds through a carbocation intermediate, while SN2 is a single-step bimolecular reaction. SN1 reactions give a mixture of products and occur more readily with tertiary alkyl halides. SN2 reactions result in inversion of configuration and are favored by primary alkyl halides and strong nucleophiles. Solvent effects and stability of carbocation intermediates also influence which reaction pathway occurs.
- Elimination reactions occur by either an E1 or E2 mechanism. E1 is a one-step reaction involving a carbocation intermediate, while E2 is a concerted, single-step reaction.
- The E1 mechanism is favored by good leaving groups, stable carbocations, and weak bases. It is non-stereospecific and does not occur with primary alkyl halides. The E2 mechanism is favored by strong bases and polar aprotic solvents. It is stereospecific and proceeds through an anti-periplanar transition state.
- Key factors that determine the mechanism include the stability of carbocation intermediates, the strength of the leaving group and base, and steric
1) The document discusses different types of nucleophilic substitution reactions including SN1, SN2, and SNi.
2) The SN1 reaction involves the formation of a carbocation intermediate and follows a two-step mechanism. The rate determining step is the formation of the carbocation.
3) The SN2 reaction is a concerted bimolecular nucleophilic substitution that occurs in one step without an intermediate. It follows second-order kinetics.
This document discusses elimination reactions, specifically E1 and E2 reactions. It explains that E1 reactions proceed through a carbocation intermediate and involve a two-step mechanism, while E2 reactions are concerted and involve both the alkyl halide and base in a single step. It also describes factors that influence the reactivity and selectivity of elimination reactions, such as substrate structure, the nature of the leaving group and base, and conformational effects.
1) Three types of elimination reactions are α-, β-, and γ-elimination which involve the loss of atoms or groups from the 1st, 2nd, and 1st/3rd positions respectively of an organic molecule.
2) The mechanisms of elimination reactions can be E1 or E2. E1 involves carbocation intermediate while E2 is concerted. Kinetic studies can determine the mechanism.
3) Factors like nature of alkyl halide, base, and solvent determine if the reaction follows E1 or E2. E2 is favored with strong base and polar aprotic solvent.
Presentation of elimination reactions-1.pptxShehrzadShafaq
The document presents information on elimination reactions. It discusses alpha and beta elimination reactions and the E1 and E2 reaction mechanisms. It provides examples of each type of elimination reaction. It also discusses factors that affect the rates of E1 and E2 reactions such as the structure of the substrate, the attacking base, the leaving group, reaction medium, temperature, and the substrate structure. The document was presented by a group of students to their organic chemistry professor as part of a course assignment.
This document discusses elimination reactions, specifically the E1 and E2 mechanisms. The E2 reaction is a single step reaction where a base abstracts two substituents from a molecule to form an alkene. The E1 reaction is a two-step reaction where the leaving group departs first to form a carbocation, followed by deprotonation to form the alkene. Both reactions follow the Zaitsev rule, forming the more substituted alkene product. The Hoffman rule states that the major product comes from the β-carbon with the most hydrogens. Tertiary substrates undergo elimination most readily due to carbocation stability in the E1 and number of β-hydrogens in E2.
The document provides information about conformations in hydrocarbons. It discusses that carbon-carbon single bonds allow rotation, leading to different conformations. Ethane is used as an example to explain staggered and eclipsed conformations. The relative stabilities of these conformations are also mentioned. Further, the document covers alkenes, alkynes and aromatic hydrocarbons. It provides their structures, properties and reactions like addition, oxidation, halogenation etc.
Elimination reactions involve the removal of two substituents from adjacent carbon atoms to form a double or triple bond. The document discusses E1 elimination reactions, which proceed through a two-step unimolecular mechanism. In the first step, a carbocation intermediate is formed. In the second step, a proton is removed from the carbocation rapidly to form the alkene product. E1 reactions favor substrates that form stable carbocations and are accelerated by polar protic solvents, weak bases, and high temperatures. The rate depends on the concentration of the substrate and the reaction follows first-order kinetics.
Alkyl halides are organic compounds containing one or more carbon-halogen bonds. They can be prepared from alkanes, alkenes, and alcohols using free radical halogenation, addition reactions, or by treating alcohols with reagents like thionyl chloride or phosphorus tribromide. Alkyl halides undergo nucleophilic substitution and elimination reactions. Nucleophilic substitution can proceed by an SN1 or SN2 mechanism depending on the substrate and conditions. The SN1 mechanism involves formation of a carbocation intermediate while SN2 is a concerted bimolecular process. Elimination reactions generate alkene products and compete with substitution. Alkyl halides are versatile
B.phram
Semester .4
Subject : Organic chemistry - III
Use as reference and also usable for examination prearation.
gtu afflitited phramacy college's student may using this ppt.
This document provides information on elimination reactions (E1 and E2), factors that influence E1 and E2 reactions, carbocation rearrangements, and reactions of conjugated dienes. Specifically, it discusses:
- The mechanisms and characteristics of E1 and E2 elimination reactions. E1 is a two-step unimolecular reaction that forms a carbocation intermediate, while E2 is a single-step bimolecular reaction.
- Factors that influence the E1 and E2 pathways such as the stability of the carbocation, the leaving group, the base, and the type of solvent used.
- Carbocation rearrangements and factors that stabilize carbocations like neighboring groups, conjugation
B.Pharm I Year II Sem. SN1 and SN2 reactions, kinetics, order of reactivity of alkyl halides, stereochemistry and rearrangement of carbocations.
SN1 versus SN2 reactions, Factors affecting SN1 and SN2 reactions.
Structure and uses of ethylchloride, Chloroform, trichloroethylene, tetrachloroethylene,
dichloromethane, tetrachloromethane and iodoform.
Alcohols, Qualitative tests for Alcohol, Structure and uses of Ethyl alcohol, chlorobutanol, Cetosterylalcohol, Benzyl alcohol, Glycerol, Propylene glycol
Organic compounds containing an electronegative atom or electron-withdrawing group bonded to a carbon undergo substitution or elimination reactions. Alkyl halides specifically undergo SN1, SN2, E1, and E2 reactions. SN1 and E1 are unimolecular reactions that proceed through a carbocation intermediate, while SN2 and E2 are bimolecular reactions. The type of reaction depends on factors like the nucleophile strength and leaving group ability.
This document provides an overview of alkyl halides for a medical biochemistry course. It defines alkyl halides as halogen-substituted alkanes and discusses their physical properties. Two common methods for preparing alkyl halides from alcohols are described: reaction with sulfur halides like thionyl chloride or phosphorus halides like phosphorus tribromide. The document also summarizes nucleophilic substitution reactions of alkyl halides and the SN1 and SN2 reaction mechanisms.
The document discusses organic chemistry concepts related to radical reactions. It covers topics like radical formation, halogenation of alkanes, the reaction of radicals with sigma and pi bonds, stereochemistry of halogenation, radical chain reactions, antioxidants, and radical halogenation at allylic carbons. It also discusses chlorofluorocarbons and their role in ozone layer depletion through a radical chain mechanism.
Colorimetry is "the science and technology used to quantify and describe physically the human color perception".[1] It is similar to spectrophotometry, but is distinguished by its interest in reducing spectra to the physical correlates of color perception, most often the CIE 1931 XYZ color space tristimulus values and related quantities.[2]
This chapter discusses alkyl halides and nucleophilic substitution reactions. Alkyl halides contain a halogen atom bonded to a carbon. They undergo nucleophilic substitution via one of two mechanisms: SN1 or SN2. The SN1 mechanism is a two-step process involving a carbocation intermediate. The SN2 mechanism is a single step with simultaneous bond breaking and making. The type of alkyl halide determines whether the reaction will proceed by SN1 or SN2, with more substituted halides favoring SN1. The stability of carbocation intermediates also influences the rates and stereochemistry of these reactions.
Redox Reaction and Electrochemical Cell (Reaksi Redoks dan Sel Elektrokimia)DindaKamaliya
An electrochemical cell converts chemical energy into electrical energy through spontaneous redox reactions. It consists of two half-cells separated by a salt bridge. In the cathode half-cell, reduction occurs as oxidized species gain electrons. In the anode half-cell, oxidation occurs as reduced species lose electrons. Electrons flow through an external circuit from the anode to the cathode. The standard electrode potential of each half-reaction predicts the cell's voltage under standard conditions.
This document discusses reduction reactions and reducing agents. It aims to teach the reader to: 1) exploit differences in reactivity between hydride and neutral reducing agents to achieve chemoselective reductions; 2) use substrate chirality to control syn vs. anti diastereoselectivity in ketone reductions; 3) rationalize reaction outcomes using transition state diagrams; 4) appreciate the versatility of transition metals in reductions; 5) understand the utility of dissolving metal reductions; and 6) use radical chemistry for deoxygenation and halide reduction. It then provides details on various hydride and neutral reducing agents, focusing on their reactivities and applications in selective reductions.
The document discusses the chemical properties of alkanes and alkenes. It explains that alkanes contain carbon and hydrogen and are saturated hydrocarbons that are very stable due to strong C-H bonds. Alkanes undergo combustion and cracking reactions. Alkenes contain carbon-carbon double bonds, which make them more reactive than alkanes and allow them to undergo addition reactions with electrophiles such as halogens. The most important reaction of alkenes is polymerization, where alkene monomers combine to form large macromolecules or polymers. Common polymers include polyethylene, polypropylene, PVC, and PTFE.
This document discusses different types of solutes in aqueous solutions. It defines strong electrolytes as substances that fully dissociate in water into ions and conduct electricity. Weak electrolytes only partially dissociate into a few ions. Nonelectrolytes dissolve in water as molecules and do not conduct electricity. Examples of strong electrolyte dissociations into ions are provided. Equivalents are defined as the amount of electrolyte or ion providing 1 mole of electrical charge. Electrolyte concentrations in IV solutions and body fluids are discussed in mEq/L.
This document provides an overview of chapter 4 from a chemistry textbook, which covers chemical reactions. It begins by defining electrolytes, non-electrolytes, and discussing the properties of aqueous solutions. It then covers the three main types of reactions that occur in aqueous solutions: precipitation reactions, acid-base reactions involving proton transfer, and redox reactions involving electron transfer. Specific examples of each reaction type are provided. Key concepts around oxidation, reduction, and oxidation numbers are also explained.
SOAL Un ipa-smp-mts-2014-kd-pengaruh-ketika-limbahAnnik Qurniawati
Dokumen tersebut berisi soal-soal ujian IPA SMP/MTs yang mencakup berbagai materi seperti gerak, kesetimbangan, kalor, listrik, optik, kimia, dan biologi. Soal-soal tersebut didukung oleh gambar atau grafik untuk memperjelas konsep yang diujikan.
SOAL Un ipa-smp-mts-2014-kd-dampak-seorang-tumpukanAnnik Qurniawati
Tes berisi soal-soal IPA tentang konsep-konsep fisika, kimia, dan biologi. Ada 30 soal pilihan ganda yang mencakup topik seperti gerak, kesetimbangan, kalor, listrik, magnet, sifat materi, senyawa kimia, sistem tubuh, dan ekologi.
SOAL Un ipa-smp-mts-2014-kd-dampak-ketika-limbahAnnik Qurniawati
Berdasarkan soal-soal pada dokumen, dokumen tersebut berisi soal-soal ujian IPA untuk SMP/MTs yang mencakup materi tentang:
- Timbangan dan keseimbangan
- Kalor dan panas
- Gerak dan energi
- Listrik dinamis
- Magnet dan medan magnet
- Kimia
- Biologi
- Lingkungan hidup
Dokumen tersebut berisi soal-soal ujian IPA SMP/MTs yang mencakup materi fisika, kimia, dan biologi. Soal-soal tersebut meliputi konsep-konsep seperti gerak, kalor, listrik, kimia anorganik dan organik, serta sistem tubuh manusia dan ekologi.
SOAL Un ipa-smp-mts-2014-kd-dampak-ditemukan-kantongAnnik Qurniawati
Dokumen berisi soal-soal ujian IPA SMP yang mencakup materi fisika, kimia, dan biologi. Terdapat soal tentang konsep-konsep seperti gerak, kesetimbangan, kalor, listrik, unsur kimia, dan sistem tubuh manusia. Jumlah soal sebanyak 32 butir.
SOAL Un ipa-smp-mts-2014-kd-dampak-seorang-bertambahAnnik Qurniawati
Dokumen tersebut berisi soal-soal ujian IPA SMP/MTs yang mencakup materi fisika, kimia, dan biologi. Soal-soal tersebut meliputi konsep-konsep seperti gerak, energi, kalor, listrik, magnet, sifat zat, dan organisme hidup."
SOAL Un ipa-smp-mts-2014-kd-cara-ditemukan-bertambahAnnik Qurniawati
Dokumen tersebut berisi soal ujian IPA SMP yang mencakup materi-materi fisika, kimia, dan biologi. Terdiri dari 31 soal pilihan ganda dan beberapa gambar untuk memahami soal.
Dokumen tersebut berisi soal ujian IPA SMP/MTs yang mencakup berbagai aspek ilmu pengetahuan alam seperti fisika, kimia, dan biologi. Terdapat 31 soal uraian yang meliputi konsep-konsep seperti timbangan, kalor, listrik, magnet, optik, mekanika, asam basa, senyawa organik, ekosistem, dan anatomi manusia.
GraphRAG for Life Science to increase LLM accuracyTomaz Bratanic
GraphRAG for life science domain, where you retriever information from biomedical knowledge graphs using LLMs to increase the accuracy and performance of generated answers
“An Outlook of the Ongoing and Future Relationship between Blockchain Technologies and Process-aware Information Systems.” Invited talk at the joint workshop on Blockchain for Information Systems (BC4IS) and Blockchain for Trusted Data Sharing (B4TDS), co-located with with the 36th International Conference on Advanced Information Systems Engineering (CAiSE), 3 June 2024, Limassol, Cyprus.
UiPath Test Automation using UiPath Test Suite series, part 6DianaGray10
Welcome to UiPath Test Automation using UiPath Test Suite series part 6. In this session, we will cover Test Automation with generative AI and Open AI.
UiPath Test Automation with generative AI and Open AI webinar offers an in-depth exploration of leveraging cutting-edge technologies for test automation within the UiPath platform. Attendees will delve into the integration of generative AI, a test automation solution, with Open AI advanced natural language processing capabilities.
Throughout the session, participants will discover how this synergy empowers testers to automate repetitive tasks, enhance testing accuracy, and expedite the software testing life cycle. Topics covered include the seamless integration process, practical use cases, and the benefits of harnessing AI-driven automation for UiPath testing initiatives. By attending this webinar, testers, and automation professionals can gain valuable insights into harnessing the power of AI to optimize their test automation workflows within the UiPath ecosystem, ultimately driving efficiency and quality in software development processes.
What will you get from this session?
1. Insights into integrating generative AI.
2. Understanding how this integration enhances test automation within the UiPath platform
3. Practical demonstrations
4. Exploration of real-world use cases illustrating the benefits of AI-driven test automation for UiPath
Topics covered:
What is generative AI
Test Automation with generative AI and Open AI.
UiPath integration with generative AI
Speaker:
Deepak Rai, Automation Practice Lead, Boundaryless Group and UiPath MVP
Unlocking Productivity: Leveraging the Potential of Copilot in Microsoft 365, a presentation by Christoforos Vlachos, Senior Solutions Manager – Modern Workplace, Uni Systems
HCL Notes and Domino License Cost Reduction in the World of DLAUpanagenda
Webinar Recording: https://www.panagenda.com/webinars/hcl-notes-and-domino-license-cost-reduction-in-the-world-of-dlau/
The introduction of DLAU and the CCB & CCX licensing model caused quite a stir in the HCL community. As a Notes and Domino customer, you may have faced challenges with unexpected user counts and license costs. You probably have questions on how this new licensing approach works and how to benefit from it. Most importantly, you likely have budget constraints and want to save money where possible. Don’t worry, we can help with all of this!
We’ll show you how to fix common misconfigurations that cause higher-than-expected user counts, and how to identify accounts which you can deactivate to save money. There are also frequent patterns that can cause unnecessary cost, like using a person document instead of a mail-in for shared mailboxes. We’ll provide examples and solutions for those as well. And naturally we’ll explain the new licensing model.
Join HCL Ambassador Marc Thomas in this webinar with a special guest appearance from Franz Walder. It will give you the tools and know-how to stay on top of what is going on with Domino licensing. You will be able lower your cost through an optimized configuration and keep it low going forward.
These topics will be covered
- Reducing license cost by finding and fixing misconfigurations and superfluous accounts
- How do CCB and CCX licenses really work?
- Understanding the DLAU tool and how to best utilize it
- Tips for common problem areas, like team mailboxes, functional/test users, etc
- Practical examples and best practices to implement right away
Communications Mining Series - Zero to Hero - Session 1DianaGray10
This session provides introduction to UiPath Communication Mining, importance and platform overview. You will acquire a good understand of the phases in Communication Mining as we go over the platform with you. Topics covered:
• Communication Mining Overview
• Why is it important?
• How can it help today’s business and the benefits
• Phases in Communication Mining
• Demo on Platform overview
• Q/A
Removing Uninteresting Bytes in Software FuzzingAftab Hussain
Imagine a world where software fuzzing, the process of mutating bytes in test seeds to uncover hidden and erroneous program behaviors, becomes faster and more effective. A lot depends on the initial seeds, which can significantly dictate the trajectory of a fuzzing campaign, particularly in terms of how long it takes to uncover interesting behaviour in your code. We introduce DIAR, a technique designed to speedup fuzzing campaigns by pinpointing and eliminating those uninteresting bytes in the seeds. Picture this: instead of wasting valuable resources on meaningless mutations in large, bloated seeds, DIAR removes the unnecessary bytes, streamlining the entire process.
In this work, we equipped AFL, a popular fuzzer, with DIAR and examined two critical Linux libraries -- Libxml's xmllint, a tool for parsing xml documents, and Binutil's readelf, an essential debugging and security analysis command-line tool used to display detailed information about ELF (Executable and Linkable Format). Our preliminary results show that AFL+DIAR does not only discover new paths more quickly but also achieves higher coverage overall. This work thus showcases how starting with lean and optimized seeds can lead to faster, more comprehensive fuzzing campaigns -- and DIAR helps you find such seeds.
- These are slides of the talk given at IEEE International Conference on Software Testing Verification and Validation Workshop, ICSTW 2022.
Sudheer Mechineni, Head of Application Frameworks, Standard Chartered Bank
Discover how Standard Chartered Bank harnessed the power of Neo4j to transform complex data access challenges into a dynamic, scalable graph database solution. This keynote will cover their journey from initial adoption to deploying a fully automated, enterprise-grade causal cluster, highlighting key strategies for modelling organisational changes and ensuring robust disaster recovery. Learn how these innovations have not only enhanced Standard Chartered Bank’s data infrastructure but also positioned them as pioneers in the banking sector’s adoption of graph technology.
Infrastructure Challenges in Scaling RAG with Custom AI modelsZilliz
Building Retrieval-Augmented Generation (RAG) systems with open-source and custom AI models is a complex task. This talk explores the challenges in productionizing RAG systems, including retrieval performance, response synthesis, and evaluation. We’ll discuss how to leverage open-source models like text embeddings, language models, and custom fine-tuned models to enhance RAG performance. Additionally, we’ll cover how BentoML can help orchestrate and scale these AI components efficiently, ensuring seamless deployment and management of RAG systems in the cloud.
Cosa hanno in comune un mattoncino Lego e la backdoor XZ?Speck&Tech
ABSTRACT: A prima vista, un mattoncino Lego e la backdoor XZ potrebbero avere in comune il fatto di essere entrambi blocchi di costruzione, o dipendenze di progetti creativi e software. La realtà è che un mattoncino Lego e il caso della backdoor XZ hanno molto di più di tutto ciò in comune.
Partecipate alla presentazione per immergervi in una storia di interoperabilità, standard e formati aperti, per poi discutere del ruolo importante che i contributori hanno in una comunità open source sostenibile.
BIO: Sostenitrice del software libero e dei formati standard e aperti. È stata un membro attivo dei progetti Fedora e openSUSE e ha co-fondato l'Associazione LibreItalia dove è stata coinvolta in diversi eventi, migrazioni e formazione relativi a LibreOffice. In precedenza ha lavorato a migrazioni e corsi di formazione su LibreOffice per diverse amministrazioni pubbliche e privati. Da gennaio 2020 lavora in SUSE come Software Release Engineer per Uyuni e SUSE Manager e quando non segue la sua passione per i computer e per Geeko coltiva la sua curiosità per l'astronomia (da cui deriva il suo nickname deneb_alpha).
UiPath Test Automation using UiPath Test Suite series, part 5DianaGray10
Welcome to UiPath Test Automation using UiPath Test Suite series part 5. In this session, we will cover CI/CD with devops.
Topics covered:
CI/CD with in UiPath
End-to-end overview of CI/CD pipeline with Azure devops
Speaker:
Lyndsey Byblow, Test Suite Sales Engineer @ UiPath, Inc.
TrustArc Webinar - 2024 Global Privacy SurveyTrustArc
How does your privacy program stack up against your peers? What challenges are privacy teams tackling and prioritizing in 2024?
In the fifth annual Global Privacy Benchmarks Survey, we asked over 1,800 global privacy professionals and business executives to share their perspectives on the current state of privacy inside and outside of their organizations. This year’s report focused on emerging areas of importance for privacy and compliance professionals, including considerations and implications of Artificial Intelligence (AI) technologies, building brand trust, and different approaches for achieving higher privacy competence scores.
See how organizational priorities and strategic approaches to data security and privacy are evolving around the globe.
This webinar will review:
- The top 10 privacy insights from the fifth annual Global Privacy Benchmarks Survey
- The top challenges for privacy leaders, practitioners, and organizations in 2024
- Key themes to consider in developing and maintaining your privacy program
Climate Impact of Software Testing at Nordic Testing DaysKari Kakkonen
My slides at Nordic Testing Days 6.6.2024
Climate impact / sustainability of software testing discussed on the talk. ICT and testing must carry their part of global responsibility to help with the climat warming. We can minimize the carbon footprint but we can also have a carbon handprint, a positive impact on the climate. Quality characteristics can be added with sustainability, and then measured continuously. Test environments can be used less, and in smaller scale and on demand. Test techniques can be used in optimizing or minimizing number of tests. Test automation can be used to speed up testing.
Pushing the limits of ePRTC: 100ns holdover for 100 daysAdtran
At WSTS 2024, Alon Stern explored the topic of parametric holdover and explained how recent research findings can be implemented in real-world PNT networks to achieve 100 nanoseconds of accuracy for up to 100 days.
Driving Business Innovation: Latest Generative AI Advancements & Success StorySafe Software
Are you ready to revolutionize how you handle data? Join us for a webinar where we’ll bring you up to speed with the latest advancements in Generative AI technology and discover how leveraging FME with tools from giants like Google Gemini, Amazon, and Microsoft OpenAI can supercharge your workflow efficiency.
During the hour, we’ll take you through:
Guest Speaker Segment with Hannah Barrington: Dive into the world of dynamic real estate marketing with Hannah, the Marketing Manager at Workspace Group. Hear firsthand how their team generates engaging descriptions for thousands of office units by integrating diverse data sources—from PDF floorplans to web pages—using FME transformers, like OpenAIVisionConnector and AnthropicVisionConnector. This use case will show you how GenAI can streamline content creation for marketing across the board.
Ollama Use Case: Learn how Scenario Specialist Dmitri Bagh has utilized Ollama within FME to input data, create custom models, and enhance security protocols. This segment will include demos to illustrate the full capabilities of FME in AI-driven processes.
Custom AI Models: Discover how to leverage FME to build personalized AI models using your data. Whether it’s populating a model with local data for added security or integrating public AI tools, find out how FME facilitates a versatile and secure approach to AI.
We’ll wrap up with a live Q&A session where you can engage with our experts on your specific use cases, and learn more about optimizing your data workflows with AI.
This webinar is ideal for professionals seeking to harness the power of AI within their data management systems while ensuring high levels of customization and security. Whether you're a novice or an expert, gain actionable insights and strategies to elevate your data processes. Join us to see how FME and AI can revolutionize how you work with data!
34. Methylenecyclohexane is not the major
product in this rxn. Give the chemical
structure of the major product and explain
why it would be the major product.
35. Alkyl Halides and Elimination Reactions
• Elimination reactions involve the loss of elements from
the starting material to form a new π bond in the
product.
General Features of Elimination
36. Alkyl Halides and Elimination Reactions
• Equations [1] and [2] illustrate examples of elimination
reactions. In both reactions a base removes the
elements of an acid, HX, from the organic starting
material.
General Features of Elimination
37. Alkyl Halides and Elimination Reactions
• Removal of the elements HX is called
dehydrohalogenation.
• Dehydrohalogenation is an example of β elimination.
• The curved arrow formalism shown below illustrates
how four bonds are broken or formed in the process.
General Features of Elimination
38. Alkyl Halides and Elimination Reactions
• The most common bases used in elimination reactions
are negatively charged oxygen compounds, such as HO¯
and its alkyl derivatives, RO¯, called alkoxides.
General Features of Elimination
39. Alkyl Halides and Elimination Reactions
• To draw any product of dehydrohalogenation—Find the
α carbon. Identify all β carbons with H atoms. Remove
the elements of H and X form the α and β carbons and
form a π bond.
General Features of Elimination
40. Alkyl Halides and Elimination Reactions
• Recall that the double bond of an alkene consists of a σ
bond and a π bond.
Alkenes—The Products of Elimination
41. Alkyl Halides and Elimination Reactions
• Alkenes are classified according to the number of
carbon atoms bonded to the carbons of the double bond.
Alkenes—The Products of Elimination
42. Alkyl Halides and Elimination Reactions
• Recall that rotation about double bonds is restricted.
Alkenes—The Products of Elimination
43. Alkyl Halides and Elimination Reactions
• Because of restricted rotation, two stereoisomers of 2-
butene are possible. cis-2-Butene and trans-2-butene are
diastereomers, because they are stereoisomers that are
not mirror images of each other.
Alkenes—The Products of Elimination
44. Alkyl Halides and Elimination Reactions
• Whenever the two groups on each end of a carbon-
carbon double bond are different from each other, two
diastereomers are possible.
Alkenes—The Products of Elimination
45. Alkyl Halides and Elimination Reactions
• In general, trans alkenes are more stable than cis
alkenes because the groups bonded to the double bond
carbons are further apart, reducing steric interactions.
Alkenes—The Products of Elimination
46. Alkyl Halides and Elimination Reactions
• The stability of an alkene increases as the number of R
groups bonded to the double bond carbons increases.
Alkenes—The Products of Elimination
• The higher the percent s-character, the more readily an atom
accepts electron density. Thus, sp2
carbons are more able to
accept electron density and sp3
carbons are more able to
donate electron density.
• Consequently, increasing the number of electron donating
groups on a carbon atom able to accept electron density
makes the alkene more stable.
47. Alkyl Halides and Elimination Reactions
• trans-2-Butene (a disubstituted alkene) is more stable
than cis-2-butene (another disubstituted alkene), but
both are more stable than 1-butene (a monosubstituted
alkene).
Alkenes—The Products of Elimination
48. Alkyl Halides and Elimination Reactions
• There are two mechanisms of elimination—E2 and E1,
just as there are two mechanisms of substitution, SN2
and SN1.
• E2 mechanism—bimolecular elimination
• E1 mechanism—unimolecular elimination
• The E2 and E1 mechanisms differ in the timing of bond
cleavage and bond formation, analogous to the SN2 and
SN1 mechanisms.
• E2 and SN2 reactions have some features in common, as
do E1 and SN1 reactions.
Mechanisms of Elimination
49. Alkyl Halides and Elimination Reactions
• The most common mechanism for dehydrohalogenation
is the E2 mechanism.
• It exhibits second-order kinetics, and both the alkyl
halide and the base appear in the rate equation i.e.
Mechanisms of Elimination—E2
rate = k[(CH3)3CBr][¯OH]
• The reaction is concerted—all bonds are broken and
formed in a single step.
52. Alkyl Halides and Elimination Reactions
• There are close parallels between E2 and SN2 mechanisms in
how the identity of the base, the leaving group and the
solvent affect the rate.
• The base appears in the rate equation, so the rate of the E2
reaction increases as the strength of the base increases.
• E2 reactions are generally run with strong, negatively charged
bases like¯OH and ¯OR. Two strong sterically hindered
nitrogen bases called DBN and DBU are also sometimes used.
Mechanisms of Elimination—E2
53. Alkyl Halides and Elimination Reactions
Mechanisms of Elimination—E2
54. Alkyl Halides and Elimination Reactions
• The increase in E2 reaction rate with increasing alkyl
substitution can be rationalized in terms of transition state
stability.
• In the transition state, the double bond is partially formed.
Thus, increasing the stability of the double bond with alkyl
substituents stabilizes the transition state (i.e. lowers Ea,
which increases the rate of the reaction according to the
Hammond postulate).
Mechanisms of Elimination—E2
55. Alkyl Halides and Elimination Reactions
• Increasing the number of R groups on the carbon with the
leaving group forms more highly substituted, more stable
alkenes in E2 reactions.
• In the reactions below, since the disubstituted alkene is more
stable, the 30
alkyl halide reacts faster than the 10
alkyl halide.
Mechanisms of Elimination—E2
56. Alkyl Halides and Elimination Reactions
Mechanisms of Elimination—E2
57. Alkyl Halides and Elimination Reactions
• Recall that when alkyl halides have two or more different β
carbons, more than one alkene product is formed.
• When this happens, one of the products usually
predominates.
• The major product is the more stable product—the one with
the more substituted double bond.
• This phenomenon is called the Zaitsev rule.
The Zaitsev (Saytzeff) Rule
58. Alkyl Halides and Elimination Reactions
• When a mixture of stereoisomers is possible from a
dehydrohalogenation, the major product is the more stable
stereoisomer.
• A reaction is stereoselective when it forms predominantly or
exclusively one stereoisomer when two or more are possible.
• The E2 reaction is stereoselective because one stereoisomer
is formed preferentially.
The Zaitsev (Saytzeff) Rule
59. Alkyl Halides and Elimination Reactions
• The dehydrohalogenation of (CH3)3CI with H2O to form
(CH3)C=CH2 can be used to illustrate the second general
mechanism of elimination, the E1 mechanism.
• An E1 reaction exhibits first-order kinetics:
Mechanisms of Elimination—E1
rate = k[(CH3)3CI]
• The E1 reaction proceed via a two-step mechanism: the bond
to the leaving group breaks first before the π bond is formed.
The slow step is unimolecular, involving only the alkyl halide.
• The E1 and E2 mechanisms both involve the same number of
bonds broken and formed. The only difference is timing. In an
E1, the leaving group comes off before the β proton is
removed, and the reaction occurs in two steps. In an E2
reaction, the leaving group comes off as the β proton is
removed, and the reaction occurs in one step.
60. Alkyl Halides and Elimination Reactions
• The rate of an E1 reaction increases as the number of R groups
on the carbon with the leaving group increases.
Mechanisms of Elimination—E1
• The strength of the base usually determines whether a reaction
follows the E1 or E2 mechanism. Strong bases like ¯OH and ¯OR
favor E2 reactions, whereas weaker bases like H2O and ROH
favor E1 reactions.
61. Alkyl Halides and Elimination Reactions
Table 8.3 summarizes the characteristics of the E1 mechanism.
Mechanisms of Elimination—E1
62. Alkyl Halides and Elimination Reactions
• SN1 and E1 reactions have exactly the same first step—formation
of a carbocation. They differ in what happens to the carbocation.
SN1 and E1 Reactions
• Because E1 reactions often occur with a competing SN1 reaction,
E1 reactions of alkyl halides are much less useful than E2
reactions.
63. Alkyl Halides and Elimination Reactions
• The transition state of an E2 reaction consists of four atoms from
an alkyl halide—one hydrogen atom, two carbon atoms, and the
leaving group (X)—all aligned in a plane. There are two ways for
the C—H and C—X bonds to be coplanar.
Stereochemistry of the E2 Reaction
• E2 elimination occurs most often in the anti periplanar geometry.
This arrangement allows the molecule to react in the lower
energy staggered conformation, and allows the incoming base
and leaving group to be further away from each other.
65. Alkyl Halides and Elimination Reactions
• The stereochemical requirement of an anti periplanar geometry
in an E2 reaction has important consequences for compounds
containing six-membered rings.
• Consider chlorocyclohexane which exists as two chair
conformers. Conformer A is preferred since the bulkier Cl group
is in the equatorial position.
Stereochemistry of the E2 Reaction
• For E2 elimination, the C-Cl bond must be anti periplanar to the
C—H bond on a β carbon, and this occurs only when the H and
Cl atoms are both in the axial position. The requirement for trans
diaxial geometry means that elimination must occur from the
less stable conformer, B.
66. Alkyl Halides and Elimination Reactions
Stereochemistry of the E2 Reaction
67. Alkyl Halides and Elimination Reactions
• Now consider the E2 dehydrohalogenation of cis- and trans-1-
chloro-2-methylcyclohexane.
Stereochemistry of the E2 Reaction
• This cis isomer exists as two conformers, A and B, each of
which as one group axial and one group equatorial. E2 reaction
must occur from conformer B, which contains an axial Cl atom.
68. Alkyl Halides and Elimination Reactions
• Because conformer B has two different axial β
hydrogens, labeled Ha and Hb, E2 reaction occurs in two
different directions to afford two alkenes.
• The major product contains the more stable
trisubstituted double bond, as predicted by the Zaitsev
rule.
Stereochemistry of the E2 Reaction
69. Alkyl Halides and Elimination Reactions
• The trans isomer of 1-chloro-2-methylcyclohexane exists
as two conformers: C, having two equatorial substituents,
and D, having two axial substituents.
Stereochemistry of the E2 Reaction
• E2 reaction must occur from D, since it contains an axial Cl
atom.
70. Alkyl Halides and Elimination Reactions
• Because conformer D has only one axial β H, E2 reaction
occurs only in one direction to afford a single product. This
is not predicted by the Zaitzev rule.
Stereochemistry of the E2 Reaction
71. Alkyl Halides and Elimination Reactions
• The strength of the base is the most important factor in
determining the mechanism for elimination. Strong
bases favor the E2 mechanism. Weak bases favor the E1
mechanism.
When is the Mechanism E1 or E2
72. Alkyl Halides and Elimination Reactions
• A single elimination reaction produces a π bond of an
alkene. Two consecutive elimination reactions produce
two π bonds of an alkyne.
E2 Reactions and Alkyne Synthesis
73. Alkyl Halides and Elimination Reactions
• Two elimination reactions are needed to remove two
moles of HX from a dihalide substrate.
• Two different starting materials can be used—a vicinal
dihalide or a geminal dihalide.
E2 Reactions and Alkyne Synthesis
74. Alkyl Halides and Elimination Reactions
• Stronger bases are needed to synthesize alkynes by
dehydrohalogenation than are needed to synthesize
alkenes.
• The typical base used is ¯NH2 (amide), used as the
sodium salt of NaNH2. KOC(CH3)3 can also be used with
DMSO as solvent.
E2 Reactions and Alkyne Synthesis
75. Alkyl Halides and Elimination Reactions
• The reason that stronger bases are needed for this
dehydrohalogenation is that the transition state for the
second elimination reaction includes partial cleavage of
the C—H bond. In this case however, the carbon atom is
sp2
hybridized and sp2
hybridized C—H bonds are
stronger than sp3
hybridized C—H bonds. As a result, a
stronger base is needed to cleave this bond.
E2 Reactions and Alkyne Synthesis
76. Alkyl Halides and Elimination Reactions
E2 Reactions and Alkyne Synthesis
77. Alkyl Halides and Elimination Reactions
• Good nucleophiles that are weak bases favor
substitution over elimination—Certain anions always
give products of substitution because they are good
nucleophiles but weak bases. These include I¯, Br¯, HS¯,
and CH3COO¯.
Predicting the Mechanism from the Reactants—SN1,
SN2, E1 or E2.
78. Alkyl Halides and Elimination Reactions
• Bulky nonnucleophilic bases favor elimination over
substitution—KOC(CH3)3, DBU, and DBN are too
sterically hindered to attack tetravalent carbon, but are
able to remove a small proton, favoring elimination over
substitution.
Predicting the Mechanism from the Reactants—SN1,
SN2, E1 or E2.
79. Predicting the Mechanism from the Reactants—SN1,
SN2, E1 or E2.
Alkyl Halides and Elimination Reactions
80. Predicting the Mechanism from the Reactants—SN1,
SN2, E1 or E2.
Alkyl Halides and Elimination Reactions