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 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
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.
Elimination reactions involve the removal of atoms or groups of atoms from adjacent carbons of a molecule, forming multiple bonds. They are endothermic reactions that occur with heat. There are two main types: alpha elimination removes two ligands from the same atom, while beta elimination removes ligands from adjacent carbons. Elimination mechanisms include E1 (unimolecular), E2 (bimolecular), and E1cb (carbocation intermediate). E1 involves carbocation formation in two steps, E2 is a single-step process, and E1cb forms a carbanion intermediate. The type of mechanism depends on factors like the substrate structure and conditions used.
This power point presentation summarizes elimination reactions, specifically 1,2 elimination reactions. It defines elimination reactions as reactions where two atoms or groups are removed from a reactant to form an unsaturated product. 1,2 elimination reactions eliminate atoms or groups from the 1 and 2 positions on a molecule. Three possible mechanisms are discussed: E2, E1, and E1cb. Evidence for the E2 mechanism includes kinetic isotope effects, the element effect showing dependence on leaving group ability, and the lack of hydrogen exchange. The Saytzeff rule and factors influencing its application, like stability and transition state crowding, are also covered.
The document discusses elimination reactions, specifically E1 and β-elimination reactions. It explains that E1 reactions proceed through a two-step unimolecular mechanism, with the first step being rate-determining. Factors that affect E1 reactions include the stability of the carbocation intermediate, steric effects, and the ability of the base to stabilize the carbocation. Rearrangements can also occur through carbocation migration to form more stable products.
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.
This document summarizes various nucleophilic substitution reactions including SN1, SN2, SN1 prime, SN2 prime, and SNi reactions. It describes the key characteristics of SN2 reactions, which proceed through a single transition state with inversion of configuration. Factors that affect SN2 reactivity include the nature of the nucleophile, electrophile, leaving group, and solvent. SN1 reactions involve ionization to a carbocation intermediate and generally give racemic products. Allylic substrates can undergo rearrangement in SN1 or SN2 reactions.
In organic chemistry, a carbonyl group is a functional group composed of a carbon atom double-bonded to an oxygen atom: C=O. It is common to several classes of organic compounds, as part of many larger functional groups. A compound containing a carbonyl group is often referred to as a carbonyl compound.
- 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
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.
Elimination reactions involve the removal of atoms or groups of atoms from adjacent carbons of a molecule, forming multiple bonds. They are endothermic reactions that occur with heat. There are two main types: alpha elimination removes two ligands from the same atom, while beta elimination removes ligands from adjacent carbons. Elimination mechanisms include E1 (unimolecular), E2 (bimolecular), and E1cb (carbocation intermediate). E1 involves carbocation formation in two steps, E2 is a single-step process, and E1cb forms a carbanion intermediate. The type of mechanism depends on factors like the substrate structure and conditions used.
This power point presentation summarizes elimination reactions, specifically 1,2 elimination reactions. It defines elimination reactions as reactions where two atoms or groups are removed from a reactant to form an unsaturated product. 1,2 elimination reactions eliminate atoms or groups from the 1 and 2 positions on a molecule. Three possible mechanisms are discussed: E2, E1, and E1cb. Evidence for the E2 mechanism includes kinetic isotope effects, the element effect showing dependence on leaving group ability, and the lack of hydrogen exchange. The Saytzeff rule and factors influencing its application, like stability and transition state crowding, are also covered.
The document discusses elimination reactions, specifically E1 and β-elimination reactions. It explains that E1 reactions proceed through a two-step unimolecular mechanism, with the first step being rate-determining. Factors that affect E1 reactions include the stability of the carbocation intermediate, steric effects, and the ability of the base to stabilize the carbocation. Rearrangements can also occur through carbocation migration to form more stable products.
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.
This document summarizes various nucleophilic substitution reactions including SN1, SN2, SN1 prime, SN2 prime, and SNi reactions. It describes the key characteristics of SN2 reactions, which proceed through a single transition state with inversion of configuration. Factors that affect SN2 reactivity include the nature of the nucleophile, electrophile, leaving group, and solvent. SN1 reactions involve ionization to a carbocation intermediate and generally give racemic products. Allylic substrates can undergo rearrangement in SN1 or SN2 reactions.
In organic chemistry, a carbonyl group is a functional group composed of a carbon atom double-bonded to an oxygen atom: C=O. It is common to several classes of organic compounds, as part of many larger functional groups. A compound containing a carbonyl group is often referred to as a carbonyl compound.
This document provides an overview of electrophilic substitution reactions. It defines electrophilic substitution as a reaction where a functional group is attached to a compound by replacing another functional group, often a hydrogen atom. It describes two main types: electrophilic aromatic substitution reactions, where an atom attached to an aromatic ring is replaced; and electrophilic aliphatic substitution reactions, where hydrogen in an aliphatic compound is usually replaced. The document also outlines the three step mechanism of electrophilic substitution reactions: 1) generating an electrophile, 2) forming a carbocation, and 3) eliminating a proton to restore aromaticity.
Alkyl halides are derivatives of alkanes where one or more hydrogen atoms are replaced by halogen atoms such as fluorine, chlorine, bromine, or iodine. They are represented by R-X, where R is an alkyl group and X is a halogen. Common methods for preparing alkyl halides include direct halogenation of alkanes, addition of hydrogen halides to alkenes and alkynes, and reactions of hydrogen halides, phosphorus halides, or thionyl chloride with alcohols. Alkyl halides undergo nucleophilic substitution and elimination reactions. They can be reduced to alkanes or used to form Grignard reagents. Common uses
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.
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.
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.
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.
This document discusses organic reaction intermediates, specifically carbocations and carbanions. It defines them as positively or negatively charged carbon-containing ions that are formed during chemical reactions and then react further to form final products. The key features, methods of formation, factors affecting stability, and synthetic applications of carbocations and carbanions are described. Inductive effects, resonance effects, and hyperconjugation influence the stability of these intermediates. Carbocations and carbanions are involved in many common organic reaction types such as eliminations, substitutions, additions, and rearrangements.
Cyclohexane exists in different conformations viz chair, boat, twist boat and half chair. These conformations possess different energies. Therefore they differ in energy.
This document provides an overview of reduction reactions in organic chemistry. It discusses various types of reduction reactions including catalytic hydrogenation, hydride transfer reactions using reagents like LiAlH4 and NaBH4, dissolving metal reductions, and others. Specific metal hydride reductions using boron and aluminum reagents like sodium borohydride, sodium cyanoborohydride, lithium aluminum hydride, and diisobutylaluminum hydride are explained in detail including their mechanisms and selectivity. Diimide reduction is also briefly covered. The document concludes with a bibliography of reference books on organic reaction mechanisms.
Carbanions are carbon atoms with a negative charge that are formed through various mechanisms. They can be classified based on their formation method such as through heterocyclic cleavage, proton abstraction using a base, decarboxylation, addition of a nucleophile to an alkene, or formation of an organometallic compound. Carbanion stability depends on factors like the electronegativity of the carbon, inductive effects, resonance effects, and attachment to sulfur or phosphorus. Aromatic carbanions and those with electron-withdrawing groups are particularly stable due to resonance delocalization. Carbanions have applications in reactions like the Perkin reaction, Claisen condensation, benzoin condensation,
Retrosynthetic analysis, definition, importance, disconnection approach, one group two group disconnection logical and illogical disconnection approach compounds containing two nitrogen atom retrosynthetic analysis of camphor, cartisone, reserpine
The document summarizes the pinacol-pinacolone rearrangement, which involves the conversion of a vicinal diol to a ketone or aldehyde in the presence of an acid. It was first described by German chemist William Rudolph Fittig in 1860. A key example is the conversion of pinacol to pinacolone using sulfuric acid. The reaction proceeds through protonation, dehydration, rearrangement, and dehydrogenation steps. The migratory aptitude is influenced by electronic effects and stability of the carbocation intermediate. The rearrangement has applications in synthesizing carbonyl compounds, cyclic ketones, spiro-compounds, and supports ring expansions and contractions.
Nucleophilic aromatic substitution is a reaction where a nucleophile displaces a good leaving group such as a halide on an aromatic ring. The document discusses several mechanisms for nucleophilic aromatic substitution including SNAr, SN1, benzyne, SRN1, and examples like the Von Richter and Smiles rearrangements. The rate is facilitated by electron-withdrawing groups on the aromatic ring that stabilize the cyclohexadienyl anion intermediate.
Alkenes and their preparation-HYDROCARBONS PART 2ritik
Alkenes can be prepared through various methods including reduction of alkynes, dehydrohalogenation of alkyl halides, dehydration of alcohols, and heating vicinal dihalogen derivatives with zinc dust. Addition reactions of alkenes follow Markovnikov's rule or anti-Markovnikov's rule in the presence of peroxides. Alkenes undergo addition reactions with halogens, hydrogen halides, water, sulfuric acid and undergo oxidation, ozonolysis, and polymerization.
This document summarizes different types of substitution reactions in aliphatic and aromatic compounds. It describes three main types of substitution reactions: free radical substitution, electrophilic substitution, and nucleophilic substitution. Free radical substitution involves radicals and occurs in non-polar solvents. Electrophilic substitution can be aliphatic or aromatic and involves attack by an electrophile. Nucleophilic substitution involves displacement by a nucleophile and can proceed by SN1, SN2, or addition-elimination mechanisms. The document provides examples and details of the mechanisms and factors that influence each type of substitution reaction.
This document discusses nucleophilic substitution reactions. It begins by defining nucleophiles as negatively charged ions or neutral molecules with a lone pair of electrons. It then explains the mechanisms of the SN2 and SN1 reactions. The SN2 is a concerted bimolecular reaction where the nucleophile attacks from the backside of the substrate, inverting the configuration. The SN1 is a unimolecular reaction that proceeds through a carbocation intermediate, allowing for retention or inversion of configuration. Finally, it discusses factors like temperature, nucleophile strength, and substrate structure that determine whether a reaction will proceed by SN1 or SN2.
This document discusses aromaticity, including its introduction, criteria for aromatic compounds, Hückel's rule, examples of aromatic and anti-aromatic compounds, and non-aromatic compounds. Aromatic compounds are cyclic, planar, and have delocalized pi electrons that follow Hückel's rule of 4n+2 pi electrons. Benzene is used to originally define aromaticity. Resonance contributes greatly to aromatic stability. Anti-aromatic compounds have 4n pi electrons and are destabilized by cyclic pi electron delocalization. Cyclooctatetraene is provided as an example of a non-aromatic compound for not being planar.
The document discusses elimination reactions where a substrate loses a small group like HCl, H2O or Cl2 during reaction to form products. It specifically discusses E2 and E1 elimination reactions of alkyl halides with strong or weak bases. E2 reactions are concerted single step reactions that are stereospecific and regioselective. E1 reactions proceed through a carbocation intermediate in two steps, are not stereospecific but are regioselective following Zaitsev's rule. The rate and mechanism depends on the concentration of base, structure of substrate and leaving group. Hofmann elimination reactions give the least substituted alkene as the major product when the leaving group is bulky like trimethylammonium.
The document summarizes elimination reactions, which involve removing two substituents from a molecule in the presence of a base. It describes the E1 and E2 mechanisms, noting that E1 is first order and involves a carbocation, while E2 is second order. E2 requires an anti-coplanar orientation of the leaving groups and occurs more readily with secondary and tertiary substrates. The orientation of elimination is also discussed based on Saytzeff's and Hofmann's rules. Stereochemistry preferences, reactivity factors, and conclusions about elimination versus substitution are provided.
This document provides an overview of electrophilic substitution reactions. It defines electrophilic substitution as a reaction where a functional group is attached to a compound by replacing another functional group, often a hydrogen atom. It describes two main types: electrophilic aromatic substitution reactions, where an atom attached to an aromatic ring is replaced; and electrophilic aliphatic substitution reactions, where hydrogen in an aliphatic compound is usually replaced. The document also outlines the three step mechanism of electrophilic substitution reactions: 1) generating an electrophile, 2) forming a carbocation, and 3) eliminating a proton to restore aromaticity.
Alkyl halides are derivatives of alkanes where one or more hydrogen atoms are replaced by halogen atoms such as fluorine, chlorine, bromine, or iodine. They are represented by R-X, where R is an alkyl group and X is a halogen. Common methods for preparing alkyl halides include direct halogenation of alkanes, addition of hydrogen halides to alkenes and alkynes, and reactions of hydrogen halides, phosphorus halides, or thionyl chloride with alcohols. Alkyl halides undergo nucleophilic substitution and elimination reactions. They can be reduced to alkanes or used to form Grignard reagents. Common uses
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.
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.
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.
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.
This document discusses organic reaction intermediates, specifically carbocations and carbanions. It defines them as positively or negatively charged carbon-containing ions that are formed during chemical reactions and then react further to form final products. The key features, methods of formation, factors affecting stability, and synthetic applications of carbocations and carbanions are described. Inductive effects, resonance effects, and hyperconjugation influence the stability of these intermediates. Carbocations and carbanions are involved in many common organic reaction types such as eliminations, substitutions, additions, and rearrangements.
Cyclohexane exists in different conformations viz chair, boat, twist boat and half chair. These conformations possess different energies. Therefore they differ in energy.
This document provides an overview of reduction reactions in organic chemistry. It discusses various types of reduction reactions including catalytic hydrogenation, hydride transfer reactions using reagents like LiAlH4 and NaBH4, dissolving metal reductions, and others. Specific metal hydride reductions using boron and aluminum reagents like sodium borohydride, sodium cyanoborohydride, lithium aluminum hydride, and diisobutylaluminum hydride are explained in detail including their mechanisms and selectivity. Diimide reduction is also briefly covered. The document concludes with a bibliography of reference books on organic reaction mechanisms.
Carbanions are carbon atoms with a negative charge that are formed through various mechanisms. They can be classified based on their formation method such as through heterocyclic cleavage, proton abstraction using a base, decarboxylation, addition of a nucleophile to an alkene, or formation of an organometallic compound. Carbanion stability depends on factors like the electronegativity of the carbon, inductive effects, resonance effects, and attachment to sulfur or phosphorus. Aromatic carbanions and those with electron-withdrawing groups are particularly stable due to resonance delocalization. Carbanions have applications in reactions like the Perkin reaction, Claisen condensation, benzoin condensation,
Retrosynthetic analysis, definition, importance, disconnection approach, one group two group disconnection logical and illogical disconnection approach compounds containing two nitrogen atom retrosynthetic analysis of camphor, cartisone, reserpine
The document summarizes the pinacol-pinacolone rearrangement, which involves the conversion of a vicinal diol to a ketone or aldehyde in the presence of an acid. It was first described by German chemist William Rudolph Fittig in 1860. A key example is the conversion of pinacol to pinacolone using sulfuric acid. The reaction proceeds through protonation, dehydration, rearrangement, and dehydrogenation steps. The migratory aptitude is influenced by electronic effects and stability of the carbocation intermediate. The rearrangement has applications in synthesizing carbonyl compounds, cyclic ketones, spiro-compounds, and supports ring expansions and contractions.
Nucleophilic aromatic substitution is a reaction where a nucleophile displaces a good leaving group such as a halide on an aromatic ring. The document discusses several mechanisms for nucleophilic aromatic substitution including SNAr, SN1, benzyne, SRN1, and examples like the Von Richter and Smiles rearrangements. The rate is facilitated by electron-withdrawing groups on the aromatic ring that stabilize the cyclohexadienyl anion intermediate.
Alkenes and their preparation-HYDROCARBONS PART 2ritik
Alkenes can be prepared through various methods including reduction of alkynes, dehydrohalogenation of alkyl halides, dehydration of alcohols, and heating vicinal dihalogen derivatives with zinc dust. Addition reactions of alkenes follow Markovnikov's rule or anti-Markovnikov's rule in the presence of peroxides. Alkenes undergo addition reactions with halogens, hydrogen halides, water, sulfuric acid and undergo oxidation, ozonolysis, and polymerization.
This document summarizes different types of substitution reactions in aliphatic and aromatic compounds. It describes three main types of substitution reactions: free radical substitution, electrophilic substitution, and nucleophilic substitution. Free radical substitution involves radicals and occurs in non-polar solvents. Electrophilic substitution can be aliphatic or aromatic and involves attack by an electrophile. Nucleophilic substitution involves displacement by a nucleophile and can proceed by SN1, SN2, or addition-elimination mechanisms. The document provides examples and details of the mechanisms and factors that influence each type of substitution reaction.
This document discusses nucleophilic substitution reactions. It begins by defining nucleophiles as negatively charged ions or neutral molecules with a lone pair of electrons. It then explains the mechanisms of the SN2 and SN1 reactions. The SN2 is a concerted bimolecular reaction where the nucleophile attacks from the backside of the substrate, inverting the configuration. The SN1 is a unimolecular reaction that proceeds through a carbocation intermediate, allowing for retention or inversion of configuration. Finally, it discusses factors like temperature, nucleophile strength, and substrate structure that determine whether a reaction will proceed by SN1 or SN2.
This document discusses aromaticity, including its introduction, criteria for aromatic compounds, Hückel's rule, examples of aromatic and anti-aromatic compounds, and non-aromatic compounds. Aromatic compounds are cyclic, planar, and have delocalized pi electrons that follow Hückel's rule of 4n+2 pi electrons. Benzene is used to originally define aromaticity. Resonance contributes greatly to aromatic stability. Anti-aromatic compounds have 4n pi electrons and are destabilized by cyclic pi electron delocalization. Cyclooctatetraene is provided as an example of a non-aromatic compound for not being planar.
The document discusses elimination reactions where a substrate loses a small group like HCl, H2O or Cl2 during reaction to form products. It specifically discusses E2 and E1 elimination reactions of alkyl halides with strong or weak bases. E2 reactions are concerted single step reactions that are stereospecific and regioselective. E1 reactions proceed through a carbocation intermediate in two steps, are not stereospecific but are regioselective following Zaitsev's rule. The rate and mechanism depends on the concentration of base, structure of substrate and leaving group. Hofmann elimination reactions give the least substituted alkene as the major product when the leaving group is bulky like trimethylammonium.
The document summarizes elimination reactions, which involve removing two substituents from a molecule in the presence of a base. It describes the E1 and E2 mechanisms, noting that E1 is first order and involves a carbocation, while E2 is second order. E2 requires an anti-coplanar orientation of the leaving groups and occurs more readily with secondary and tertiary substrates. The orientation of elimination is also discussed based on Saytzeff's and Hofmann's rules. Stereochemistry preferences, reactivity factors, and conclusions about elimination versus substitution are provided.
1. Quaternary alkylammonium hydroxide undergoes elimination on heating to give the corresponding alkene through an E2 reaction.
2. Elimination reactions can occur through either an E1 or E2 mechanism. E2 reactions are favored with strong bases and hindered substrates, occurring through a concerted mechanism without a carbocation intermediate. E1 reactions involve the formation of a carbocation intermediate and are favored with weaker bases and good leaving groups.
3. Both substitution and elimination reactions are possible depending on factors like the nucleophilicity of the reagent, the stability of any carbocation intermediate, and the ability of the substrate to undergo the concerted E2 mechanism. Strong nucle
The document discusses several topics related to chemistry:
1) The voltage needed to create an electron is about one million volts, the same voltage as lightning. This high voltage accelerates electrons from the sky to the ground.
2) Alcohols are derivatives of hydrocarbons where an –OH group replaces a hydrogen. They can act as both acids and bases.
3) Phenols have a hydroxyl group bonded directly to a benzene ring. They are named based on the carbon the hydroxyl group is bonded to, such as phenol itself or cresols which are methyl phenols.
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.
Pharmaceutical Chemistry, SN Reaction, Mr. Jimmy Alexander ,Associate Profes...JIMMYALEX8
The document discusses nucleophilic substitution reactions SN1 and SN2. It provides details about:
- The mechanisms of SN1 and SN2 reactions, which involve nucleophilic attack on an alkyl halide substrate.
- Factors that affect the rates of SN1 and SN2 reactions, including the nature of the substrate, nucleophile, leaving group, and solvent.
- The characteristics of SN1 and SN2 reactions, where SN1 is unimolecular and first-order and SN2 is bimolecular and second-order.
The document discusses different types of substitution reactions including nucleophilic substitution, electrophilic substitution, and free radical substitution. It provides details on the mechanisms, kinetics, stereochemistry and factors affecting the rate of nucleophilic substitution reactions SN1 and SN2. SN1 follows a unimolecular mechanism involving a carbocation intermediate while SN2 follows a bimolecular mechanism with a single concerted transition state. The document also discusses electrophilic aromatic substitution reactions and addition and elimination reactions of alkenes and alkynes.
6578b504bd0d770018c06553_##_Hydrocarbons Class Notes (One Shot) .pdfrainaman0704
The document discusses organic chemistry topics related to hydrocarbons including solvents, electrophiles, nucleophiles, reactions of alkanes, alkenes, alkynes and benzene, physical properties, acid-base reactions, stereochemistry of alkene reactions, and preparation of alkenes and alkynes. It provides examples of reactions such as halogenation, hydrogenation, oxidation, ozonolysis, hydration and discusses concepts such as Markovnikov's rule, anti-Markovnikov addition, and stereochemistry.
The document summarizes various organic reaction mechanisms including:
1) Free radical substitution, electrophilic addition, nucleophilic substitution, elimination, addition-elimination, electrophilic substitution, esterification, alkaline hydrolysis, nucleophilic addition.
2) Specific mechanisms are described for hydration of alkenes, addition polymerization, bromination of alkenes, nucleophilic substitution, elimination, dehydration, esterification.
3) The formation of polymers like polyamides, polyesters through reactions of dibasic acids and diamines or diols are summarized.
(i) Non-classical carbocations display delocalization of sigma bonds through 3-center-2-electron bonds in bridged systems. Neighboring group participation can assist reactions by donating electrons through lone pairs, pi bonds, aromatic rings, or sigma bonds.
(ii) The pinacol-pinacolone rearrangement involves the migration of an alkyl group from one carbon to another after the loss of a leaving group from a vicinal diol. The migration is assisted by delocalization of the carbocation intermediate onto the oxygen atom.
(iii) In asymmetrical glycols, the group with greater ability for carbocation delocalization, such as phenyl, will migrate preferentially over
Alkenes contain carbon-carbon double bonds which give them unique reactivity and properties. There are two types of bonds in a C=C double bond - a sigma bond and a pi bond. The pi bond is weaker and is responsible for alkenes being more reactive than alkanes. Alkenes exhibit geometric isomers (cis/trans or E/Z) due to the rigidity of the pi bond. Common methods for synthesizing alkenes include elimination reactions and dehydrohalogenation reactions using a strong base. Alkenes are important industrially as monomers for polymers such as polystyrene and PTFE.
Organoborane chemistry deals with organoboron compounds that contain carbon-boron bonds. Key reactions of organoboranes include hydroboration of alkenes, oxidation of organoboranes to alcohols, isomerization of organoboranes at high temperatures, protonolysis with carboxylic acids, and carbonylation with carbon monoxide. Carbonylation can produce aldehydes, ketones, or alcohols depending on reaction conditions and presence of migrating groups.
This document discusses various electrophilic addition reactions involving alkenes, including:
1. Markovnikov's rule and the mechanisms of halogenation, halohydrin formation, oxymercuration, and hydroboration reactions.
2. The stereochemistry and selectivity of addition for these reactions. Anti addition and Markovnikov selectivity are common.
3. Other reactions producing diols from alkenes, such as osmium tetroxide catalyzed dihydroxylation, epoxide openings, and permanganate hydroxylation.
The document discusses various methods for preparing hydrocarbons such as alkanes, alkenes, and alkynes. It describes 6 methods for preparing alkynes including from calcium carbide, by dehalogenation of tetrahalides, and by chloroform and silver powder. It also summarizes techniques for preparing alkanes and alkenes including reduction, Wurtz reaction, dehydration of alcohols, and Kolbe's electrolysis. Key reactions covered are Birch reduction, Lindlar's catalyst, hydroboration-oxidation, oxymercuration-demercuration and their mechanisms.
(i) The document discusses elimination reactions, specifically the E2 and E1 mechanisms.
(ii) The E2 reaction is bimolecular and results in retention of stereochemistry. The E1 reaction is unimolecular and results in loss of stereochemistry.
(iii) Key factors that influence whether an elimination reaction proceeds by E2 or E1 include temperature, solvent, and the stereoelectronic effects of the starting material. Higher temperatures and polar protic solvents favor E1, while less sterically hindered substrates favor E2.
Synthon or Disconnection or Retrosynthesis Approach in Organic Synthesis. This document discusses the key concepts and approaches of retrosynthesis including: 1) Disconnecting a target molecule into logical fragments through breaking bonds to obtain starting materials, 2) It is the reverse of chemical synthesis, 3) Terminologies such as disconnection, synthon, and reagents, 4) Basic rules for preferred disconnections.
The document provides solutions to sample problems from Chapter 10 on nucleophilic substitution at the carbonyl group. The first problem suggests reagents to synthesize the drug phenaglycodol in three steps: addition of cyanide to a ketone, addition of an alcohol to the nitrile, and double addition of an organometallic reagent to an ester. The second problem explains why direct ester formation from carboxylic acids and alcohols works in acid but not base, while other methods use base. The third problem predicts the success of potential carbonyl substitutions based on leaving group pKa values. The last problem provides mechanisms for reactions involving an amine, alcohol, and acid chloride.
Pinacol pinacolone rearrangement involves conversion of 1,2 - diols to carbonyl compounds in presence of acid catalyst with change in carbon skeleton. It is an example of whitmore shift.
This document summarizes different types of reactions that alkyl halides undergo: nucleophilic substitution and elimination reactions. It describes the SN2, SN1, E2 and E1 reaction mechanisms in detail. The key points are:
- SN2 is a single-step reaction that proceeds with inversion of configuration. It is sensitive to steric effects.
- SN1 is a two-step reaction involving carbocation formation. It can lead to loss of chirality and is favored for tertiary alkyl halides.
- E2 is a concerted elimination reaction that is stereospecific. E1 proceeds through a carbocation and is not stereospecific.
- The type of reaction depends on the structure
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Elimination reaction
1. Elimination Reaction
Elimination reactions involve the loss of elements from the starting material to form
a new π bond in the product.
Alkyl halides (RX) undergo elimination with bronsted bases. The elements of HX are
lost and alkene are formed.
X, OH, OR, N2
+, N3, H2O+, NR3
+ and SR2
+
Leaving groups
Classification
α-elimination (1,1)
β- elimination (1,2)
γ- elimination (1,3)
β- elimination
E1
E2
E1CB
2. Substitution and Elimination in alkyl halides
Br
Br
fast
H2O or OH
OH
t-butyl bromide
t-butanol
Substitution on t-butyl bromide invariably follow SN1 mechanism. The
following reaction can not be speeded up by 1) changing the nucleophile from
H2O to OH-, 2) increasing the concentration of OH-.
With conc. NaOH
rate = k [t-BuBr]
Br
+ OH HOH Br rate = k [t-BuBr] [OH-]
t-butyl bromide
isobutene
(2-methylpropene)
Br
OHH
r=k[t-BuBr][OH-] HOHBr
Elimination occurs when the nucleophile attacks H instead of carbon
E2 (elimination bimolecular)
3. Elimination of t-butyl happens because here the Nu- (OH) is basic. Hydrogen is
not acidic but proton removal occurs because Br- is a good leaving group.
Rate = k2[t-BuBr][OH-]
O H
t-b u ta n o l
O H 2
B r
fa s t
B r
t-b u ty l b ro m id e
Nucleophilic substitution of t-BuOH with HBr
H2SO4 H + S
O O
OHO
OH
H
OH2
H
t-butanol in H2SO4 does not undergo substitution but elimination. HSO4
- is a weak
nucleophile.
4. Role of nucleophile in Elimination vs Substitution
Basicity
H
X
Attackhereleadstosubstitution
Attackhereleadstoelimination
Cl OEt
Cl
SN1
HOEt
EtOH
pKaofEtOH2=-7
-H+
Weak base: substitution
C l
E tO -
C l
H
O E t-
p K a E tO H = 1 6
Strong base: elimination
5. Size of the nucleophile
Getting at a more exposed hydrogen atom in an elimination reaction is much easier,
which means if we use a bulky and basic nucleophile elimination becomes preferred
over substitution.
B r
B rH
O H
K O H O H
S N 2
B r K O t-B u
E 2
H
B r
H
H
O
Small nucleophile: substitution
large nucleophile: elimination
Large alkyl substituent makes it hard for oxygen to attack at carbon but there is no
problem in attacking hydrogen.
6. Temperature
2 molecules 3 molecules
Elimination
2 molecules 2 molecules
Substitution
ΔS elimination > ΔS substitution
ΔG = ΔH − 𝑇ΔS
This equation says that a reaction in which ΔS is positive becomes more
favourable (ΔG is more –ve) at higher temperature. Elimination should therefore
be favoured at high temperature.
H
R
H
H
R
X
H
R
H
H
R
Base
H
R R
H
rds
Rate=k[alkyl halide]
E1 elimination
E1 describes an elimination reaction E in which the rate-determining step is
unimolecular and does not involve the base. The leaving group leaves in first step
and the proton is removed in a separate step.
7. E2 elimination
H
H
R
R
H
X
base
H
RR
H
Rate = k[Base] [alkyl halide]
E 2 describes an elimination that has a bimolecular (2) rate determining step that must
involve the base . Loss of leaving group is simultaneous with removal of the proton by
the base.
Factors that affect the nature of elimination
High conc. of base favours E2
Strong base favours E2 over E1
Substrate structure for E1
If the starting material is tertiary alkyl halide it would substitute only by SN1. But it
eliminate either by E1 (with weak base) or E2(with strong bases).
E1 occurs with substrates which ionise to give stable carbocations. Ex: tertiary,
benzylic alkyl halides, allylic etc .
Base
9. Role of leaving group
Any good leaving group will lead a faster E1 and E2 reaction.
OH is never a leaving group in elimination reaction. It is converted to tosylate or
mesylate for elimination.
H3C
S
O
O
Cl S
OO
H3C Cl
Tosyl chloride Mesyl chloride
O H
S
OO
C l
H 3 C
O T S
t-BuoK/E2
10. Stereoselectivity of elimination
Stereoselectivity- Whether the resulting alkene is cis or trans
Regioselectivity- Where is double bond is located in the product
Ph
OH
Ph
HOHH
Only one alkene possible
Two regioisomeric alkene possible
OH
and/or
H+
trisubstituted
alkene
disubstitutedalkene
Two stereoisomeric alkenes possible
Ph
OHH+
Ph Ph
and/or
trans cis
11. E alkenes are thermodynamically stable than Z alkenes.
Ph
OHH+
Ph Ph
and/or
95% E alkene 5% Z alkene
H2SO4
HO
Ph
CH3
H
H
H
Ph
CH3
H2O
H
H
H H
Ph
CH3
H
H
H2O
Ph
CH3
Geometry of the product
depends on conformation
about this bond
The new π bond can be formed if the vacant p orbital of the carbocation and the
breaking of C-H bond are aligned parallel.
Ph
H
H
HCH3
lowenergy
intermediate
Ph
H
H
H3C H
Highenergy
intermediate
12. Regioselectivity in E1
OH
HBr,H2O
Major Minor
More substituted alkenes are more stable.
π-system of the double bond is stabilized when the empty π* antibonding orbital can
interact with filled σ bonding orbital of C-H bond. More the C-C, C-H bonds, more stable
is the alkene.
H
H
H
CH3
H
HCH3
H3C
H
H
H
H
H
H
HH
H
H
C
H
H
H
H
H
H
Increasing substitution allows more and more C-H and C-C bonds to interact with π*.
(Saytzev Product)
13. E2 is highly sterioselective
In E2 the new π bond is formed by overlap of σ bonding orbital of C-H and σ* orbital of
C-X bond. Two orbitals have to lie in the same plane for the best overlap.
H
X HX
There are two possible overlaps where H and X are coplanar.
H
X HX
X HX
H
Antiperiplanner
(staggered)
Syn-periplanner
Eclipsed
The anti-periplanar conformation is more stable because it is staggered. E2
elimination takes place preferentially from anti-periplanar conformation.
14. 81%but2-ene
19%
Br
H
H CH3
Br
CH3H
H
H3C H
Br
CH3H
major
minor
2-Bromobutane has 2 conformers. But the one with less hindered leads to the
more of product. Hence E isomer predominates.
Stereospecificity of E2
When there is only one proton to take part in elimination, there is no choice of
antiperiplanar TS. In that case E2 leads to the production of a single isomer as a
direct result of mechanism of the reaction and stereochemistry of starting
material.
16. CH3
Cl
CH3 CH3
ratio of 1:3
A
Cl
NaOEt
250 times slower
B
???Most substituted is the
major product
Cl
CH3
H
Cl
CH3
OEt
A has Cl axial all the time ready for E2 where as B has Cl axial only in minute proportion of the
molecule that happen not to be in lowest energy state. Concentration of reactive molecule
is low so rate is low.
Cl
H
CH3
H
H
H
H
CH3
Cl
OEt
Reactivity of diastereomers A and B are different when treated with NaOEt.
NaOC2H5
NaOC2H5
18. Hoffmann elimination product takes place in the following four cases.
Bulky base
When leaving group is poor such as F-, NR3
+ , SR2
+.
Steric hinderance at β carbon
When alkyl halide contains one or more double bond.
Poor leaving
group
F
H
F
H
H2C
H
OCH3
F
F
H
O C H 3
δ-
δ-
Base begins to abstract proton before
leaving group leaves . –Ve charge
develops on carbon. Transition state has
carbanion character.
NaOCH3 NaOCH3
More
stable
Less
stable
20. Regiselectivity in E2
Cl
KOCEt3
OH
H3PO4
120C
E1, more substituted alkene Less substituted alkene
with hindered base
Br
NaOC2H5t-BuOK
69%31%73%26%
Base attacks methyl – H because
they are less hindered
More substituted product
with less hindered base
E1 reaction gives more substituted alkene.
E2 reactions may give more substituted alkene, but become more regioselective
for the less substituted alkene with more hindered bases.
21. E1CB Elimination unimolecular conjugate base
OOH
H
pKa=20
acidic
KOH
O
The base can remove –H before the leaving group departs. The resulting anion is stable.
OOH
H
KOH
O
OH
OH
OOH O
The leaving group is not lost from starting material it is lost from the conjugate base.
Hence E1CB mechanism. Although OH is not a leaving group in E2 it can be a leaving
group in E1CB. Establishment of conjugation in the product assists loss of OH-.
rds
23. Q. Write the rate equation for the following reaction.
R R
O O H
O H
R R
O
R R
O O H
O H H 2 O
R R
O O H
ra te
c o n s ta n t = k
R R
Oe q u illib riu m
c o n s ta n t = KA.
K
R R
O O H
R R
O O H
H 2O
O H
therefore
R R
O O H
=
K
H 2O R R
O O H
O H
rate = k
K
H 2O
R R
O O H
O H = constant x
R R
O O H
O H
=