Topic 20 3 elimination reactions
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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.
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Cycloaddition reactions: combination of two words "cyclo" and "addition", which means addition of two molecules to form a new ring system.
Reterocycloaddition reactions : reverse of cycloaddition reactions is known as reterocycloaddition reactions
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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.
9. NBS
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This document discusses carbanions, which are negatively charged carbon-containing species. It describes the structure of carbanions as sp3 hybridized and tetrahedral. Carbanions are stabilized by several factors, including inductive and resonance effects. The stability increases with increased s-character of the carbon atom and delocalization of the negative charge. Carbanions are nucleophilic and can be formed through deprotonation, decarboxylation, metal reduction, or addition to multiple bonds. They have applications in reactions like aldol condensation, Michael addition, Grignard reagents, and the Perkin reaction.
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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.
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An organic species which has a carbon atom bearing only six electrons in its outermost shell and has a positive charge is called carbocation.
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Aromatic Carboxylic acids: Carboxylic acids have an aryl group bound to the carboxyl group is known as aromatic carboxylic acids. The general formula of an aliphatic aromatic carboxylic acid is Ar-COOH.
Acidity of carboxylic acid:
A carboxylic acid may dissociate in water to give a proton and a carboxylate ion. Dissociation of a carboxylic acid involves breaking an O-H bond gives a carboxylate ion with the negative charge spread out equally over two oxygen atoms, compared with just one oxygen atom in an alkoxide ion. The delocalized charge makes the carboxylate ion more stable therefore; dissociation of a carboxylic acid to a carboxylate ion is less endothermic.
Preparation Methods:
1. Oxidation:
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2. Grignard reagents (from CO2):
Carboxylic acid can be prepared by the reaction of Grignard reagent (alkyl magnesium halide) with carbon dioxide (CO2) in presence of dry ether. Grignard reagents react with carbon dioxide to forms a magnesium carboxylates which on hydrolysis by dilute HCl produces carboxylic acids.
3. Hydrolysis of nitrile:
The hydrolysis of nitrile or cyanide in presence of dilute acid to forms a carboxylic acid. In this reaction –CN group is converted to a –COOH group.
4. Hydrolysis Reactions:
All the carboxylic acid derivatives can be hydrolyzed into the carboxylic acid in the acidic or basic media; the hydrolysis reaction is fast and occurs in presence of water with no acid or base catalyst.
1. From Ester (Hydrolysis of ester): Ester can be hydrolyzed in either acidic or basic medium to yield carboxylic acid. The ester is heated with an excess of water contains strong acid or base catalyst.
Properties of Carboxylic Acids:
1. Low molecular weights carboxylic acids are colourless liquid at room temperature i.e. lower member ate liquid up to C9 and have characteristic odors whereas higher members are solid.
2. Carboxylic acids are polar organic compound. Low molecular weight carboxylic acids (first four members) are soluble in water whereas solubility in water decrease as molecular weight and chain lengthing increases.
3. Aromatic acids are insoluble in water.
4. Carboxylic acids have higher melting and boiling point due to their capacity to readily form stable hydrogen-bonded dimers.
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2) The conjugate base is more labile than the original complex and undergoes an SN1 reaction by slowly dissociating chloride, forming a pentacoordinated intermediate.
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2) The products of SN2 reactions with cyanide ions and ammonia are nitriles and amines, respectively.
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1. Carbenes are neutral molecules containing a divalent carbon atom with six electrons and two substituents. They exist as either singlet or triplet states depending on the electronic spin.
2. Carbenes can be generated through reactions such as α-elimination of halogenated compounds with bases, thermal decomposition of diazo compounds, and metal-catalyzed decomposition of diazo carbonyl compounds.
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The combination of a carbonyl group and a hydroxyl on the same carbon atom is called a carboxyl group. Compounds containing the carboxyl group are called carboxylic acids. The carboxyl group is one of the most widely occurring functional groups in organic chemistry.
Aromatic Carboxylic acids: Carboxylic acids have an aryl group bound to the carboxyl group is known as aromatic carboxylic acids. The general formula of an aliphatic aromatic carboxylic acid is Ar-COOH.
Acidity of carboxylic acid:
A carboxylic acid may dissociate in water to give a proton and a carboxylate ion. Dissociation of a carboxylic acid involves breaking an O-H bond gives a carboxylate ion with the negative charge spread out equally over two oxygen atoms, compared with just one oxygen atom in an alkoxide ion. The delocalized charge makes the carboxylate ion more stable therefore; dissociation of a carboxylic acid to a carboxylate ion is less endothermic.
Preparation Methods:
1. Oxidation:
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2. Grignard reagents (from CO2):
Carboxylic acid can be prepared by the reaction of Grignard reagent (alkyl magnesium halide) with carbon dioxide (CO2) in presence of dry ether. Grignard reagents react with carbon dioxide to forms a magnesium carboxylates which on hydrolysis by dilute HCl produces carboxylic acids.
3. Hydrolysis of nitrile:
The hydrolysis of nitrile or cyanide in presence of dilute acid to forms a carboxylic acid. In this reaction –CN group is converted to a –COOH group.
4. Hydrolysis Reactions:
All the carboxylic acid derivatives can be hydrolyzed into the carboxylic acid in the acidic or basic media; the hydrolysis reaction is fast and occurs in presence of water with no acid or base catalyst.
1. From Ester (Hydrolysis of ester): Ester can be hydrolyzed in either acidic or basic medium to yield carboxylic acid. The ester is heated with an excess of water contains strong acid or base catalyst.
Properties of Carboxylic Acids:
1. Low molecular weights carboxylic acids are colourless liquid at room temperature i.e. lower member ate liquid up to C9 and have characteristic odors whereas higher members are solid.
2. Carboxylic acids are polar organic compound. Low molecular weight carboxylic acids (first four members) are soluble in water whereas solubility in water decrease as molecular weight and chain lengthing increases.
3. Aromatic acids are insoluble in water.
4. Carboxylic acids have higher melting and boiling point due to their capacity to readily form stable hydrogen-bonded dimers.
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2) The conjugate base is more labile than the original complex and undergoes an SN1 reaction by slowly dissociating chloride, forming a pentacoordinated intermediate.
3) Several experiments provide evidence that the reaction follows a conjugate base mechanism, including second-order kinetics and the rate being independent of hydroxide concentration at high levels.
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This document discusses nucleophilic substitution reactions, specifically SN1 and SN2 mechanisms. SN1 is a two-step reaction that proceeds through a carbocation intermediate, depending on the concentration of the substrate. SN2 is a one-step bimolecular reaction where bond breaking and formation occur simultaneously. Tertiary halogenoalkanes typically undergo SN1, while primary halogenoalkanes usually undergo SN2 due to steric and inductive effects. Factors like the nature of the halogen, halogenoalkane, and nucleophile affect the rate of these substitution reactions.
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Carbohydrates and lipids are both important macronutrients that provide energy. Carbohydrates include sugars, starches, and fiber. They provide 4 calories per gram and energy storage. Lipids include fats and are the body's main form of long-term energy storage. Fats are made of fatty acids and glycerol. Carbohydrates and lipids are broken down and absorbed in the small intestine, and their levels in the bloodstream are regulated by hormones like insulin and glucagon to maintain homeostasis. A balanced intake of carbohydrates and fats from whole foods is recommended.
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2) It also discusses percent yield calculations. For the example reaction of gold (III) chloride and lead, the theoretical yield of gold is calculated to be 9.09g based on the given amount of gold (III) chloride.
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2012 topic 4.2 vsepr theory
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2012 topic 4.1 bonding - metallic
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IB Chemistry on HNMR Spectroscopy and Spin spin coupling
This document provides an overview of nuclear magnetic resonance (NMR) spectroscopy. It discusses how certain nuclei can absorb electromagnetic radiation due to their spin and magnetic moment. NMR spectroscopy is used to determine organic structures and for medical imaging. The key features of 1H NMR spectra are described, including the number of peaks, peak areas, chemical shifts, and splitting patterns due to spin-spin coupling. Examples are given to illustrate how the number of equivalent protons on neighboring carbons determines the splitting pattern.
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This document provides an overview of exothermic and endothermic reactions, calorimetry, and how to calculate enthalpy changes. It discusses key concepts like:
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- 1. IB Chemistry Power Points Topic 20 Organic Chemistry www.pedagogics.ca Elimination Reactions
- 2. Elimination of HBr from halogenoalkanes Recall: nucleophilic substitution of a bromoalkane
- 3. Elimination of HBr from halogenoalkanes Recall: nucleophilic substitution of a bromoalkane
- 4. Elimination of HBr from halogenoalkanes Recall: nucleophilic substitution of a bromoalkane Reaction occurs when bromoethane is added to a dilute NaOH solution. If conditions change, the nature of the reaction will change
- 5. Elimination of HBr from halogenoalkanes An elimination reaction is one where a small molecule is removed from the reactant molecule. Substitution OH- + C2H5Br C2H5OH + Br- Elimination OH- + C2H5Br C2H4 + H2O + Br- Which reaction occurs depends on the reacting conditions.
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- 9. Elimination reaction mechanisms E1 mechanism - similar to SN1 - unimolecular process - carbocation intermediate - typical of tertiary substituted alkyl halides
- 10. Elimination reaction mechanisms How the reactions happen – the role of OH- The hydroxide ion hits one of the hydrogen atoms in the alkyl halide and pulls it off. ACTS as a BASE! (proton acceptor) This leads to a cascade of electron pair movements resulting in the formation of a carbon-carbon double bond, and the loss of the halogen as R-.