Organic Chemistry: Advanced Reaction Mechanisms, Synthesis, and Nomenclature Study Guide

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Organic Chemistry Reaction Mechanisms and Synthesis

Wolff–Kishner Reduction of Aldehydes and Ketones

The Wolff–Kishner reduction is a method for converting aldehydes and ketones to alkanes using hydrazine and a strong base under high temperature.

Key Reaction: Aldehyde/ketone + H2NNH2, KOH, heat → Alkane
Mechanism: Formation of hydrazone intermediate, followed by base-induced elimination of nitrogen to yield the alkane.
Example: Cyclohexyl phenyl ketone treated with Wolff–Kishner conditions yields cyclohexylbenzene.

Cyanohydrin Formation

Cyanohydrins are formed by the nucleophilic addition of cyanide to carbonyl compounds. The reaction can occur in both acidic and basic conditions, but is commonly performed in basic medium using KCN.

Key Point: Cyanohydrin formation is possible in basic conditions with KCN.
Equation:
Example: Acetone + KCN → Acetone cyanohydrin

Protecting Groups in Synthesis

Protecting groups are used to temporarily mask functional groups during multi-step synthesis to prevent unwanted reactions.

Common Protecting Group: tert-Butyldimethylsilyl (TBDMS) ether for alcohols
Application: Protect alcohol, perform Grignard addition to ketone, then deprotect to yield desired alcohol.
Example: Cyclopentanone with a protected alcohol allows selective Grignard addition.

Nomenclature and Functional Group Identification

IUPAC Naming of Aldehydes and Ketones

Systematic naming follows rules for identifying the longest carbon chain containing the carbonyl group and assigning locants.

Key Terms: Aldehyde (-al), Ketone (-one)
Example: 2-Phenylpropanal: A three-carbon chain with a phenyl group at C-2 and an aldehyde at C-1.

Carboxylic Acids and Derivatives

Fischer Esterification

Fischer esterification is an acid-catalyzed reaction between a carboxylic acid and an alcohol to form an ester and water.

General Equation: (acid catalyst)
Example: Propionic acid + isopropanol → isopropyl propionate + water

Decarboxylation of β-Keto Acids

Decarboxylation is the loss of CO2 from carboxylic acids, especially β-keto acids, upon heating.

Key Point: β-Keto acids readily undergo decarboxylation due to stabilization of the transition state.
Equation:
Example: 3-oxopentanoic acid decarboxylates to butanone.

Acid-Catalyzed Esterification Reactions

Major products of acid-catalyzed esterification depend on the reactants and the acid used.

Example: Isobutyric acid + ethanol → ethyl isobutyrate
Example: Ethanol + nitric acid → ethyl nitrate

Advanced Synthesis and Organometallic Chemistry

Organocuprate Reagents in Synthesis

Organocuprates (Gilman reagents) are used for conjugate addition to α,β-unsaturated carbonyl compounds and for coupling reactions.

Key Reagent:
Application: Four-step synthesis may involve halogenation, organocuprate addition, oxidation, and other transformations.

Nitrile Nomenclature and Structure

Nitriles are named by identifying the longest carbon chain and the position of substituents.

Example: 4,4-diethylhexanenitrile: Hexane backbone, two ethyl groups at C-4, nitrile at C-1.

Reactivity of Esters and Hydrolysis

Esters undergo hydrolysis under acidic or basic conditions, breaking either the acyl–oxygen or alkyl–oxygen bond.

Key Point: Under basic conditions, acyl–oxygen bond breaks, yielding carboxylate and alcohol.
Equation:

Carbamate and Anhydride Structures

Carbamates are esters of carbamic acid; anhydrides are formed from two carboxylic acids.

Example: Phenyl N-ethyl carbamate: Phenyl group attached to carbamate, ethyl group on nitrogen.
Example: p-Nitrobenzoic anhydride: Two p-nitrobenzoic acid units joined via anhydride linkage.

Reactivity and Mechanistic Insights

Hydrolysis Reactivity of Esters

Reactivity toward hydrolysis depends on the nature of the alkyl or aryl group attached to the ester.

Key Point: Benzyl esters are generally more reactive than phenyl esters due to the stability of the benzyl carbocation intermediate.

Haloform Reaction

The haloform reaction converts methyl ketones to carboxylate ions and haloforms (e.g., CHCl3).

Key Point: Only methyl ketones can form haloforms because only they can have three halogen atoms on the α-carbon.
Equation:

Enolate Ion Resonance Structures

Enolate ions are formed by deprotonation of α-hydrogens in carbonyl compounds and are stabilized by resonance.

Example: Cyclopentane-1,3-dione and methyl acetoacetate enolate ions show delocalization of negative charge between oxygen atoms.

LDA-Mediated Enolate Formation and Alkylation

Lithium diisopropylamide (LDA) is a strong, non-nucleophilic base used to generate enolates for alkylation reactions.

Key Steps: Enolate formation, alkylation, and subsequent reactions to yield substituted ketones.

Decarboxylation and Synthesis of Cyclic Ketones

Decarboxylation of β-keto esters is a common method for synthesizing cyclic ketones.

Key Reaction: β-Keto ester + acid/heat → cyclic ketone + CO2

Tables

Decarboxylation Table

Compound	Decarboxylation upon heating?
β-Keto acid	Yes
Simple ester	No

Haloform Reaction Table

Compound Type	Forms Haloform?	Reason
Methyl ketone	Yes	Can have three halogens on α-carbon
Other ketones	No	Cannot form good leaving group

Hydrolysis Reactivity Table

Compound	Reactivity toward hydrolysis
Benzyl propionate	More reactive
Phenyl propionate	Less reactive

Additional info:

Some mechanistic details and resonance structures were inferred for completeness.
Tables were constructed to summarize key comparisons and reactivity trends.