A. What two sets of reagents (each consisting of a carbonyl...

Name: Problem 49, Chapter 16: Organic Chemistry
Uploaded: 2020-09-30T17:02:19-08:00
Duration: 12 min 42 s
Channel: Zubair Abdulla
Description: a. What two sets of reagents (each consisting of a carbonyl compound and phosphonium ylide) can be used for the synthesis of each of the following alkenes? b. What alkyl halide is required to prepare each of the phosphonium ylides? c. What is the best set of reagents to use for the synthesis?

a. What two sets of reagents (each consisting of a carbonyl compound and phosphonium ylide) can be used for the synthesis of each of the following alkenes? b. What alkyl halide is required to prepare each of the phosphonium ylides? c. What is the best set of reagents to use for the synthesis?

a. What two sets of reagents (each consisting of a carbonyl compound and phosphonium ylide) can be used for the synthesis of each of the following alkenes?
b. What alkyl halide is required to prepare each of the phosphonium ylides?
c. What is the best set of reagents to use for the synthesis?

Key Concepts

Alkyl Halide

Alkyl halides are used in the preliminary step of preparing phosphonium salts from phosphines. The choice of the alkyl halide defines the alkyl substituent on the phosphonium ylide, which in turn influences the structure of the final alkene produced in the Wittig reaction.

Carbonyl Compound

Carbonyl compounds, which include aldehydes and ketones, act as the electrophilic partners in the Wittig reaction. Their polarized carbonyl group (C=O) is susceptible to nucleophilic attack by the phosphonium ylide, leading to the formation of an oxaphosphetane intermediate and subsequently the alkene product.

Reagent Selection and Stereoselectivity

Choosing appropriate combinations of carbonyl compounds and alkyl halides is key to controlling the stereochemistry and substitution pattern of the alkene product in the Wittig reaction. Different sets of reagents can preferentially lead to the formation of either E or Z isomers, making the reagent selection crucial for achieving the desired stereochemical outcome.

Wittig Reaction

The Wittig reaction is an essential carbon-carbon bond forming method in organic synthesis, where a carbonyl compound reacts with a phosphonium ylide to produce an alkene and a phosphine oxide. This reaction proceeds via a [2+2] cycloaddition to form an intermediate that then decomposes, making it a popular and versatile strategy for constructing double bonds.

Phosphonium Ylide

A phosphonium ylide is a reactive intermediate characterized by a carbanion adjacent to a positively charged phosphorus atom. It is typically prepared by the alkylation of a phosphine with an alkyl halide followed by deprotonation with a strong base. This ylide's nucleophilic carbon is what attacks the electrophilic carbonyl compound in the Wittig reaction.

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