Holot CH3 H3C Ph₂p-CHCH3 Aldehydes and ketones are converted into alkenes by means of a direct nucleophilic addition called the Wittig reaction. In the reaction, a triphenylphosphorine ylide, also called a phosphorane, adds to an aldehyde/ketone to give a four-membered cyclic intermediate called an oxaphosphetane. The oxaphosphetane is not isolated but instead spontaneously decomposes to release triphenylphosphine oxide and an alkene. L CXT CH3 H₂C Br-CH₂CH3 :PPh3 The ylide is formed by reaction of triphenylphosphine, a good nucleophile, with a primary alkyl halide in an SN2 reaction, followed by deprotonation of the carbon with a strong base, such as butyllithium. The carbonyl carbon and the carbon originally bonded to the halogen become the two carbons with the double bond in the product alkene CH3 The real value of the Wittig reaction lies in its ability to yield an alkene of predictable structure, as the C=C bond is precisely where the C-O bond was in the reactant and no isomers (other than E/Z isomers) are formed. Draw curved arrows to show the movement of electrons in this step of the mechanism. Arrow-pushing Instructions Ph3P-CH₂CH3 Br Ph3P=O 76

Holot CH3 H3C Ph₂p-CHCH3 Aldehydes and ketones are converted into alkenes by means of a direct nucleophilic addition called the Wittig reaction. In the reaction, a triphenylphosphorine ylide, also called a phosphorane, adds to an aldehyde/ketone to give a four-membered cyclic intermediate called an oxaphosphetane. The oxaphosphetane is not isolated but instead spontaneously decomposes to release triphenylphosphine oxide and an alkene. L CXT CH3 H₂C Br-CH₂CH3 :PPh3 The ylide is formed by reaction of triphenylphosphine, a good nucleophile, with a primary alkyl halide in an SN2 reaction, followed by deprotonation of the carbon with a strong base, such as butyllithium. The carbonyl carbon and the carbon originally bonded to the halogen become the two carbons with the double bond in the product alkene CH3 The real value of the Wittig reaction lies in its ability to yield an alkene of predictable structure, as the C=C bond is precisely where the C-O bond was in the reactant and no isomers (other than E/Z isomers) are formed. Draw curved arrows to show the movement of electrons in this step of the mechanism. Arrow-pushing Instructions Ph3P-CH₂CH3 Br Ph3P=O 76

Organic Chemistry

8th Edition

ISBN:9781305580350

Author:William H. Brown, Brent L. Iverson, Eric Anslyn, Christopher S. Foote

Publisher:William H. Brown, Brent L. Iverson, Eric Anslyn, Christopher S. Foote

Chapter17: Carboxylic Acids

Section: Chapter Questions

Problem 17.44P

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