lecture 16.2

Lecture 16.2 - Organic Organic H BrownWilliam H BrownChristopher S FooteChristopher S FooteBrent L IversonBrent L IversonAldehydes

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Unformatted text preview: 16-16-11Organic Organic ChemistryChemistryWilliam H. BrownWilliam H. BrownChristopher S. FooteChristopher S. FooteBrent L. IversonBrent L. Iverson16-16-22Aldehydes Aldehydes & & KetonesKetones Chapter 16Chapter 1616-16-33Addition of HCNAddition of HCN◆HCN adds to the C=O group of an aldehyde or ketone to give a cyanohydrin◆Cyanohydrin:Cyanohydrin: a molecule containing an -OH group and a -CN group bonded to the same carbon2-Hydroxypropanenitrile(Acetaldehyde cyanohydrin)+HC NCH3C-C NCH3CHOHHO16-16-44Addition of HCNAddition of HCN◆Mechanism of cyanohydrin formation•Step 1: nucleophilic addition of cyanide to the carbonyl carbon•Step 2: proton transfer from HCN gives the cyanohydrin and regenerates cyanide ion-+H3CCH3COCO -H3CH3CCNNCCO -H3CH3CC NNH CCCH3CH3CO-HNC N++-16-16-55CyanohydrinsCyanohydrins◆The value of cyanohydrins•acid-catalyzed dehydration of alcohol gives an alkene•catalytic reduction of the cyano group gives a 1° aminePropenenitrile(Acrylonitrile)+acidcatalyst2-Hydroxypropanenitrile(Acetaldehyde cyanohydrin)CH3CHC NNCH2=CHCH2OOHCHCOHN2H2NiOHCHCH2NH22-Amino-1-phenylethanol(racemic)+Benzaldehydecyanohydrin(racemic)16-16-66Wittig ReactionWittig Reaction◆The Wittig reaction is a very versatile synthetic method for the synthesis of alkenes from aldehydes and ketones Triphenyl-phosphine oxideMethylene-cyclohexaneA phosphoniumylide++-+CH2Ph3P=OPh3P-CH2CyclohexanoneO16-16-77Phosphonium YlidesPhosphonium Ylides◆Phosphonium ylides are formed in two steps:•Step 1: nucleophilic displacement of iodine by triphenylphosphine•Step 2: treatment of the phosphonium salt with a very strong base, most commonly BuLi, NaH, or NaNH2Ph3PCH3-IPh3P-CH3ITriphenylphosphine++SN2Methyltriphenylphosphonium iodide(an alkyltriphenylphosphine salt)CH3CH2CH2CH2- Li +H-CH2-PPh3I--CH2-PPh3CH3CH2CH2CH3LiIA phosphoniumylideButaneButyllithium+++++16-16-88Wittig ReactionWittig Reaction◆Phosphonium ylides react with the C=O group of an aldehyde or ketone to give an alkene•Step 1: nucleophilic addition of the ylide to the electrophilic carbonyl carbon•Step 2: decomposition of the oxaphosphatane CR2OCH2Ph3PCH2-:OCR2Ph3POCR2...
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This note was uploaded on 03/30/2008 for the course CHEM 262 taught by Professor Forbes during the Spring '08 term at UNC.

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Lecture 16.2 - Organic Organic H BrownWilliam H BrownChristopher S FooteChristopher S FooteBrent L IversonBrent L IversonAldehydes

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