Chapter 16 Aldehydes and Ketones I: Nucleophilic Addition to the Carbonyl Group

Transcription

1 Aldehydes and Ketones I: Nucleophilic Addition to the arbonyl Group

2 16.1 Introduction

3 Aldehydes and ketones contain an acyl group bonded either to hydrogen or to another carbon. Acyl group δ + δ 120 sp arbonyl group Formaldehyde General formulas for an aldehydes ' General formulas for a ketones

4 16.2 Nomenclature of Aldehydes and Ketones

5 Aldehydes are named by replacing the terminal e of the corresponding alkane name with al. The longest chain selected as the base name must contain the group, and the carbon is always numbered as carbon 1. Methanal (Formaldehyde) 3 Ethanal (Acetaldehyde) l hloropentanal 3 2 Propanal (Propionaldehyde) Phenylethanal (Phenylacetaldehyde)

6 For more complex aldehyde in which the group is attached to a ring, the suffix -carbaldehyde is used. Benzenecarbaldehyde (benzaldehyde) yclohexanecarbaldehyde 2-naphthalenecarbaldehyde 2-

7 Ketones are named by replacing the terminal e of the corresponding alkane name with one. The chain selected for the base name is the longest one that contains the ketone group, and the numbering begins at the end nearer the carbonyl carbon exanone 3- (common name: Ethyl propyl ketone) exen-2-one ,4-exanedione 2,4-

8 Some ketones have common names that are retained in the IUPA system Acetone Acetophenone Benzophenone propanone 1-phenylethanone diphenylmethanone (dimethyl ketone) (methyl phenyl ketone) (diphenyl ketone) When - group are named as substituents, they are called alkanoyl or acyl groups. 3 Acyl Formyl Acetyl Benzoyl

9 If another functional groups or a are present and the doubly bonded oxygen must be considered a substituent, the prefix oxo- is used xopentanal xohexanoic acid 4-2'-xocyclohexanecarbaldehyde 2'-

10 16.3 Physical Properties

11 Molecules of aldehyde (or ketone) cannot hydrogen bond to each other. They rely only on intermolecular dipole-dipole interactions and therefore have lower boiling points than the corresponding alcohols.

12 Aldehydes and ketones can form hydrogen bonds with water and therefore low molecular weight aldehydes and ketones have appreciable water solubility

13 16.4 Synthesis of Aldehydes

14 16.4A Aldehydes by xidation of 1 Alcohols 2 P

15 16.4B Aldehydes by eduction of Acyl hlorides, Esters, and Nitriles 2 LiAl 4 LiAl 4 2 Li ( 3 ) 3 Al ( 3 ) 3 ( 3 ) 3 2 ( 3 ) 2 Al 2 ( 3 ) 2 Lithium tri-tert-butoxyaluminium hydride LiAl(-t-Bu) 3 Diisobutylaluminium hydride i-bu 2 Al or DIBAL-

16 l (1) LiAl(-t-Bu) 3, 78 (2) 2 ' N (1) DIBAL-, hexane, 78 (2) 2 (1) DIBAL-, hexane, (2) 2 l Pd-BaS S-quinoline osenmund reduction

17 16.5 Synthesis of Ketones

18 16.5A Ketones from Alkenes, Arenes, and 2 Alcohols Ketones (and aldehydes) by ozonolysis of alkenes (1) 3, (2) 2 /Zn Ketones from arenes by Friedel-rafts acylations l or () 2 /All 3 Ketones from 2 alcohols by oxidation 2 r 4

19 16.5B Ketones from Alkynes + 2 gs 4 2 S A vinylic alcohol (unstable) Enol form 3 Ketone Keto form Keto-enol tautomerizations

20 16.5 Ketones from Lithium Dialkylcuprates l + ' 2 uli ' + 'u + Lil l + ( 3 ) 2 uli Et (81%)

21 16.5B Ketones from Nitriles 'MgX N MgX ' 3 + N 'Li N Li ' 3 + '