Chapter 13: Aldehydes and Ketones

Before you can learn about aldehydes and ketones, you must first know something about the nomenclature of carboxylic acids since many of the names of aldehydes and ketones are derived from the names of the corresponding carboxylic acids. Carboxylic acids: R-COOH, R-CO2H, Common names: HCO2H formic acid formica ant CH3CO2H acetic acid acetum vinegar CH3CH2CO2H propionic acid “first salt” CH3CH2CH2CO2H butyric acid butyrum butter CH3CH2CH2CH2CO2H valeric acid valerans

ALDEHYDES COMMON NAMES STEM PLUS ALDEHYDE HCHO HCO2H FORMALDEHYDE FORMICA - ANTS FORMIC ACID CH3CHO CH3COOH ACETALDEHYDE ACETUM - SOUR ACETIC ACID CH3CH2CHO CH3CH2CO2H PROPIONALDEHYDE PROTOS PION - FIRST FAT PROPIONIC ACID CH3CH2CH2CO2H CH3CH2CH2CHO BUTYRALDEHYDE BUTRYM - BUTTER BUTYRIC ACID CH3CH2CH2CH2CH2CHO CH3CH2CH2CH2CH2CO2H CAPROALDEHYDE CAPER - GOAT CAPROIC ACID

Naming Aldehydes IUPAC: Replace -e with -al. The aldehyde carbon is number 1. If -CHO is attached to a ring, use the suffix - carbaldehyde. Chapter 18

Common Formaldehyde Acetaldehyde Propionaldehyde Butyraldehyde IUPAC Methanal Ethanal Propanal Butanal

Nomenclature

Aromatic aldehydes are usually designated as derivatives of the simplest aromatic aldehyde, Benzaldehyde. Benzaldehyde p-Nitrobenzaldehyde o-Hydroxybenzaldehyde p-Methoxtbenzaldehyde

Ketones: Structure and Nomenclature General formula: RCOR’ (R and R’=alkyl or aryl) Common name: listing the alkyl substitutents attached to the carbonyl group, followed by the word ketone. IUPAC system: relpace the ending –e by the suffix –one. The chain is numbred in such a way as give the lowest number to the C=O group. Common Dimethyl ketone Methyl phenyl ketone Methyl vinyl ketone Diphenyl ketone Acetone Acetophenone Benzophenone IUPAC Propanone Phenyl ethanone 3-Buten-2-one Diphenylmethanone

(o)phenones: Derived from common name of carboxylic acid, drop –ic acid, add –(o)phenone.

Cyclopentylpropanone 3-Ethyl-2-hydroxycyclohexanone 5-Oxohexanal

Boiling Points More polar, so higher boiling point than comparable alkane or ether. Cannot H-bond to each other, so lower boiling point than comparable alcohol. => Chapter 18

Solubility Good solvent for alcohols. Lone pair of electrons on oxygen of carbonyl can accept a hydrogen bond from O-H or N-H. Acetone and acetaldehyde are miscible in water. => Chapter 18

Aldehydes synthesis 1) oxidation of primary alcohols: RCH2-OH + K2Cr2O7 (potassium dichromate)  RCH=O+ H2 RCH2-OH + C5H5NHCrO3Cl  RCH=O+ H2 (pyridinium chlorochromate, or PCC) [With other oxidizing agents, primary alcohols  RCOOH]

Aldehyde synthesis: Primary alcohols

Aldehyde synthesis: 2) reduction of acid chloride

Ketone synthesis: 1) oxidation of secondary alcohols

Ketone synthesis: 2) Friedel-Crafts acylation Aromatic ketones (phenones) only!

Friedel Crafts acylation does not work on deactivated rings.

Acetals andHemicetals Acetal: two –OR groups bonded to the same carbon Hemiacetal: one –OR group and one –OH group bonded to the same carbon

Enolization Keto-Enol Tautomerism Tautomerism: interconversion between two structures that differ by the placement of an atom or group Slow in neutral conditions, sped up in acid or base catalyzed systems Enol content is very small, <<<1% for most aldehydes and ketones