Aldehydes and Ketones — Part 1: Structure, properties and preparation: visual lesson, ISC Class 12 Chemistry

Lesson

Carbonyl compounds

Part 1 — aldehydes (R–CHO) and ketones (R–CO–R′): names, structure, properties and preparation.

In this lesson you will

Name aldehydes and ketones by IUPAC rules and describe the carbonyl group
Explain the boiling points of carbonyl compounds compared with alcohols and alkanes
Write equations to prepare aldehydes and ketones from alcohols, alkenes, alkynes, acid chlorides, calcium salts, nitriles and esters

Table of familiar carbonyl compounds
Compound	Where you meet it
Methanal (formalin, 40%)	Preserving biological specimens; resins
Propanone (acetone)	Nail-polish remover; solvent
Butanone	Industrial solvent
Vanillin (an aldehyde)	Flavour of vanilla
Camphor (a ketone)	Medicines, pujas

Concept

Nomenclature

Aldehydes: replace -e of the alkane by -al; the CHO carbon is C-1. Ketones: replace -e by -one, with the lowest locant for C=O. Common names come from the related acids (formaldehyde, acetaldehyde) or alkyl groups + ketone.

Table of names of aldehydes and ketones
Structure	Common name	IUPAC name
HCHO	Formaldehyde	Methanal
CH₃CH₂CHO	Propionaldehyde	Propanal
(CH₃)₂CHCHO	Isobutyraldehyde	2-Methylpropanal
CH₃COCH₂CH₃	Ethyl methyl ketone	Butan-2-one
CH₃CH₂COCH₂CH₃	Diethyl ketone	Pentan-3-one
CH₃CH=CHCHO	Crotonaldehyde	But-2-enal

Diagram

Structure of the carbonyl group

The carbonyl carbon is sp²: three σ bonds in a plane at about 120°, and a π bond to oxygen. C=O is polar (C δ+, O δ−) and is represented as a resonance hybrid of C=O and C⁺–O⁻. The carbon is attacked by nucleophiles; the oxygen by electrophiles (H⁺).

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