Aldehydes and Ketones - Part 1 | Organic Chemistry 2

Aldehydes and ketones are studied in this chapter: name, properties and synthesis of carbonyls, addition reactions: addition of hydride and organometallic reagents, addition of water, addition of alcohols, addition of ammonia and its derivatives

Nomenclature of Carbonyls

Name: the -ane ending of the corresponding alkane is replace by -al (aldehyde) or by -one (ketone)

The rules for naming alcohols  also apply to carbonyls, except that it is not necessary to specify the position of the aldehyde ⇒ always carbon 1
Carbaldehyde: aldehyde functional group is attached to a ring and the carbon of -CHO is carbon 1
Cycloalkanones: ketone functional group is part of the ring and carbon of the CO is carbon 1


Aldehydes and ketones take precedence over alcohols, alkenes and alkynes. Aldehydes takes precedence over ketones. If aldehydes or ketones do not have priority, the prefixes formyl- (aldehyde) and acyl- (ketone) or oxo- (ketone in the presence of an aldehyde) must be used


Properties of Carbonyls


C=O bond of carbonyls: 

short, strong and very polar


The carbon of the C=O bond of carbonyls are sp2 hybridized ⇒ trigonal planar geometry

Absorption spectroscopy: 

NMR: 1H δ ~ 9-10 ppm (H of aldehyde); 13C δ ~ 200 ppm
IR: C=O stretching ⇒ intense band ~ 1690-1750 cm-1


 Reactivity of Carbonyls:

Synthesis of Carbonyls

Oxidation of Alcohols (see Chapter 8 - Organic Chemistry 1):


Oxidation of Allylic Alcohols:


Ozonolysis of Alkenes (see Chapter 2 - Organic Chemistry 2):


Hydration of Alkynes (see Chapter 3 - Organic Chemistry 2):


Friedel-Crafts Acylation (see Chapter 5 - Organic Chemistry 2):

Mechanisms of Addition Reactions


Under basic conditions: nucleophilic addition-protonation (nucleophilic attack first)


Under acidic conditions: electrophilic protonation-addition (electrophilic attack first)

Additions of Hydrides and Organometallic Reagents

Additions of Water


Base-catalyzed hydration:


Acid-catalyzed hydration:

Additions of Alcohols

Formation of hemiacetal:


Same as for the addition of water, H2O being replaced by ROH ⇒ catalyzed by acids or bases


Formation of acetal:


  1. Hemiacetal formation under acidic conditions (see acid-catalyzed hydration - addition of H2O)
  2. Acetal formation via an acid-catalyzed SN1:



Synthetic Strategy:

Acetal is widely used as protecting group: acetal formation is reversible and carbonyl is transformed into a non-reactive ether-like moiety ⇒ carbonyl protection against nucleophilic attacks (base, LiAlH4, RMgX). 1,2-ethanediol is typically used to form a cyclic acetal:

Additions of Ammonia and its Derivatives

Formation of imine:



Formation of enamine: