Aldehydes and Ketones | Organic Chemistry 2

The aldehydes and ketones are studied in this chapter: the naming and properties of carbonyls, their synthesis, the addition reactions: additions of hydride and organometallic reagents, addition of water, addition of alcohols, addition of ammonia and its derivatives.

Naming the Carbonyls

The -ane ending of the corresponding alkane is replace by -al (Aldehyde) and by -one (Ketone).
 

Same rules as alcohols (except that the position of aldehyde does not have to be specified ⇒ always 1).
When -CHO attached to a ring: carbaldehyde (and carbon bearing the -CHO is C1).
When -CO is part of a ring: cycloalkanones (and carbon of -CO is C1).
 

Aldehyde and Ketone take precedence over Alcohol, Alkene and Alkyne.
Aldehyde takes precedence over Ketone.
If Aldehyde or Ketone
do not have priority: prefix formyl- (Aldehyde) and acyl- (Ketone) or oxo- (Ketone in the presence of an Aldehyde).

 

Properties of Carbonyls

C=O bond: short, strong and very polar
Hybridization: sp⇒ trigonal planar

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

with Nu = Nucleophile and E = Electrophile (generally H+ in this chapter)

 

Mechanisms:

Basic Conditions: Nucleophilic Addition-Protonation (Nucleophile attack first)
 

 

Acidic Conditions: Electrophilic Protonation-Addition (Electrophile attack first)
 

Additions of Hydride and Organometallic Reagents

Review from Chapter 8 - Organic Chemistry 1:
 

Additions of Water

 

Mechanisms:

Base-Catalyzed Hydration:
 

 

Acid-Catalyzed Hydration:
 

Additions of Alcohols

Same mechanism as for addition of water (H2O is replaced by ROH) ⇒ catalyzed by both acids and bases.

 

Mechanism:

Step 1: Hemiacetal generation under acid condition (see Acid-Catalyzed Hydration - Addition of H2O).

Step 2: Acetal generation - Acid-catalyzed SN1:
 


 

Synthetic Strategy:

Use Acetal as Protecting Group: Acetal formation is reversible and Carbonyl is transformed into a unreactive ether-like moiety ⇒ Protection of Carbonyl from nucleophilic attack (base, LiAlH4, RMgX).
1,2-ethanediol is generally used to form a cyclic acetal:
 

Additions of Ammonia and Its Derivatives

Mechanism:

 

 

Mechanism: