Aldehydes and Ketones | Organic Chemistry 2
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: sp2 ⇒ 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)
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
Additions of Alcohols
Same mechanism as for addition of water (H2O is replaced by ROH) ⇒ catalyzed by both acids and bases.
Step 1: Hemiacetal generation under acid condition (see Acid-Catalyzed Hydration - Addition of H2O).
Step 2: Acetal generation - Acid-catalyzed SN1:
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