ALDEHYDES & KETONES (ALKANALS & ALKANONES). ALDEHYDES & KETONES (ALKANALS & ALKANONES). The simplest aldehyde is formaldehyde (CH 2 O). It is the only aldehyde without an alkyl group attached to the carbonyl C. Aldehydes & ketones both contain the carbonyl group.
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(ALKANALS & ALKANONES)
Aldehydes & ketones both contain the carbonyl group.
All other aldehydes, such as acetaldehyde (CH3CHO), have one alkyl group and one H attached to the carbonyl C.
DEN(O-C) = (3.5-2.5) = 1.0 (a polar bond)
The weak p bond breaks as the Nu:- adds, so that C remains tetravalent ( 5 bonds).
Aldehydes and Ketones are Electrophiles
IUPAC Nomenclature of Aldehydes
Aldehydes: in open chains:
Aldehydes: attached to rings:
Ketones: in both open chains and rings:
An olefinic ketone is named as an ‘enone’, literally: “#-alken-#-one”.
methyl isobutyl ketone (MIBK)
g-methoxypropyl phenyl ketone
-chloroethyl isopropyl ketone
Some historic names persist:
(c) methyl benzyl ketone
butanedial bromomethyl b-bromoethyl ketone 2,4-pentanedione
(c) methyl vinyl ketone
Mild oxidation of 1° Alcohols: (with anhydrous oxidants, PCC in CHCl2 or Collins reagent (CrO3 in pyridine).
Dry ice (solid CO2) sublimes at –78°C.
Reduction of acid chlorides,esters, and nitriles.
Only 1 equivalent of very cold DIBAH is used to avoid further reduction of the aldehyde to an alcohol.
Oxidation of 2° Alcohols: with mild (anhydrous) oxidants, moderate, or strong oxidants, e.g., H2CrO4, HNO3, KMnO4, NaOCl, etc.
Friedel Crafts Acylation of Aromatics: yields ketones when an acid chloride is used as the electrophile.
Hydration of Alkynes: with Hg+2 and H3O+ yields an enol, that ‘tautomerizes’ to a ketone.