Aldehydes other characteristic absorptions

The carbonyl-group carbon atoms of aldehydes and ketones have characteristic 13C NMR resonances in the range 190 to 215 8. Since no other kinds of carbons absorb in this range, the presence of an NMR absorption near 200 8 is clear evidence for a carbonyl group. Saturated aldehyde or ketone carbons usually absorb in the region from 200 to 215 8, while aromatic and a,p-unsaturated carbonyl carbons absorb in the 190 to 200 5 region. 

It is now necessary to deduce the nature of the carbonyl function (i.e. whether it is an aldehyde, ketone, ester, etc.). Each of these functional groups (with the exception of ketones) exhibits further characteristic and identifiable absorption bands due to the attachment of atoms other than carbon to the carbonyl carbon atom. Thus an aldehyde should exhibit a double band in the region of 2830-2700 cm-1, due to stretching of the C—H bond in the aldehydic group. A car-... 

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