Solvent-dependent stabilization of the E configuration of propargylic secondary amides.
Secondary amides typically exist 98-99% in the Z rotamer to avoid steric repulsion between the substituent on the carbonyl carbon and the nitrogen. In contrast, secondary amide 3a displays 24% E rotamer at room temperature in aqueous solution. The analogous ester displays 6% E rotamer in chloroform, which suggests that the relatively high E conformer population observed for 3a in water results in part from the low steric bulk of the sp-hybridized carbons and in part from the hydrophobic effect.
Gardner
R R
RR
Department of Chemistry, University of Wisconsin, Madison, Wisconsin 53706, USA.
McKay
S L
SL
Gellman
S H
SH
D000577:Amides / Q000737:chemistry* / Q000378:metabolism*; D002725:Chloroform / Q000378:metabolism*; D009682:Magnetic Resonance Spectroscopy; D012997:Solvents / Q000378:metabolism; D013237:Stereoisomerism; D014867:Water / Q000378:metabolism*
D000577:Amides; D012997:Solvents; D014867:Water; D002725:Chloroform