An Infrared Study of the Steric Effects of Alkyl Substituents on the N–H Stretching Absorptions of sym-Dialkylureas

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Abstract
By examining their N–H stretching absorptions in the hydrogen-bonding system, the steric effects of the substituent on the C=O or N–H group have been studied for sym-disubstituted alkylureas of the RHNCONHR′ type in carbon tetrachloride. By comparing the estimated percentage of the monomer, it is concluded that the steric effects are not large enough to convert the trans conformation into the cis conformation, though the branched alkyl groups may prevent another molecule from approaching more strongly than the normal alkyl groups. Correlations among some spectral parameters have been examined, such as the estimated percentage of the monomer, the frequency shift upon hydrogen-bond formation, the apparent integrated absorption intensity, and the halfintensity width of the associated band.
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