Steric factors affecting hydrogen-bonding between amide groups

The infra-red spectra of aseries of N-monosubstituted amides R · CONH · R′[R or R′ CH₃, C₂H₅, CH(CH₃)₂, C(CH₃)₃] in carbon tetrachloride solution have been recorded in the region 3600 cm⁻¹ −2800 cm⁻¹. The shift in the NH stretching frequency on hydrogen—bonding (Δν  ν_monomeric — ν_associated) has been found to be proportional to the estimated area (B) of the association band, and to the width at half-height (ν_{$\text{1}\text{2}$}) of this band. B was also found to be proportional to the concentration ratio ϱ=$\text{C}{}_{\mathrm{associated}}\text{C}{}_{\mathrm{monomeric}}$

In a series of secondary amides where R  R′  n-C₃H₇ to n-C₆H₁₃ inclusive, Δν, ν_{$\text{1}\text{2}$}, and B were essentially constant.