AbstractThe self‐association ofN‐acetylglycineN,N‐dimethylamide,N‐acetyl‐L‐valineN,N‐dimethylamide, andN‐acetyl‐L‐phenylalanineN,N‐dimethylamide in carbon tetrachloride was investigated by using ir and1H‐nmr methods. It was concluded from ir measurements that the associated species is the dimer formed as a result of the simultaneous formation of two intermolecular hydrogen bonds. This is supported by the results of1H‐nmr measurements. Thermodynamic quantities for the association were determined from the temperature and concentration dependence of the NH proton chemical shifts of the sample solutions. Compared with the Gly derivative,L‐Val andL‐Phe derivatives have larger values of −ΔHfor association, which shows good correlation with ΔvNHvalues, the difference between the maxima of the monomer and dimer bands, obtained from ir spectra. This is due to the less stable monomer conformation and to the stronger intermolecular hydrogen bonding of the dimers inL‐Val andL‐Phe derivatives. The line shapes of both methyl proton resonances ofL‐Val residue and methylene proton resonances ofL‐Phe residue were found to vary with concentration and temperature of the sample solutions. These data indicate that the rotation about the Cα—Cβbond is restricted by the steric hindrance present in the associated dimers. All these experimental results can be related to the fact thatL‐Val andL‐Phe derivatives have a warped framework because of the bulky side chains,