Can. J. Chem. 58, 1372 (1980. Thermodynamic parameters for the self-association of N-methylformamide and N-methylacetamide in CCI, solvent have been determined by infrared spectroscopy. The pure base calorimetric method was used to determine the enthalpy of hydrogen bond complex formation of N-methylformamide and N-methylacetamide with N,N-dimethylformamide, N,N-dimethylacetamide, ethyl acetate, and dioxane. Comparison of the calorimetric and spectroscopic results show that the dimers of N-methylformamide and N-methylacetamide are linear with hydrogen bond enthalpies of -2.9 and -3.9 kcal mol-' respectively. The carbonyl group of N-methylacetamide was found to be a better proton acceptor than the carbonyl of N-methylformamide in agreement with theoretical predictions. N-methylacetamide was found to be a better proton donor than N-methylformamide in disagreement with theoretical predictions. The dimer self-association constants appear to be larger than previously reported.

The rate constants for benzene and toluene were found to be nearly equal In any given alcohol except methanol, for which the experimental scatter was large. We have therefore taken the average value, k1 = 1,3 X 106 M"1 s'1, for both benzene and toluene in methanol at 299 K. (23) E.

The pure-base calorimetric method has been used to determine enthalpies of formation for hydrogen-bonded complexes of pyrrole, indole, and imidazole with various bases. These enthalpies are compared to those obtained by other methods. Frequency shifts determined in CC14 solvent have been used to findrelationships for N-H-O and N-H-N adducts. From these relationships, hydrogen-bond enthalpies have been calculated for bases not determined by the pure-base method. The systems investigated have been used as models to calculate enthalpies of formation for the more complex nucleic acid base pairs. Comparison of enthalpies calculated from the model compounds is made to enthalpies determined by theoretical and other experimental methods.

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