Our investigations concerning the protonaffmity of aliphatic amines have been confined so far to primary unbranched species. In order to gain further information about the applicability and the limitations of the statements derived from the results of the previous calculations, we extended our investigations to some tertiary, secondary and branched primary amines. Correlations between the experimental protonaffinities and the Mulliken charges of the nitrogen atom and the NHx-group (x = 0, 1, 2) of the amines, as well as those of the NHx + 1 ,-group of the corresponding ammonium cations have been found. However, these correlations only hold within the different groups of amines (primary, secondary and tertiary) and not between them. A somewhat better correlation throughout all groups is found if one compares the charges of the protons in the NHx + 1-groups of the ammonium cations with the experimental protonaffinities of the parent amines but deviations from the expected order are found in this case, too. This shows the limited value of charges as calculated by the methods used here, in predicting the relative order of protonaffinities of amines if they belong to different groups.

CNDO/S-CI-calculations of rotational strengths of the disulfide moieties in Ribonuclease A, 2-zinc- and 4-zinc-insuline-dimers based on X-ray data have been performed. Appropriate RThe sign of the calculated rotatory strength of the longest wavelength transition coincides in most cases with that predicted by the quadrant rule for disulfides. For dihedral angles near 90° the energies of the two longest wavelength transitions are found to be nearly degenerate. However there is a net contribution of their rotatory strengths whereas with the quadrant rule this is expected to be negligible.

The polarizabilities of some primary, secondary, and tertiary amines have been calculated with the MINDO/3-FP-method. The calculated values are found to correlate with the experimental polarizabilities and with those determined by the method of Miller and Savchik in a satisfying manner. In addition atomic polarizabilities have been calculated according to the method of Metzger. Averaging over the calculated mean atomic polarizabilities of hydrogen, carbon, and nitrogen yields increments which, when used to recalculate molecular polarizabilities, lead to values which correlate in an excellent manner with those determined from densities and refraction indices by means of the Lorenz-Lorentz-equation.Because different nitrogen increments have been determined for primary, secondary and tertiary amines, the parameters presented here make it possible to distinguish between constitutional isomers as long as they belong to different groups (i.e. primary, secondary, and tertiary amines), something which cannot be done using the method of Miller and Savchik. The increments derived do not only allow to predict the polarizabilities of primary, secondary and tertiary amines but can be used to calculate the corresponding values for hydrazines and polyfunctional amines with equal success.