Normal coordinate analysis of 4-aminopyridine. Effect of substituent on pyridine ring in metal complexes of 4-substituted pyridines.

The normal coordinate analysis has been performed for 4-aminopyridine (4-apy) assuming C2v molecular symmetry. A Urey-Bradley force field has been used. The force constants are adjusted to fit the observed frequencies for 4-apy and its deuterated species. The vibrational assignment has been made on the basis of the calculated frequencies and potential energy distributions. The calculated frequencies were in good agreement with the observed frequencies. The substituent effect upon the M-nitrogen (ligand) (L = 4-methlypyridine, 4-ethylpyridine, 4-vinylpyridine. 4-aminopyridine and 4-cyanopyridine) and pyridine ring frequencies has also been investigated. The frequency shifts are found to be sensitive to the substituent in the 4-position of the pyridine ring.