Urey-Bradley force field of 4-ethylpyridine

A normal coordinate analysis is carried out to obtain the Urey-Bradley force constants for 4-ethylpyridine (4-etpy) assuming an under C_2ν point group. These constants are adjusted to fit the observed frequencies for 4-etpy and its deuterated species. The calculated frequencies allowed the vibrational assignments of the normal modes of 4-etpy. These assignments are confirmed by the calculations of the potential energy distributions on 4-etpy. Additional information is obtained from the vibrational spectra of Cd (4-etpy)₂ M (CN)₄ (M=Cd, Hg) and calculated wavenumbers of metal (Cd) bonded 4-etpy. It is shown that the ring vibrations in pyridine are to be effected upon metal substitution. These results have also provided certainty for the vibrational assignments.