APPLICATION OF NORMAL COORDINATE CALCULATIONS TO CONFORMATIONAL ANALYSIS

Abstract

Normal coordinate calculations have been used to show that the preferred conformer of trans-methyldiazene ($CH_{3}$-N=N-H) is the S (staggered) rotamer (in-plane CH bond trans to N=N bond). This finding is the consequence of fitting a 22-parameter potential function to the 56 observed fundamental of the $d_{0}$, $d_{1}$, $d_{3}$ and $d_{4}$ isotopic species. The backward elimination $strategy^{1}$ was used to guide the separate refinements of the S and E (eclipsed) rotamers. A similar treatment is being applied to cis-dimethyldiazene, for which an ab initio calculation has predicted a lowest energy for the SS $conformer.^{2}$ Results of fitting potential functions to SS and EE conformers will be reported.