
TY  - JOUR
A1  - Riggs, NV 
A1  - Radom, L 
T1  - A Simple Model for the Mean and Difference of NH-Stretching Frequencies for NH<sub>2</sub> Groups, and Its Application to Results of Some <I>ab initio</I> Vibrational-Frequency Calculations
JF  - Australian Journal of Chemistry
JO  - Aust. J. Chem.
Y1  - 1988
VL  - 41
IS  - 3
SP  - 387
EP  - 396
KW  - 
UR  - https://doi.org/10.1071/CH9880387 
N2  - The expression for the sum of the eigenvalues of the 2&#215;2 GF matrix for two interacting NH bonds suggests that the mean NH-stretching frequency for an NH2 group should be closely proportional to ( &#931;f )&#189;, where &#931;f is the sum of the two corresponding force constants. Ab initio results for the NH2 groups in various conformations of ethanamine , hydrazine and 1,1-dimethylhydrazine confirm such constancy to within 0.1%. The corresponding expression for the difference of the eigenvalues suggests, counterintuitively, that the difference of NH-stretching frequencies for an NH2 group in a given molecular system should also be largely proportional to ( &#931;f )&#189; and, except for the gauche conformation of 1,1-dimethylhydrazine, ab initio results for the above molecules support this suggestion to within ±14 cm-1. In the exceptional case, the difference of NH-stretching force constants makes a much larger than usual contribution. Relative values of the force constants for various molecular species may be interpreted in terms of the relative geometries and effects of donation of lone-pair electrons at an adjacent centre into antibonding N-H orbitals at the given centre. 
ER  -

