Normal coordinate analyses of 3,5-dichlorophenylcyanamide

The structure of 3,5-dichlorophenylcyanamide c-C₆H₃Cl₂-NHCN was investigated by DFT-B3LYP and ab initio MP2 calculations with the 6-311+G** basis set. The planar to perpendicular rotational barrier was calculated to be of about 5 kcal mol^-1 at both levels of calculation. The stability of the planar structure of the molecule was explained on the basis of conjugation effects between the cyanamide-NHCN moiety and the phenyl c-C₆H₅ ring in agreement with earlier NMR results. The CNC and the HNC bond angles were calculated to be about 120° especially by MP2 calculation, which is consistent with sp² (planar -NH-CN group) and not sp³ (pyramidal -NH-CN group) structure. The vibrational frequencies of the d₀, d₁ and d₃ species of 3,5-dichlorophenylcyanamide and the potential energy distributions among symmetry coordinates of the normal modes of the parent molecule were computed at the DFT-B3LYP level. The calculated infrared and Raman spectra of the molecule were plotted. Complete vibrational assignments were made on the basis of isotopic substitution and normal coordinate calculations.