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.Figure Potential curves for the internal rotation in 3,5-dichlorophenylcyanamide as determined by DFT-B3LYP/6-311+G** (solid) and MP2/6-311+G** (dotted) calculations