Post-resonance Raman and theoretical studies on 1,3,2,4-benzodithiadiazines, formally anti-aromatic compounds

DFT calculations on 1,3,2,4-benzodithiadiazine (1) and its 5-F (2), 6-Cl (3 ) and 7-CH3 (4) derivatives showed these compounds to have essentially non- planar molecular conformations. The vibrational (IR and Raman) spectra of 1 -4 were measured and assigned on the basis of the results of the theoretica l calculations. N=S=N anti-symmetric and symmetric stretching modes were fo und at similar to 1220-1230 and similar to 965-975 cm(-1), respectively. Re sonance Raman spectra of 1-4 were obtained with the 514.5, 496.5, 488.0, 47 6.5 and 457.9 nm excitation lines of an Argon laser, and a post-resonance R aman effect was observed. The Raman excitation profiles revealed a weak but definite pi -interaction of the carbocyclic and heterocyclic parts of the molecules which became stronger on going from 1 to 2. Comments on the possi ble existence of antiaromaticity for the title compounds in a planar confor mation are given.