The molecular structure and vibrational spectrum of 4-chlorostyrene

The molecular structure and vibrational spectrum of 4-chlorostyrene have been investigated by ab initio and DFT calculations combined with infrared/Raman and Inelastic Neutron Scattering (INS) spectroscopies. The molecular geometry has been optimized at different levels of theory, RHF, MP2, B3LYP and B3PW91, with an assortment of basis sets, 6-31G*, 6-311G** and 6-311++G**. Hartree-Fock and MP2 results predict a non-planar structure while DFT predicts a planar geometry for the basis sets essayed in this work. Simulations of the infrared and INS spectra point out the 4-chlorostyrene is planar or nearly planar in solution and in solid state. Vibrational assignments of the fundamental modes have been corroborated by harmonic force fields calculated using both the scaled and refinement formalisms, the latter with and without the use of INS intensities, and yielding final rms deviations of 5, 7 and 2 cm−1, respectively. The vibrational spectrum for 4-chlorostyrene has been also predicted from a common force field fitted using data from six styrene derivatives recently studied and obtaining a rms deviation of 10 cm−1.