Investigation of the structures, potential energy surface, transition states and vibrational frequencies of a vitamin E precursor-chroman in S0 and S1 states: DFT based computational study

The twisted structure is found to be the most stable conformer of chroman in S0 and S1 states at various levels of theoretical calculations. The barrier to planarity is calculated to be 3500 ± 300 cm−1 in S0 with the twisting angle as 30.5° and the corresponding values of barrier as 3800 cm−1 and twisting angle as 29° in S1. These values deviate little with the different levels of calculations. Theoretical IR and Raman spectra are calculated. Two characteristic low-frequency vibrations are found and their values are compared with the closely related compounds. Potential energy curves corresponding to twisting and bending motions are found out. Three transition states are identified.