CONFORMATIONS OF ETHYLBENZENE (CH3-CH2-PH) - AN AB-INITIO STUDY

The potential energy surface (PES) of ethylbenzene has been studied as a two-rotor problem: E = f(chi(1), chi(2)), where chi(1) and chi(2) a re the rotational angles around the two C-C bonds. The computed result s of ethylbenzene are compared with similar data on F-CH2-Ph and CH3-P h. The results obtained allow for the following conclusions: (i) in ad ddition to the well established global minimum chi(1) = 180 degrees an d chi(2) = 90 degrees ethylbenzene has a second stable conformer, of h igher energy, at chi(1) = 180 degrees and chi(2) = 0 degrees; (ii) in the global minimum the benzene ring is non-planar, and (iii) the relat ive stability of ethylbenzene with respect to toluene is associated wi th a conformational readjustment, when going from toluene to ethylbenz ene, rather than electronic effect associated with the methyl group.