A DYNAMIC NMR STUDY OF RESTRICTED ROTATION OF TWO SUBSTITUTED PHENYL GROUPS AN A CIS-1,2-DIPHENYLCYCLOBUTANE

Article abstract of DOI:10.1016/S0040-4020(01)89807-0

Dimethyl 2,2',6,6'-tetrachloro-β-truxinate (1) displays restricted rotation of its phenyl groups as evidenced by lineshape analysis of the dynamic 1H and 13C NMR spectra with the following activation parameters: ΔH<*> 10.98 +/- 0.24 kcal mol ^-1, ΔS<*> -4.38 +/- 0.99 cal mol^-1K^-1.In the transition state for rotation the two phenyl groups are perpendicular to one another and the act of rotation involves one phenyl group at a time.The major contribution to the barrier of rotation has its origin in the chlorine atoms.X-ray analysis of 1 yields a structure with an angle of pucker of 14.3 deg for the cyclobutane ring in which one chl orine group hovers over the cyclobutane ring while the two chlorines of the other phenyl group avoid the cyclobutane ring.