Conformation and Stereodynamics of Symmetrically Ortho-Disubstituted Aryl Carbinols and Aryl Ethers.

CAN 146:273814 AN 2007:52513 CAPLUS (COPYRIGHT (C) 2008 ACS ON SCIFINDER (R)) ABSTRACT BY MAKING USE OF LOW-TEMP. DYNAMIC NMR SPECTROSCOPY, THE ROTATION BARRIERS ABOUT THE SP3-SP2 BOND HAVE BEEN DETD. IN A NO. OF HINDERED BENZYL ALCS. SYM. SUBSTITUTED IN THE ORTHO POSITIONS, THE SUBSTITUENTS BEING F, CL, BR, AND ME. THE FREE ENERGIES OF ACTIVATION COVERED THE RANGE 4.6-10.1 KCAL MOL-1. AB INITIO COMPUTATIONS MATCHED SATISFACTORILY THE TREND OF THESE VALUES AND PREDICTED THE CONFORMATION ADOPTED BY THESE COMPDS. IN ONE CASE, THIS RESULT COULD BE ALSO CONFIRMED BY THE X-RAY DIFFRACTION STRUCTURE. IN THE CASE OF THE CORRESPONDING ME ETHERS TWO BARRIERS COULD BE MEASURED, CORRESPONDING TO THE PASSAGE ACROSS TWO DISTINGUISHABLE TRANSITION STATES: THE HIGHER BARRIERS COVERED THE RANGE 5.0-8.1 KCAL MOL-1 AND THE LOWER ONES THE RANGE 4.7-6.2 KCAL MOL-1.