| Abstract
| - By making use of low-temperature dynamic NMR spectroscopy, the rotation barriers about the sp3−sp2bond have been determined in a number of hindered benzyl alcohols symmetrically substituted in theortho positions, the substituents being F, Cl, Br, and Me. The free energies of activation covered therange 4.6−10.1 kcal mol-1. Ab initio computations matched satisfactorily the trend of these values andpredicted the conformation adopted by these compounds. In one case, this result could be also confirmedby the X-ray diffraction structure. In the case of the corresponding methyl ethers two barriers could bemeasured, corresponding to the passage across two distinguishable transition states: the higher barrierscovered the range 5.0−8.1 kcal mol-1 and the lower ones the range 4.7−6.2 kcal mol-1.
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