By making use of low temperature dynamic NMR spectroscopy the rotation barriers about the sp3-sp2 bond have been determined in a number of hindered benzyl alcohols symmetrically 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 compounds. In one case this result could be also confirmed by the X-ray diffraction structure. In the case of the corresponding methyl 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.

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

LUNAZZI, LODOVICO;MANCINELLI, MICHELE;MAZZANTI, ANDREA
2007

Abstract

By making use of low temperature dynamic NMR spectroscopy the rotation barriers about the sp3-sp2 bond have been determined in a number of hindered benzyl alcohols symmetrically 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 compounds. In one case this result could be also confirmed by the X-ray diffraction structure. In the case of the corresponding methyl 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.
JOURNAL OF ORGANIC CHEMISTRY
D. Casarini; L. Lunazzi; M. Mancinelli; A. Mazzanti
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/11585/47447
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