Methyl and tert-Butyl Rotation in Solid 5-tert-butyl-4-hydroxy-2-methylphenyl sulfide

Posted May 12th, 2010 at 1:52 pm.

Laura Popa
Mentor: Professor Peter Beckmann

We conduct variable temperature (90 K – 330 K) and variable frequency (8.50, 22.5, and 53.0 MHz) solid state 1H nuclear magnetic resonance (NMR) relaxation experiments on a sample of 5-tert-butyl-4-hydroxy-2-methylphenyl sulfide. The goal is to study the intramolecular reorientation of the methyl and tert-butyl groups present in this molecule and to correlate the motions of these groups with the molecular and crystal structure.

The reorientation of the methyl and tert-butyl groups is modeled by the motion of random quantum mechanical hopping, described by Poisson statistics, with an average time between hops modeled using the Canonical Ensemble. Due to their position in the molecule, different intramolecular groups need different energies to reorient. Previous experiments on planar aromatic molecules have shown that the methyl group that is in the plane of the aromatic structure reorients at the same rate as the entire tert-butyl group. The two out-of-plane methyl groups reorient at a different rate. By fitting the dependence of the 1H relaxation rate on temperature and NMR frequency, values of the rotational barriers for methyl and tert-butyl rotors are obtained.

Filed under: 2008,Beckmann, Dr. Peter,Popa, Laura by Ann Dixon

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