Methyl and t-Butyl Group Reorientation in Planar Aromatic Solids: Low-Frequency Nuclear Magnetic Resonance Relaxometry and X-Ray Diffraction

Autor: Carolyn A. Buser, Frank B. Mallory, Arnold L. Rheingold, Clelia W. Mallory, Gene M. Rossi, Kathleen Gullifer, Peter A. Beckmann
Rok vydání: 2003
Předmět:
Zdroj: ChemInform. 34
ISSN: 1522-2667
0931-7597
DOI: 10.1002/chin.200346278
Popis: We have synthesized 3-t-butylchrysene and measured the Larmor frequency ω/2π (= 8.50, 22.5, and 53.0 MHz) and temperature T (110–310 K) dependence of the proton spin–lattice relaxation rate R in the polycrystalline solid [low-frequency solid state nuclear magnetic resonance (NMR) relaxometry]. We have also determined the molecular and crystal structure in a single crystal of 3-t-butylchrysene using x-ray diffraction, which indicates the presence of a unique t-butyl group environment. The spin-1/2 protons relax as a result of the spin–spin dipolar interactions being modulated by the superimposed reorientation of the t-butyl groups and their constituent methyl groups. The reorientation is successfully modeled by the simplest motion; that of random hopping describable by Poisson statistics. The x-ray data indicate near mirror-plane symmetry that places one methyl group nearly in the aromatic plane and the other two almost equally above and below the plane. The NMR relaxometry data indicate that the nearly in...
Databáze: OpenAIRE
Externí odkaz: