title: Unusual effects in variable temperature powder NMR spectra of the methyl group protons in 9,10-dimethyltriptycene-d₁₂.
abstract: Variable temperature (1)H wide line NMR spectra of polycrystalline 9,10-dimethyltriptycene-d12 deuterated in the aromatic positions were studied. The spectra show different patterns in an unrepeatable dependence on the way of preparation of the powdered samples. Simultaneously, no anomalies were seen in the MAS and CPMAS proton-decoupled room-temperature (13)C spectra as well as in powder X-ray diffraction patterns. The effects observed in the (1)H spectra are tentatively explained in terms of a phenomenological model. For one of the examined samples it afforded a consistent interpretation of the entire series of temperature dependent spectra in terms of structural non uniformity of the solid material studied. Quantum character of the stochastic dynamics of the methyl groups in the investigated compound was confirmed, although these dynamics are close to the classical limit where the familiar random jump model applies.
authors.affiliation: Institute of Physical Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, 01-224 Warszawa, Poland.
authors.forename: P
authors.initials: P
authors.lastname: Bernatowicz
authors.affiliation: Institute of Physical Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, 01-224 Warszawa, Poland.
authors.forename: T
authors.initials: T
authors.lastname: Ratajczyk
authors.affiliation: Institute of Organic Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, 01-224 Warszawa, Poland.
authors.forename: P
authors.initials: P
authors.lastname: Kalicki
authors.affiliation: Institute of Organic Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, 01-224 Warszawa, Poland. Electronic address: sszym@icho.edu.pl.
authors.forename: S
authors.initials: S
authors.lastname: Szymanski
keywords: Methyl group dynamics; NMR line shape analysis; Solid state NMR; Structural disorder