title: Monitoring a simple hydrolysis process in an organic solid by observing methyl group rotation.
abstract: We report a variety of experiments and calculations and their interpretations regarding methyl group (CH3) rotation in samples of pure 3-methylglutaric anhydride (1), pure 3-methylglutaric acid (2), and samples where the anhydride is slowly absorbing water from the air and converting to the acid [C6H8O3(1) + H2O → C6H10O4(2)]. The techniques are solid state1H nuclear magnetic resonance (NMR) spin-lattice relaxation, single-crystal X-ray diffraction, electronic structure calculations in both isolated molecules and in clusters of molecules that mimic the crystal structure, field emission scanning electron microscopy, differential scanning calorimetry, and high resolution1H NMR spectroscopy. The solid state1H spin-lattice relaxation experiments allow us to observe the temperature dependence of the parameters that characterize methyl group rotation in both compounds and in mixtures of the two compounds. In the mixtures, both types of methyl groups (that is, molecules of 1 and 2) can be observed independently and simultaneously at low temperatures because the solid state1H spin-lattice relaxation is appropriately described by a double exponential. We have followed the conversion 1 → 2 over periods of two years. The solid state1H spin-lattice relaxation experiments in pure samples of 1 and 2 indicate that there is a distribution of NMR activation energies for methyl group rotation in 1 but not in 2 and we are able to explain this in terms of the particle sizes seen in the field emission scanning electron microscopy images.
authors.affiliation: Department of Physics, Bryn Mawr College, 101 North Merion Ave., Bryn Mawr, PA 19010-2899, USA. Electronic address: pbeckman@brynmawr.edu.
authors.forename: Peter A
authors.initials: PA
authors.lastname: Beckmann
authors.affiliation: Department of Chemistry, Bryn Mawr College, 101 North Merion Ave., Bryn Mawr, PA 19010-2899, USA.
authors.forename: Joseph M
authors.initials: JM
authors.lastname: Bohen
authors.affiliation: Nanoscale Characterization Facility, Singh Center for Nanotechnology, University of Pennsylvania, 3205 Walnut St., Philadelphia, PA 19104-3405, USA.
authors.forename: Jamie
authors.initials: J
authors.lastname: Ford
authors.affiliation: Department of Chemistry, Bryn Mawr College, 101 North Merion Ave., Bryn Mawr, PA 19010-2899, USA.
authors.forename: William P
authors.initials: WP
authors.lastname: Malachowski
authors.affiliation: Department of Chemistry, University of Pennsylvania, 231 South 34 Street, Philadelphia, PA 19104-6323, USA.
authors.forename: Clelia W
authors.initials: CW
authors.lastname: Mallory
authors.affiliation: Department of Chemistry, Bryn Mawr College, 101 North Merion Ave., Bryn Mawr, PA 19010-2899, USA.
authors.forename: Frank B
authors.initials: FB
authors.lastname: Mallory
authors.affiliation: Laboratory for Research on the Structure of Matter, University of Pennsylvania, 3231 Walnut St., Philadelphia, PA 19104-6202, USA.
authors.forename: Andrew R
authors.initials: AR
authors.lastname: McGhie
authors.affiliation: Department of Chemistry and Biochemistry, University of California, San Diego, 5128 Urey Hall, 9500 Gilman Dr., La Jolla, CA 92093-0358, USA.
authors.forename: Arnold L
authors.initials: AL
authors.lastname: Rheingold
authors.affiliation: Laboratory for Research on the Structure of Matter, University of Pennsylvania, 3231 Walnut St., Philadelphia, PA 19104-6202, USA.
authors.forename: Gilbert J
authors.initials: GJ
authors.lastname: Sloan
authors.affiliation: Department of Materials Science and Engineering, School of Engineering and Applied Science, University of Pennsylvania, 3231 Walnut St., Philadelphia, PA 19104-6202, USA.
authors.forename: Steven T
authors.initials: ST
authors.lastname: Szewczyk
authors.affiliation: Key Laboratory for NeuroInformation of Ministry of Education, School of Life Science and Technology, University of Electronic Science and Technology of China, 4 North Jianshe Rd., 22nd Section, Chengdu 610054, China.
authors.forename: Xianlong
authors.initials: X
authors.lastname: Wang
authors.affiliation: Department of Chemistry, Eastern Illinois University, 600 Lincoln Ave., Charleston, IL 69120-3099, USA.
authors.forename: Kraig A
authors.initials: KA
authors.lastname: Wheeler
keywords: Chemical conversion by hydrolysis; Electronic structure calculations in molecular clusters; Methyl group rotation; Molecular solids; Scanning electron microscopy in organics; Single-crystal X-ray diffraction