Scalar Relaxation of the Second Kind. A Potential Source of Information on the Dynamics of Molecular Movements. 4. Molecules with Collinear C鈥揌 and C鈥揃r Bonds

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• 作者：Piotr Bernatowicz ; Dominika Kubica ; Micha艂 Ociepa ; Artur Wody艅ski ; Adam Gryff-Keller
• 刊名：Journal of Physical Chemistry A
• 出版年：2014
• 出版时间：June 12, 2014
• 年：2014
• 卷：118
• 期：23
• 页码：4063-4070
• 全文大小：280K
• 年卷期：v.118,no.23(June 12, 2014)
• ISSN：1520-5215

文摘

Continuing studies based on measurements of the nuclear spin relaxation rates running via the SC2 mechanism (scalar relaxation of the second kind), we present in this work the results obtained for three molecules: 9-bromotriptycene, 1,3,5-tribromobenzene, and 1-(2-bromoethynyl)-4-ethynylbenzene in which C鈥揃r bond and one of C鈥揌 bonds are collinear. Separation of saturation鈥搑ecovery or inversion鈥搑ecovery curves of ¹³C NMR signals of bromine-bonded carbons in the investigated compounds on two components has provided the longitudinal SC2 relaxation rates of these carbons in ⁷⁹Br- and ⁸¹Br-containing isotopomers. These data have enabled experimental determination of the bromine鈥揷arbon spin鈥搒pin coupling constants and relaxation rates of quadrupole bromine nuclei, hardly accessible by direct measurements. At the same time the rotational diffusion parameters describing the reorientation of the C鈥揃r vectors have been determined for the investigated molecules on the basis of the dipolar relaxation of protonated carbons. These diffusion parameters are crucial for interpretation of the bromine relaxation rates. The values of the indirect ¹J(¹³C,⁷⁹Br) coupling constants, magnetic shielding of carbon nuclei and quadrupole coupling constants of bromines, determined for the investigated compounds, have been compared with the results of the theoretical calculations which take into account relativistic effects. The origin of some divergences between the results obtained by different methods has been discussed.