H/D Isotope Effect on 77Se NMR Chemical Shifts in 8-Methyl-1-(arylselanyl)naphthalenes and Related Selenides: Nonbonded C─H—Se Through-Space Versus Through-Bond Mechanisms
77Se NMR chemical shifts of methyl-d3 derivatives of 8-methyl-1-(phenylselanyl) naphthalene (1) and 8-methyl-1-(p-anisylselanyl)naphthalene (2) are observed 0.25 and 0.20 ppm upfield from 1 and 2, respectively. The observations must be the reflection of the nonbonded interactions of the C─H—Se 3c-4e type in 1 and 2. The mechanism is elucidated by means of crystallographic and theoretical investigations. The nonbonded distance between Se and CMe (2.989 Å) is observed to be shorter than the sum of the van der Waals radii of the two by 0.91 Å in 2. 1 and 2 may be in equilibrium between conformers A and B in solution, where Se─Ci is perpendicular to the naphthyl plane in A and it is on the plane in B. Natural bond orbital (NBO) analysis on 1 revealed that the nonbonded np(Se)— *(C─H) interaction contributes in A, whereas nonbonded ns(Se)— *(C─H) and double (C─H)— *(Se-C) interactions operate in B.
Keywords: Ab initio calculations; H/D isotopic effect; NMR; natural bond orbital analysis; nonbonded C─H—Se interaction; structures
Document Type: Research Article
Affiliations: Department of Material Science and Chemistry, Faculty of Systems Engineering, Wakayama University, Wakayama, Japan
Publication date: 01 June 2009
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