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
摘要:
Se-77 NMR chemical shifts of methyl-d(3) 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 C-Me (2.989 angstrom) is observed to be shorter than the sum of the van der Waals radii of the two by 0.91 angstrom in 2. 1 and 2 may be in equilibrium between conformers A and B in solution, where Se-C-i 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 n(p)(Se)-sigma *(C-H) interaction contributes in A, whereas nonbonded n(s)(Se)-sigma *(C-H) and double sigma (C-H)-sigma *(Se-C) interactions operate in B.
H/D Isotope Effect on <sup>77</sup>Se NMR Chemical Shifts in 8-Methyl-1-(arylselanyl)naphthalenes and Related Selenides: Nonbonded C─H—Se Through-Space Versus Through-Bond Mechanisms
作者:Satoko Hayashi、Kentaro Yamane、Waro Nakanishi
DOI:10.1080/10426500902947807
日期:2009.6.23
Se-77 NMR chemical shifts of methyl-d(3) 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 C-Me (2.989 angstrom) is observed to be shorter than the sum of the van der Waals radii of the two by 0.91 angstrom in 2. 1 and 2 may be in equilibrium between conformers A and B in solution, where Se-C-i 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 n(p)(Se)-sigma *(C-H) interaction contributes in A, whereas nonbonded n(s)(Se)-sigma *(C-H) and double sigma (C-H)-sigma *(Se-C) interactions operate in B.