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.