Prediction of an inverse heavy-atom effect in H-C-CH(2)Br: bromine substituent as a pi acceptor.
A comparison of spin-orbit coupling calculated [CASSCF(6,6)/(cc-pVDZ on C,H and VDZ+P on Br] for bromomethylcarbene and methylcarbene predicts a highly unusual inverse heavy-atom effect by the Br substituent, particularly at geometries near the syn conformation. This behavior is due to a vacant 4d orbital on the Br atom acting as a weak pi-electron acceptor and overwhelming the even weaker effect of the pi-symmetry lone pair donor 4p orbital, which in itself would cause a small normal heavy-atom effect.
Havlas
Zdenek
Z
Institute of Organic Chemistry and Biochemistry and Center for Complex Molecular Systems and Biomolecules, Academy of Sciences of the Czech Republic, 16610 Prague 6, Czech Republic.
Michl
Josef
J