127733-37-3Relevant articles and documents
Optically active amines. 34.1 Application of the benzene chirality rule to ring-substituted phenylcarbinamines and carbinols
Pickard, Simeon T.,Smith, Howard E.
, p. 5741 - 5747 (2007/10/02)
The negative sign of the 1Lb, Cotton effects (CEs) from about 250 to 270 nm in the circular dichroism (CD) spectra of (R)-α-phenylethylamine and (R)-α-phenylethyl alcohol and other phenylalkylcarbinamines and carbinols is determined by vibronic borrowing from allowed transitions at shorter wavelength. On ring substitution, bond transition moments are induced in the benzene ring bonds adjacent to the attachment bond of the chiral group, resulting in enhanced coupling of the 1Lb transition with the chiral group. A sign reversal for the 1Lb, CEs on para substitution with an atom or group with a positive spectroscopic moment (C1, CH3) can be viewed as the overshadowing of the vibronic contribution by an induced contribution of opposite sign On para substitution with a group with a negative spectroscopic moment (CF3, CN), the sign of the 1Lb CEs is unchanged since the vibronic and induced contributions have the same sign. Meta substitution by an atom or group will result in bond moments in an opposite sense from that caused by the same atom or group in the para position. Thus on meta substitution by a group with a positive spectroscopic moment (C1, CH3), both the vibronic and induced contributions have the same sign, and the sign of the 1Lb CEs is the same as that of the unsubstituted parent. For meta substitution by a group with a negative spectroscopic moment (CF3, CN), the sign of the induced contribution is opposite to that of the vibronic contribution. In the case of CF3 and CN groups, the latter is more important than the former, and the sign of the 1Lb CEs is the same as that of the unsubstituted parent. Ortho substitution again reverses the sense of the induced bond transition moments from that induced by the same meta substituents. Thus, provided the position of the substituent and its spectroscopic moment are taken into account the absolute configuration of substituted phenylmethylcarbinamines and carbinols can often be assigned.
