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Correlation of the Circular Dichroism of Unsubstituted and Ring-Substituted Chiral Phenylcarbinamines with Their Absolute Configurations

Howard E. Smith ; Department of Chemistry, Vanderbilt University, Nashville, Tennessee 37235, USA

Sažetak

The sign of the 1~ Cotton effects (CEs) at about 250-27D
nm of the benzene chromophore of unsubstituted chiral phenylcarbinamines and their salts is determined by vibronic borrowing from the lBb-allowed transition at shorter wavelength. For these chiral phenylcarbinamines and their salts of the same generic
absolute configuration, the sign of their lLb CEs is the same.
On ring substitution, however, transition moments are induced
in the benzene ring bonds adjacent to the attachment bond of
the chiral group, resulting in enhanced coupling of the lLb
transition with the chiral group. Since the sign of the induced
contribution to the lLb CEs is determined by the spectroscopic
moment of the ring substituent and its position with respect to
the chiral group, the sign of the induced contribution may be
predicted to be the same or opposite to that of the vibronic
contribution. A reversal of the sign of the lLb CEs with ring
substitution is thus the overshadowing of a vibronic contribution
by an induced contribution of opposite sign. When both the
vibronic and induced contributions have the same sign, the sign
of 1Lb CEs is unchanged.

Ključne riječi

Hrčak ID:

175393

URI

https://hrcak.srce.hr/175393

Datum izdavanja:

30.6.1989.

Posjeta: 790 *