We show that, within a simple version of the bond polarizability model based on the approximation of axially-symmetric bonds, the polarized Raman optical activity is simply double the depolarized in a given band. Many of the bands in preliminary polarized and depolarized Raman optical activity spectra obtained with a new optical multichannel instrument accord with this result, which indicates that this and related models provide a useful starting point for interpreting ROA spectra in terms of structural detail. Additionally, our spectra imply that isotropic contributions can usually be neglected in most Raman optical activity bands, but that electric quadrupole contributions, while smaller than magnetic dipole contributions, are still usually significant.
A fully computer-controlled Raman optical activity spectrometer equipped with an intensified diode array detector is described. Despite using a conventional single-lens light collection system for simplicity, both polarized and depolarized Raman optical activity spectra can be obtained rapidly and routinely. A novel double grating spectrograph design permits good spectra to be obtained down to 50cm-' in liquids. Natural spectra of the chiral samples (-)-a-pinene and (+)-methylcyclohexanone and magnetic spectra of iridium (IV) hexachloride are presented.
The contribution of carbonyl deformation co-ordinates to normal modes is discussed in the context of the Raman optical activity of chiral molecules containing a carbonyl group attached to a cyclic system. A comparison of the Raman optical activity spectra of 3-methylcyclohexanone and 3-methyl methylenecyclohexane provides convincing evidence for the dominant role of carbonyl deformations in the generation of the large couplet at about 500 cm-' in 3-methyl cyclohexanone. The spectra of nopinone, P-pinene and 5-methylcyclohex-2-ene-lone are also discussed. Finally, a model bond polarizability theory of Raman optical activity in carbonyl deformations is presented.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.