MU Chemistry 416 FS97

Articles on Exciton Chirality


A Chiroptical Method for Determining the Absolute Configuration of Allylic Alcohols. Nobuyuki Harada, Jun Iwabuchi, Yoichi Yokota, and Hisashi Uda J. Am. Chem. Soc. 1981, 103, 5590-5591.
Exciton coupling is not limited to degenerate chromophores. These authors extend the method to a non-degenerate system of the two chromophores benzoate and alkene. The benzoate band at 230 nm (pi -> pi*) is the long-wavelength band and the 195 nm (pi -> pi*) band of the alkene is the short wavelength band. Positive chirality thus means that the first Cotton effect (the one at higher wavelength, which is the benzoate absorption) is positive. (Note that Figure 2 shows only the negative Cotton effect of the long-wavelength band.)

Preparation of chiral allylic alcohols using Rhizopus nigricans. Use of the Harad-Nakanishi exciton chirality method for verifying configurational assignments of allylic alcohols. Satoru Ito, Masaji Kasai, Herman Ziffer, and J. V. Silverton J. Can. Chem. 1987, 65, 574-582.
An application of Harada's method to the determination of the stereochemistry of allylic alcohols. The para-bromine works just like the benzoate itself.

Structure and Absolute Stereochemistry of the Epoxyquinol LL-C10037alpha and Related Metabolites from Steptomyces LL-C10037. Ben Shen, Yvonne G. Whittle, Steven J. Gould and Douglas A. Keszler J. Org. Chem. 1990, 55, 4422-4426.
These authors extend the method to a non-degenerate system of the two chromophores para-bromobenzoate and enone. The benzoate band at 250 - 260 nm (pi -> pi*) is the long-wavelength band and the 210 nm (pi -> pi*) band of the enone is the short wavelength band. Make sure you understand Figure 1 full well.

Synthesis of the 6-Benzoyl Derivative of 1-Deoxy-1-oxo-7-desacetylkolin and an Unambiguous Assignment of the Absolute Stereochemistry of Forskolin. Leander J. Vlades III and Masato Koreeda J. Org. Chem. 1991, 56, 844-846.
A very nice demonstration of the use of benzoyl derivatives to determine the absolute stereochemistry of diols. Make sure you understand Figure 1 full well.

Absolute Sense of Twist of the C12-C13 Bond of the Retinal Chromophore in Bovine Rhodopsin on Excition-Coupled CD Spectra of 11,12-Dihydroretinal Analogues. Qiang Tan, Jihong Lou, Babak Borhan, Elena Karnaukhova, Nina Berova, and Koji Nakanishi Angew. Chem. Int. Ed. Engl. 1997, 36, 2089-2093.
This is an excellent paper for several reasons. To begin with, would any of you have expected that the 11-cis-retinal chromophore in native rhodopsin is not planar? Come on, be honest! Next, take a look at the UV/Vis and CD spectra in Figure 1. Try to understand the arguments presented to explain the origin of the alpha and beta bands. Finally, the main point of the paper lies with the conformational analysis via the excition chirality of the non-degenerate bichromophoric system generated by the saturation of the C11-C12 bond. Make sure to understand Figure 4 full well.