25 OPTICAL ROTATORY DISPERSION OF NITROBENZENE DERIVATIVES

Nagai U., Kurumi M., Iga H.

doi:10.24496/tennenyuki.13.0_187

A number of o-nitrobenzoyl derivatives of optically active secondary alcohols and L-α-amino acids were prepared and found to show Cotton effect around 330nm in their optical rotatory dispersion. Most o-nitrobenzoyl esters of R-configuration showed negative Cotton effect and those of S-configuration showed positive one. But, a few exceptions were observed. Each of the o-nitrobenzoyl esters is considered to be a mixture of conformers C and D, and normally the population of D is negligibly small. But, in such cases as in compounds (II), (XII), and (XV), the population of the conformer D becomes significant. Because the axial isopropyl group in (II) and the angular methyl group in (XII) interact with the nitro group repulsively to result in decreased population of the conformer C. In (XV), the conformer D has significant population because the bulkiness of the substituent L is nearly equal to that of S. So, these exceptional cases can be explained since the conformers C and D have inverse contributions to ORD amplitude according to the sector rule introduced, generally. The sector rule proposed for aliphatic nitro compounds were extended to the Cotton effect of these o-nitribenzoates giving four sectors around the asymmetric centres concerned. All the molecular amplitudes observed were rationalized thus in terms of conformational analysis and the sector rule. All the N-o-nitrobenzoyl L-α-amino acids so far examined showed negative Cotton effect. Conversion of the acids into their eaters or carboxylate ions shifted the amplitudes more positive. These shifts were also interpreted on the basis of their conformation and the sector rule.

25 OPTICAL ROTATORY DISPERSION OF NITROBENZENE DERIVATIVES

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