Optical Studies With Chloro-Nitroso Camphane Derivatives With an Additional Paper on the Photoelectric Polarimetry and Low-Temperature Absorption Spectroscopy of (-)-beta-Caryophyllene Nitrosite

Abstract

The following C1, C10- substituted chloro-nitrosocamphanes have been synthesised: The effect of irradiation with polychromatic red light was determined by both spectrophotometric and polarimetric measurements. The absorption spectra of compounds (b) - (e) showed bathochromic shifts after short exposure while that shown by (a) was hypsochromic. The reinvestigation of the spectra of the previously described chloro-nitrosocamphanes (f) and (g) (R = Me and CH2SO3 H+. Py respectively), also revealed changes in l max. after irradiation. Thus all chloro-nitrosocamphanes investigated showed, to varying degrees, changes in their spectra after irradiation. The Cotton effects and C2- configurations of (a), (b) and (g) were opposite those for the parent camphane (f). The irradiation of (a) and (f) resulted in the rapid inversion of their initially opposite curves of rotatory dispersion with a simultaneous displacement of their spectra in different directions. These observations are interpreted in terms of a 2:2' - mutarotation which gives the diastereoisomer with different molecular constants and hence a different spectrum. The polarimetric and absorption measurements for (b) and (g) however, are not easily reconciled with this hypothesis. Irradiation resulted in much greater increases in absorption on the long-wave side of l max. , while their Cotton effects did not change sign. Indeed for comparable changes in their spectra, the rotation of (b) changed by only 166 compared with the 1460 shown by (f). Various alternative causes of band-shift are discussed and shown by experiment to be untenable. The possibility of Wagner-Meerwein and Nametkin rearrangements induced by light is discussed and shown to provide a qualitative interpretation of the differences in the photo-processes of (b) and (g) on the one hand and (a) and (f) on the other. On this basis, the stereochemistry of the molecules determines the nature of the process. Experiments, in which it was hoped to differentiate between photomutarotation and intramolecular rearrangement in (b) and (g), are described. Although it was shown that, like (f) , the product of irradiation of (b) was isomeric with the starting material, the results of these experiments are inconclusive. The substituted chloro-nitrosocamphanes are shown to be theoretically capable of asymmetric photolysis but with greatly impaired efficiency