Acta Chimica 4. (1954)
1. szám - M. Láng–M. Vizesy: Investigation of the spectra of diastereoisomers (Preliminary communication)
INVESTIGATION OF THE SPECTRA OF DIASTEREOISOMERS (PRELIMINARY COMMUNICATION) L. LÁNG and M. VIZESY (Central Research Institute for Physics, Department for Spectroscopy, Budapest) Received February 28, 1953 We have investigated the ultraviolet absorption spectra of four diastereoisomer pairs (ethanol solvent). In these compounds, restricted rotation must be assumed ; consequently, no absolute cis and trans configuration can be attributed to them. They can only be referred to as having a more cis than trans constitution and vice versa. The designations »cis« and »trans« are used in this sense in this treatise. The objective of the present investigation was to find out whether there existed a measurable and characteristic difference between the spectra of diastereomere differing only in the cis and trans constitution, respectively, of their side-chains, and so whether it was sufficient to allow of a successful quantitative determination of any of the two diastereomers in the presence of the other. Our experiments have proved that there does exist a measurable difference between the spectra of such compounds and that, even though it be very small, it is sufficient for a quantitative analysis to be made, provided suitable methods are used. As no other method for constitutional investigation was available to us, the problem arose how to relate the obtained ultraviolet absorption spectra (Figures 1—4) to the corresponding dl-modifications. In the compounds investigated we tried to establish their constitution* by the following consideration : The side-chain of the benzene-ring is saturated and contains two asymmetric carbon atoms. Owing to its saturation it exerts but a substitutional effect on the ultraviolet spectrum of the basic compound, its own absorption in the examined spectrum-range being zero or, at any rate, insignificant. From such a substitutional effect small or no displacement towards the longer wavelengths can be expected. On the other hand, it seems quite probable, that the difference in the relative positions of the groups attached to the asymmetric carbon atoms causes a different change in the extinction coefficients of the basic compound, since the influence of the side-chain as a whole is the resultant of the field-effects of its components. In this respect we assume that the spectra of the trans isomers differ in the same way from the spectra of the corresponding * Table I. The relative positions of the groups attached to the asymmetric carbon-atoms are represented according to our theoretical consideration.