The structure of the benzene ring in C 6 (CH 3 ) 6

Abstract

Since benzene itself is not crystalline at ordinary temperatures the study of the benzene nucleus or ring has had to be referred to certain of its derivatives. The most hopeful line of attack appeared to be in the direction of the fully substituted derivatives, such as C 6 Cl 6 , or else by way of compounds such as naphthalene and anthracene which contain more than one ring. The results so far obtained, however, have only shown that the ring is centro-symmetrical, a fact confirmed by the recent examination of crystalline benzene itself, that its approximate width (given by the difference in lengths of the naphthalene and anthracene molecules) is 2∙49 Å., and that there exist in the nucleus two periodicities of about 1∙28 and 2∙66 Å. If the ring be supposed to consist of six carbon atoms of diameter 1∙54 arranged as in the diamond pattern, then periodicities of 1∙26 and 2∙52 would exist, the width of the ring itself being 2∙52. If, on the other hand, the benzene nucleus is a plane ring of six carbon atoms of diameter 1∙42, such as occurs in the graphite structure, then the periodicities would be 1∙23 and 2∙46, the width of the ring being 2∙46 (fig. 1). The experimental observations ( loc. cit .) could not definitely decide between these alternative structures, and no other criterion was found which would distinguish with certainty between a puckered and a plane ring. One of the chief difficulties encountered in the study of these various benzene derivatives was that the unit cell invariably contained more than one molecule, a fact which necessarily complicated any structure determination by introducing the question of relative orientations.