X-ray analysis of the dibenzyl series V-Tolane and the triple bond.

The detailed structure of stilbene has recently been described (Robertson and Woodward 1937) and a theoretical discussion of the resonance problem in that type of molecule is now given by Penney and Kynch (1938). The crystal symmetry and dimensions of a number of compounds are closely similar to those of stilbene, and it is possible to make use of this isomorphism to carry out a very direct analysis of these other structures. In X-ray analysis it is generally necessary in the first place to assume some model for the structure and then adjust the parameters by a process of trial and error until a fair measure of agreement is obtained between the calculated and the observed values of the structure amplitudes. Subsequent refinement of the parameter values can then be attained by the application of Fourier series methods. With an isomorphous series of the present kind, however, when the structure of one member has been accurately determined, it is often possible to eliminate the first and most laborious part of the analysis for the other members, and proceed to the solution directly by the successive application of Fourier series methods.