An X-Ray Study of Liquid Benzene, Cyclohexane and Their Mixtures

X-ray (Mo K alpha) studies were made of pure benzene, pure cyclohexane, and their mixtures, using a Geiger-Mueller counter with balanced filters. The benzene showed at 25°C a rather sharp intense peak at the customary 8°40′ and a new broader peak of about one-eighth intensity at 4°20′. The cyclohexane showed a similar pair of peaks at 8°0′ and 4°0′. The mixtures all showed a broad peak of low intensity reaching from 4°0′ to 4°20′ and three sharp peaks at 8°0′, 8°20′, and 8°40′ superimposed on a broad peak which reached from about 8°0′ to about 8°40′. The positions of the three sharp peaks were not affected by the proportions of the two components, and their relative intensities were independent of amount of stirring. The customary shift with temperature was observed on all peaks. The results are consistent with a cybotatic type of picture. Benzene is pictured as having short-lived highly organized groups of —B–B–B–B— floating in a chaotic sea of disorganized benzene molecules. The peak at 8°40′ is thought to be due to the presence of vibrating groups whose extreme positions simulate groups of —B–B–B–B–B–B— and —B–B–B–B–B–B—. Cyclohexane would contain similar groups of —C–C–C–C—. The mixtures are assumed to contain —B–B–B–B—, —C–C–C–C—, and —B–C–B–C—. The presence of any considerable amount of more complicated groupings is obviously highly improbable.