The far ultra-violet spectra of styrene, $\alpha $-methyl styrene, phenyl acetylene, phenyl cyanide and phenyl isocyanate are described. Many of the observed regions of absorption are correlated with those of the benzene spectrum. The important fact emerges that, with increasing conjugation of the side chain with the ring, the benzene 1980 A absorption moves much farther to long wave-lengths than do the benzene 2600 and 1790 A absorptions. $\alpha $-Methyl styrene shows a shift to the violet of certain regions of its spectrum relative to styrene. Phenyl isocyanate has a spectrum much closer to that of benzene than have the other molecules discussed.