High-resolution electronic spectroscopy experiments on several substituted benzenes in the gas phase have revealed a remarkable sensitivity of the orientation of the SI-So transition moment (TM) in the:molecular frame to the conformation of the attached group. Here, we explore the origins of this effect by performing ab initio calculations on five conformationally flexible benzenes (toluene, ethylbenzene, n-propylbenzene, 2-phenethyl alcohol, and 3-phenylpropionic acid) using the configuration interaction singles method (6-31G* basis set). Comparisons of the theoretical predictions with the experimentally determined parameters show that there are two principal sources of the observed sensitivity: a "through-bond" effect caused by rotation of the substituent about the bond connecting it to the ring, which breaks the C-S symmetry of the parent molecule, and a "through-space" effect, apparently caused by interactions of the side chain orbitals with,the rt orbitals of the ring. "Purely electrostatic" interactions between the ring and the tail, while significant in some cases, result in TM orientations that do not agree with experiment. All three types of interactions produce mixings of the ring pi* orbitals, which in turn can lead to L-1(a)/L-1(b) excited electronic state:mixing in the isolated molecule. Possible photochemical and photophysical consequences of this effect are discussed.