In order to gain a deeper understanding of the relationship between molecular structure and liquid crystal properties, accurate data is required on single molecule properties of mesogenic fragments and molecules. This thesis applies a pseudopotential plane wave total energy method to calculate molecular properties of prototypical mesogenic fragments and the molecule 4-n-pentyl-4'-cyanobiphenyl (5CB) from first principles. Optimised molecular structures, vibrational properties and torsional potentials are determined and found to compare well with experimental observations and other ab initio investigations. A study is made of the transferability of torsional potentials between mesogenic fragments and 5CB. Also investigated is the conformation-dependence of dipole and quadrupole moments. The strength of the coupling is found to depend sensitively on the molecular structure and the conformation-dependence of quadrupole moments is found to significantly influence inter-molecular interactions. Finally, by combing first principles calculations with an empirical mean field approximation, conformational distributions of the alkyl tail in 5CB are examined.