In this contribution, we report a quantitative analysis of gas-phase ultraviolet photoelectron spectra (HeI) of model compounds such as cyclopentane, cyclohexane, and cycloallcyl-1-alkane derivatives, by means of outer-valence Green's function (OVGF) calculations. These spectra and their OVGF theoretical simulations are also compared with UPS measurements on alpha -cycloalkyl-omega -alkanethiol monolayers adsorbed on gold. This theoretical study analyses the dependence of valence ionization spectra of saturated hydrocarbons on structural characteristics (configuration, conformation, and torsional flexibility).