Following a recently succesfull measurement of the structure of a monolayer of n-butane adsorbed on MgO we wish to perform neutron diffraction measurements of monolayers of cyclohexane and ethylene adsorbed on MgO (100) surface. Adsorption isotherm measurements have been performed using our state-of-the-art adsorption apparatus and we would like to extend our studies to include cyclic alkanes and the alkenes. We hope that the structural determination will help us to understand the subtle interplay between intermolecular and molecule-substrate interactions by comparing the structures with those of these hydrocarbons adsorbed on graphite (already known).