Order parameters in hydrocarbon chains

Order in lipid bilayers is often described by order parameters S_CD, S_HH and S_chain which are rather directly obtained from deuterium NMR, proton NMR and ESR spectroscopy respectively. A relation is derived that makes one of these parameters redundant from purely geometrical reasons. Further, the effect of conformational disorder upon these order parameters is investigated theoretically using a trans—gauche model. Corrections from the finite of the trans—gauche wells and from non-fixed valence angles are shown to be negligible.