Triesterified phospholipid model compounds have been synthesized and extensively studied with 300-MHz 'H NMR in the monomer phase in order to get additional support for the effect of conformational transmission induced by a P(4-coord) into a trigonal bipyramidal P(5-coord) transition, as was suggested by Merkelbach and Buck. To elucidate any conformational preferences around the C2-C3 bond, the stereospecifically deuterated precursor l,2-dihexanoyl-(3R)-sn-[3-2H]glycerol was synthesized. The results reveal that a coordinational change of phosphorus from four to five is transmitted in a significant increase in population of the conformer, in which the vicinally substituted oxygens 0 -2 and 0 -3 are trans located. The impact of this transmission seems not to be restricted to conformational changes in the adjacent C2-C3 bond, but is also present in specific rotations around the C'-C2 bond, thereby shifting the C'-C2 conformational equilibrium towards a decreased contribution of the trans arrangement of the acyl chains. As a consequence the interchain distance will be reduced and thus van der Waals interactions will be maximized. The results are interpreted in terms of increased electron density on 0-3 when axially located in a P(5-coord) trigonal bipyramidal compound, thereby introducing enhanced electrostatic repulsions within the oxygen pairs 0-3,0-2 and 0-3,O-1. Relaxation of this energetically unfavourable geometry leads to the observed conformational shifts. Absence of conformational transmission, as found in P(5-coord) trigonal bipyramidal compounds with the 2-ester group substituted for an alkyl moiety, can be considered as additional support for the introduced concept. In the alkyl part of the model phospholipids, however, no conformational changes were observed by means of I3C NMR. Extrapolating this outcome to more condensed phases, a proposition could be made about the mechanism by which conformational changes in the head-group and/or glyceryl backbone will be compensated.Phospholipids have been the subject of numerous conformational studies in order to get some insight in their behaviour in biomembranes [l, 21. In this paper we wish to present some experimental results on the conformational transmission from the phospholipid head-group towards the hydrocarbon chains upon a coordinational change of phosphorus from four to five. The role of P(5-coord) trigonal bipyramidal (TBP) intermediates in phospholipid membranes as a trigger for ion transport has been discussed by Merkelbach and Buck [3, 41. These intermediates, visualized as the result of an attack of, for instance, water on a P(4-coord) geometry, are stabilized by a pseudo-six-membered ring in an equatorial arrangement, originating from the choline moiety by charge attraction.Earlier theoretical and experimental investigations conducted in this laboratory on 5-phosphorylated tetrahydrofurfuryls [5, 61, which possess essentially the same P-0-C-C-0 Abbreviations. TBP, trigonal bipyramidal; P(5-coord), 5-COOrdinated phosphorus.Enzymes. Diaphorase from...