= Solution
The <phosphorus> centre is approximately tetrahedral, with three P–C <sigma bonds> and one short terminal P–O bond. Both $\mathrm{Me_3P{=}O}$ and $\mathrm{Me_3P^+{-}O^-}$ are useful Lewis contributors; \b[the bond is strongly polar and has additional multiple-bond character]. <oxygen> lone-pair donation into suitable P–C antibonding combinations provides a description of the additional stabilization without requiring a substantial localized phosphorus-3d/oxygen-2p <pi bond>. A combined diffraction and orbital study illustrates this sigma-bond/negative-hyperconjugation description.<Computational and experimental approaches to the molecular structure of the HCl adduct of Me3PO by Andreas Orthaber and others>[§3.2 and Fig. 2a–c, orbital analysis of free Me3PO]{ref}
Compared with the phosphate triester, this compound's methyl substituents are less <electron> withdrawing. The comparison of the two terminal P–O stretching force constants and the appropriate experimental control is given with the triester below.
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