The flexible, oily tails of a common engine additive control its electrical charge more than its solid core.
April 24, 2026
Original Paper
Conformational Dependence of Dipole Moments in Zinc Dialkyldithiophosphates: Unexpected Dominance of Alkyl Chain Configurations
ChemRxiv · chemrxiv.15002328/v1
The Takeaway
ZDDP is a molecule used in almost every motor oil to prevent engine wear by sticking to metal surfaces. Engineers assumed the electrical pull of the molecule came from its dense, polar center. It turns out the floppy alkyl chains on the outside actually dominate the molecule's overall dipole moment. Even though these tails are technically non-polar, their configuration dictates how the molecule behaves. This counterintuitive finding helps explain why different versions of this additive perform better in certain engines.
From the abstract
Molecular dipole moments are required for empirical correlations used to estimate thermophysical properties of zinc dialkyldithiophosphates (ZDDPs), an important class of anti-wear additives. We calculated dipole moments for three ZDDPs and their precursor dialkyldithiophosphates using density functional theory and explicitly accounted for their dependence on molecular conformation. We unexpectedly found that dipole ∗Corresponding author. Email: [email protected] moments are highly sensitive to