Accurate modeling of molecular electrostatic properties is one of the most important aspects of the Drude force field. As shown in Table , the optimized parameters yielded gas-phase total dipole moments and their components that were in good agreement with their QM target values. An interesting challenge arose when fitting the dipole components of MBOA and 2HEB due to the asymmetric electron density distribution on the ring carbons as a consequence of their proximity to the ester group. Given the rotation about the ester carbon-ring carbon bond, we averaged the ESP charge density between ortho and para ring carbons, yielding a smaller dipole moment, which was used as target in our fitting protocol.