Equilibrium bond lengths are very similar among the three force fields (Figure ), but there are noticeable differences among the force constants (Figure ) Thus, compared to GAFF v1.7, SMIRNOFF99Frosst tends to have slightly larger bond force constants, except for the O-H hydroxyl bond force constant, which is much stronger. In GAFF v2.1, the O-H hydroxyl bond force constant is very close to that of SMIRNOFF99Frosst, but the carbon-oxygen bond constants are distinctly weaker.