Spatial minima in the electrostatic potential

ab initio calculations show that the equilibrium position of the proton is in the molecular plane. The 0-H hond length is 0.96A and the H-O-C angle is 116° at the HF/6-31h-G level. Thus the hond length is 0.27 A shorter and the bond angle is 13° smaller than predicted from the position of the Vmin. Still the Vmin prediction is remarkably good, particularly if we consider that the gas phase proton affinity of acetone is 196.7 kcal/mol, more than three times the magnitude of the Vmin- 

CH3NH2 -84.3(1) Lone pair Outside N, along C-N bond. 

CH30H -60.6 (2) Lone pair Outside 0, above and below plane defined by C-O-H. 

CH3F -30.6 (3) Lone pair Outside F, 124° angle with F-C bond. 

C2H4 -24.7 (3) r-region Outside C-C bond, above and below molecular plane. 

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