Molecular face（MF） is a molecular intrinsic characteristic contour（MICC） with calculating and describing the electron density（ED） on it. MF not only gives the molecular boundary surface， but also shows the interaction sites and reactivity indicators， including the frontier ED（MFED）. M06-2X/6-311G（d，p） level of theory was employed to study proton transfer reactions of the singlet and triplet hydroxyl carbene molecules and their derivatives and to calculate their respective activation energies. It is shown that the substitutes with the strong electron?withdrawing and electron?donating groups make the activation energies of the singlet hydroxyl carbene reaction increase, whereas the substituent ─CN with the biggest electron?withdrawing group makes the activation energy of the triplet hydroxyl carbene reaction increase. Moreover， other substitutes with the strong electron-donating group make the activation energies of the singlet hydroxyl carbene reaction increase， whereas they make the activation energies of the triplet hydroxyl carbene reaction decrease. The strong electron-withdrawing groups make the activation energies of these reactions decrease. MF was used to explore the reactions mentioned above. Their MFs represent the changes of the molecular faces， and connect the reactive sites and change trend of the involved physical properties. There is a linear correlation of the difference between the maximum electron density around the C atom and the minimum electron density around the H atom of the singlet hydro-xyl carbene reactants and their corresponding reaction activation energies.
