Proton transfer to strong bases

Atom A is more negative than atom B => the proton of H—A is more positive than that of H—B => the proton of H—A will be held less strongly => the proton of H—A will separate and be transferred to a base more readily. 

Because of its high negative charge density, the oxide ion is a very strong Bronsted base. Therefore, when an ionic oxide is placed in water, there is proton transfer to produce hydroxide ions. 

The weights of the covalent and ionic solutions in the MCSCF-MI wave function are strongly dependent upon the H-Cl distance. When such distance is close to its value in isolated hydrogen chloride, the covalent solution weighs more than the ionic one. The opposite trend is observed when the H-Cl distance is such as to justify a picture where the proton is transferred to the base. In all cases, the covalent function turned out more important, with the ionic structure much less stable. This result concerning the NH3 -I- HCl system has been recently confirmed by dementi et al. [23] for the complex in the gas phase. 

Every oxide ion accepts a proton in water, so O2 is an example of a strong base. In other words, proton transfer to oxide ions goes to completion in water. 

The half-life of a base hydrogen-bonded to a strong acid can be very short indeed since proton transfer can occur by tunnelling thus the rate coefficient for proton transfer to water hydrogen-bonded to H30+ has been estimated at 1014 s-1 (Crooks, 1977). For the nitrations in concentrated sulphuric acid as solvent, H2S04 and HSO should take the place of H30+ and H20 in (34) (cf. Cox, 1974). 

Fig. 2. (a) Proton transfer in water, (b) Proton transfer from strong acid to strong base, (c) Proton transfer from weak acid to weak base. 

Steric eifects can also be caused by other types of strain. 1,8-Bis(diethyla-mino)-2,7-dimethoxynaphthalene (8) is an extremely strong base for a tertiary amine (pZa of the conjugate acid = 16.3 compare 7/,7/-dimethylaniline, pA a = 5.1), but proton transfers to and from the nitrogen are exceptionally slow slow enough to be followed by a UV spectrophotometer. Compound 8 is severely strained because the two nitrogen lone pairs are forced to be near each other. Protonation reheves the strain one lone pair is now connected to a hydrogen, which forms a hydrogen bond to the other lone pair (shown in 9). 

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