Secondary hydrogen isotope effects. Part 5. Acid and base strengths: corrigendum and addendum

Abstract

The effect of deuteriation of the methylene group on the acid strength of phenylacetic acid and the base strength of benzylamine are reinvestigated, using both the differential potentiometric method described in Part 1 of this series and a newly developed differential n.m.r. method, which is described. The differential potentiometric method is established to be sound, but the ΔpK_a values reported earlier could not be reproduced and are withdrawn in favour of the following values, obtained by the old method and confirmed by the new: PhCD₂CO₂H–PhCH₂CO₂H, ΔpK_a( pK_a^D– pK_a^H)= 0.005 ± 0.003; PhCD₂NH₃⁺–PhCH₂NH₃⁺, ΔpK_a= 0.032 ± 0.001.