  The Broensted and Lowry acid base theory is based on the capacity of proton
donation or acceptance (in the presence or absence of a solvent) whereas the
Lewis acid base theory is based on the propensity of electron pair acceptance
or donation. We explore through DFT calculation the obvious question whether
these two theories are in conformity with each other. We use pKa as the
descriptor for the Broensted and Lowry acidity. The DFT descriptors like
ionization potential, electron affinity, electronegativity, hardness and global
electrophilicity are computed for 58 organic and inorganic acids. The
fractional electron transfer, del(N) and the associated energy change, del(E)
for the reaction of these acids with trimethyl amine (a strong base) are used
as the possible descriptors for the Lewis acidity. A near exponential decrease
in del(N) and (-del(E)) values is observed in general with an increase in pKa
values. The findings reveal that a stronger Broensted acid in most cases
behaves as a stronger Lewis acid as well. However it is not necessarily true
for all acids.
