How can we calculate pKa?
MOPAC includes a pKa calculation, as a new keyword in PM6, for the pKa of the most acidic hydrogen atom attached to an oxygen.
MOPAC is available in Chem3D, with usage methods for pKa included in Chem3D's online help. For more technical details on MOPAC's pKa calculations, see http://www.openmopac.net/pKa_table.html
In ChemDraw Professional, the pKa calculation is done by Molecular Networks (MolNet) . In some cases the algorithm cannot calculate the value, so you will see an N/A value instead.