A lewis acid is one that has the ability to accept electrons. A lewis base is one that has the ability to donate electrons. It is difficult to determine from the structure, without looking at orbital and electronic properties, the strength of a lewis acid and base. The most common acid and base classification for organic chemists, however, is the Bronsted-Lowry acid and base definition. Bronsted acids have the ability to donate a proton .
Bronsted bases have the ability to accept electrons .
Determining the acid or base strength from an organic structure becomes slightly more complex. It is extremely important to remember that acid strength is based upon the stability of the resulting anion . Phenol, for example, is about 1,000,000 times stronger than cyclohexanol because the resulting anion can delocalize its electrons around the ring through resonance, effectively stabilizing it. Electons on phenol are stabilized by resonance, cyclohexane has no resonance structures Resonance is not the only factor that effects acid and base strength. The conjugate base anion can be stabilized by inductive electron pull by highly electronegative side groups.