In general, bases are special Nucleophiles, where the proton is always
the electrophile. Common bases are hydroxide OH-, and amide
NH2-, and the conjugate base of a weak acid like
acetate CH3CO2-. Nucleophiles can also
go after other nuclei, especially C+ (carbocations) -- where
the electrophile is the carbon nucleus. So all nucleophiles go after nuclei
and bases are a special case where the nucleus is always a proton. We will
discuss in some detail later how to determine when a nucleophile will go
after a proton and when a nucleophile will more likely go after a carbon
nucleus.
The mode of eletrophilic addition goes as follows. We can see the bond
pivot on Ca or Cb:
