Nucleophile is any negative ion or any neutral molecule that has at least one unshared electron pair. Alkene act as a Nucleophile Halide ion act as a Nucleophile Sodium borohydride is the transfer of a hydride ion, from the metal to the carbonyl carbon. In this transfer the hydride ion acts as nucleophile. Solution Nucleophile is any negative ion or any neutral molecule that has at least one unshared electron pair. Alkene act as a Nucleophile Halide ion act as a Nucleophile Sodium borohydride is the transfer of a hydride ion, from the metal to the carbonyl carbon. In this transfer the hydride ion acts as nucleophile..