Good nucleophiles include RO-, -NH2, Cl-, Br-, I-, F-, CN-, -OH and RCO2-. Both negatively charged and neutral nucleophiles exist. Negatively charged nucleophiles are better than neutral ones and result in faster reaction rates. A few neutral nucleophiles include H2O, NH3, ROH and RCOOH.
Nucleophiles should be good Lewis bases, meaning that they have electrons to share with other atoms. The same reactive atom can be neutral or negatively charged, depending on the nucleophile. Oxygen is neutral in H2O but negatively charged in -OH. Nucleophilicity and basicity increase from right to left on the periodic table. As electronegativity increases, nucleophilicity decreases.