The process of nucleation in complex solutions may be dependent upon chemical reactions and changes in species stoichiometry occurring locally. Several studies have attributed the multi-step nature of nucleation to these factors. Simulating reactive crystallization events is often beyond the scope of classical molecular simulations using semi-empirical, non-reactive force fields. As such, this review focuses on simulating nucleation from building blocks which are already present in the parent solution phase. These examples, however, highlight the importance of simulation practitioner's understanding of the chemical speciation and valency of molecular and ionic species involved in crystal formation.