Room temperature P-31 magic angle sample spinning (MAS) nuclear magnetic resonance (NMR) is used to study the phosphine chalconide species coordinating the surface of CdSe nanocrystallites. Two surface species are identified : trioctylphosphine oxide (TOPO) and trioctylphosphine selenide (TOPSe). The TOPO coordinates Cd surface sites while trioctylphosphine (TOP) coordinates Se to produce surface TOPSe species. Chemical removal of TOPSe linkages produces CdSe nanocrystallites passivated exclusively with TOPO. A double resonance experiment (P-31 and Se-77) characterizes the TOPSe species. Quantitative studies indicate coordination to nearly all surface Cd atoms and allows the development of a model for the morphology of an average crystallite surface.