We report a family of substituted thiocarbonates, thiocarbamates, and thioureas and their reaction with cadmium oleate at 180-240 °C to form zincblende CdS nanocrystals (d = 2.2-5.9 nm). To monitor the kinetics of CdS formation with UV-vis spectroscopy, the size dependence of the extinction coefficient for λ max (1S e-1S 1/2h) is determined. The precursor conversion kinetics span five orders of magnitude depending on the precursor structure (2˚-thioureas > 3˚-thioureas ≥ 2˚-thiocarbamates > 2˚-thiocarbonates > 4˚-thioureas ≥ 3˚-thiocarbamates). The concentration of nanocrystals formed by the nucleation reaction increases with increasing precursor conversion reactivity, allowing the final size to be controlled by the precursor structure. 1 H NMR spectroscopy is used to monitor the reaction of dip -tolyl thiocarbonate and cadmium oleate where dip -tolyl carbonate and oleic anhydride coproducts can be identified. These coproducts further decompose into p-tolyl oleate and p-cresol. The spectral features of CdS nanocrystals produced from thiocarbonates are exceptionally narrow (95-161 meV FWHM) compared to those made from thioureas (137-174 meV FWHM) under otherwise identical conditions, indicating that particular precursors nucleate narrower size distributions than others. Additional nanocrystal synthesis and precursor coproduct identification Figures S1-S23 and 1 H, 13 C{ 1 H}, and 19 F{ 1 H} NMR characterization of molecules. (PDF)

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