The effect of substitution, hybridization, and solvent on the properties of the C center dot center dot center dot HO single-electron hydrogen bond has been investigated with quantum chemical calculations. Methyl radical, ethyl radical, and vinyl radical are used as the proton acceptors and are paired with water, methanol, HOCII and vinyl alcohol. Halogenation (Cl) of the proton donor strengthens this type of hydrogen bond. The methyl group in the proton donor and proton acceptor plays a different role in the formation of the C center dot center dot center dot HO single-electron hydrogen bond. The former is electron-withdrawing, and the latter is electron-donating, both making a constructive contribution to the enhancement of the interaction. The contribution of the methyl group in the proton acceptor is.larger than that in the proton donor. The increase of acidity of the proton is helpful to form a single-electron hydrogen bond. As the proton acceptor varies from the methyl radical to the vinyl radical, the interaction strength also increases. The solvent has an enhancing influence on the strength of the C center dot center dot center dot HO single-electron hydrogen bond. These factors affect the C center dot center dot center dot HO single-electron hydrogen bond in a similar way that they do other types of hydrogen bonds.