The Appel reaction uses a carbon tetrahalomethane and triphenylphosphine to convert a primary or secondary alcohol to an alkyl halide. First triphenylphosphine forms a phosphonium ion by abstracting a halogen from carbon tetrahalomethane. The alcohol then attacks the phosphonium ion, generating an oxyphosphonium intermediate. An SN2 displacement by the halide ion produces triphenylphosphine oxide and the alkyl halide. Inversion of configuration occurs if the carbon is asymmetric.