Any hydrocarbon, independent of its degree of unsaturation, can be converted into a monohalide by removing a hydrogen atom from the hydrocarbon and replacing it with a halogen. Therefore, the monohalide will have an odd number of hydrogens. A dihalide will have an even number of hydrogens, etc. Remember, this rule is being applied only to alkyl halides. To determine the degree of unsaturation of a halide, remove the halogen from the formula and replace it with hydrogen. Do the computation as though the compound were the new hydrocarbon. For example, C5 H7Cl becomes C5 H8 which has two degrees of unsaturation.
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