MCQ Detailed View

Primary alkyl halides form a major class of organic compounds that play an important role in substitution and elimination reactions. An alkyl halide, also called haloalkane, is an organic compound in which one or more hydrogen atoms of an alkane are replaced by halogen atoms such as fluorine, chlorine, bromine, or iodine. The classification of alkyl halides into primary, secondary, and tertiary depends on the nature of the carbon atom directly attached to the halogen.

In a primary alkyl halide, the halogen atom is attached to a carbon atom that is bonded to only one other carbon atom. This means that the halogen-bearing carbon is a primary carbon. For example, in CH₃CH₂Cl (ethyl chloride), the carbon bonded to chlorine is attached to just one other carbon atom, making it a primary halide. If the halogen is bonded to a carbon that is connected to two other carbons, it is called a secondary alkyl halide, and if bonded to a carbon connected to three other carbons, it is called a tertiary alkyl halide.

The distinction between primary, secondary, and tertiary alkyl halides is very important because it directly affects their reactivity. For instance, primary alkyl halides generally undergo SN2 (bimolecular nucleophilic substitution) reactions more easily due to less steric hindrance. On the other hand, tertiary alkyl halides favor SN1 reactions because the carbocation formed during the reaction is more stable.

Understanding this classification helps students solve exam questions quickly and also provides a foundation for predicting reaction mechanisms in organic chemistry. Therefore, the correct answer is that in primary alkyl halides, the halogen-bearing carbon is bonded to one other carbon atom.