Free radical substitution occurs on what type of hydrocarbon?

Free radical substitution occurs on what type of hydrocarbon?

• A. Aromatics
• B. Alkanes
• C. Alkenes
• D. Alcohols

Answer: (B)

Free radical substitution happens with saturated hydrocarbons—the alkanes. Under UV light, a halogen molecule splits into halogen radicals. A chlorine radical pulls a hydrogen off an alkane, creating an alkyl radical. This radical then reacts with another halogen molecule to form the substituted product and regenerate the halogen radical, allowing a chain reaction to continue. Alkanes have C–H bonds but no C=C bonds, so the reaction proceeds by abstraction and substitution of hydrogen. In contrast, alkenes react differently: halogens add across the double bond rather than replacing a hydrogen. Aromatics undergo electrophilic substitution on the ring, not a radical substitution. Alcohols aren’t hydrocarbons, and their typical reactions with halogens follow different pathways. So the type of hydrocarbon for free radical substitution is alkanes.

Free radical substitution happens with saturated hydrocarbons—the alkanes. Under UV light, a halogen molecule splits into halogen radicals. A chlorine radical pulls a hydrogen off an alkane, creating an alkyl radical. This radical then reacts with another halogen molecule to form the substituted product and regenerate the halogen radical, allowing a chain reaction to continue. Alkanes have C–H bonds but no C=C bonds, so the reaction proceeds by abstraction and substitution of hydrogen.

In contrast, alkenes react differently: halogens add across the double bond rather than replacing a hydrogen. Aromatics undergo electrophilic substitution on the ring, not a radical substitution. Alcohols aren’t hydrocarbons, and their typical reactions with halogens follow different pathways. So the type of hydrocarbon for free radical substitution is alkanes.