General formula for alkenes?

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Study for the IGCSE Organic Chemistry Test. Engage with flashcards and multiple-choice questions, complete with hints and detailed explanations. Prepare effectively to excel in your exam!

Multiple Choice

General formula for alkenes?

Explanation:
Alkenes have a carbon–carbon double bond. Introducing a double bond reduces the hydrogen count by two compared with the corresponding alkane, which has the formula CnH2n+2. So for an open-chain alkene with n carbon atoms, the hydrogen count is 2n, giving the general formula CnH2n. This matches common examples like ethene (C2H4) and propene (C3H6). If the molecule forms a ring or contains more than one unsaturation, the formula changes (cycloalkenes have CnH2n−2, and alkynes have CnH2n−2).

Alkenes have a carbon–carbon double bond. Introducing a double bond reduces the hydrogen count by two compared with the corresponding alkane, which has the formula CnH2n+2. So for an open-chain alkene with n carbon atoms, the hydrogen count is 2n, giving the general formula CnH2n. This matches common examples like ethene (C2H4) and propene (C3H6). If the molecule forms a ring or contains more than one unsaturation, the formula changes (cycloalkenes have CnH2n−2, and alkynes have CnH2n−2).

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