General formula for alkenes?

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Prepare for the IGCSE Organic Chemistry Exam. Study with flashcards and multiple choice questions, each question has hints and explanations to ensure you understand the core concepts. Get ready for your test with confidence!

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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