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Which of the following is the correct formula for the first member of the alkene series?
C ₄ H ₈
C ₂ H ₄
C ₃ H ₆
C ₅ H ₁₀
C ₂ H ₄
Alkenes follow the general formula C(n)H(2n). Since an alkene must contain a carbon-carbon double bond, 'n' must be at least 2.
Alkenes follow the general formula C(n)H(2n). Since an alkene must contain a carbon-carbon double bond, 'n' must be at least 2.
Define Alkene Series
The general chemical formula for the alkene homologous series is C(n)H(2n), where 'n' represents the number of carbon atoms.
Establish Structural Minimum
An alkene requires a carbon-carbon double bond (C=C). Since a double bond cannot exist with only one carbon atom, the smallest integer for 'n' is 2.
Apply Formula for n=2
Substitute n=2 into the formula: C(2)H(2*2) = C₂H4. This is Ethene, the first member of the series.
A: C4H8 corresponds to n=4 (Butene, 3rd member); C: C3H6 corresponds to n=3 (Propene, 2nd member); D: C5H10 corresponds to n=5 (Pentene, 4th member).
B is correct because the alkene general formula is C(n)H(2n), and with n=2 (the minimum required for a double bond), we get C2H4.
Remember that Alkanes (n=1), Alkenes (n=2), and Alkynes (n=2) have different starting members due to structural constraints.
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