Question

ethene, propene and butene are three consecutive members of the alkene homologous series. the structural formulas of the molecules are given.

1. which of the following is not a property for ethene, propene and butene to be categorised as the same homologous series?

a all molecules have the same functional group.
b all molecules have the same general formula.
c each molecule differs from its preceding member by a \\(-\text{ch}_2\\) group.
d each molecule differs from its preceding member by its density.

Explanation:

Analyze characteristics of a homologous series

• Members share the same functional group (carbon-carbon double bond \(C=C\) for alkenes).
• Members share the same general formula (\(C_nH_{2n}\) for alkenes).
• Consecutive members differ by a structural unit of \(-\text{CH}_2-\).

Evaluate the given options

• Option A is a true property of a homologous series.
• Option B is a true property of a homologous series.
• Option C is a true property of a homologous series.
• Option D is not a defining property for categorizing compounds into the same homologous series, as physical properties like density change gradually rather than remaining a constant defining rule for categorization.

Answer:

• (A) All molecules have the same functional group.
• (B) All molecules have the same general formula.
• (C) Each molecule differs from its preceding member by a \(-\text{CH}_2-\) group.
• (D) Each molecule differs from its preceding member by its density. (Correct answer)