# Definition of a Homologous Series

My textbook states that members of a homologous series have the same general formula (ex. $$\ce{C_{n}H_{2n}}$$ for alkenes) as they only differ from one to another by additional $$\ce{CH_2}$$ (methylene) groups. However, alkenes can have more than 1 carbon-carbon double bond, which should alter their general formula right?

• Luke here for good definition and description. – Mathew Mahindaratne Jan 19 at 6:43
• @MathewMahindaratne Are you suggesting that members of a homologous series need not have the general formula, only the same functional group? – David Lu Jan 19 at 6:56
• Read carefully and look at examples given. – Mathew Mahindaratne Jan 19 at 7:12
• There is the series for dienes and whatever number of double bounds you may wish to count and classify. Also , if the number of double bounds gets higher, usually trends and comparison is interesting with respect of the latter different n. This leads to a series, in a way, except that is of analogous rather than homologous - oligo- and polyenes. – Alchimista Jan 19 at 7:24
• If a molecule has more than one double bond C=C, it is not an alkene. It is an alkadiene, or an alkapolyene. – Maurice Jan 19 at 15:55