Question

Is `"butane"` an homologue of `"butane"`?

Answer 1

I take it your question relates to butane, `n-C_4H_10`, and but-2-ene, `H_3C-CH=CHCH_3`? No they are NOT homologues.

Explanation:

Butane is an alkane, with general formula `C_4H_10`. But-2-ene has general formula `C_4H_8`, and is an olefin, an alkene.

A useful concept to develop is the idea of the degree of unsaturation; each degree of unsaturation corresponds to a DOUBLE BOND or a RING. An carbon chain of `n` carbons thus has `(2n+2)` hydrogen atoms if it is saturated. You can see the relationship between butane, `C_4H_10`, and unsaturated `C_4H_8` (it could be cyclobutane, but here it is butene). The `C_4H_8` formula has 2 hydrogens less than the unsaturated formula, and thus an olefinic bond OR a ring junction MUST be present.