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General Formulae

A homologous series is a class that can be represented by a general formula.
Below are a few general formulae. They are all assumed to have one functional group.
The restrictions on n are necessary since the smallest allowable value for n would represent the smallest compound in that series.
As an example, the smallest ester would need TWO carbons, hence n would start at 2, but the smallest acid can have 1 carbon, and n would start at 1. etc.

Alkane:
C_nH_2n+2 (n=1,2,3..)

Cycloalkane:
C_nH_2n (n=3,4,5...)

Alkene:
C_nH_2n (n=2,3,4...)

Alkyne:
C_nH_2n-2 (n=2,,3,4...)

Alcohol:
C_nH_2n+2O or C_nH_2n+1OH (n=1,2,3...)

Acid:
C_nH_2nO₂ (n=1,2,3...)

Ester:
C_nH_2nO₂ (n=2,3,4...)

Amine:
C_nH_2n+3N (n=1,2,3...)

Amide:
C_nH_2n+1NO (n=1,2,3...)

Aldehyde:
C_nH_2nO (n=1,2,3...)

Ketone:
C_nH_2nO (n=3,4,5...)