Question

What is the general formula for substituted aromatic compounds, and substituted arenes in particular?

Answer 1

I am not sure what you want......`C_6H_5X`?

Explanation:

And of course, `C_6H_5X` specifies four degrees of unsaturation: 3 formal double bonds, and a ring. The `X` group (commonly used for halogens) could be any functional group.

Answer 2

I can think of general formulas for two homologous series of aromatic compounds.

Explanation:

In organic chemistry, a homologous series is a group of compounds with the same general formula, usually obtained by varying by the number of carbon atoms.

Based on the number of `"CH"_2` groups

If we start with benzene and add `"CH"_2` groups, we get the series

`"C"_6"H"_6, "C"_7"H"_8,"C"_8"H"_10, "C"_9"H"_12, …`

It is common to start the general formula for a homologous series with `n = 1`.

This gives us the general formula

`"C"_text(n+ 5)"H"_text(2n + 4), n = 1, 2, 3, …`

Based on the Hückel `4n + 2` rule

This gives us the series of annulenes:

`"C"_6"H"_6, "C"_10"H"_10, "C"_14"H"_14, "C"_18"H"_18, …`

If we start the series with `n = 1`, we get the general formula for another aromatic series:

`"C"_text(4n+2)"H"_text(4n+2), n = 1, 2, 3, …`