Question

What is the molecular formula for hexane, cyclohexane, and toluene?

Answer 1

You can easily look these up, but let's just figure it out without drawing it first...

n-Hexane has six carbons and is a saturated hydrocarbon. It is the most simple compound of the three. As a straight-chained alkane, it has the general formula `"C"_n "H"_(2n+2)` to account for terminal hydrogens. So, it must be `"C"_6"H"_14`.

Cyclohexane is simply the same compound as a ring, giving it a general formula of `"C"_n "H"_(2n)`. So then it is just `"C"_6"H"_12` to account for the absence of terminal hydrogens.

Toluene is the "common" name for methylbenzene. Benzene is `"C"_6"H"_6`, so methylbenzene adds `"CH"_3` and takes away one `"H"`, making it `"C"_7"H"_8`; or better, `"C"_6"H"_5"CH"_3`.