Question

What is the structure of an organic species that has a formula of `C_9H_18` in which ALL the hydrogens are equivalent?

Answer 1

`"Hexamethylcyclopropane..........?"`

Explanation:

I could not find a picture of this, and for all I know the molecule is unknown. A cyclopropyl ring, however, substituted with 6 methyl groups, fits your requirement. There are 6 methyl carbons attached to the three-membered ring, and all of them are `CH_3` groups.

Answer 2

Anor277 is correct! hexamethylcyclopropane!

Explanation:

To solve this, one must first recognize that the only way to get all primary hydrogens is to have all the hydrogens on methyl groups, `CH_3`.

There are 18 hydrogens.

That means there are 18/3 methyl groups.

That means we will need 6 carbons for the methyl groups.

That leaves 3 carbons to make up the support structure.

You could put them in a straight chain, but when you do that you end up with too many hydrogens and two of those hydrogens are tertiary:

This is the same problem you have with alkanes: two too many hydrogens for a linear alkane. You solve that by making it a cycloalkane!

And there you have it! At least, that's how I reasoned through it.