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Naming hydrocarbons (alkanes) urgent help

Hey guys,

I am absolutely terrible with naming hydrocarbons! I've been practising it, and I understand the simple ones, E.g. - Drawing 2-methlypentane, hexane, etc.. But the harder ones such as 2,3,3-trimethlypentane?!? What are the numbers saying? I understand 'tri' means there are 3 methly groups and pentane is 5 carbons in the longest chain, but I get confused with the numbers!

Any help would be greatly appreciated

Reply 1

TirnanF

The position of each methyl group along the longest carbon chain. 2,3 dimethyl pentane: C-C-C-C-C will have a methyl group connected to the second and third carbon.

Posted from TSR Mobile

Reply 2

Pigster

Sorry to rub it in, but there is no 2,3,3-trimethylpentane. Whoops. Thanks charco, migraine talking.

Starting from one end, number the carbon atoms. The 2,3,3 etc. just tell you which carbon atoms the methyl groups are attached to. 1x CH3 joined to carbon 2 and 2x CH3 to carbon 3. When naming, always use the lowest numbers you can (yes I know there is more to it, but that usually does the trick at A-level, in case anyone butts in with point of first difference).

(edited 9 years ago)

Reply 3

charco

Study Forum Helper

Original post by Pigster

Sorry to rub it in, but there is no 2,3,3-trimethylpentane.

Why?

Reply 4

dis0rder

Original post by rm_27

for 2,3,3 trimethylpentane the numbers represent where the methyl groups are on the carbon chain: there are three methyl groups (tri-), one on carbon #2, two on carbon #3

i was struggling massively last year, what really helped me is sitting down for about 5 hours and naming as many of them as possible, then checking them, and each one that i named wrongly i'd do again until i got it right - try to UNDERSTAND why and where you went wrong. i know you said you're already practising, just do more and more of it and you will understand it eventually :biggrin: