Section 1.1 pg 7

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keyanabogan 2J
Posts: 17
Joined: Wed Sep 21, 2016 2:56 pm

Section 1.1 pg 7

Postby keyanabogan 2J » Tue Mar 07, 2017 2:11 pm

In this section, an example is given where it asks to name the molecule structure given. But, in the given the molecule structure it states that there are 5 carbon atoms and 3 methyl substituents.
I'm just confused on how you would determine which ones would be considered the 3 methyl, and which ones would count as the 5 carbons included in the root?

It also gives the name of the molecule as 2, 2, 4-trimethylpentane as it would be named with the IUPAC system. But, it refers to its common name as isooctane.
However, I thought that molecule with 5 or more carbon atoms use the prefix neo-?

Rochelle Ellison 2H
Posts: 29
Joined: Wed Sep 21, 2016 3:00 pm

Re: Section 1.1 pg 7

Postby Rochelle Ellison 2H » Tue Mar 07, 2017 7:15 pm

When counting the carbons to determine the name of the parent chain, you have to look for the longest chain. In order to determine which carbons can be part of the chain you could try tracing a line with your finger between all the connected carbons. If you have to pick up your finger or go backwards then that is the end of the carbon chain. So basically you have to find the largest number of carbons that can be linked without reaching a dead end. In the example on page 7 there are 5 carbons could be linked in this way (only one of the two CH3s at the end of the molecule can be counted because they are both branched from the same carbon). The remaining carbons must be part of substituents.

Also iso- is used when 2 CH3s and 1 H is bonded to 1 carbon in a chain and neo- is used when 3 CH3s and no Hs are bonded to 1 carbon in a chain. Yes neo- can only be used when there 5 or more carbons but that doesn't mean that it will be used every time there are more than 5 carbons. You always have to look at the connectivity to determine which to use.

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