Geometric isomers for C6H14!

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Regina Chi 2K
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Geometric isomers for C6H14!

Postby Regina Chi 2K » Wed Mar 11, 2015 3:45 pm

This is question 6 on the 2011 practice final exam. They asked for geometric isomers (2 with a 5 carbon main chain and 2 with a 4 carbon main chain) and I understand how they got their answers. For the molecular formulas, would it matter if we have the parts of the main chain not in parentheses? And how would we arrange how to write the molecular formula in general from just looking at the line structure?

Neil DSilva 1L
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Re: Geometric isomers for C6H14!

Postby Neil DSilva 1L » Wed Mar 11, 2015 4:43 pm

I'm not sure about your first question. For your second question, you can write a molecular formula from a line structure by going from left to right and writing down what you see. For example, for 2-methylpentane, the molecule starts with a CH3 on the leftmost side, followed by two CH2's (which they grouped together since they are the same), follwed by a CH, followed by two CH3's attached to the carbon of the CH (which is, again, grouped together, since they are the same). That gives you the molecular formula in the solution.

Jenna Kovsky 1I
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Re: Geometric isomers for C6H14!

Postby Jenna Kovsky 1I » Wed Mar 11, 2015 7:18 pm

For your first question, when a part of the main chain is put in parentheses because it's being repeated, then that's just to make things simpler, and it can still be written out if you want to write it without the parentheses. Side chains, however (for example, the methyl group), do need to be in parentheses.

Chem_Mod
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Re: Geometric isomers for C6H14!

Postby Chem_Mod » Wed Mar 11, 2015 7:25 pm

Neil has correctly explained the second part of your question.
For the first part, it does not matter if you do not include the main chain components in parenthesis. For example,
for 2-methylpentane,
you can write,
CH3CH2CH2CH(CH3)2 instead of CH3(CH2)2CH(CH3)2
But NOTE: in both the cases I have written substituent in parenthesis
Always you MUST write substituents in parenthesis in these cases, otherwise it would not have any meaning.

Chem_Mod
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Re: Geometric isomers for C6H14!

Postby Chem_Mod » Wed Mar 11, 2015 7:29 pm

Yes Jenna is correct absolutely!


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