Heretohelp!
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So basically this is the question:
"There are nine structural isomers of molecular formula C4H8Br2 , three of which have branched carbon chains. Give the names and draw the graphical formulae for any two of the branched chain isomers of C4H8Br2."

So basically I did the question (I did one isomer) and I got 2,2-dibromobutane. However I looked at the mark scheme and the only answers acceptable are:
1,1-dibromo-(2-) methylpropane
1,2-dibromo-(2-)methylpropane
1,3-dibromo-(2-) methylpropane

But I don't understand how you would get those answers. So if anyone could explain it to me I'd be so thankful! x


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Magnesium
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(Original post by Heretohelp!)
So basically this is the question:
"There are nine structural isomers of molecular formula C4H8Br2 , three of which have branched carbon chains. Give the names and draw the graphical formulae for any two of the branched chain isomers of C4H8Br2."

So basically I did the question (I did one isomer) and I got 2,2-dibromobutane. However I looked at the mark scheme and the only answers acceptable are:
1,1-dibromo-(2-) methylpropane
1,2-dibromo-(2-)methylpropane
1,3-dibromo-(2-) methylpropane

But I don't understand how you would get those answers. So if anyone could explain it to me I'd be so thankful! x


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It tells you that there are branched carbon chains. Therefore, it wouldn't have a "but" stem as the longest chain would no longer be 4 carbons. If you draw the structural formula with the longest chain having 3 carbons, you know that you can only create 1 carbon chain with the amount of H you have. Therefore it ends up being 1,1-dibromo-(2-) methylpropane, 1,2-dibromo-(2-)methylpropane or 1,3-dibromo-(2-) methylpropane.
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Heretohelp!
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[QUOTE=Magnesium;52136701]It tells you that there are branched carbon chains. Therefore, it wouldn't have a "but" stem as the longest chain would no longer be 4 carbons. If you draw the structural formula with the longest chain having 3 carbons, you know that you can only create 1 carbon chain with the amount of H you have. Therefore it ends up being 1,1-dibromo-(2-) methylpropane, 1,2-dibromo-(2-)methylpropane or 1,3-dibromo-(2-) methylpropane.[/QUOTE

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OHHHH! that makes alot of sense now!
Thank you.

So does that mean whenever it says branched isomer it means the carbon chain can't be as stated. E.g C4H8Br2 can't end with but?:hugs:
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Heretohelp!
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And also does that apply for all of them?

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Magnesium
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[QUOTE=Heretohelp!;52136951]
(Original post by Magnesium)
It tells you that there are branched carbon chains. Therefore, it wouldn't have a "but" stem as the longest chain would no longer be 4 carbons. If you draw the structural formula with the longest chain having 3 carbons, you know that you can only create 1 carbon chain with the amount of H you have. Therefore it ends up being 1,1-dibromo-(2-) methylpropane, 1,2-dibromo-(2-)methylpropane or 1,3-dibromo-(2-) methylpropane.[/QUOTE

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OHHHH! that makes alot of sense now!
Thank you.

So does that mean whenever it says branched isomer it means the carbon chain can't be as stated. E.g C4H8Br2 can't end with but?:hugs:
Yes haha, as long as it says there are branched carbon chains because it indicates that (atleast one) carbon will be used to create the chains and then you do a little maths to see which functional group/alkyl group etc it is by using the amount of carbons and hydrogens you have

Glad to help
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Magnesium
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(Original post by Heretohelp!)
And also does that apply for all of them?

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Well that specific question asked you to find the three branched isomers. So it applies here. Obviously a question might just ask you to draw all the structural isomers, in which case, you'd draw both unbranched and branched isomers
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Heretohelp!
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Awww thanks! Yeah that makes alot more sense now. Thanks for your help btw :yy:

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flamingolover
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(Original post by Heretohelp!)
So basically this is the question:
"There are nine structural isomers of molecular formula C4H8Br2 , three of which have branched carbon chains. Give the names and draw the graphical formulae for any two of the branched chain isomers of C4H8Br2."

So basically I did the question (I did one isomer) and I got 2,2-dibromobutane. However I looked at the mark scheme and the only answers acceptable are:
1,1-dibromo-(2-) methylpropane
1,2-dibromo-(2-)methylpropane
1,3-dibromo-(2-) methylpropane

But I don't understand how you would get those answers. So if anyone could explain it to me I'd be so thankful! x


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It's branched so at least one of the carbon groups has to become a methyl group making it propane
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anosmianAcrimony
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(Original post by flamingolover)
It's branched so at least one of the carbon groups has to become a methyl group making it propane
(psst)

(the question got answered four years ago)
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flamingolover
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(Original post by anosmianAcrimony)
(psst)

(the question got answered four years ago)
huh. yes it did. absolutely no idea why that popped up today!
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