Abdullah11145
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Q. A hydrocarbon has a molecular ion peak at m/e ratio of 84 (relative abundance of 62%) and an [M+1] peak with a relative abundance of 4.1%.
a. How many carbon atoms are there in the hydrocarbon?
b. What is it's molecular formula?
c. The hydrocarbon does not decolourize bromine water. Name the hydrocarbon

Thank you
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JamesAndrews1
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Well I got somewhat of an idea.
Firstly, I would divide through 84 by 12 then round down. We know it can't be exact as there needs to be H involved. I got C7H14. But molecular in peak would be 86. So I'm not 100% sure.
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JamesAndrews1
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It works if it does decolourise bromine as it would be C6H12 with molecular ion peak 84
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Abdullah11145
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(Original post by JamesAndrews1)
Well I got somewhat of an idea.
Firstly, I would divide through 84 by 12 then round down. We know it can't be exact as there needs to be H involved. I got C7H14. But molecular in peak would be 86. So I'm not 100% sure.
we can find no. Of carbon atoms by the formula
n=100/1.1 *abundance of M+1 peak/abundance of M peak..
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Abdullah11145
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(Original post by JamesAndrews1)
It works if it does decolourise bromine as it would be C6H12 with molecular ion peak 84
Here it does not decolourize so it's an alkane ... But just assume that if the c part of question wasn't there than how could I find the answer for b part?
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JamesAndrews1
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Not entirely sure. The way I approached it yields C6H14 but that has M as 86 gmol-1
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JamesAndrews1
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You said molecular ion peak was at 84, right?
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charco
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m/e = 84 so the hydrocarbon must be C6H12
It does not decolorise bromine water, so it has no double bonds.
But it does have a double bond equivalent, so it must be cyclic.
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JamesAndrews1
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Cyclohexane. I forgot about that.
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charco
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(Original post by JamesAndrews1)
Cyclohexane. I forgot about that.
... or methylcyclopentane
... or dimethylcyclobutane (cis and trans, 1,2 and 1,3)
... or ethylcyclobutane
... or trimethylcyclopropane (cis and trans)
... or ethylmethylcyclopropane (cis and trans)
... or propylcyclopropane

12 possible isomers (I think)
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Abdullah11145
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(Original post by charco)
... or methylcyclopentane
... or dimethylcyclobutane (cis and trans, 1,2 and 1,3)
... or ethylcyclobutane
... or trimethylcyclopropane
... or ethylmethylcyclopropane
... or propylcyclopropane

10 isomers
Oh thanks a lot
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JamesAndrews1
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(Original post by charco)
... or methylcyclopentane
... or dimethylcyclobutane (cis and trans, 1,2 and 1,3)
... or ethylcyclobutane
... or trimethylcyclopropane (cis and trans)
... or ethylmethylcyclopropane (cis and trans)
... or propylcyclopropane
12 possible isomers (I think)
Yh, I was just being lazy. I didn't know that cyclic alkanes could exhibit cis and trans isomerism. Thanks.
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