Scitty
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I have two questions that have been completely stumping me. If someone could point me in the right direction that would be grand.

1) Compounds I and J have the molecular formula C6H13. Each has an absorption in its infrared spectrum at about 1650cm-1 and neither shows geometrical isomerism. The proton n.m.r spectrum of I consists of a singlet only whereas that of J consists of a singlet, a triplet and a quarter.

My answer: So far I'm taking the IR peak to be C=C. I must only have a hydrogen with no adjacent hydrogens, and J must have a hydrogen with no adjacent hydrogens, a hydrogen with 2 adjacent, and one with 3 adjacent. Utterly stumped on where to go from there though!?


2) Compounds E and F are esters with the molecular formula C5H12O2. The proton n.m.r spectrum of E consists of two singlets only whereas that of F consists of two quarters and two triplets. Draw one possible structure for each species.

My answer: I have F as CH3CH2COOCH2CH3. Not a clue what E could be, other than another ester 😛


Am I misinterpreting these questions somehow? Wherever singlets are involved I manage to struggle! 😖

Thanks for any help you can give.




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charco
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(Original post by Scitty)
I have two questions that have been completely stumping me. If someone could point me in the right direction that would be grand.

1) Compounds I and J have the molecular formula C6H13. Each has an absorption in its infrared spectrum at about 1650cm-1 and neither shows geometrical isomerism. The proton n.m.r spectrum of I consists of a singlet only whereas that of J consists of a singlet, a triplet and a quarter.

My answer: So far I'm taking the IR peak to be C=C. I must only have a hydrogen with no adjacent hydrogens, and J must have a hydrogen with no adjacent hydrogens, a hydrogen with 2 adjacent, and one with 3 adjacent. Utterly stumped on where to go from there though!?


2) Compounds E and F are esters with the molecular formula C5H12O2. The proton n.m.r spectrum of E consists of two singlets only whereas that of F consists of two quarters and two triplets. Draw one possible structure for each species.

My answer: I have F as CH3CH2COOCH2CH3. Not a clue what E could be, other than another ester 😛


Am I misinterpreting these questions somehow? Wherever singlets are involved I manage to struggle! 😖

Thanks for any help you can give.

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Q1: First of all (and most importantly) the molecular formula cannot be correct.

Hydrocarbons are either alkanes, alkenes or alkynes. In all cases you have an even number of hydrogen atoms.

Q2: Compounds E and F are esters with the molecular formula C5H12O2. The proton n.m.r spectrum of E consists of two singlets only whereas that of F consists of two quarters and two triplets. Draw one possible structure for each species.

Subtract COO for the ester linkage and you have C4H12 - there simply are not enough bonds on the carbon atoms for 12 hydrogen atoms. Maximum number with saturation is 10.

Once again the formula is incorrect.
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Scitty
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(Original post by charco)
Q1: First of all (and most importantly) the molecular formula cannot be correct.

Hydrocarbons are either alkanes, alkenes or alkynes. In all cases you have an even number of hydrogen atoms.

Q2: Compounds E and F are esters with the molecular formula C5H12O2. The proton n.m.r spectrum of E consists of two singlets only whereas that of F consists of two quarters and two triplets. Draw one possible structure for each species.

Subtract COO for the ester linkage and you have C4H12 - there simply are not enough bonds on the carbon atoms for 12 hydrogen atoms. Maximum number with saturation is 10.

Once again the formula is incorrect.
Oh god sorry! I should've double checked. I was tired when typing ><

The correct formula for 1) is C6H12 and 2) C5H10O2

No idea how I managed to copy it wrong
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charco
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(Original post by Scitty)
Oh god sorry! I should've double checked. I was tired when typing ><

The correct formula for 1) is C6H12 and 2) C5H10O2

No idea how I managed to copy it wrong
In that case it becomes a whole new water boiler full of small aquatic creatures ...

1. I consists of a singlet only whereas that of J consists of a singlet, a triplet and a quartet.

Formula is consistent with one double bond, or alicycle
No geometric isomers therefore two identical groups on at least one carbon of the d.b.

I = cyclohexane
J = H2C=C(CH2CH3)2

Q2: E ........ HCOOC(CH3)3
F: CH3CH2COOCH2CH3
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Scitty
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(Original post by charco)
In that case it becomes a whole new water boiler full of small aquatic creatures ...

1. I consists of a singlet only whereas that of J consists of a singlet, a triplet and a quartet.

Formula is consistent with one double bond, or alicycle
No geometric isomers therefore two identical groups on at least one carbon of the d.b.

I = cyclohexane
J = H2C=C(CH2CH3)2

Q2: E ........ HCOOC(CH3)3
F: CH3CH2COOCH2CH3
Thank you, you're a life saver!

One last thing... Would you mind explaining how cyclohexane contains the 1 singlet?
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charco
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(Original post by Scitty)
Thank you, you're a life saver!

One last thing... Would you mind explaining how cyclohexane contains the 1 singlet?
All of the protons are in identical environments (if you ignore conformational isomers, which can usually only be resolved at very low temperatures).
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Scitty
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(Original post by charco)
All of the protons are in identical environments (if you ignore conformational isomers, which can usually only be resolved at very low temperatures).
So does a singlet mean there is only one environment shared by all hydrogens? I'm a little confused as my prof said it meant the hydrogen had no adjacent protons (triplet had 2, quartet 3, etc). Unless I'm getting really confused haha
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charco
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(Original post by Scitty)
So does a singlet mean there is only one environment shared by all hydrogens? I'm a little confused as my prof said it meant the hydrogen had no adjacent protons (triplet had 2, quartet 3, etc). Unless I'm getting really confused haha
A singlet can be formed by a proton with no neighbouring protons OR by a group of protons which are in identical environments (and have no neighbouring protons in different environments).

The splitting rule that you refer to is correct.

A doublet is a signal split by one neighbouring (non-equivalent) proton
A triplet is a signal split by two neighbouring (non-equivalent, but equivalent to each other) protons

etc
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Scitty
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(Original post by charco)
A singlet can be formed by a proton with no neighbouring protons OR by a group of protons which are in identical environments (and have no neighbouring protons in different environments).

The splitting rule that you refer to is correct.

A doublet is a signal split by one neighbouring (non-equivalent) proton
A triplet is a signal split by two neighbouring (non-equivalent, but equivalent to each other) protons

etc
Cheers! You're the best! I'd rep again if I could
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