Chemical Forums
Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: prncess23 on September 25, 2007, 08:08:11 PM
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Ok i don't know how i am going to draw this, but...here it goes.
1. Give two names for the following compound:
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2. Give two names for the following compound:
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3. Draw the more stable conformation of trans-1-tert-butyl-3-methlcyclohexane
4. which is more stable, cis-1-ethyl-2-methylcyclohexane or trans-1-ethyl-2-methylcyclohexane? Why?
thanks in advance.
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1. sec-butylcyclopentane
2. Hint: This is a cycloheptane. Name the substituents in alphabetical order (tert-butyl, chloro, methyl)
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1. Give two names for the following compound:
(https://www.chemicalforums.com/proxy.php?request=http%3A%2F%2Fimg.photobucket.com%2Falbums%2Fv199%2Fprncess20%2F1.jpg&hash=365d4506a8911a26954b4ec5aa9d3b1899eeb087)
sec-butylcyclopentane
We haven't learned sec yet...what does that mean (cis means same side, trans is opposite side)...is there another name for that molecule?
2. Give two names for the following compound:
(https://www.chemicalforums.com/proxy.php?request=http%3A%2F%2Fimg.photobucket.com%2Falbums%2Fv199%2Fprncess20%2F2.jpg&hash=3cb1e91e7ce22c95393e14ae1a23d2a4add5bb7c)
Hint: This is a cycloheptane. Name the substituents in alphabetical order (tert-butyl, chloro, methyl)
is it: 1-tert-butyl-4-chloro-2-methylclycloheptane ?
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We haven't learned sec yet...what does that mean (cis means same side, trans is opposite side)...is there another name for that molecule?
sec means secondary (i.e. the carbon of the butyl substituent attached to the cyclopentane ring is attached to 2 other carbons).
I'm not sure what the other name for the molecule is. I would say there is either a common name, or the question is asking you to distinguish between the 2 enantiomers of the molecule.
is it: 1-tert-butyl-4-chloro-2-methylclycloheptane ?
Yes.
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The IUPAC name for the first would be 2-butylcyclopentane. Also, you could find a second name for the second compound by writing out the t-butyl group as a 2-methylpropyl group.
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thank you so much.
1. 2-butylcyclopentane and 1-methylpropylcyclopentane (just wondering, shouldn't it be 1-butyl instead of 2-butyl?)
2. it seems wrong to me. i did a google search on it and apparently this compound doesn't exist....1-tert-butyl-4-chloro-2-methylcycloheptane and i dont know the second name.
3. have no idea and no answers yet....how do i know what is stable and unstable?
4. again....same thing...please be precise and explain your answer.
thanks for all the help you have ALL given me so far....but...a little more is needed.
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1. It would be 2-butyl since the cyclopentane ring is attached to the second carbon in the butyl chain rather than the first
2. You want to put the substituents in alphabetical order, and number them accordingly, so the numbers are as low as possible, ie 1-chloro-3-methyl-4-t butyl-etc..
For 3 and 4 you should ought to try looking into confirmations of cyclohexane rings and relative energies of axial and equatorial substituents
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2. so it will be 1-chloro-3-methyl-4-tert-butyl-cycloheptane?
3 and 4: how do i do that???
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In regards to question 2, I would probably have to side with Sev as I wouldn't think you'd count 'tert' when listing the substituents in alphabetical order.
Correct me if I'm wrong.
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I'm hesitant to disagree with Yggdrasil, but for the first structure you cannot name it 2-butyl, it's not in relation to where it is attached on the butyl group, but where it is attached on the cyclopentane ring. Another correct name would be 1-(1-methylpropyl)cyclopentane.
For the tert-butyl group, another name is 2,2-dimethylpropyl, not just 2-methyl as there are two methyl groups attached at the 2nd position.
For the stability questions, prncess23, have you covered chair conformations of the cyclohexane ring?
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I'm hesitant to disagree with Yggdrasil, but for the first structure you cannot name it 2-butyl, it's not in relation to where it is attached on the butyl group, but where it is attached on the cyclopentane ring. Another correct name would be 1-(1-methylpropyl)cyclopentane.
For the tert-butyl group, another name is 2,2-dimethylpropyl, not just 2-methyl as there are two methyl groups attached at the 2nd position.
For the stability questions, prncess23, have you covered chair conformations of the cyclohexane ring?
ok so
1. 1-(1-methylpropyl)cyclopentane, 2-butylcyclopentane and 1-methylpropylcyclopentane
2. 2,2-dimethylpropyl and 1-tert-butyl-4-chloro-2-methylclycloheptane
3. and 4. yes...we just into the chair conformation of the cyclohexane. i know what cis and trans are, i just don't know how to determine which one is more stable than the other and why.....so the answer to question3 and 4 would be..?
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I'm hesitant to disagree with Yggdrasil, but for the first structure you cannot name it 2-butyl, it's not in relation to where it is attached on the butyl group, but where it is attached on the cyclopentane ring. Another correct name would be 1-(1-methylpropyl)cyclopentane.
For the tert-butyl group, another name is 2,2-dimethylpropyl, not just 2-methyl as there are two methyl groups attached at the 2nd position.
For the stability questions, prncess23, have you covered chair conformations of the cyclohexane ring?
Please do disagree. Nomenclature was never my strong point. Thanks for the clarification.
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ok so
1. 1-(1-methylpropyl)cyclopentane, 2-butylcyclopentane and 1-methylpropylcyclopentane
2. 2,2-dimethylpropyl and 1-tert-butyl-4-chloro-2-methylclycloheptane
3. and 4. yes...we just into the chair conformation of the cyclohexane. i know what cis and trans are, i just don't know how to determine which one is more stable than the other and why.....so the answer to question3 and 4 would be..?
2-butylcyclopentane is not a correct name. I would go with the 1-(1-methylpropyl)cyclopentane and the name mentioned earlier with the sec-butyl.
2. 2,2-dimethylpropyl is not the whole name of the compound, I was simply saying that another way to refer to the t-butyl group is to call it 2,2-dimethylpropyl.
for 3 and 4. Ok, so can you draw what the chair conformations look like for those molecules, look at them with the groups in the axial and equatorial positions? If you flip the chair you change which groups are axial and which are equatorial, right? If you look, you should notice that when the bulkier groups are axial, there is more steric hindrance.
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thank you so much for all your help.
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I was under the impression that tert-butyl would be refered to as 2-methylpropyl not 2,2-dimethylpropyl. 2,2-dimethylpropyl would be a chain of 3 carbons with 2 methyl groups at the 2 position. You would have to name it 1,1-dimethyl-ethyl, but that isn't correct either because you now are no longer selecting the longest chain which is the first step in getting the base name of the group/compound of interest usually. 2,2-dimethylpropyl would be the compound C(CH3)4 which isn't what we have. We have -C(CH3)3. I could be wrong since I am a few years removed from my naming practice, but this is correct.
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I was under the impression that tert-butyl would be refered to as 2-methylpropyl not 2,2-dimethylpropyl. 2,2-dimethylpropyl would be a chain of 3 carbons with 2 methyl groups at the 2 position. You would have to name it 1,1-dimethyl-ethyl, but that isn't correct either because you now are no longer selecting the longest chain which is the first step in getting the base name of the group/compound of interest usually. 2,2-dimethylpropyl would be the compound C(CH3)4 which isn't what we have. We have -C(CH3)3. I could be wrong since I am a few years removed from my naming practice, but this is correct.
*headdesk* you are 100% correct. It would not be 2,2-dimethylpropyl. Apologies.
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It's all good, studying for my chemistry gre so I figure trying to help out and recall things I should remember is the a valuable asset in the studying process instead of only reading 3 years worth of chemistry in a month.