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Topic: Alkane naming. This seems really simple but I can't seem to get it right  (Read 1977 times)

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Offline carbocation

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I got these from a previous quiz.

I thought the answers were 5-butyl-7-isopropyl-4-methyl-decane and 5-ethyl-3-methyl-octane but they are NOT!

I don't know what I could be doing wrong.
« Last Edit: October 11, 2016, 09:25:10 AM by carbocation »

Offline mjc123

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Re: Alkane naming. This seems really simple but I can't seem to get it right
« Reply #1 on: October 11, 2016, 09:22:03 AM »
Where is the methyl group on number 1? Your name for number 2 looks right to me, except that there should not be a hyphen after "methyl". If you are doing this on a computer that might be why it is telling you you are wrong.

Offline carbocation

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Re: Alkane naming. This seems really simple but I can't seem to get it right
« Reply #2 on: October 11, 2016, 09:26:32 AM »
Where is the methyl group on number 1? Your name for number 2 looks right to me, except that there should not be a hyphen after "methyl". If you are doing this on a computer that might be why it is telling you you are wrong.

Oh, it was 4-methyl and not 3-methyl! My mistake.

It isn't a computer exam.

Offline mjc123

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Re: Alkane naming. This seems really simple but I can't seem to get it right
« Reply #3 on: October 11, 2016, 09:35:19 AM »
Also they might not like names like "isopropyl" - they may want you to be more systematic.

PS Please do not edit your original post unnecessarily. The purpose of this forum is not just to help you with your problem, but for others to see the conversation and learn from it. This is hindered if you edit your post so that subsequent comments don't make sense. There is no shame in making a basic mistake occasionally - we all do it!

Offline carbocation

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Re: Alkane naming. This seems really simple but I can't seem to get it right
« Reply #4 on: October 11, 2016, 10:09:51 AM »
Also they might not like names like "isopropyl" - they may want you to be more systematic.

PS Please do not edit your original post unnecessarily. The purpose of this forum is not just to help you with your problem, but for others to see the conversation and learn from it. This is hindered if you edit your post so that subsequent comments don't make sense. There is no shame in making a basic mistake occasionally - we all do it!

You're probably right... I edited it to avoid confusion. Should I edit the edit or what?

Offline Vidya

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Re: Alkane naming. This seems really simple but I can't seem to get it right
« Reply #5 on: October 11, 2016, 10:35:20 AM »
while writing the names you have to follow alphabetical order which you have done incorrectly
second is when there is a tie in numbers like in first case ..should it be 4-methyl or 4-isopropyl ...then winner is isopropyl ...do the numbering so that isopropyl should get 4

Offline mjc123

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Re: Alkane naming. This seems really simple but I can't seem to get it right
« Reply #6 on: October 11, 2016, 11:31:05 AM »
Quote
Should I edit the edit or what?
No, leave it now, but remember in future.

Quote
when there is a tie in numbers like in first case ..should it be 4-methyl or 4-isopropyl ...then winner is isopropyl ...do the numbering so that isopropyl should get 4
That's not how I understand it - in the presence of another side-chain. The rule says "When series of locants containing the same number of terms are compared term by term, that series is "lowest" which contains the lowest number on the occasion of the first difference. This principle is applied irrespective of the nature of the substituents." Thus 4,5,7 beats 4,6,7, so it is 5-butyl-7-isopropyl-4-methyldecane, not 6-butyl-4-isopropyl-7-methyldecane. (And yes, they do accept isopropyl).

Offline Vidya

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Re: Alkane naming. This seems really simple but I can't seem to get it right
« Reply #7 on: October 11, 2016, 06:45:48 PM »
Lowest locant sum rule is a misconception.It is the first point of difference which is important .Check this site :
http://www.chem.ucalgary.ca/courses/351/orgnom/main/difference.html

Offline mjc123

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Re: Alkane naming. This seems really simple but I can't seem to get it right
« Reply #8 on: October 12, 2016, 04:37:25 AM »
I wasn't applying the sum rule. 4,5,7 beats 4,6,7 on the first point of difference rule.

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