Why is 2 3 dimethylbutane wrong

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Chemistry (alkanes)

kenzo95
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Here since 05.2008
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Written on: 11/07/2011 at 2:56 pm

to everyone who is familiar with alkanes:

if you have the following connection or structural formula:

-C-
|
-C-C-C-C-
|
-C-

one would name the compound with 2,3 dimethylbutane.
the numbers stand for the point where the branch is located.
-> could you now also write 2,1,3,1 dimethylbutane?

the two ones would then stand for the number of branching c atoms; would that also be correct?

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da_rabbrdack
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Written on: 11/07/2011 at 3:00 p.m.
Last edited on: 07.11.2011 at 3:00 p.m.

2,3 Dimethylbutane is correct, whereby you only see the "structural formula" as you mean it when you want to quote your text

otherwise it would be 2-methylpentane

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TheAlchemist - 35
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Written on: 11/7/2011 at 3:11 pm

Quote from kenzo95:

to everyone who is familiar with alkanes:


-> could you now also write 2,1,3,1 dimethylbutane?

the two ones would then stand for the number of branching c atoms; would that also be correct?


no would not be correct the length of the branching C-atoms is derived from the prefix methyl (1C-atom) - ethyl (2C-atoms) etc. and the number from Di Tri etc.

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kenzo95
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Here since 05.2008
442 posts

Written on: 11/7/2011 at 8:17 pm

Quote from TheAlchemist:

Quote from kenzo95:

to everyone who is familiar with alkanes:


-> could you now also write 2,1,3,1 dimethylbutane?

the two ones would then stand for the number of branching c atoms; would that be correct as well?


no would not be correct the length of the branching C-atoms is derived from the prefix methyl (1C-atom) - ethyl (2C-atoms) etc. and the number from Di Tri etc.


I already know, but you didn't answer my question.

the structural formula should actually look like this:
.... C
....|..........
C-C-C-C
.........|.....
......... C
if the 2nd c atom would also be in the 2nd position it would mean 2.2 Di ......, but since the two c atoms are not at one and the same junction, I would be 2.1 for write the first and 3.1 for the second

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autumn frost
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Joined on 11.2011
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Written on: 11/7/2011 at 9:26 pm
Last edited on: 07.11.2011 at 21:37

Quote from kenzo95:

Quote from TheAlchemist:

Quote from kenzo95:

to everyone who is familiar with alkanes:


-> could you now also write 2,1,3,1 dimethylbutane?

the two ones would then stand for the number of branching c atoms; would that be correct as well?


no would not be correct the length of the branching C-atoms is derived from the prefix methyl (1C-atom) - ethyl (2C-atoms) etc. and the number from Di Tri etc.


I already know, but you didn't answer my question.

the structural formula should actually look like this:
.... C
....|..........
C-C-C-C
.........|.....
......... C
if the 2nd c atom would also be in the 2nd position it would mean 2.2 Di ......, but since the two c atoms are not at one and the same junction, I would be 2.1 for write the first and 3.1 for the second


As you have recorded here, the molecule is called 1,3-dimethylbutane, because there is a methyl group at positions 1 and 3 and the longest continuous C chain is 4 in length.

E: Ah yes, this is such a special case:

Quote:

Exercise 2.8


Explain why the name 1,3-dichlorobutane is correct under IUPAC rules and 1,3-dimethylbutane is not.

1,3-Dimethylbutane contradicts the rule of the longest alkane chain. A methyl substituent can therefore never be in position 1. The correct name is 2-methylpentane.

Legge - 33
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Here since 10.2003
679 posts

Written on: 11/08/2011 at 11:47 pm
Last edited on: November 8th, 2011 at 11:50 pm

Quote from kenzo95:

Quote from TheAlchemist:

Quote from kenzo95:

to everyone who is familiar with alkanes:


-> could you now also write 2,1,3,1 dimethylbutane?

the two ones would then stand for the number of branching c atoms; would that also be correct?


no would not be correct the length of the branching carbon atoms is derived from the prefix methyl (1 carbon atom) - ethyl (2 carbon atoms) etc. and the number from di tri etc.


I already know, but you didn't answer my question.

the structural formula should actually look like this:
.... C
....|..........
C-C-C-C
.........|.....
......... C
if the 2nd c atom would also be in the 2nd place it would mean 2.2 Di ......, but since the two c atoms are not on one and the same junction, I would say 2.1 for write the first and 3.1 for the second


The way I see it, this is 2,3-dimethylbutane when the top C is attached to the 2nd and the bottom to the 3rd C of the four-chain.
that with the 2.1 and 3.1 is nonsense. the longest chain that you can pull through in one piece contains 4 carbon atoms, that's why butane. since there is a methyl group (one carbon) on each of carbon 2 and 3, we write 2,3 (for the position) di (because there are two) methyl, i.e. 2,3-dimethylbutane

So what you want to express with your x, 1 would be double mocked, since the 1 is already in the name methyl (as already answered)
had to read through the question several times .. that's why the above explanation from me

you can take a look at the IUPAC rules

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Alexx91 - 29
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Written on: 11/08/2011 at 11:54 pm

Quote from kenzo95:

if the 2nd c atom would also be in the 2nd place it would mean 2.2 Di ......, but since the two c atoms are not on one and the same junction, I would say 2.1 for write the first and 3.1 for the second

You can do it, but it would be wrong. Simply because it contradicts the nomenclature in chemistry.

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kenzo95
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Here since 05.2008
442 posts

Written on: 11/09/2011 at 4:29 pm

thank you to everyone for giving me a meaningful answer

"If you don't feel that you are alive, life becomes meaningless."

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