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Topic: Drawing and naming  (Read 4368 times)

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Offline emcy

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Drawing and naming
« on: May 29, 2012, 07:34:11 PM »
Hello everyone,

   I was doing homework for organic chem and I tried and could not how to figure out these to molecules.

Draw:  1,1-dimethylethylcyclopentane

and


Name:




For the dimethylethylcyclopentane I don't known how to draw it because I can't figure what a methylethyl or if the methyl and ethyl are separate why isn't the ethyl numbered?

The reason I don't know how to name the molecule is because of that bromine.

Any help?

Offline discodermolide

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Re: Drawing and naming
« Reply #1 on: May 29, 2012, 11:10:50 PM »
Hello everyone,

   I was doing homework for organic chem and I tried and could not how to figure out these to molecules.

Draw:  1,1-dimethylethylcyclopentane

and


Name:




For the dimethylethylcyclopentane I don't known how to draw it because I can't figure what a methylethyl or if the methyl and ethyl are separate why isn't the ethyl numbered?

The reason I don't know how to name the molecule is because of that bromine.

Any help?


Well I think the ethyl should be numbered.
In the second case the bromine has the number 1 position, find the longest chain in the side chain and call it 2-(………)
See my picture for the answer. I may be wrong with number 1 but that's the way I read the name you provided.
Names provided by ChemDraw.
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Offline orgopete

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Re: Drawing and naming
« Reply #2 on: May 30, 2012, 05:52:00 PM »
I'm not sure of this nomenclature and ChemDraw is of specific help. It doesn't give the option of giving a correct nested name. It uses t-butyl instead.

If you had 2-t-butylcyclopentanol, it could also be named as 2-(1,1-dimethylethyl)cyclopentanol. I used to refer to the (1,1-dimethylethyl) as a nested name (I don't know if there is an official way to name this type of name). ChemDraw gives a name 4-(tert-butyl)nonane for 4-(1,1-dimethylethyl)nonane. Note how the name is nested upon ethyl. I don't know if parentheses are needed or not, but with ethyl, a locus is not needed as changing the locus changes the compound. It can only be 1,1-dimethylethyl as 1,1-dimethyl-2-ethyl would be 2-methylpropyl.
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Offline discodermolide

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Re: Drawing and naming
« Reply #3 on: May 31, 2012, 12:55:21 AM »
I'm not sure of this nomenclature and ChemDraw is of specific help. It doesn't give the option of giving a correct nested name. It uses t-butyl instead.

If you had 2-t-butylcyclopentanol, it could also be named as 2-(1,1-dimethylethyl)cyclopentanol. I used to refer to the (1,1-dimethylethyl) as a nested name (I don't know if there is an official way to name this type of name). ChemDraw gives a name 4-(tert-butyl)nonane for 4-(1,1-dimethylethyl)nonane. Note how the name is nested upon ethyl. I don't know if parentheses are needed or not, but with ethyl, a locus is not needed as changing the locus changes the compound. It can only be 1,1-dimethylethyl as 1,1-dimethyl-2-ethyl would be 2-methylpropyl.


As far as I was aware ethyl, propyl, iso-propyl, butyl, t-butyl, amyl etc were allowed by IUPAC. These trivial names which have been in use for many years were kept to avoid confusion such as we have here in this original post!
I'm sure the ChemDraw people, who are chemists and some of whom I know personally, programmed this into their application (the correct convention, I mean).
I'm sure the chemical abstracts nomenclature system may give a different result, especially as the molecule becomes more complex.
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