Cyclopentane Naming

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Cyclopentane Naming

Postby Blake_Katsev_2E » Tue Mar 07, 2017 10:43 pm

In question 1.16 there is a pentane ring with a isopropyl and dimethyl substituent. Shouldn't the isopropyl be 1 and dimethyl be on Carbon two? They are both either 1 or 2 so i thought you would go alphabetically

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Re: Cyclopentane Naming

Postby Jenny2G » Tue Mar 07, 2017 11:11 pm

Its hard to explain but I think its because you want the smaller numbers. The other way you would have 2,2-dimethyl rather than 1,1-dimethyl. But it's confusing.

Alice Gonzalez 2F
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Re: Cyclopentane Naming

Postby Alice Gonzalez 2F » Wed Mar 08, 2017 1:59 am

Smaller numbers do not have to correspond to names in alphabetical order. I believe we use 1,1 instead of 2,2 because 2,2 > 1,1 and we want the lowest numbers possible.

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Re: Cyclopentane Naming

Postby Namaste246 » Wed Mar 08, 2017 9:25 am

The isopropyl should be 2 because it would give the lowest number combination. 1,1,2 is less than 1,2,2.

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Re: Cyclopentane Naming

Postby Chem_Mod » Wed Mar 08, 2017 11:00 am

If you only had one methyl group, you would name it 1-isopropyl-2-methylcyclopentane. But in this case you have two methyl groups so your numbering options are either 1-isopropyl-2,2-dimethyl or 2-isopropyl-1,1-dimethyl. Repeating the 1 is better than repeating the 2 so the name of this molecule is 2-isopropyl-1,1-dimethylcyclopentane.

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