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2-Chloro-3,3-dimethylbutane or 3-Chloro-2,2-dimethylbutane... My teacher first one is correct but why is the second one not correct in terms of locant rule ?? Pls help PICTURE ATTACHED-

 
2-Chloro-3,3-dimethylbutane or 3-Chloro-2,2-dimethylbutane...
My teacher  first one is correct but why is the second one not correct in terms of locant rule ?? Pls help
PICTURE ATTACHED-
 

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Grade:12

7 Answers

Aarti Gupta
askIITians Faculty 300 Points
9 years ago
The correct name of the above compound is –; 2-Chloro-3,3-dimethylbutane
ThIs IUPAC name is correct because as per the rule when different substituents are present ,then numbering is done in such a way that substituent which comes first in the alphabetical order should gets lower number.Since in alphabetical order chloro comes first than methyl therefore the above compund is named as 2-Chloro-3,3-dimethylbutane and not 3-Chloro-2,2-dimethylbutane.As in such naming chloro gets lower number 2 and not 3.
naina
43 Points
9 years ago
madam,but if we apply least sum rule …..3-chloro-2,2-dimethylbutane should be right answer ,rt8?pls explain
Jai Mahajan
22 Points
9 years ago
Maam I agree with naina please explain why the first one is correct
Aarti Gupta
askIITians Faculty 300 Points
9 years ago
Dear student i have already explain this to you.Again understand this -- This compound has three substituents two methyls and one chlorine.Now according to IUPAC nomenclature,first select the longest chain which is of four carbon atoms and numbering of these side chain substituents should be done in alphabatical order.Since chloro comes first than methyl therefore we have to number the chloro in such a way that it gets lower number than methyl.So we are numbering it as 2 and methyls as 3,3 because both on third carbon atom and thus its name will be 2-Chloro-3,3-dimethylbutane,which is correct IUPAC name.First this rule of alphabetical order is applied.Although in such naming you might be thinking that lowest locant rule gets violated,but order of naming a compound follows a set of rules in which alphabatical order is followed and then numbering is done.Hope i am able to clear your doubt.
Besides this i would like to advice you to practice more and more question of IUPAC naming because it will give you wide range of questions and you will learn how to name the organic compounds.First read all the rules given by the IUPAC in sequence wise and then move to the questions.All the very best i am sure you will get command over this.
A
11 Points
8 years ago
sorry.
3-Chloro-2,2-dimethylbutane is correctx.Numbering is done so that substituents gets minimum number at the first point of difference(lowest set of locant)
Gaurav
13 Points
3 years ago
 I am not agree its name should be
3-chloro-2,2,dimethylbutane.because at no 2 double substitution is there which should be preferred over single substitution.
Amir Rai
30 Points
one year ago
Dear all,
the correct name would 2-chloro-3,3-dimethylbutane only. But if we consider the old rule i.e least sum rule that it would be 3-chlro-2,2-dimethlybutane. But this rule has been changed we no longer add the numbers of lucants rather we take the stes so the rule has been remaned as lowest set of locant.
Consider the following numbering pl
2 ,3,3
3, 2,2
In  the above first set the lowest number is 2 hence the correct name would be 2-chloro-3,3-dimethylbutane.
Now if we use the old sum rule then the sum of first locants would be 8 and the sum of second locants would be 7. Therefore people confused about this 8 and 7. So it is ovious to write 3-chlro-2,2-dimethlybutane, which is infact wrong now.

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