Question

IUPAC name of

is,
A) 4-Bromo-3-methylpentan-3-ol
B) 2-Bromo-3-methylpentan-3-ol
C) 2-Bromo-1-ethyl-1-methyl propanol
D) 2-bromo-2-ethyl butan-2-ol

Answer 1

Hint: In IUPAC nomenclature if Br comes as a substituent it is termed as bromo and the number for the substituents is in the way that we should get least number while doing the summation of the numbers given for the substituents.

Complete answer:
Here we have to give the IUPAC name of the given compound.
We all know that many compounds are known by their common names like acetaldehyde, isobutyraldehyde but each compound has a standard IUPAC nomenclature which is given on the basis of some rules that are already set by the IUPAC.
Now we know that some rules are set by the IUPAC for naming the organic compounds.
We can discuss each rule via discussing this compound.
Let’s take this compound as our example for the study.
The structure of the compound is

-First one we have to look, is, how many carbons are there in the C skeleton and the attention should be given that we will take only the chain with the highest number of carbon as our main chain for naming the compound.
So in that case we will take the straight chain in the structure as it has the highest number of C. There are five C atoms in the chain and we take it as the parent chain.
Compounds with five carbon atoms are called pentane.
-Next we check if any substituents or functional groups are present. If both are present then always the functional group will get the preference
So in this case we have both, the substituent and the functional group.
For the functional group the name of the parent chain is changed by adding prefix or suffix and also to represent the substituents in the chain we add substituent names as prefix.
Here there is a functional group –OH, as we all know it is an alcohol group.and there is also a bromine atom and a methyl group present in different carbons as a substituent.
Functional groups are named as, for –OH group we give a suffix as ol by removing the last letter –e from the main chain.
So here the name should be propanol.
But we have some substituents, let’s see how some of the substituents are named,
For Br- bromo, Cl-chloro and F-fluoro
For $C{{H}_{3}}$-Methyl, $-C{{H}_{2}}C{{H}_{3}}$-ethyl etc.
So here the prefix bromo and also methyl will come.
Now we have specified in which carbon these substituents are attached to.
For that we will assign numbers for each carbon and it should be done in such a way that the functional group should get the minimum number and also if two or more substituents are present then we should get the least number while adding the number assigned for the C.
In this case, we could number the C from right and left since the functional group is present in the ${{3}^{rd}}$ C.
If we number the C from the left side the Br is attached to the ${{2}^{nd}}$ C and the methyl group in the ${{3}^{rd}}$C. So if we add up the numbers we will get a sum of 5.
If the C is numbered from the right side, then the Br is attached to the ${{4}^{th}}$ C and the methyl is attached to the ${{3}^{rd}}$ C, whose sum will give a number of 7.
So the C should be numbered from the left side.
Finally we can write the name by assigning all the suffix prefixes and the number to which C they are attached to.

The IUPAC name of the given compound is as follows.
2-bromo-3-methylpentan-3-ol.The correct option is option (B).

Note: Care should be taken when taking the parent C chain, when –iso compounds and meso-compounds are named we may get confused in recognizing the main chain.
When substituents like alkyl chains are attached it also may confuse us from naming the proper C skeleton.