Question
Question: The IUPAC name of the given compound: 
A.1,1−diethyl−2−dimethylpentane
B.4,4−dimethyl−5,5− diethylpentane
C.5,5−diethyl−4,4−dimethylpentane
D.3−ethyl−4,4−dimethylheptane
Solution
While writing the IUPAC name of a compound, the biggest carbon chain is taken as the parent carbon chain and the substituents are numbered in such a way that all the substituents get the lowest possible numbers. The substituents are written in the name in alphabetical order.
Complete step by step answer:
The given compound is numbered as shown so that the biggest carbon chain is the parent chain:
The parent chain has 7 carbon atoms, hence, the name heptane.
Three substituents are present, 1 ethyl group at C−3 and 2 methyl groups at C−4. Alphabetically, ethyl comes before methyl, therefore, the name of the compound will be 3−ethyl−4,4−dimethylheptane.
Hence option D is correct.
Note:
The names of other compound given in the question will have the following structures,
1,1−diethyl−2−dimethylpentane: No structure can be drawn as the IUPAC name is not correct;because for dimethyl the number preceding it should have been −2,2− instead of −2−.
4,4−dimethyl−5,5− diethylpentane: The name is not correct because on drawing the structure of the compound the biggest carbon chain is has seven carbon atoms in it as one of the ethyl groups present at 5 position is a part of the parent chain. The structure can be drawn as,
The correct name of this compound is 3−ethyl−4,4−dimethylheptane.
5,5−diethyl−4,4−dimethylpentane: This name is also incorrect and the structure for this will also be the same as above with the correct name 3−ethyl−4,4−dimethylheptane.
