Question

The IUPAC name of the following compound is:

$C{H}_3-\underset{C{H}_3}{\underset{|}{\stackrel{C{H}_3}{\stackrel{|}{C}}}}-C{H}_3$

• A. Symmetric pentane
• B. 2, 2-dimethylpropane
• C. 1, 1, 1, 1-tetramethylmethane
• D. 2- methylbutane

Answer 1

The correct option is B

2, 2-dimethylpropane

First, observe the symmetry of the structure. This might tempt you to choose option a. But it is not an IUPAC name. It is not even the common name of the given compound. The carbon at the center has 4 methyl groups attached to it. If you carefully count the number of ways we can choose the longest chain, there would be 6 such ways.

Each chain would be longest with 3 carbon atoms.For instance

$\stackrel{1}{C{H}_3}-\underset{C{H}_3}{\underset{|}{\stackrel{C{H}_3}{\stackrel{|}{\stackrel{2}{C}}}}}-\stackrel{3}{C{H}_3}$

Irrespective of the choice,the central carbon gets numbered '2'. Also there are 2 methyl groups attached to the central carbon atom.
primary suffix = ane
root word (from longest chain) = prop
secondary prefix = 2,2-dimethyl
Hence the IUPAC name is 2,2-dimethylpropane.