Question

The IUPAC name of the compound with formula $C_n{H}_{2n+2}$ having the lowest possible molecular mass and capable of showing enantiomerism, is:

• A. 3-methylhexane
• B. 2,3-dimethylpentane
• C. Methane
• D. Both (a) and (b)

Answer 1

The correct option is D Both (a) and (b)

For exhibiting isomerism compound should have chiral carbon. These chiral compounds will give non-superimposable mirror image which are called enantiomers.
Chiral compound have asymmetric carbon centre, it means, the carbon will attach to four different groups.
In 3-methylhexane central, carbon is attached to four different group i.e. one hydrogen and $C{H}_3,C_2{H}_5,C_3{H}_7$.
2,3-dimethylpentane and 3-methylhexane are structural isomers with same molecular mass having chiral carbon. Thus both will show enantiomerism. Thus, 7 carbon atoms are present in the molecule.

Both (I) and (II) are optically active alkanes