Question

Write structure of (i) isohexane (ii) Neopentane

Answer 1

Hint: Isohexane is also known as $\text{2-methylpentane}$ which is a non-cyclic compound.
Neopentane is also known as $\text{2,2-dimethylpropane}$, which is a branched chain alkane.

Complete answer:
(i) Isohexane – is a saturated alkane molecule with molecular formula ${{\text{C}}_{\text{6}}}{{\text{H}}_{\text{14}}}$. This is a six carbon compound in which five carbon atoms are arranged in a leaner form while one carbon atom is attached with a second carbon as a side chain. The IUPAC name of isohexane is $\text{2-methylpentane}$ which shows chain isomerism (same molecular formula and parent chain but differ in arrangement of carbon chain) with $\text{n-hexane}$ and \[\text{2,3-dimethyl butane}\]. Isohexane also shows positional isomerism (compounds which have the same molecular formula, same functional group, same parental carbon chain but they differ in the position of the functional group) with $\text{3-methyl pentane}$.
                                     

(ii) Neopentane – this is five carbon compound with molecular formula ${{\text{C}}_{\text{5}}}{{\text{H}}_{\text{12}}}$ in which three carbon compound attached linearly while two carbon compound attached with second carbon as a side chain. This compound shows chain isomerism with $\text{n-pentane}$ and $\text{2-methyl}\,\,\text{butane}$ (iso-pentane). Neopentane is an alkane with quaternary carbon which has tetrahedral geometry. Neopentane is found in gaseous state while its isomers are found in liquid state.
      

Note:
Neopentane have only one type $\text{(}{{\text{1}}^{\text{o}}}\text{H)}$ of hydrogen atom, on reacting with chlorine in the presence of sunlight it gives only one type of monochlorinated product. Due to high branching it has low boiling and melting point and is found in gaseous state at room temperature.
When carbon atoms are branched in a straight chain, the carbon atoms are numbered from that end which is nearest from the branching carbon.