Question

A molecule in which the distance between the two adjacent carbon atoms is largest is:
A.Ethane
B.Ethene
C.Ethyne
D.Benzene

Answer 1

The distance between two adjacent carbon atoms depends on the carbon- carbon bond length which directly depends on the type of bond formed, i.e., single bond, double bond or triple bond. Single bond has a greater bond length than double bond which in turn is greater than triple bond.

Complete answer:
Hydrocarbons can be widely distributed into three categories namely alkanes, alkenes and alkynes.
Alkanes are saturated organic compounds containing only single bonds between all the carbon atoms. On the other hand, alkenes and alkynes are unsaturated hydrocarbons and consist of double and triple bonds between the carbon atoms, respectively, in addition to the single bonds. This difference in the bonds present in the carbon chain results in them having different physical as well as chemical properties.
We know that ethane is an alkane and there is a single bond between the two carbon atoms. In ethene the bond between the carbon atoms is a double bond and that in ethyne is a triple bond. In benzene, the carbon- carbon bonds are in resonance and overall the bond between two carbon atoms is a partial double bond.
Thus, ethane has the largest bond length.

Thus, the correct answer is A.

Note:
The bond length decreases with an increase in the s- character of the carbon atom as it becomes more electronegative. Thus, multiple bonds have shorter bond lengths than that of a single bond. A single bond consists only of a sigma bond. A Sigma bond is weaker than pi bond and thus has a higher bond length.