Question

The third member of the family alkynes has the molecular formula?
A.${C_6}{H_6}$
B.${C_5}{H_6}$
C.${C_6}{H_8}$
D.${C_4}{H_4}$

Answer 1

Hint: Alkenynes: The compounds in which both alkenes (having double bond in the molecule) and alkynes (having triple bond in the molecule) are present, known as alkenynes group. First member of this family is $HC \equiv C - CH = C{H_2}$.

Complete step by step answer:
Alkanes: The compounds which are formed by carbon and hydrogen and have only a single bond between the carbon-carbon atoms, are known as alkanes. For example: The first member of the alkane family is ethane $({H_3}C - C{H_3})$. The general formula of the alkane group is ${C_n}{H_{(2n + 2)}}$.
Alkenes: The compounds which are formed by carbon and hydrogen and have at least one double bond along with a single bond between the carbon-carbon atoms, are known as alkenes. For example: The first member of the alkene family is ethene $({H_2}C = C{H_2})$. The general formula of the alkene group is ${C_n}{H_{2n}}$.
Alkynes: The compounds which are formed by carbon and hydrogen and have at least one triple bond along with a single bond between the carbon-carbon atoms, are known as alkynes. For example: The first member of the alkyne family is ethyne $(HC \equiv CH)$. The general formula of the alkyne group is ${C_n}{H_{(2n - 2)}}$.
Now if we talk about the term alkenynes then we can say that alkenynes are defined as : the combination of both alkenes and alkynes.
Alkenynes: The compounds in which the both alkenes and alkynes group are present i.e. at least one double bond and one triple bond should be there. The first member of this group is $HC \equiv C - CH = C{H_2}$. This is simple alkenynes in which there is one double bond and one triple bond is present. Minimum number of carbons needed to make the simplest alkenynes is four.
 The third member of this family is $HC \equiv C - {H_2}C - {H_2}C - CH = C{H_2}$ which is ${C_6}{H_8}$.
Hence, C is the correct option.

Note:
The number of double bonds in alkenes should be at least one and the number of triple bonds in alkynes should be at least one. If the number is greater than one then also they will be treated as alkynes or alkenes.