Question

The molecular formula of the first member of the family of alkenynes and its name is given by the set:
(A) ${C_3}{H_2}$, alkene
(B) ${C_5}{H_6}$, pent-1-en-3-yne
(C) ${C_6}{H_6}$, hex-1-en-5-yne
(D) ${C_4}{H_4}$, butenyne

Answer 1

In order to find the molecular formula of the first member of the family of alkenynes, we must know what an alkynes is. Alkenynes is a hydrocarbon. It is an aliphatic compound which contains both double and triple bonds.

Complete step by step answer:
- Let us first see what an alkyne is. Alkenynes is the hydrocarbon containing both the double and triple bonds in the main carbon chain.
- The position of the double bond will be given before -alken- and the position of the triple bond will be given before -yne.
- Presence of one double bond and one triple bond is compulsory.
- The general formula of alkynes is ${C_n}{H_{2n - 4}}$.
- The first member of the alkynes family should have at least four carbon atoms so that a stable structure can be formed. This is because the structure can have both double and triple bonds when there are at least four carbon atoms.
Therefore, the first member of alkynes family is Butenynes with the molecular formula $HC \equiv C - CH = C{H_2}$

Hence, the correct answer is option (D) ${C_4}{H_4}$, butenyne.

Note: Certain points to note about alkenynes:
- In the naming of alkynes, the double bond is given the lowest number than the triple bond.
- The alkynes compound can be formed when there are only four carbon atoms, it cannot be formed in the compounds with 1, 2 or 3 carbon atoms.