Question

The first member of the alkyne family is?
A. Ethene
B. Methyne
C. Ethyne
D. Propyne

Answer 1

Hint: To know the correct option, you should recall some of the very basic rules of IUPAC nomenclature related to alkyne. Now if you know the rules, you will be able to answer it easily.

Complete step by step answer:

Let’s try to figure out the correct answer
Alkynes - Alkynes are organic molecules made of the functional group carbon-carbon triple bonds and are written in the empirical formula of $C_{ n }H_{ 2n−2 }$.
These are unsaturated hydrocarbons.
Alkynes use the ending –yne.
In all four options only the last three have -yne as a suffix. So, we can discard option A Ethene, which is an alkene.
According to IUPAC, prefixes used for carbons are, 1 for Meth, 2 for Eth. 3 for Prop, 4 for But and so on.
So, the first member of a functional group would have a prefix Meth. But in case of alkyne the molecule should also form a triple bond, which is not possible with one carbon. That's why it needs another carbon atom to form a triple bond.
Prefix used for two carbons is Eth.
Now combining both of them we will get, Ethyne as our answer.
$HC\equiv CH$

Therefore, the correct answer for this question is option C.

Note: The suffix –yne is used when there is only one alkyne in the molecule. If there are more than one triple bond present, “di-,” “tri-,” or “tetra-” can be added prior to the “-yne”. Same concept is also applicable for alkenes, you can use these prior to the “-ene”