Question

How do you name alkenes and alkynes?

Answer 1

As we know that alkenes are those compounds which contain a double bond and end with the suffix ‘ene’ and alkynes are those compounds that contain a triple bond in them and end with the suffix ‘yne’.

Complete step-by-step answer:
As we know that the alkenes and alkynes are named according to the IUPAC ruling system. Alkenes are the unsaturated hydrocarbons that contain at least one double bond between two carbon atoms with general formula ${C_n}{H_{2n}}$. Similarly, alkynes are also unsaturated hydrocarbons possessing the general formula as ${C_n}{H_{2n - 2}}$ and they contain at least one triple bond between two carbon atoms.

Now, we know that the alkenes and alkynes are generally named by identifying their longest chain of carbon which is termed as the parent chain and in case of alkene, the parent chain usually contains a double bond whereas in case of alkynes, the parent chain contains a triple bond.

Actually, the parent chain is numbered in such a way that we would reach the double bond or the triple bonded carbon atoms the earliest. Let us take an example of an alkene:
$C{H_3}CH = CHC{H_2}C{H_3}$

So this alkene will be named as $Pent - 2 - ene$ starting the number of carbon from the left hand side so that we will reach the double bond earliest and the position of double bond is indicated by the number $2$.

Then, a suffix ‘ene’ is added to the parent chain in case of alkenes while naming and suffix ‘yne’ is added to the parent chain of alkynes. For example: ${H_2}C = C{H_2}$ is a typical alkene and is known as Ethene and $HC \equiv CH$ is a typical alkyne named as Ethylene.

Note: Always remember that the longest chain is always numbered from that end which would provide us with the lowest number to the carbon atom where the double bond or the triple bond is present in case of unsaturated hydrocarbons.