Question

Which among the following is the correct IUPAC name of isoamylene?
(a) ${\text{Pent - 1 - ene}} $
(b) $2 - {\text{Methylbut - 2 - ene}} $
(c) $3 - {\text{Methylbut - 1 - ene}} $
(d) $2 - {\text{Methylbut - 1 - ene}} $

Answer 1

Hint :To know organic compounds, we have to memorize a few basic points. The base part of the names reflects the number of carbon atoms present in the parent chain. The suffix of the name reflects the type of functional group that is present in the parent chain.

Complete Step By Step Answer:
If a hydrocarbon has a double bond in it, the suffix $ - {\text{ene}} $ is used. The position of the double bond in the parent chain is indicated by placing the number of the first carbon of the double bond directly in front of the base name. The structure of isoamylene is as follows:

Here, the longest possible parent chain will have four carbon atoms. Give numbering to the carbon atoms in the parent chain. There is a double bond in the hydrocarbon, so the suffix $ - {\text{ene}} $ should be used. The double bond is at position $2 $. We should write the position of the double bond in front of the base name. As the parent chain has four carbon atoms, so we use $ - {\text{but}} $. There is a methyl group attached to the second carbon atom, so the IUPAC name will be: $2 - {\text{Methylbut - 2 - ene}} $
Therefore, option B is the correct answer.

Note :
Remember to number the parent chain in such a way that the multiple bonds have the lowest numbers. If there is more than one double bond in the given hydrocarbon, the suffix is generally expanded to include a prefix indicating the number of double bonds present in the hydrocarbon.