The IUPAC name of the compound : $CH_{3}-CH=CH-C\equiv C-CH_{3}$ is:

Question

Accepted Answer

The IUPAC name of the compound $CH_{3}-CH=CH-C\equiv C-CH_{3}$ is correctly given as Option 3: Hexa-2-ene-4-yne. Let's break down the reasoning behind this naming and why the other options are incorrect.

### Explanation for Option 3: Hexa-2-ene-4-yne

1. **Longest Carbon Chain**: The compound has a total of six carbon atoms, which is indicated by the prefix "Hexa-". This is the longest continuous chain that includes both the double bond (ene) and the triple bond (yne).

2. **Numbering the Chain**: According to IUPAC rules, the chain should be numbered in such a way that the multiple bonds get the lowest possible numbers. Starting from the left, the double bond (ene) is at the second carbon, and the triple bond (yne) is at the fourth carbon. Hence, the name includes "2-ene" and "4-yne".

3. **Order of Multiple Bonds**: In IUPAC nomenclature, when both double and triple bonds are present, the compound is named as an "enyne", with the double bond (ene) mentioned before the triple bond (yne) in the name, regardless of their positions.

### Why Other Options are Incorrect

1. **Option 1: Hexa-4-ene-2-yne**
   - This option incorrectly numbers the positions of the double and triple bonds. The numbering should give the lowest possible numbers to the multiple bonds, which is achieved by "2-ene" and "4-yne", not "4-ene" and "2-yne".

2. **Option 2: 1,4-Dimethyl but-3-ene-1-yne**
   - This name suggests a different structure with two methyl groups and a four-carbon chain, which does not match the given compound. The compound in question has a six-carbon chain without additional methyl groups.

3. **Option 4: Propargyl propene**
   - This name implies a structure with separate propargyl and propene groups, which is not the case here. The compound is a single continuous chain of six carbons with both double and triple bonds, not separate groups.

In conclusion, Option 3: Hexa-2-ene-4-yne is the correct IUPAC name for the compound $CH_{3}-CH=CH-C\equiv C-CH_{3}$, as it accurately reflects the structure and follows the IUPAC naming conventions.