Animated Solution for Chemistry - Organic Chemistry: The IUPAC name for the following compound is

When faced with a complex organic molecule, the first step is always to identify the principal functional groups. In this structure, we observe two key features: a carbon-carbon double bond ($C=C$) and a carbon-carbon triple bond ($C\equiv C$). These multiple bonds dictate the selection of our main carbon chain.

Choosing the Main Chain

According to IUPAC nomenclature rules, the principal carbon chain must be the longest continuous chain that contains the maximum number of multiple bonds.

If we trace the molecule from the terminal $=C{H}_2$ group on the left, through the backbone, and end at the terminal $\equiv CH$ group on the right, we successfully encompass both the double and triple bonds. Counting the carbons along this path gives us a total of $7$ carbon atoms. Therefore, the root word for our parent chain is hept.

Numbering the Chain

Once the main chain is established, we must number it to assign the lowest possible locants (numbers) to the multiple bonds as a set. Let's evaluate both directions:

1. Left to Right: The double bond starts at carbon $1$, and the triple bond starts at carbon $6$. The locant set is $(1,6)$. 2. Right to Left: The triple bond starts at carbon $1$, and the double bond starts at carbon $6$. The locant set is also $(1,6)$.

We have a tie! When the locant sets are identical from both ends, a crucial IUPAC tie-breaker rule comes into play: the double bond (-en) is given priority over the triple bond (-yne) for the lower number. Consequently, we must number the chain from left to right.

With the numbering locked in (left to right), we can now pinpoint our substituents: - At carbon $3$, there is a methyl group ($-C{H}_3$). - At carbon $4$, there is a propyl group ($-C{H}_{2}C{H}_{2}C{H}_3$). - At carbon $5$, there is another methyl group ($-C{H}_3$).

We combine identical substituents using prefixes, giving us $3,5$-dimethyl. When assembling the final name, substituents are listed in alphabetical order, ignoring prefixes like 'di' or 'tri'. Since 'm' (methyl) comes before 'p' (propyl), the prefix part of the name is $3,5$-dimethyl-$4$-propyl.

Finally, we append the parent chain name. The $7$-carbon chain with a double bond at $1$ and a triple bond at $6$ is named hept-$1$-en-$6$-yne. Notice that the 'e' from 'ene' is dropped because the following suffix '-yne' starts with a 'y'.

Putting it all together, the complete IUPAC name is: $3,5$-dimethyl-$4$-propylhept-$1$-en-$6$-yne