Animated Solution for Chemistry - Organic Chemistry: The IUPAC name of

When faced with a skeletal structure in organic chemistry, the very first step is to translate the zig-zags into a mental map of carbon atoms. Every vertex and every end of a line represents a carbon atom. Our primary objective is to identify the longest continuous carbon chain, which will serve as the parent alkane.

By tracing the horizontal-like path from one end to the other, we count exactly $7$ carbon atoms. This establishes our parent chain as heptane. It is crucial to verify that no other path yields a longer chain. In this molecule, any path branching off into the substituents results in a shorter or equal length chain, confirming heptane as the correct parent.

Once the parent chain is locked in, we must identify the groups attached to it. Looking at the structure, we observe three distinct branches:

1. Two single-line branches attached to the same carbon. A single line represents a $-{\text{CH}}_3$ group, known as a methyl group. 2. One branch consisting of two line segments. This represents a $-{\text{CH}}_2{\text{CH}}_3$ group, known as an ethyl group.

Now comes the critical step of numbering the parent chain. The IUPAC rules mandate that we number the chain from the end that gives the lowest possible locants (numbers) to the substituents. We must evaluate both directions:

- Numbering Left to Right: The substituents fall on carbons $4$, $4$, and $5$. This gives us the locant set $(4,4,5)$. - Numbering Right to Left: The substituents fall on carbons $3$, $4$, and $4$. This gives us the locant set $(3,4,4)$.

To determine the winner, we apply the First Point of Difference Rule. We compare the sets term by term: $3$ versus $4$. Since $3<4$, the set $(3,4,4)$ is lower. Therefore, the correct numbering is from right to left.

The final step is to assemble the name by listing the substituents alphabetically. The name of the substituent is what matters for alphabetization, not any numerical prefixes like di-, tri-, or tetra-.

- Ethyl starts with 'E'. - Methyl starts with 'M'.

Since 'E' comes before 'M', we list the ethyl group first, followed by the two methyl groups. Combining the locants, substituents, and the parent chain, we arrive at the final, systematic IUPAC name: