Organic Nomenclature Practice Test 2026 – The Complete All-in-One Guide to Master Chemical Naming!

The IUPAC name for a branched alkane with the formula C5H12 that includes a methyl branched group is 2-Methylbutane.

To understand this, we start by recognizing that the molecular formula C5H12 corresponds to an alkane with five carbon atoms. When identifying the longest continuous carbon chain, this structure can be arranged as a four-carbon chain (butane) with a methyl group (−CH3) attached to the second carbon.

In the case of 2-Methylbutane, the longest chain is butane (four carbons), and the methyl group is attached to the second carbon atom in that chain. This naming follows the IUPAC conventions: the longest continuous carbon chain is prioritized for naming, and the substituents (like the methyl group) are numbered in a way that gives them the lowest possible locants.

Thus, the name 2-Methylbutane accurately describes this branched alkane structure, clearly indicating the position of the methyl substituent on the butane chain. The other choices either misidentify the structure or do not correctly reflect the rules of nomenclature regarding the longest chain and substituent positioning.