Name this branched-chain alkane with the formula C5H12.

Name this branched-chain alkane with the formula C5H12.

• A. 2-Methylbutane
• B. Hexane
• C. Pentane
• D. Heptane

Answer: (A)

Alkanes with five carbons can be arranged as a straight chain or with a branch. The formula C5H12 fits five carbons in a saturated hydrocarbon, so there are two common isomers: a straight-chain pentane and a branched form. The branched one is formed by taking four carbons in a butane chain and attaching a methyl group to carbon 2, giving 2-methylbutane. This name comes from the longest chain being four carbons (butane) with a methyl substituent on carbon 2. It’s also known as isopentane. The other options would have the wrong number of carbons (hexane has six, heptane seven) or would be the straight-chain isomer (pentane) rather than branched.

Alkanes with five carbons can be arranged as a straight chain or with a branch. The formula C5H12 fits five carbons in a saturated hydrocarbon, so there are two common isomers: a straight-chain pentane and a branched form. The branched one is formed by taking four carbons in a butane chain and attaching a methyl group to carbon 2, giving 2-methylbutane. This name comes from the longest chain being four carbons (butane) with a methyl substituent on carbon 2. It’s also known as isopentane. The other options would have the wrong number of carbons (hexane has six, heptane seven) or would be the straight-chain isomer (pentane) rather than branched.