is a liquid paraffinic hydrocarbon containing seven carbon atoms in the molecule, which may be straight-chain (normal) or branched-chain (iso). Heptane can be used in place of hexane where a less volatile solvent is desired, as in the manufacture of certain adhesives and lacquers, and in extraction of edible and commercial oils. Heptane is blended with isooctane to create a standard reference fuel in laboratory determinations of octane number.

Heptane has nine isomers:

• Heptane (n-heptane), CH₃CH₂CH₂CH₂CH₂CH₂CH₃, straight chain of seven carbon atoms.
• 2-Methylhexane, CH₃CH(CH₃)CH₂CH₂CH₂CH₃, chain of six carbon atoms, and a methyl group attached to the second.
• 3-Methylhexane, CH₃CH₂CH(CH₃)CH₂CH₂CH₃ (chiral), chain of six carbon atoms, and a methyl group attached to the third.
• 2,2-Dimethylpentane, CH₃C(CH₃)₂CH₂CH₂CH₃, chain of five carbon atoms, and two methyl groups attached to the second.
• 2,3-Dimethylpentane, CH₃CH(CH₃)CH(CH₃)CH₂CH₃ (chiral), chain of five carbon atoms, and methyl groups attached to the second and third.
• 2,4-Dimethylpentane, CH₃CH(CH₃)CH₂CH(CH₃)CH₃, chain of five carbon atoms, and methyl groups attached to the second and fourth.
• 3,3-Dimethylpentane, CH₃CH₂C(CH₃)₂CH₂CH₃, chain of five carbon atoms, and two methyl groups attached to the third.
• 3-Ethylpentane, CH₃CH₂CH(CH₂CH₃)CH₂CH₃, chain of five carbons, and an ethyl group attached to the third.
• 2,2,3-Trimethylbutane, CH₃C(CH₃)₂CH(CH₃)CH₃, chain of four carbon atoms, with two methyl groups attached to the second, and one to the third