Heptane

Heptane (also known as dipropyl methane, gettysolve-C or heptyl hydride) is an alkane with the chemical formula H₃C(CH₂)₅CH₃. Heptane has nine isomers, or eleven if enantiomers are counted:

• Heptane (n-heptane), H₃C–CH₂–CH₂–CH₂–CH₂–CH₂–CH₃, straight chain of seven carbon atoms.
• 2-Methylhexane, H₃C–CH(CH₃)–CH₂–CH₂–CH₂–CH₃, chain of six carbon atoms, and a methyl group attached to the second.
• 3-Methylhexane, H₃C–CH₂–C^*H(CH₃)–CH₂–CH₂–CH₃ (chiral), chain of six carbon atoms, and a methyl group attached to the third.
• 2,2-Dimethylpentane, (H₃C)₃–C–CH₂–CH₂–CH₃, chain of five carbon atoms, and two methyl groups attached to the second.
• 2,3-Dimethylpentane, (H₃C)₂–CH–C^*H(CH₃)–CH₂–CH₃ (chiral), chain of five carbon atoms, and methyl groups attached to the second and third.
• 2,4-Dimethylpentane, (H₃C)₂–CH–CH₂–CH–(CH₃)₂, chain of five carbon atoms, and methyl groups attached to the second and fourth.
• 3,3-Dimethylpentane, H₃C–CH₂C(CH₃)₂–CH₂–CH₃, chain of five carbon atoms, and two methyl groups attached to the third.
• 3-Ethylpentane, H₃C–CH₂–CH(CH₂CH₃)–CH₂–CH₃, chain of five carbons, and an ethyl group attached to the third.
• 2,2,3-Trimethylbutane, (H₃C)₃–CH(CH₃)–CH₃, chain of four carbon atoms, with two methyl groups attached to the second, and one to the third.[1]

Additional recommended knowledge

Essential Laboratory Skills Guide

Daily Visual Balance Check

Recognize and detect the effects of electrostatic charges on your balance

The straight-chain isomer n-heptane is the zero point of the octane rating scale. It is undesirable in petrol, as it burns explosively, causing engine knocking, as opposed to branched-chain octane isomers, which burn more slowly and give better performance. Its choice for the zero point of the scale was due to the availability of very high purity n-heptane, unmixed with other isomers of heptane or other alkanes, distilled from the resin of Jeffrey Pine. Other sources of heptane and octane, produced from crude oil, contain a mixture of different isomers with greatly differing ratings, so do not give a precise zero point.

Uses

Heptane, as well as its many isomers, are widely applied in laboratories as a totally non-polar solvent. Being a liquid, it is ideal for transport and storage. In the grease spot test, heptane is used to dissolve the oil spot to show the previous presence of organic compounds on a stained paper. This is done by shaking the stained paper in a heptane solution for about half a minute.

Heptane is also used as a medium to distinguish bromine from iodine from aqueous mixtures. While both bromine and iodine appear brown in aqueous media, bromine remains brown when dissolved in heptane, while iodine turns purple when mixed with heptane.

Heptane is commercially available as the rubber cement solvent Bestine.

References