What Are the Structures of the 9 Isomers of Heptane?

Written by robert alley
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What Are the Structures of the 9 Isomers of Heptane?
Chemistry chalkboards contain diagrams of molecules like heptane. (Jupiterimages/BananaStock/Getty Images)

A colourless liquid obtained from petroleum, heptane is highly flammable and considered dangerous. It contains seven parts carbon and 16 parts hydrogen, or C7H16. The nine isomers of heptane, each with its own name, all possess the same molecular weight, that is, they all have seven carbon atoms and 16 hydrogen atoms. Each isomer's atoms are arranged in a different manner or structure.

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Heptane

The first and basic isomer of C7H16 goes by the name Heptane. It provides the basic chemical structure for all other isomers. Its structure has the seven carbon atoms lined up a straght horizontal chain. The hydrogen atoms are attached as follows; each of five interior carbon atoms have two hydrogen atoms attached, one on top and one on the bottom. The two end carbon atoms each have three hydrogen atoms attached; one on top, one on bottom and the third hydrogen on the end. The result is two horizontal rows of seven hydrogen atoms,one on the top of the carbon chain and the other on the bottom. The final two hydrogen atoms are placed on each end of the carbon chain.

Methyl Groups

Two isomers are formed by the attached of a methyl group, which is represented by CH3. One isomer is called 2-methylhexane and the other 3-methylhexane. The numbers 2 and 3 refer to the placement of the methyl group on the carbon chain, indicating the number of the carbon atom. The structure consists of six carbon atoms in a chain with the methyl group attached to either the second or third carbon atom.

Dimethyl Groups

Four isomers fall into this group. The beginning structure for the isomers is a chain of five carbon atoms. One isomer is 2,2-dimethylpentane. The others are named 2,3-dimethylpentane, 2,4-dimethylpentane and 3,3-dimethylpentane. The numbers again refer to the placement of the methyl group on the five carbon chain. 2,2 means two methyl groups attached to the second carbon atom. 2,3 means one methyl group attached to the second carbon atom and one group attached to the third carbon atom. 2,4 means one methyl group at carbon atom two and one at carbon atom 4. 3,3 indicates both methyl groups attached to the third carbon atom.

Ethylpentane

Designated 3-ethylpentane, the basic structure of this isomer begins with a chain of five carbon atoms. An ethyl group, C2H5, is attached to the middle, or third, carbon atom.

Trimethylbutane

Known as 2,2,3-trimethylbutane, this isomer of heptane starts with a chain of four carbon atoms. Two methyl groups attach to the second carbon atom and one methyl group attaches to the third carbon atom.

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