Chemistry
Textbooks
Boundless Chemistry
Organic Chemistry
Aliphatic Hydrocarbons
Chemistry Textbooks Boundless Chemistry Organic Chemistry Aliphatic Hydrocarbons
Chemistry Textbooks Boundless Chemistry Organic Chemistry
Chemistry Textbooks Boundless Chemistry
Chemistry Textbooks
Chemistry
Concept Version 12
Created by Boundless

Drawing Hydrocarbon Structures

Hydrocarbon structures can be drawn from the IUPAC names of chemical compounds by starting with the carbon backbone and adding substituents.

Learning Objective

  • Identify the structure of a hydrocarbon from its IUPAC name


Key Points

    • Hydrocarbons frequently have both historical and IUPAC names; the IUPAC names can be used to draw the chemical structures.
    • To draw a hydrocarbon structure, start with the carbon backbone, which can include a ring structure.
    • After the carbon backbone is drawn, add the substituent groups and the double and triple bonds that are indicated by the prefixes and suffixes in the chemical name.

Term

  • isomer

    Any of two or more compounds with the same molecular formula, but with a different structure.


Full Text

Hydrocarbons can be drawn in several equally valid ways. The most common method is using the bond line formula, which is ubiquitous for its simplicity.

Bond Line Structures for Hydrocarbons

To draw a hydrocarbon using the bond line method, place your pencil on a piece of paper. This first dot represents one carbon atom. To continue, draw a short, straight line. Now the hydrocarbon represented by the short, straight line is two carbon atoms in length; it has two ends.

To increase the number of carbon atoms in your drawn structure, change direction and continue with a short, straight line. In addition to the two ends, there is now a vertex that represents a third carbon atom. The angle created by the three carbon atoms should be in the region of 110 degrees.

Extending the line with more and more vertices produces a longer carbon chain.

Hexane

The bond line structure of hexane can be illustrated by a kinked line with four vertices. Each vertex, as well as the two ends, represents a carbon atom.

Note that no carbon atom is explicitly written; they are implicit from the number of vertices plus the two ends. Additionally, no hydrogen atoms are written. Convention assumes that every bond line structure includes enough hydrogen atoms so that all carbon atoms in the structure make four bonds. All non-hydrogen and carbon atoms should be written explicitly, however.

Drawing Carbon Skeletons

Hydrocarbon structures are drawn starting with the carbon backbone, which is the longest branch, and are named according to the alkane series: one carbon, "meth-"; two carbons, "eth-"; three carbons, "prop-"; etc. Compounds that start with "cyclo-" are drawn starting with the ring structure.

Methane

Ball-and-stick model of methane.

For example, 3-ethyl-hexane could be represented by first drawing the hexane backbone, then adding an ethyl (two-carbon) chain extending from the third carbon of the backbone.

3-Ethyl hexane

Notice the two carbon chain that stems from the third carbon atom in the hexane structure.

Drawing Double and Triple Bonds

Compounds ending with "-ane" consist of solely single bonds in the carbon skeleton. The presence of double or triple bonds is determined by the suffix "-ene" or "-yne," respectively, and the positioning of the bond is defined by the numbering in the name of the structure.

When including an alkene bond in your hydrocarbon structure, aim for 120 degree bond angles about each doubly-bonded carbon. In the case of alkyne bonds, simply draw the triple bond in-line with the carbon atoms immediately bound to the alkyne carbons.

2-Pentyne

Four out of the five carbons in 2-pentyne are drawn in-line with one another.

Kekulé Structures

Kekulé structures are less commonly used than bond line structures because they are more tedious to draw. The difference is that in Kekulé structures, carbon atoms are signified with C at the vertices, and hydrogen atoms bonded to carbon are explicitly drawn.

Kekulé structure for benzene

Kekuléstructure for benzene, drawn with the C for carbon atoms and with all hydrogen atoms shown.

3D Structures

The 3D configuration for substituent groups on chemical structures is often indicated by shading bonds to indicate those that are above and below the plane of the paper. These bond angles follow the sp, sp2, and sp3 hybridization patterns of the atoms in the carbon backbone.

Methane structure

Notice the shading of the hydrogen bonds to indicate they are not all in the same plane.

[ edit ]
Edit this content
Prev Concept
Reactions of Alkanes
Cycloalkanes
Next Concept
Subjects
  • Accounting
  • Algebra
  • Art History
  • Biology
  • Business
  • Calculus
  • Chemistry
  • Communications
  • Economics
  • Finance
  • Management
  • Marketing
  • Microbiology
  • Physics
  • Physiology
  • Political Science
  • Psychology
  • Sociology
  • Statistics
  • U.S. History
  • World History
  • Writing

Except where noted, content and user contributions on this site are licensed under CC BY-SA 4.0 with attribution required.