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DRAWING ORGANIC MOLECULES

The depiction of organic molecules is critical to their discussion. In organic chemistry a particular short hand is used, called line notation, to simplify structures with many carbons and hydrogens. In general, lines are used to denote bonding pairs of electrons. As shown in Figure 3.1, one line is two electrons shared by neighboring atoms. Two parallel lines, like an equation sign, indicate a double bond, or four shared electrons. A set of three parallel lines between two atoms indicates a triple bond, or six shared electrons.

Bonds in line notation

Figure 3.1. Bonds in line notation

Because there are so many carbons involved in organic chemistry, and most carbons have some hydrogens attached to them, two further simplifications are made. One, instead of writing each carbon, the atomic symbol for them is generally omitted. If multiple carbons are omitted in a row, then the line is drawn in a zig-zag fashion, with each angle break in the line indicating the presence of a carbon. Additionally, hydrogen atoms are usually (but not always) omitted. They are not indicated in any way. It is assumed that every carbon will have four bonds, and any bonds not drawn already are to a hydrogen atom. The process of simplifying a molecular structure is shown in Figure 3.2.

Simplifying molecular structures to line notation. Top

Figure 3.2. Simplifying molecular structures to line notation. Top: ethane. Middle: acetone (formal name 2-propanone). Bottom: 2-chloro-1-butene

 
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