How to Draw Structural Formula

The structural formula always appears in my post every time. It describes the shape, form, and properties of the molecule. In this post I will briefly summarize the rules for writing structure formulas. There may be no new information for those who studied organic chemistry in college.

In the structural formula, lines between elements represent covalent bonds. Each element has a fixed number of bonds with other elements. For example, hydrogen can form one bond, carbon four, nitrogen three, oxygen two, and fluorine one. Bonds between two elements are not limited to a single bond; they can be connected by two or three lines and are called double or triple bonds.

Number of bonds each element can form

You can write all the carbons and hydrogens in the structural formula, but it would be very tedious if the molecules are complicated. In most organic molecules, carbon and hydrogen appear so frequently that these elemental symbols are commonly omitted. Carbon chains can be represented by lines only. In this case, the angle between the lines should be 120 degrees for a beautiful drawing. Molecules actually have a three-dimensional structure, but by drawing them in this way, a shape close to the actual structure can be drawn on a plane.

All these figure describe the same molecule (octane)

However, there are cases where 120 degrees is not possible, such as in cyclic compounds.


Furthermore, the hydrogen bonded to carbon can be omitted. For example, if only two bonds are written from a given carbon, the other two are bonded to hydrogen. The only hydrogen that can be omitted is the one bonded to carbon; hydrogen bonded to other elements cannot be omitted.

Hydrogen can be omitted

These are the minimum rules you should know. You’ll enjoy every post a lot more now!

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