Drawing Organic Structures

Ever looked at a cloud formation and wondered at its shapes? Sometimes, it’s Winnie the Pooh, Snoopy the Dog, a dragon, or a man jet skiing. Perhaps the images we spawn are our association with the world we live in and relate to. Maybe it was this association that the scientist who drew the first sawhorse projections tried to analogize when relating the unseen with the seen. We may never know! Still, the Sawhorse projection is said to be similar to a carpenter’s sawhorse or a mule, used to support a plank for sawing.

August Kekulé (1866) was the first to propose the alternating single and double bond structure of benzene that can only be possible if carbon could join other carbon atoms and form a ring.

The first time the use of two dots or a colon (:) to represent two electrons acting as connecting links between the two atoms was proposed by G.N. Lewis in 1916.

In his landmark paper, ‘the atom and the molecules,’ he attempted to draw molecular structures using dots to represent the covalent nature of the chemical bonds, now popularly known as the Lewis structures.

So, a molecule of Cl₂ was Cl : Cl, two electrons connecting two Cl atoms.

Organic compounds in which carbon atoms are joined in a ring, unlike the open-chain counterparts, are represented using the polygon formula. These cyclic polygons do not show carbon and hydrogen atoms. The corner of a polygon represents a carbon atom with its required number of hydrogen atom(s), and the sides of the polygon represent a carbon-carbon bond.

Molecular models are tools used for classroom or research to visualize better and interpret three-dimensional structures of organic molecules. The toolkit can be made of wood, plastic, metal, or other materials.

These models are digitally represented using computer graphics covered under molecular modelling, a branch of chemistry that uses computational and theoretical methods to model and mimic the molecule's behaviour in chemical and biological environments.

What is a Bond-Line or Skeletal Formula?

Carbon and Hydrogen containing bonds are chemically inert; still, they form the backbone of many organic compounds. They provide a skeletal framework that can contain other heteroatoms or functional groups. 

Such a carbon-hydrogen-containing chain of compounds together with other atoms or groups of atoms are conveniently represented using zig-zag lines, called the bond-line or skeletal formula.

Certain conventions are used to represent three-dimensional structures of organic molecules on paper. Using simple lines, solid (dark), and dashed wedges, a 3D image of a molecule can be perceived on two-dimensional paper.

What is a Condensed Structural Formula?

The condensed structural formula provides the shortest way to understand the atoms and their numbers, their connection with respect to each other, and therefore, visualize the compounds' structure without elaborately drawing it, but by writing it in a single line.

So, if the elaborate structure of butanoic acid look like A, the condensed structural formula would look like B.

The Lewis dot structures are used to show the shared electron pairs between the bonded atoms in the molecule and the lone pairs of electrons if any. The representative structures follow the octet rule wherein the atoms combine by either transfer of electrons (loss or gain) or by sharing of valence electrons in a way that the valence shell of the atoms attains the octet configuration.

The electrons involved are shown as dots. A single bond is made up of two electrons, a double four and a triple bond six. Similarly, an atom can have one, two or three lone pairs of electrons.