Structural representations of organic compounds

Introduction

The structural formula of a chemical compound is a graphical representation of the molecular structure to show that how the atoms are arranged. The chemical bonding inside the molecule is shown, either explicitly or implicitly. There are three common representations which used in publications: text, Lewis type and line-angle formula. Also many other formats are used, as in chemical databases, like SMILES, InChI and CML.

Structural formulas give a representation of the molecular structure. Chemists mostly describe a chemical reaction or synthesis by using structural formulae instead of chemical names, because the structural formulas allow the chemist to observe the molecules and the changes that occur.

Many chemical compounds are present in different isomeric forms, which have different structures but the same overall chemical formula. A structural formula indicates the arrangements of atoms in a mannered way which a chemical formula cannot do.

Text formulas

In early organic chemistry publications, when use of graphics was strictly limited, a text-based system came for describing organic structures in a line of text. Although this system tends to break down with complex cyclic compounds, it remains a easier way to represent simple structures.

CH₃^–CH₂^–OH or CH₃CH₂OH

Lewis structures

Lewis structures are flat graphical formulas which show the atom connectivity, but do not give information about the three-dimensional structure of molecules. This notation is commonly used for small linear molecules. A single line shows a single bond or single electron pair. Two and three lines show double and triple bonds, respectively. Alternatively, dots (•) are used to show single electrons. This is called as Lewis Dot Structure.

Three-dimensional structures

Several methods are present to picturize the three-dimensional arrangement of atoms in a molecule.

Fischer projection

The Fischer projection is commonly used for linear monosaccharides. The vertical backbone is implicit to form a bridge-like structure on the paper plane with the substituents sticking up.

Perspective drawings of cyclic conformations

Perspective drawing is a three-dimensional perspective of a cyclic compound, also shows the structure of the ring, as it is an example a chair conformation.

Newman projection and sawhorse projection

The Newman projection and the sawhorse projection are used for depicting the stereochemistry at two connected carbon atoms.

Skeletal formulas

Skeletal formulas are the standard information for more complex organic molecules. Carbon (C) atoms are represented by the vertices (corners) and termini of line segments which are not marked with an atomic symbol. Each carbon atom is in turn thought to bear enough hydrogen atoms to give the carbon atom four bonds.

Stereochemistry in skeletal formulas

Chiral property in skeletal formulas is denoted by the Natta projection method. Solid or dashed wedged bonds symbolize bonds pointing above-the-plane or below-the-plane of the paper, respectively.