Conformational Analysis of Acyclic Hydrocarbons

Molecules are dynamic assemblies of atoms chemically linked by single or multiple bonds. Hence, all atoms as well as groups of atoms are in perpetual motion, vibrating and rotating about chemical bonds. The deformation of chemical bonds due to vibration (stretching, wagging, etc.) of atoms is quantized and it is not the subject of conformational analysis. However, the rotation of atoms about the single bonds is the subject of conformational analysis. Conformation of a molecule can be defined as a spatial arrangement of its atoms (or ligands) in a molecule that is obtained by free rotations about single bonds. Hence, the conformations are interconvertible by rotation about the single bonds. When an atom that carries no substituent rotates about a single bond that links it to another atom, which does or does not carry a substituent, the rotation will not change the spatial arrangement of atoms in that molecule and therefore there will be no change in conformation due to rotation, as shown in Fig. 2.1 for molecules of hydrogen (1), chlorine (2), and water (3).