Chapter 11, Problem 11.72SP

Interpretation Introduction

Interpretation:

Whether compound I or compound II that has a higher temperature associated with phase transition from solid to liquid has to be explained.

Concept introduction:

Liquid crystals are defined as a phase in which substance exhibits properties of both liquids and solids. Liquid crystal flow like liquid but their arrangement of molecule as well as intermolecular forces is like solid.

Liquid crystal molecules are made up of six-membered rings with on terminal polar group, a linkage group and a side chain of carbon atoms. Each carbon atom in liquid crystal molecules has trigonal planar geometry.

The molecules are rigid. The rigidity is increased due to presence of double-bonded linkage groups such as $\text{C}=\text{N}$.

The terminal polar groups exhibit strong intermolecular forces such as strong dipole-dipole interaction or dipole−induced dipole interaction and hydrogen bond.

Types of liquid crystal are as follows:

• Nematic Liquid crystal.
• Smectic Liquid crystal.

1. Nematic Liquid crystal: The molecules in the nematic phase are in same direction and can move around freely very much like that of liquid. In this, the axis is parallel but the ends are not aligned.

2. Smectic Liquid crystal: The molecules in the smectic phase are perpendicular to the plane and are aligned in layers. In these, long axis is parallel and also their ends are aligned.