Explain how the three different parts of the molecule contribute to the properties of the compound used in electrical display devices.

CN:

\({{\text{C}}_{\text{5}}}{{\text{H}}_{{\text{11}}}}\):

:

Describe and explain in molecular terms the workings of a twisted nematic liquid crystal.

CN

makes molecule polar, ensures common orientation which can be changed by electric field;

C₅H₁₁

prevents close packing of molecules;

molecules rigid and rod shaped;

Accept chemical stability for second or third mark not both.

liquid crystal between two glass plates which have scratches at 90° to each other;

molecules form a twisted arrangement between plates due to intermolecular bonds;

when polarizers are aligned with scratches, light will pass through film and pixel will appear bright;

applied voltage aligns polar molecules and pixel appears dark;

In (a), very few candidates scored full marks.

In (b), candidates struggled greatly in trying to explain in molecular terms the workings of a twisted nematic liquid crystal.