Optical Activity: When Light Meets Molecules

The video tutorial explains how optical activity is measured using a polarimeter, which consists of a light source, two Nicole prisms (polarizer and analyzer), and a detector. The light used should be plane polarized, typically yellow light from sodium. The tutorial describes how to detect optical activity by passing unpolarized light through a polarizer, creating plane polarized light, and then through a sample tube. If the light's direction changes, the compound is optically active (chiral); if not, it is inactive (achiral). Optically active compounds are further classified as dextro rotatory (right rotation) or levorotatory (left rotation), represented as D or + and L or -, respectively.

What is the primary function of a polarimeter?

• To analyze the chemical composition of a sample

• To calculate the density of a liquid

• To determine the optical activity of a compound

• To measure the temperature of a compound

Which type of light is typically used in a polarimeter?

• Blue light with a wavelength of 4500 angstroms

• Green light with a wavelength of 5200 angstroms

• Red light with a wavelength of 7000 angstroms

• Yellow light with a wavelength of 5890 angstroms

What does it mean if the angle of rotation measured by the analyzer is zero?

• The compound is chiral

• The compound is optically inactive

• The compound is dextro rotatory

• The compound is levo rotatory

How is a dextro rotatory compound represented?

• R or /

• D or +

• C or *

• L or -

What is the term used for compounds that rotate plane polarized light to the left?

• Dextro rotatory

• Optically inactive

• Achiral

• Levo rotatory