Specific Rotation: Measuring Optical Activity

The video tutorial explains the concept of optical activity and specific rotation, a constant value measured in degrees. It details how specific rotation is calculated and represented, using examples of dextro and levo rotatory compounds. A problem-solving section demonstrates the effect of concentration on observed rotation, emphasizing that specific rotation remains constant regardless of concentration or temperature. The tutorial also covers racemic mixtures, which are optically inactive, and introduces the concept of optical purity, calculated as a percentage of the observed specific rotation relative to an optically pure enantiomer.

What does the 'D' in the specific rotation symbol [α]D^T represent?

• The degree of rotation

• The diameter of the test tube

• The wavelength of the D line of sodium

• The density of the compound

How is specific rotation calculated?

• By dividing the observed rotation by the concentration and length of the sample tube

• By multiplying the observed rotation by the concentration and length of the sample tube

• By adding the observed rotation to the concentration and length of the sample tube

• By subtracting the observed rotation from the concentration and length of the sample tube

What is the specific rotation of a compound that rotates plane polarized light to the left?

• Negative

• Zero

• Positive

• Undefined

If the concentration of a solution is doubled, what happens to the observed rotation?

• It becomes zero

• It is doubled

• It is halved

• It remains the same

What does a positive specific rotation indicate about a compound?

• It has no specific rotation

• It is optically inactive

• It is dextro rotatory

• It is levo rotatory

What is a racemic mixture?

• A mixture of only dextro isomers

• A mixture with no optical activity

• A mixture of only levo isomers

• A mixture of dextro and levo isomers in equal quantities

How is optical purity calculated?

• By adding the observed specific rotation to the specific rotation of an optically pure enantiomer

• By subtracting the observed specific rotation from the specific rotation of an optically pure enantiomer

• By multiplying the observed specific rotation by the specific rotation of an optically pure enantiomer

• By dividing the observed specific rotation by the specific rotation of an optically pure enantiomer and multiplying by 100%