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Stereoisomerism

Optical activity and plane-polarised light

  • 3 things to know
  • Component 2

Overview

Plane-polarised light, optical activity and instrument used to measure optical rotation.

What you need to know

Answer each one before you reveal it.

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Key term

What is plane-polarised light, how is it produced, and what does it mean to call a substance optically active?

Key term

What is plane-polarised light?

Key term

Define optical activity.

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    What is plane-polarised light?

    Model answer

    Light whose vibrations have been restricted to a single plane containing the direction of travel.

  2. 2

    How is plane-polarised light produced?

    Model answer

    By passing ordinary light through a polarising filter, which transmits only the vibrations in one plane.

  3. 3

    Define optical activity.

    Model answer

    Optical activity is the ability of a substance to rotate the plane of plane-polarised light passed through it.

  4. 4

    What effect does a single enantiomer have on plane-polarised light?

    Model answer

    It rotates the plane of polarisation through a characteristic angle in one direction.

  5. 5

    How do the effects of the two enantiomers of a compound compare?

    Model answer

    They rotate the plane by equal angles in opposite directions.

  6. 6

    What name is given to an isomer that rotates the plane clockwise?

    Model answer

    The dextrorotatory isomer, labelled with a plus sign.

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