Vernier Software and Technology
Vernier Software & Technology

Identification of Organic Unknowns Using Polarimetry

Introduction

Polarimetry is a common device for distinguishing between optically active stereoisomers, i.e., enantiomers. This makes it a very important instrument in organic chemistry because the optical rotation of a molecule can dictate what reactions it will undergo. This is true for most chiral molecules, including organic, inorganic, and biological compounds. An enantiomer will consistently have the same specific rotation under identical experimental conditions. To determine the specific rotation of the sample, use Biot’s law:

{\alpha} = {\it{\text{[}}{\alpha}{\text{]}}{\ell}{\text{c}}}

where α is the observed optical rotation in units of degrees, [α] is the specific rotation in units of degrees (the formal unit for specific rotation is degrees dm-1 mL g-1, but scientific literature uses just degrees), ℓ is the length of the cell in units of dm, and c is the sample concentration in units of grams per milliliter.

In the following procedure, you will investigate the differences between different optical isomers of sugars, amino acids, and natural products using polarimetry.

Objectives

In this experiment, you will

  • Calculate the specific rotation of sugars, amino acids, and natural products using a Polarimeter.
  • Identify an unknown compound based on specific rotation.

Sensors and Equipment

This experiment features the following Vernier sensors and equipment.

Additional Requirements

You may also need an interface and software for data collection. What do I need for data collection?

Experiment 7 from Organic Chemistry with Vernier Lab Book

<i>Organic Chemistry with Vernier</i> book cover

Included in the Lab Book

Vernier lab books include word-processing files of the student instructions, essential teacher information, suggested answers, sample data and graphs, and more.

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