The experimental data obtained when a chiral molecule interacts with plane-polarized light is called:

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11ecba2d_129f_f478_a3bf_a5cdfcce76b5_MD0008_00 Normal light is made of light waves that oscillate in all planes perpendicular to the direction of propagation. When light encounters a polarizer, only waves that are aligned with the polarizer can pass. Therefore, all the light that passes through the polarizer oscillates in one direction. This resulting uniform light is known as plane-polarized (linear) light. Chiral molecules rotate plane-polarized light; the angle of rotation, known as the specific rotation, is unique for each chiral molecule and must be determined experimentally. A molecule's specific rotation contains direction (+ or −) and magnitude. Rotations that are clockwise are (+) whereas those that are counterclockwise are (−). Enantiomers have specific rotations of equal magnitude but in opposite directions. (Choice A) A polarimeter is the instrument used to measure the rotation of polarized light. (Choice B) The R or S configurations are based on the priority ranking of substituents on a stereocenter, and are not correlated to the direction chiral molecules rotate plane-polarized light. Therefore, stereocenter configuration cannot be used to predict specific rotation, or vice versa. (Choice D) An infrared spectrum is obtained from irradiation of a molecule with infrared light, causing bond vibrations and stretching at different frequencies. The amount of light absorbed by the molecule is recorded and displayed as the percent transmittance versus wavenumber on the infrared spectrum. Educational objective: Specific rotation measures the direction (+ or −) and magnitude (angle) of rotation by which chiral molecules rotate plane-polarized light. This value is a physical characteristic of chiral molecules, is unique for each molecule, and must be determined experimentally.

The Experimental Data Obtained When a Chiral Molecule Interacts with Plane-Polarized