Consider the following ball-and-stick model. Elements other than hydrogen and carbon are labeled. If the specific rotation of this substance is +2.6°, then what is the specific rotation of the following substance?
A) +2.6°
B) −2.6°
C) 0°
D) +5.2°
E) −5.2°

Question

Consider the following ball-and-stick model. Elements other than hydrogen and carbon are labeled.   If the specific rotation of this substance is +2.6°, then what is the specific rotation of the following substance?
A) +2.6° 
B) −2.6° 
C) 0° 
D) +5.2° 
E) −5.2°

Quizplus · Accepted Answer

The specific rotation of a substance is a physical property that depends on the chemical nature of the compound and its concentration, as well as the wavelength of the light used. It is given by the formula [α] = α / (c*l), where α is the observed rotation in degrees, c is the concentration of the sample in grams per milliliter, and l is the path length of the sample cell in decimeters. Since the chemical nature of the compound has not changed in the second substance, it is reasonable to assume that the specific rotation will be the same as before. However, because the configuration of the molecule has changed due to the substitution of the chlorine atom for one of the hydrogens attached to a carbon, the direction of rotation will be reversed. Therefore, the correct answer is B) −2.6°.

Consider the Following Ball-And-Stick Model