Question

What is the value of the specific rotation of the glucose molecule?

Answer 1

Under standard conditions, the specific rotation of glucose is typically reported at a concentration of 10 grams per 100 milliliters of water (10 g/100 mL), using a sodium D-line wavelength of 589.3 nanometers (nm), and at a temperature of 20 degrees Celsius.

The specific rotation, denoted as \( [\alpha] \), is a property of optically active substances, like glucose, that describes the angle by which the substance rotates the plane of polarized light. The specific rotation is defined by the equation:

\[ [\alpha] = \frac{\alpha}{c \cdot l} \]

Where:

• \(\alpha\) is the observed rotation, measured in degrees (°),
• c is the concentration of the solution in grams per milliliter (g/mL),
• l is the path length of the sample in decimeters (dm).

For glucose under standard conditions:

• Concentration (\( c \)) = 10 g/100 mL = 0.1 g/mL,
• Path length (\( l \)) is typically 1 dm (standard length for polarimetry),
• The wavelength used for measurement is 589.3 nm, corresponding to the sodium D-line wavelength.

The temperature of 20°C is commonly used because the specific rotation can vary with temperature.

Therefore, the specific rotation of glucose is typically reported using these standard conditions, and any deviations in concentration, wavelength, or temperature should be noted to ensure accuracy in measurements.