1. What is Specific Rotation?

Definition: Specific rotation is a property of optically active compounds that measures how much they rotate plane-polarized light.

Purpose: It helps identify and characterize chiral compounds and determine their purity or concentration.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• \( [\alpha]_D \) — Specific rotation (degrees)
• \( \alpha \) — Observed rotation (degrees)
• \( l \) — Path length (dm)
• \( c \) — Concentration (g/mL)

Explanation: The observed rotation is divided by the product of the path length and concentration to give the standardized specific rotation.

3. Importance of Specific Rotation

Details: Specific rotation is crucial in chemistry for identifying chiral molecules, determining enantiomeric excess, and characterizing substances.

4. Using the Calculator

Tips: Enter the observed rotation in degrees, path length in decimeters (dm), and concentration in grams per milliliter (g/mL). Length and concentration must be > 0.

5. Frequently Asked Questions (FAQ)

Q1: What does the D subscript mean in [α]_D?
A: It indicates the measurement was taken using the D-line of sodium (589 nm wavelength).

Q2: What are typical specific rotation values?
A: Values range from -180° to +180° depending on the compound. For example, sucrose is +66.5° and camphor is +44.3°.

Q3: Why is path length measured in decimeters?
A: This is the standard unit for polarimetry measurements, making specific rotation values comparable across different experiments.

Q4: How does temperature affect specific rotation?
A: Specific rotation is temperature-dependent, so measurements should include temperature (usually 20°C or 25°C).

Q5: What if my compound is in a solvent other than water?
A: The solvent should be specified (e.g., [α]_D²⁰ (c=1, CHCl₃)) as it can affect the rotation.