Organic Chemistry Lab: Thin-Layer Chromatography (TLC)

Overview of TLC

• TLC is a method to monitor reactions in organic chemistry.
• It involves two phases:
  • Stationary Phase: Typically a silica gel-coated plate.
  • Mobile Phase: Solvent or mixture of solvents used in a developing chamber.

Steps in the TLC Process

Preparing the TLC Plate

• Spotting: Use a spotter to apply a small spot from your reaction flask onto the TLC plate.
  • Purpose: To determine if the reaction mixture contains single or multiple compounds.

Setting Up the Developing Chamber

• Add Mobile Phase: Pour a small amount of solvent into the chamber.
  • Ensure level is low to avoid submerging the spot.
• Paper Wick: Insert a piece of paper to saturate the chamber with solvent vapors.
  • Check that the paper is wet to confirm saturation.

Developing the TLC Plate

• Insert Plate: Place the TLC plate inside the developing chamber.
• Close the Chamber: Prevents volatile organic solvents from evaporating.
• Capillary Action: The mobile phase travels up the plate through capillary action.
• Marking the Solvent Front: Use a pencil to mark how far the mobile phase traveled.

Visualizing the Results

• UV Lamp: Shine a UV lamp to visualize spots.
  • Aromatic compounds usually fluoresce under UV light.
• Interpreting Spots: Each spot corresponds to a different compound in the mixture.
  • Example: Two spots indicate a two-component mixture.

Analyzing the Results

• Polarities:
  • Stationary Phase (silica gel): Very polar.
  • Mobile Phase: Less polar than silica gel.
• Spot Movement:
  • Less movement indicates higher polarity (attraction to silica gel).
  • More movement indicates lower polarity (attraction to the mobile phase).

Example: Identifying Compounds

• Naphthalene: Nonpolar, corresponds to the spot that moves further.
• Benzoic Acid: Polar due to the carboxyl group, corresponds to the spot that moves less.

Summary of TLC Process

1. Spot the plate.
2. Place in the developing chamber with a mobile phase.
3. Allow the mobile phase to rise.
4. Remove the plate and use UV light to visualize spots.
5. Compare spots based on polarity to identify compounds.