Organic Chemistry Lab 315 Fall, 2016

Preparation for Lab The experimental procedure that will be followed is linked to the syllabus http://mason.gmu.edu/~sslayden/Lab/315/ 315expts.htm Please print it and bring it with you. The reading assignment from Pavia (which you do not have in your textbook) is available in “Course Content” on BlackBoard.

DUE DATES Today Next Week At beginning of lab – Extraction of Caffeine Report Problem #2, Part II, Spectroscopy Problem Set At end of lab -- copy of laboratory notebook pages for today's experiment (do not turn in your pre-lab notes or in-class notes) Next Week Part II, #3 Spectroscopy Problem Set Thin-layer Chromatography Report (see instructions on webpage)

Chromatography Chromatography separates components in a mixture based on the differences in their intermolecular interactions between a stationary phase and a moving phase. Phases can be solid, liquid, or gas. In this course we will learn TLC (solid stationary phase/liquid moving phase) and gas chromatography (GC) (solid stationary phase/gas moving phase).

Thin-layer Chromatography In this TLC experiment, the stationary phase is solid silica, thinly coated on a plastic plate. Silica is a polar substance with many –OH (hydroxyl) groups. The moving phase is dichloromethane, a moderately polar solvent. The components of a mixture will partition between the stationary and moving phases, depending on the extent of their interactions in the two phases.

Thin-layer Chromatography The components of the mixture to be separated are fluorene, fluorenol, and fluorenone. The names give an indication of the functional groups that are present in each compound. The compounds are named above in order of increasing polarity. The interactions among the stationary phase, the moving phase, and the components are complex and the elution order may surprise you!

Thin-layer Chromatography The separation of components is measured by the “retention factor”, Rf. I If all TLC conditions remain the same, the Rf would be constant for each compound (not easily achievable).

Experiment Notes Follow the procedure in the TLC experiment (linked to the syllabus page). The amount of solvent in the developing chamber depends on where you draw the baseline and spot your samples. Pay attention to your technique for spotting and placing the plate in the chamber – this is one experiment where you may need to start over!

Experiment Notes Carefully place the plate in the developing chamber, straight down so the solvent starts ascending the plate evenly (not at an angle). Remember to trace the solvent front with a pencil when you remove the chromatogram from the jar.

Experiment Notes Visualization of components – a different procedure The visualization chamber consists of a mixture of iodine (I2) and silica gel. Put the developed TLC in the visualization chamber & screw the lid tightly (2 plates in each jar is OK – back to back). Slowly oscillate the jar, making sure to coat the chromatogram with the mixture. Continue until dark spots appear. Take out the plate, shake off the silica-iodine from the surface & immediately outline the spots with a pencil.

Experiment Notes Be sure to accurately draw a picture of your developed chromatogram in your notebook (see procedure instructions). Give the developed chromatogram to me, with your name at the top.

Report for Next Week Fill in the Report Form Attach a photocopy of the drawing of the developed chromatogram from your notebook. more TBD

Weekly Clean-up Abdelmageed, Eman Choksi, Hemani J.