The main reaction section of your prelab should show the two general
chemical equations (using R groups) for the reactions you will carry out.
There is no need to write the specific reaction in the prelab for each
alkyl halide. However, you should know what the products that formed are
in each case where there was a reaction, and be prepared to write
reactions after the lab is finished for all those alkyl halides that did
react. For your prelab you should prepare a table that shows the
structure of the alkyl halides, pertinent physical properties and hazards,
and provides columns (separately for the SN1 and SN2 tests) in which you
will record your time data and observations once you actually run the
reactions.
Occasionally we substitute one or two different alkyl halides for some of
the ones specified in the lab manual for this experiment, or omit one or
two. Check the organic dispensing hood to see which alkyl halides we will
actually be using. Also, note the important difference between a phenyl
halide and a benzyl halide. Take care to use the names and structures
correctly.
When you are actually conducting the experiment you should be able to run
several reactions simultaneously. When dispensing the sodium iodide in
acetone or silver nitrate in ethanol solutions into your test tubes,
measure the volume needed for one reaction in the first of your test tubes
and simply estimate the volume needed in each of the other tubes. In
other words, set up a series of test tubes and dispense the test reagents
into each one.
Add the appropriate alkyl halide to each one, noting the time each is
added and the length of time for a reaction to occur (if it does). Upon
adding the appropriate alkyl halide to each tube, be sure to mix the
reaction well by flicking the bottom of the test tube as you hold it
firmly in your fingers. (DO NOT STOPPER THE TEST TUBES OR COVER THEM WITH
YOUR FINGER IN ORDER TO INVERT THEM FOR MIXING. Always consider a stopper
or cap a source of potential leakage and contamination unless you have
taken precautions against these things. DO NOT USE PARAFILM IN SITUATIONS
WHERE THE PARAFILM COULD ENCOUNTER ORGANIC LIQUIDS OR VAPORS.) Place
those tubes that didn't react at room temperature in the appropriate
higher temperature water bath.
After you have run all of the reactions and recorded your data, explain
why each alkyl halide behaved as it did under each set of reaction
conditions. Consider variables such as substrate structure, nature of the
leaving group, nature of the nucleophile, solvent, temperature, and any
other pertinent factors.
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Craig B. Fryhle, Ph.D. Office 206-535-8314 FAX 206-536-5055
Associate Professor Email fryhle@u.washington.edu
Department of Chemistry URL http://rainier.chem.plu.edu/fryhle.html
Pacific Lutheran University
Tacoma, Washington 98447 ^ ^ ^ ^ ^ ^
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