Leaving the Lab

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It is reasonable to leave the laboratory:

• If your reaction has been stirring at a constant temperature for one hour and is less than 25% complete
• If you have successfully run the reaction before and know it can be left safely
• If your reaction proceeds under mild conditions at room temperature and you have checked it twice by TLC

It is not reasonable to leave the laboratory:

• During time-sensitive steps (reaction, quench, and workup)
• In the middle of column chromatography
• If unstable compounds are not stored properly

Repercussions of leaving an experiment unattended:

• Solvent evaporated during refluxing due to a poor seal.
• Stirring stopped.
• Reaction became heterogeneous during slow addition, complicated mixing.
• Slow addition mechanism stopped, so reagent was not added to the flask properly.
• The desired reaction occurred cleanly, but then (a) a byproduct started to form, so the reaction appears to be nonselective (b) the product decomposed under the reaction conditions.
• Unwanted fluctuation of temperature
• You forgot to add a reagent or miscalculated, and no reaction occured at all. You could have corrected the problem, but you didn't notice in time.
• You don't know how long the reaction took.
• You don't know if the reagent was consumed at the same rate as the substrate, or if it just gradually decomposed on its own.
• You will not see the formation of intermediates, which can be an important indication of reaction progress.