[Kkosakow]

Frequently, published protocols list "overnight" as a time period for running a reaction or letting something precipitate, etc. and I always use it in my personal lab notebook, but I was wondering whether this term correlates to a quantifiable length of time.

Let's say a scientist sets up an experiment before they leave for the day, and quench it first thing in the morning--this time frame varies dramatically between individuals. Perhaps it is the classic 9:00AM-5:00PM schedule, or perhaps it is more similar to my own 7:00AM-4:00PM/7:00PM-11:00PM. Or even if said reaction were set up at lunch time and left it to be worked up te following day at the noon hour as well, this qualifies as overnight as well.

I understand that the time period can be clarified through experimentation: if a reaction is woefully incomplete post work up, I could just leave it for longer next time, and deduce through iteration. However, a window of time-expectation for this lab lingo would be tremendously appreciated! What do you consider to be overnight? And when you see overnight written in a procedure, what do you take this to mean in your own attempts?

Thank you for reading!

[orgopete]

I don't consider overnight to be very significant, except that it may reflect how the reaction was actually performed. If I set up three similar reactions that I knew would be virtually complete in 10 minutes, but I used my time to set up the other reactions, I might simply let them stir "overnight" and work them up the next morning. You might anticipate how I might be creating a sequence in which I again will not have run my reaction early in the day and another overnight.

There are many reactions that result in good yields and high purity, and may have a description of "overnight" associated with them. If I repeated that reaction, my instincts are to run it overnight. This would simply indicate that I was lazy.

Question: if a reaction is 50 percent complete after 12 hrs, how long might it take to be 90 percent complete? If a reaction is 100 percent complete "overnight", how long would it take to reach 50 percent?

[Dan]

However, a window of time-expectation for this lab lingo would be tremendously appreciated! What do you consider to be overnight?

I take it to mean that the reaction completes within 12-18 h, and that the product is stable under the reaction conditions (i.e. it can be left for an unnecessarily long period without complications).

And when you see overnight written in a procedure, what do you take this to mean in your own attempts?

It varies depending on the reaction. If, based on my own experience with similar reactions, I expect it to take >12 h, I will just set it up last thing in the evening. That way I can use the hood space for other reactions during the day.

If I am in a situation where I have the space to spare, or it is a reaction I suspect will actually complete within 6 h, I will set it up during the day and monitor the reaction to get a more accurate idea of how long it actually takes. I recently ran a Sonogashira reaction with a reported reaction time of 3 days at elevated temperature - I was skeptical, and set it up after lunch. It was complete when I ran the first TLC at 45 minutes.

My opinion is that if you can spare the space, set up an "overnight" reaction in the morning. If you end up having to leave it 24 h, it shouldn't be detrimental, but if it's actually complete quite quickly this is useful information in terms of organizing your time if you come to repeat the experiment.

[Corribus]

with a reported reaction time of 3 days at elevated temperature

I.e., they set it up on Friday evening and came back in on Monday.

We used to do cross-coupling rxns "overnight" all the time. When it came to reporting procedures in manuscripts, we reported the actual time of reaction (14 h or some such). This is consistent with my view on experimental sections, which should be a description of what you did, not what is the best way to do it.

[siddy29]

Overnight seems like a vague term if you are performing a synthesis. If it is using for drying or creation of layers during solvent extraction, it maybe acceptable. They really should mention time otherwise we just have to improvise based on the progress of our own reaction.