[Unco]

Undergrad here doing research. I have been monitoring a reaction by tlc, taking one every 2 hours. Right now I have a TLC spot where it is UV active when the developing solvent (Ethyl Acetate) hasn't all evaporated off of the plate, but it is not UV active when the solvent is evaporated. The spot stains a dark pinkish color in anisaldehyde, and it only appeared in the crude and cospot lane (so it's not any of the starting material).

The question is: is the spot a valid spot? as in it's a spot that indicate a product is formed or it's nothing since it's not UV active once the solvent evaporated?

[kriggy]

Im not sure but it might be that it is some reaction intermediate that evaporates together with ethyl acetate?

[Dan]

Sounds like it's volatile. Maybe one of your reagents?

What's the reaction?

[siddy29]

I think kriggy is quite right but that would be true when your reaction is still in progress. You need to  find out the approximate time of the completion of your reaction. I am assuming it is quite long because you are taking TLCs after every two hours. If you are doing this reaction for the first time it would be wiser to take TLCs at shorter time intervals. Since, you are waiting for your product spot to appear, might I suggest noting colour changes or turbidity changes that may indicate product formation. When your product spot comes it will be definite so don't worry yourself over spots that don't remain on the card once it is dry. Hope this helps    

[Unco]

Thanks guys for the response. Unfortunately I can't tell you guys what the reaction is since my mentor plans to include it in his paper   but in the end i took an NMR of that thing after running a column on the crude and find that it's just another byproduct haha.