[walter.white]

Can you tell me anyone how to use thin layer chromatography for check (monitoring) organic synthesis, I want to know that how many spot should to make in plate. example. during the synthesis of Nitrobenzene, how we must to spot reagents and which reagents (benzene or HNO3 or H2SO4 or all),and in synthesis of aspirine exmaple, and how to choose solvent for dissolve reagents and mixture of solvets for eluation

[Acadasol]

For reaction monitoring using TLC, you need to spot the starting material against the reaction mixture and a co-spot which has both the starting material and the reaction mixture. In your case, I will spot benzene against the reaction mixture. Since benzene is UV active. For the solvent, you need a less polar like hexane and a more polar like Ethyl acetate to make the mixture of the solvent for elation. I hope this help.

[kriggy]

Yeah, like acadasol said. I will just add that ou dont have to do the co-spot of starting material and reaction mixture IMO. For nitration just do benzene and mixture spot. The mobile phase you need to find out, hexane and EtAc mixture is good but you must experiment to find what works best. Idealy you want starting material to move just a little form the beggining while your product to move further away.

[TheUnassuming]

I think you might benefit from picking up Zubrick's Organic Lab Survival Manual.   It will teach you many of the basic techniques you will need throughout the synthetic process. 

[walter.white]

If we are synthesis a new compound (unknown), which substance should to spot in plate, example A + B = C, which substance shpuld to spot, examp;e if A is an aldehyde and B an amine,
 

[kriggy]

Both? Since if you test only one you are not sure which of the other spots is your product

[Babcock_Hall]

Sometimes the reactants or the products differ greatly in polarity.  I have sometimes found that to monitor one compound requires a different solvent system than to monitor another compound in the same reaction.

[walter.white]

ok, but my question is during the new compounds (synthesis) A + B = C,should I to spot A,B and C or only A with C or B with C, 

[Babcock_Hall]

Arguably the disappearance of A or B will be easier to monitor than the appearance of C, but it is somewhat situation-dependant.  I think one would need more information than you have supplied so far.  Which reagent is limiting, A or B?  Is one or both UV-active?  Do you have any chemical means at your disposal of detecting one of the reactants selectively?  There exist TLC sprays for many functional groups, including one or both of the ones you listed.

BTW I am a little bit lost.  Your first post seemed to be about the nitration of benzene, but you also mentioned an aldehyde and an amine.