Question

These questions are from The Wittig Reaction: Chemiluminescence.

1. Predict the order of elution of a mixture of 9-anthraldehyde and (E)-9-(2-phenylethenyl)-anthracene on a TLC plate using a 5:1 hexanes/ethyl acetate eluent mixture.

2. How do you predict that cooling and warming your chemiluminescence reaction mixture after initial mixing will affect the reaction?

3. A glow stick contains: a dye molecule, an oxalate ester, and hydrogen peroxide. Two of these components have to be separated until it is time to use the glow stick. Which two components need to be kept separate prior to use? Why?

Answer 1

1. Of the two given compounds, 9-anthraldehyde is a highly polar moiety due to the aldehyde functional group while the other moiety, being purely an aromatic hydrocarbon with extensive conjugation is a relatively very non-polar, fluorescent molecule. Thus, if a 5:1 solution of ethyl acetate in hexanes is used as the eluent, it is likely that the fluorescent hydrocarbon goes towards the top of the TLC plate, being more non-polar while the aldehyde stays near the bottom with a lower retention factor. But, due to the highly non-polar anthracene attached to the aldehyde, like benzaldehyde, it will have relatively high retention factor. Thus, approximately, the hydrocarbon will elute to the top of the TLC while the aldehyde is found below it. A possible Rf value difference between the two will range between 0.2-0.4.