Hi. I\'m going through the mechanism for the thiamine HCl catalyzedcondensation

Question

Hi. I'm going through the mechanism for the thiamine HCl catalyzedcondensation of benzaldehyde to benzoin and have run into aproblem. After thiamine attaches to the first benzaldehyde moleculeit undergoes an intramolecular proton transfer from the carbonylcarbon to oxygen. The rationale for this transfer and the resultingnegative charge on carbon is that resonance structures can bedrawn. I don't have a problem drawing the resonance structureresulting from the flow of electrons onto the thiamine ring but I'mhaving problems drawing the second structure. Can someone help?I've attached a drawing. Thanks! http://i39.tinypic.com/9ktnd0.jpg Hi. I'm going through the mechanism for the thiamine HCl catalyzedcondensation of benzaldehyde to benzoin and have run into aproblem. After thiamine attaches to the first benzaldehyde moleculeit undergoes an intramolecular proton transfer from the carbonylcarbon to oxygen. The rationale for this transfer and the resultingnegative charge on carbon is that resonance structures can bedrawn. I don't have a problem drawing the resonance structureresulting from the flow of electrons onto the thiamine ring but I'mhaving problems drawing the second structure. Can someone help?I've attached a drawing. Thanks! http://i39.tinypic.com/9ktnd0.jpg

Explanation / Answer

http://www.rutchem.rutgers.edu/discus/messages/26/Benzoin_Condensation_Lecture_Outline-1373.pdf go to page 2 for mechanism

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