8B-handout-jan16-key - because it is not available to grab...

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8B Handout key, jan 16 Draw the conjugate base for cyclohexanol and phenol and explain which is more acidic. The phenol is more acidic because the conjugate base of the phenol has an anion that is more stable, delocalized with resonance stabilization. The cyclohexanol anion is not delocalized, so it is less stable, making the anion a strong base, and the alcohol a weaker acid. Practice problems: a) Which nitrogen in imidazole is the most basic? Imidazole is aromatic. Nitrogen B is the most basic because it has a lone pair that is more available to grab a proton (this nitrogen is like pyridine) Nitrogen A has a lone pair that is part of the aromatic pi system (this nitrogen is like pyrrole). b) Which nitrogen in purine is the least basic? Only one of the nitrogens has lone pair electrons that are part of the pi-system (this nitrogen is like pyrrole), this nitrogen (indicated with the arrow) is the least basic
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Unformatted text preview: because it is not available to grab a proton. All of the other nitrogens are like pyridine and they are sticking out and available to grab a proton. c) Which of the OH groups in this molecule (show at the right) is more acidic? Draw the conjugate base (that will result if only one OH group is deprotonated). t he oxygen that is directly attached to the benzene ring is more acidic because the anion will be stabilized by resonance delocalization (you can draw resonance structures with the negative charge spread out in the ring) d) Explain why nitro-phenol is more acidic than phenol. Draw the conjugate base for each molecule. See scanned lecture notes for answer. OH N O O OH nitro-phenol phenol OH phenol OH cyclohexanol conjugate base conjugate base O O N NH imidazole A B N N N H N purine HO OH O OH...
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This note was uploaded on 03/12/2009 for the course CHE 8B taught by Professor Lievens during the Winter '07 term at UC Davis.

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