2014_L8_PiBondsElectrophiles2

Ka gemdiols aka hydrates oh o c r1 chm1321 r2 h

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Unformatted text preview: water is amphipro(c: proton donor AND acceptor Brønsted Acid and Brønsted Base Lewis Acid and Lewis Base Electrophile and Nucleophile CHM1321 π bonds as electrophiles 16 •  hydra(on of carbonyls forms 1,1 ­geminal diols a.k.a. gem ­diols a.k.a. hydrates OH O C R1 CHM1321 R2 + H 2O π bonds as electrophiles C R1 OH R2 17 OH O C H H + H 2O C H OH H OH O C H 3C CHM1321 CH 3 + H 2O π bonds as electrophiles C H 3C OH CH 3 18 CHM1321 π bonds as electrophiles 19 CHM1321 π bonds as electrophiles 20 •  catalyst is not consumed in the overall reac(on •  addi(on of the catalyst accelerates BOTH the forward and reverse reac(ons equally “MICROSCOPIC REVERSIBILITY” •  has no effect on the overall final equilibrium posi(on •  base accelerates the reac(on by ac(va(ng the nucleophile •  acid accelerates the reac(on by ac(va(ng the electrophile CHM1321 π bonds as electrophiles 21 •  switching water with an alcohol yields hemi ­acetals OH O C R1 R2 + R 3OH C R1 R2 OR 3 •  usually, the equilibrium favours the reactants –  one excep(on… CHM1321 π bonds as electrophiles 22 •  the intramolecular reac(on to give a 5 or 6 membered ring: CHM1321 π bonds as electrophiles 23 •  sugars a.k.a. carbohydrates a.k.a. polyhydroxyaldehydes •  cycliza(on creates a new chiral centre = anomeric carbon •  the 2 resul(ng diastereoisomers are called ANOMERS CHM1321 π bonds as electrophiles 24 •  hemi ­acetals are reversible •  can be hydrolyzed back to the star(ng aldehyde CHM1321 π bonds as electrophiles 25 •  if we add two equivalents of ROH, we get an acetal OR 3 O C R1 R2 + 2 R 3OH C R1 R2 OR 3 •  forward reac(on is only possible with acid catalysis •  drive equilibrium forward by using excess alcohol and by removing the water formed (Dean ­Stark trap) CHM1321 π bonds as electrophiles 26 •  diols are oaen used as PROTECTING GROUPS •  added to temporarily protect carbonyl groups A A PG A CHM1321 B B C PG π bonds as electrophiles 27 O H CHM1321 ? O + Br H π bonds as electrophiles OH O H 28 •  imines and cyanohydrins CHM1321 π bonds as electrophiles 29...
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This note was uploaded on 03/12/2014 for the course CHM 1321 taught by Professor Flynn during the Spring '08 term at University of Ottawa.

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