Question

5. Molecules with an-OH group directly bonded to a C-C sp hybridized carbon are called "enol"'s. The types of chemical reactions which enols undergo are substantially different from those of normal alcohols. By considering the Brensted-Lowry and Lewis acid/base reactivity of an enol, you can predict a few of these differences. (a) Ethenol, the simplest "enol", can react as a BL. base in three different places, by gaining a proton at either of the two carbons or on the oxygen. Draw all three possible BL acid/base reactions, including the "arrow-pushing" mechanism for each, between ethenol and HCI. Draw all non-three-strikes RS's for each conjugate acid. (9 points) (b) Which of the conjugate acids you drew above is the most stable? Why? (2 points) (c) Enols rapidly undergo a process called "tautomerization" in the presence of acid, by which they are converted to isomeric carbonyl compounds. For example, ethenol is rapidly converted ethanal in aqueous acid by two successive BL acid/base reactions, the first of which is one of the reactions you drew in part (a). Using the most stable conjugate acid from part (a), draw a second BL acid/base reaction in which that conjugate acid loses a proton (using Cl as a BL base) to become ethanal. (3 points) (d) Ethenol can also potentially react as a BL acid by donating a proton from any one of the three atoms- either carbon or the oxygen - but one of these is a clear "winner". Draw the electron- pushing mechanism of a BL reaction between ethenol and a genera BL base B:, and draw resonance structures of the conjugate base of ethenol. (6 points) H.

just need (e) to (h)

Answer 1

5 e)

Ethenol is more acidic than ethanol because upon treatment with an alkali ethenol forms enolate anion which stabilized by resonance (resonance hybrid of two structures I and II given below).

On the other hand, ethanol does not have suitable resonance structures to stabilize it

и ои,

c h-cho- tho Ch-ch-0-11 tou

f)

1 c -

g)

Nuc + NuL

h)

но и сси — Фо, и и о