Keto-enol Tautomerism under basic conditions – Part 2

Keto-enol Tautomerism under basic conditions – Part 2

October 24, 2019 0 By William Morgan


Hello good people. I would like to give
an alternative reaction mechanism to
keto-enol tautomerization under basic
conditions. And it is quite possible that
this reaction mechanism here is somewhat easier to follow and understand.
Aright. The principles remain the same. We are
simply going to push electrons a little
bit differently. So, the lone pair
electrons of the base will be attracted
to the alpha hydrogen. So, recall this is
our alpha carbon, and this is our alpha
hydrogen. The electrons that were between
the alpha hydrogen and alpha carbon will
form a pi bond between carbon two, pardon me,
between carbon 2 and 3. And the pi
electrons between carbon 2 and the
oxygen will end up on the oxygen. So, we
will get a water molecule and this
particular anion here. What is the next
step?
Remember we are still going towards our
enol form. So, we need to form the alcohol.
Ok. The lone pair electrons of the
negatively charged oxygen will be
attracted to the hydrogen on the water
molecule. And the electrons between the
hydrogen and the oxygen on the water
molecule will end up on the oxygen. And
so we will get our enol. So, we have a
double bond between carbon number 2 and carbon number 3, and the carbon number 2
is also attached to an alcohol
functional group. Alright. Now we need
to go back, back to the keto form. So, what will happen? Well,
pardon me, the lone pair electrons of the
base will be attracted to this hydrogen
here on the alcohol. And the electrons
that were the bond between the hydrogen
on the alcohol and the oxygen will end
up on the oxygen again, which will bring
us back to a water molecule and our
anion. So, what is the final step? Well, we
are trying to get to the ketone.
So, these oxy … No, not these oxygens, pardon me. These
lone pair electrons on the oxygen, on the
negatively charged oxygen, will end up
between the oxygen and carbon number 2,
while the pi bond electrons between
carbon 2 and 3 will be attracted
to the hydrogen on the water molecule.
And finally the electrons between the
hydrogen and the oxygen of the water
molecule will end up on the oxygen. And
that will bring us back to the beginning
where once again we have our ketone and
we have our hydroxide, our base. That is
all for now, and I will see you on the
flip side.