ok so let's look at this compound right here, we've got a compound with several
hydroxyl groups on it and now we're gonna see what happens when we use two
different oxidizing agents, so we have PCC in excess and KMnO4 in excess
and so if you're not sure what these do you may once again want to check out my
tutorial on oxidation-reduction in the organic chemistry playlist and try to
use that the differing levels of oxidative ability of
those two compounds to be able to draw the correct resulting products
ok so we're looking at these two oxidizing agents and we know that
oxidizing agents, if we're going to oxidize a carbon we're increasing the
number of bonds to oxygen that that carbon is participating in so we have a
couple of different hydroxyl groups attached to carbons that could
potentially be oxidized so let's compare PCC, pyridinium chlorochromate and
KMnO4, potassium permanganate, we have to understand that PCC is a weaker
oxidizing agent and potassium permanganate is a stronger oxidizing agent so let's
review really quickly what these do to different kinds of alcohols. PCC is gonna
take a primary alcohol and it oxidizes it only to the aldehyde level, it is not
gonna be able to go further than that
whereas potassium permanganate will take a primary alcohol and convert it to the
carboxylic acid functional group level. in terms of a secondary alcohol though
they will actually both do the same thing, they will generate a ketone and
then both of them for a tertiary alcohol there will be no reaction. now the reason
for the secondary and tertiary is as follows, it is easy for an oxidizing
agent to
to replace a carbon-hydrogen bond with a carbon-oxygen bond but for a secondary
alcohol like this one right here, so once again this is primary right this is
secondary and this is tertiary, that's the substitution at those centers
and so what we're looking at here for a primary or a primary position this is
gonna be no problem
PCC will take this to the aldehyde level right there whereas KMnO4
will take that to the carboxylic acid level as we just stated, and that's
because in a primary position there are two hydrogen atoms here and so KMnO4
is able to replace both of those carbon-hydrogen bonds with carbon
oxygen bonds over here there's one carbon-oxygen bond now there are three
carbon-oxygen bonds, and that's the maximum oxidative capacity at that
position and now if we're looking at a secondary position there is only one
hydrogen here there is one implied hydrogen and so there's only one carbon
hydrogen bond to replace with a carbon-oxygen so that is why regardless of the
strength both of these oxidizing agents are gonna bring that to the ketone
functional group level. so once again secondary alcohol is gonna go to ketone. now when we're
looking at a tertiary alcohol though if we're looking at a hydroxylated tertiary
carbon there is no hydrogen atom there, there is no carbon-hydrogen bond that can be
replaced with a carbon-oxygen bond in order to oxidize at that position we
would have to break a carbon-carbon bond which is much less favorable, it's much
less feasible so neither of these oxidizing agents have the capacity to
break a carbon-carbon bond and so that is why this position remains unchanged
and there is no oxidation taking place at that position
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