today we're gonna look at ozonolysis reactions and so if you're not familiar
with these check out my tutorial on ozonolysis, what we've got is some
substrate that will undergo ozonolysis and we need to draw the product
and then we've got the products of an ozonolysis reaction we want to draw the
reactant that they came from
so go ahead and give these a shot.
the thing we want to remember about ozonolysis is that ozonolysis will cleave double bonds and replace each
carbon that was participating in the double bond with a carbonyl so when
we're doing ozonolysis in the forward direction we have to identify any double bonds in this
case we've only got one of them so we're going to cleave that double bond
that's what's going to happen we're gonna pull it apart and each
carbon that was participating in the double bond will now be a carbonyl
carbon. that is what ozonolysis does. so in the forward direction
sometimes it can be useful to number your carbons just to make sure that you
dont lose or gain any carbons because that's not what is going to happen, we're
not adding or or losing any material, we are just transforming carbons that were in
a double bond into carbonyl carbons. so let's number of these 1, 2, 3, 4, 5, 6 now when we
write that out
we've got 1, 2, 3, 4, 5, 6 so we've got our six carbons now recall what we said, that
the carbons that were participating in the double bond now are carbonyl carbons
so carbon one we've drawn a carbonyl carbon 6 we've drawn a carbonyl and then
if there's anything else on the molecule, nothing has changed so that needs
to be drawn where it was, as it happens there was a methyl on carbon 3, so that
methyl on carbon three is still gonna be there so that's what's interesting about
doing ozonolysis on a cycloalkene
because instead of what we would expect, pulling it apart into two molecular
fragments we've actually just turned a cyclic molecule into a linear molecule
that's a very useful transformation
now let's take a look at these ozonolysis products that we have well if
ozonolysis takes the two carbons that were in the double bond and turns
them into carbonyls, if we're doing retrosynthetic analysis all we need to do is
take the two carbonyls and basically smash together so this is the
carbonyl carbon right there, this is the carbonyl carbon right there in the
forward direction these two carbons must have been participating in a double bond
with one another, because when ozonolysis cleaved that double bond, it
generated those two carbonyl carbons so let's draw, we can basically draw this
fragment right so here's the cyclohexane and then we'll call that carbon one and
then we'll call this 2, 3, 4, 5. what we can do we'll just take the cyclohexane as
rendered and that's going to be carbon one and then over here we can have 2, 3, 4, 5
now this is somewhat arbitrary we could have drawn that in the other direction
with the methyl there and ethyl there but the point is that carbon 1 and carbon 3
because carbons one and three are the carbonyl carbons in the product then
those must have been the carbons that were participating in a double bond with
one another in the reactant so that's why the double bond has to be between those
carbons. a very common error to do that correctly but then have the other carbon
material shift around in some way but that's why numbering the carbons is so
easy and so helpful because if we know that there's one and three and those have
a double bond then we know that three was also connected to two so it's gotta
still be connected to 2, 3 was also connected to four and five so it's gotta
still be connected to 4 and 5, this is the correct product of ozonolysis
and then given these products this was the correct reactant to produce those
in an ozonolysis reaction.
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