Let’s assign the NMR splittings and I have an analogy that I call a story of
balconies. Here you have the molecule of 1-propanol that is the structure
inside of the rectangle. Here you will have four different proton signals in
the proton NMR. This OH is an exchangeable proton. It is an exchangeable
because in the presence of deuterated water it can become an OD group
instead of an OH. That is why it’s called an exchangeable. We’re going to
represent here this CH3 group represents that balcony. This CH2 group here
represents the balcony in the middle and this other CH2 group represents this
balcony and the OH group will represent that balcony on the right side. In each
of these balconies we’re going to represent the protons as people and
then you will see that they look like neighbors. In the first balcony we’re
going to have a family of three represented by the CH3. Here’s the
dad, tall guy, here’s the mom and they have a son. In the second balcony we have
a couple of newlyweds. They are two husband and wife. The next family is a
single mother and a daughter. The mom is saying hi to the family on the far left
balcony and the daughter knows the little kid because they go to school
together and they know each other. On the right side we have a big dude. He is
rich. He has his own suite. These buildings are joined by a wall but they
are not really connected. There are no doors or passages to get to from one
building to another. This guy on the right side is rich. He is well fed. He is
really round and big. I say this to remind me that he looks like the OH
group. He is lonely though. He is completely detached from the neighbors and
that is due to the long pair of electrons that the oxygen have that make this
isolation happen. The family on the far left will integrate to three. The
newlyweds will integrate to two protons because they represent two people. The
mother and the daughter will also integrate to two and the rich man
represents one person. Thus it will integrate for one proton. He is by
himself. He is alone. That will be the integration. That is how these signals
will be integrated. Three to two to two to one (3:2:2:1). That is the ratio that you will
see when you have the spectrum. The splitings that you will have is that the
family of three will have two neighbors. The newlyweds in the middle will have a
total of five neighbors. The mother and the daughter only have the newlyweds
next to them. So they will only have two neighbors and the rich man has zero
neighbors. He is isolated. If we apply the n+1 rule we know that these two
neighbors will add one. Two plus one then the five neighbors will add one and the
two neighbors will also add one. The OH again will be isolated. The splitting
nowl will be a triplet for the first family. The newlyweds will have a
signal called a sextet because five plus one is equals to six and the next
family will also have a triplet because they will also be two plus one. The OH
will show as a broad singlet and it will look something like this. What we will
see in the proton NMR is the following. We will have a triplet for this first
signal that will integrate to three hydrogens. The signal for the newlyweds
will be a sextet and we will have one two three four five and six. This signal
will integrate to two hydrogens. That represents their signal. Think of it as
their signature. Then the triplet for the mother and daughter will have also three
peaks but it will be different from the first triplet because it will integrate
to two hydrogens. Then the rich man will be represented as a broad singlet that
will integrate to one hydrogen.
