- Today, we are gonna
talk about strategies
to ace the MCAT organic chemistry section.
Many students struggled with
organic chemistry in college
and assume that they need to know
all of the organic chemistry
they learned in undergrad
in order to succeed on the MCAT.
In addition, many students
who have taken practice exams
find themselves getting
tripped up by questions
that seem to require long mechanisms
or memorization of specific
details to answer correctly.
That sounds like you, you are not alone
and we are here to help.
(keys click)
(swooshes)
I'm Vikram Shaw, MCAT
expert and 528 scorer.
In this video, we'll go over
where you can expect to see
organic chemistry on the MCAT,
in addition to study
strategies you can use
to attack complex problems.
My goal for this video is for
you to walk away understanding
which topics are on the exam,
how to approach organic chemistry problems
you encounter on the exam,
and how to study your mistakes
so you can achieve your
best score on the MCAT.
Let's get started.
How much organic chemistry
is actually on the MCAT?
First, a little MCAT Ochem overview.
When you take the MCAT,
the exam is broken down
into four sections.
The first section tests you
on Chemistry and Physics
with 59 questions.
44 of these questions are passage-based
while 15 are standalone questions.
Organic chemistry falls into
this Chemistry and Physics,
or Chem/Phys section.
Even though you spent one or two semesters
studying organic chemistry in undergrad,
you will not likely see
as much organic chemistry
as you might expect on the actual exam.
So, let's break it down by the numbers:
According to the test makers at the AAMC,
Ochem will be about 15% of
your Chemistry/Physics section,
give or take 5%.
So, that means between 10 to 20%
of your MCAT Chemistry/Physics
section will focus on Ochem.
In other words, your
exam will likely contain
between six and 12 questions
discussing organic chemistry.
Since Chemistry/Physics is
only one of four sections,
organic chemistry plays
an even smaller role
in your overall score.
You may be surprised to find
out that organic chemistry
will actually be only about
three to 5% of your entire exam,
or six to 12 questions out
of 230 total questions.
Why do we mention this?
If you are studying on a time crunch,
you should prioritize
higher-yield material
over memorizing complicated
organic chemistry reactions.
Here, we will teach you how
to focus on the high-yield,
big picture material in order
to maximize both your score
and your time.
First, however, we will
cover a general overview
of the topics that they will
test you about on test day,
and then we will cover study strategies
you can use to answer difficult questions.
Students often wonder what
organic chemistry topics
will show up, so we've
broken it down for you here
into a few general topics.
The way the AAMC frames organic chemistry
in their MCAT content guide
is based on functional groups.
If we think way back to organic chemistry,
a functional group is an
important piece of a molecule
that is responsible for
the molecule's chemistry.
In other words, the
functional group tells us
how the molecule is going to behave.
Since functional groups
are the centerpiece
of how the AAMC talks about
organic chemistry on the test,
we will introduce the
topics you need to know
as individual functional groups,
and then dive into study
strategies you can use
to maximize your score on MCAT
organic chemistry questions.
The topics are:
Topic one: Aldehydes and ketones,
which includes carbohydrates;
Topic two: Alcohols;
Topic three: Carboxylic acids;
Topic four: Acid derivatives,
which include lipids;
Topic five: Phenols;
Topic six: Cyclic aromatic compounds.
In addition to these functional groups,
you should also be familiar
with experimental techniques,
such as the following:
Topic seven: Separations
and purifications;
Topic eight: Spectroscopy.
Now, let's look at study strategies
you can use to maximize your score.
MCAT Organic Chemistry
Strategy number one is simple:
know the structure of functional groups
like the back of your hand.
If someone asks you to draw an aldehyde,
it should be second nature.
You should have the same
level of memorization
of organic chemistry functional groups
as you do over amino acids.
So, you should know what the
following functional groups
look like at a bare minimum:
Carbonyl, Aldehyde,
Ketone, Acetal, Hemiacetal,
Imine, Enamine, Aldol,
Alcohol, Carboxylic acid,
Amide, Ester, Anhydride, and Phenol.
If you know the structure,
that will help you even more
with MCAT Organic Chemistry
Strategy number two:
Know the properties of functional groups
so that you can understand
how they will react.
Let's look at a commonly tested example:
the carboxylic acid functional group.
If you draw out the structure
of a carboxylic acid,
you will notice that
there are important parts
of the molecule that
contribute to how it reacts
with other molecules.
For example, the oxygen double
bonded to the central carbon
has some interesting properties.
What is more electronegative,
oxygen or carbon?
If you said oxygen, that is correct!
Oxygen wants electrons
a lot more than carbon.
So, the oxygen will pull
on those electrons harder,
causing it to have a
partial negative charge.
As a result, the carbon will then have
a partial positive charge.
Why is that important?
It is important because
this makes the carbon
a reactive atom now.
The carbon really wants electrons
due to its partial positive charge,
making it an electrophile,
or something that likes electrons.
And something with an
extra pair of electrons,
or a nucleophile, can
now attack the carbon
and engage in interesting chemistry.
Understanding these properties
for each functional group
that we just mentioned will help you solve
organic chemistry problems
without having to remember
specific and complicated
organic chemistry reactions.
Make sure to pay special attention
to understanding the
carbonyl functional group,
which is any carbon double
bonded to an oxygen,
and the properties we just talked about
as the MCAT loves to test students on it.
Now, let's look at MCAT
organic chemistry strategy number three:
Understand experimental techniques
commonly used in organic
chemistry such as separations,
purifications, and spectroscopy.
The MCAT will expect you to be familiar
with these basic organic chemistry tools,
and we'll walk through the
basics of each one here.
Before doing that, however,
I want to remind you
that anytime you miss an MCAT
organic chemistry question
while doing practice, be sure to go back
and review that question,
write down what you needed
to know, and study it.
And you shouldn't just do this
for practice organic chemistry questions,
you should do it for all
practice questions that you take.
Now, let's walk through
separations and purifications.
You will need to be
familiar with extractions,
distillation, and various
forms of chromatography.
What is the underlying goal
for these different approaches?
We want to separate two
or more chemical compounds
from one another, and we can use
the different properties of
the compounds to do this.
For example, let's look at extractions.
Think back to your organic chemistry lab
when you separated aqueous
and organic phases in a flask.
Why did you do this?
The goal was to separate
your compound of interest
from other compounds in the flask.
If your compound was two benzene rings,
would you expect it to be in
the aqueous or organic layer?
Remember, benzene is a six-carbon ring
with the double bonds.
In chemistry, like dissolves like.
The aqueous layer will dissolve molecules
that are similar to water,
meaning molecules that
are polar or hydrophilic.
The organic layer, on the other hand,
will dissolve molecules that
are nonpolar and hydrophobic.
Benzene does not have
any functional groups
that would make it
polar, and it is made up
of only nonpolar C-H bonds.
Therefore, we would expect to find benzene
in the organic layer.
Since we know that our
compound of interest
is in the organic layer, all we have to do
is collect the organic layer
in order to have a pure compound.
Next, distillation separates compounds
based on their boiling point,
and thinking back to general chemistry,
boiling point is determined
based on intermolecular forces.
Molecules with weaker
intermolecular forces
will have lower boiling points.
If we take another look
at benzene and water,
which most likely has
a lower boiling point?
Both molecules engage in
Var der Waals interactions,
and benzene will have some
hydrophobic interactions.
Water, however, can
engage in hydrogen bonding
and dipole-dipole interactions.
Therefore, benzene has
weaker intermolecular forces
and a lower boiling point.
Distillation will separate
these two compounds
based on those different boiling points.
Chromatography follows
a very similar logic:
we will use molecular interactions
to separate compounds.
Two common approaches
are gas chromatography
and liquid chromatography,
but the principle behind both is the same.
In chromatography, there are two phases:
a stationary phase that doesn't move
and a mobile phase that passes
through the stationary phase.
The stationary and mobile phase
have different chemical properties.
For example, the stationary
phase may be nonpolar
while the mobile phase is polar.
Let's say a polar molecule
was used as a sample.
The molecule would likely
travel more closely
with the polar mobile phase,
causing it to elute more
quickly in gas chromatography
or run higher on a paper
chromatography plate.
Now that we've broadly looked
at separations and purifications,
let's move on to our
final topic: spectroscopy.
You should be familiar with
both IR and NMR spectroscopy,
though you likely won't have to know them
at the same level of detail you did
in undergraduate organic chemistry.
IR spectroscopy is a
spectroscopic technique
that provides information
about the functional groups
present in a molecule.
It is often used to measure
the progress of a reaction
in organic chemistry.
The MCAT organic chemistry
section will expect you to know
two big peaks at a bare minimum.
The first is a narrow
peak at 1,700 wavenumbers
that indicates the presence
of a carbonyl group
while the second is a broad peak
between 3,100 and 37 wavenumbers
that indicates the
presence of an -OH group.
Let's look at a practice question:
A researcher performs an organic reaction
in which a benzene with
an alcohol substituent
turns into a benzene with
an aldehyde substituent.
Which of the following peaks
may appear for the product
in IR spectroscopy?
A, Broad, 3,500 wavenumbers;
B, Sharp, 3,500 wavenumbers;
C, Broad, 1,700 wavenumbers;
or D, Sharp, 1,700 wavenumbers.
The question is asking
for the product peak,
so we want to know what
would appear in a benzene
with an aldehyde substituent.
Thinking back to our functional groups,
what does an aldehyde contain?
If you said a carbonyl
group, you are correct.
Like I stated earlier, a
carbonyl group will show itself
as a narrow or sharp peak
at 1,700 wavenumbers,
so D is our correct
answer for this question.
Finally, MCAT organic
chemistry may ask you questions
about NMR spectroscopy,
which is a technique used to gain insight
into the chemical
composition of a molecule.
An NMR spectra is quite complex,
but thankfully the MCAT will not ask you
extremely complex questions about NMR.
Instead, you should be familiar
with benchmark numbers,
similar to IR.
Here are the numbers you
should be familiar with,
and each describes a shift
you would see on the graph
for a specific chemical bond:
Hydrogens on sp3 carbons: zero
to three parts per million;
Hydrogens on sp2 carbons:
4.6 to 6.0 parts per million;
Hydrogens on sp carbons: two
to three parts per million;
Aldehyde hydrogens: nine
to 10 parts per million;
Carboxylic acid hydrogens:
10.5 to 12 parts per million;
and Aromatic hydrogens: six
to 8.5 parts per million.
These are a brief introduction
to the high-yield organic chemistry topics
you will see on the MCAT,
and be sure to study any
additional Ochem topics
you see on official AAMC practice exams
in order to succeed on the MCAT.
By now, we have covered
the general overview
of MCAT organic chemistry,
and you have a toolbox of study strategies
to attack your practice problems
and increase your MCAT
Chemistry/Physics score.
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Thanks for watching and
we'll see you next time!
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