Simplifying MCAT Organic Chemistry

MCAT organic chemistry test prep

While Organic Chemistry makes up a smaller portion of the MCAT, understanding the distinctions between types of organic reactions is essential. This will outline several foundational strategies for tackling chemistry on the MCAT, without pure memorization. Having a strong comprehension of organic reactions will allow you to save valuable time on the test and narrow down your multiple-choice options.

Key Player Identification

Our first step when tackling an unfamiliar reaction with multiple reagents is to determine which component is the nucleophile versus electrophile.

Screen Shot 2022-06-01 at 11.06.22 AMA nucleophile will typically be an atom or molecule with a surplus of negative charge, namely an extra electron pair. This nucleophile is looking to attack a more electrophilic, or electron deficient, atom. Common electrophiles include those bonded to electronegative or electron-withdrawing groups or atoms participating in a dipole.

Movement of electrons

For the MCAT, it is essential to identify these two key players first, so that we can track the flow of electrons and eventually solve with our most stable configuration. I always found it helpful to draw an arrow from the nucleophile to the electrophile, showing the movement of electrons as the nucleophile “attacks” the electrophile with electrons. To remember this, I think that the nucleophile would love a nucleus or positive charge, so it gives its electrons to another atom. By giving away electrons, the nucleophile is less negative, therefore gaining positivity.

Screen Shot 2022-06-01 at 11.07.13 AM

In this simple SN2 reaction, we can see that the nucleophile, the carbon in the nitrile which has a negative charge, attacks the carbon attached to the electron-withdrawing bromine. It is helpful to track both electron movements separately, so you can ensure your answer contains the appropriate number of electrons (none are lost!). In blue, we have the carbon’s electrons attacking the bromoalkane and forming a new carbon-carbon bond. The electrons from the original carbon-bromine bond, move onto bromine giving it a full set of 8 electrons and a new negative charge. Don’t forget that in SN2 reactions, there is a backside attack so the stereochemistry reverses in the new bond formed by the attack. 

Once the major movement of electrons can be predicted, we want to establish what the most stable form will be. Electrons move to the most stable configuration and seek to balance charge differences, with a few exceptions. By keeping this in mind, you can eliminate answer choices that would not realistically occur and, of course, any that break the octet rule. 

There are, of course, a few reactions that you should know well as they occur frequently in biochemistry. These include the dehydration reactions and others involved in the citric acid cycle. On the exam, however, if you are pressed for time, you can use your deep understanding of electrophiles and nucleophiles to eliminate answer choices and find the most reasonable solution quickly!

Comments

topicTopics
academics study skills MCAT medical school admissions SAT college admissions expository writing strategy English MD/PhD admissions writing LSAT physics GMAT GRE chemistry biology math graduate admissions academic advice interview prep law school admissions ACT language learning test anxiety premed career advice MBA admissions personal statements homework help AP exams creative writing MD test prep study schedules computer science Common Application mathematics summer activities history secondary applications philosophy organic chemistry economics research supplements grammar 1L PSAT admissions coaching dental admissions law psychology statistics & probability legal studies ESL CARS PhD admissions SSAT covid-19 logic games reading comprehension calculus engineering USMLE mentorship Spanish parents Latin biochemistry case coaching verbal reasoning AMCAS DAT English literature STEM admissions advice excel medical school political science skills French Linguistics MBA coursework Tutoring Approaches academic integrity astrophysics chinese dental school gap year genetics letters of recommendation mechanical engineering units Anki DO Social Advocacy algebra art history artificial intelligence business careers cell biology classics data science diversity statement geometry kinematics linear algebra mental health presentations quantitative reasoning study abroad tech industry technical interviews time management work and activities 2L AAMC DMD IB exams ISEE MD/PhD programs Sentence Correction adjusting to college algorithms amino acids analysis essay athletics business skills cold emails fellowships finance first generation student functions graphing information sessions international students internships logic networking poetry proofs resume revising science social sciences software engineering trigonometry writer's block 3L Academic Interest EMT FlexMed Fourier Series Greek Health Professional Shortage Area Italian JD/MBA admissions Lagrange multipliers London MD vs PhD MMI Montessori National Health Service Corps Pythagorean Theorem Python Shakespeare Step 2 TMDSAS Taylor Series Truss Analysis Zoom acids and bases active learning architecture argumentative writing art art and design schools art portfolios bacteriology bibliographies biomedicine brain teaser burnout campus visits cantonese capacitors capital markets central limit theorem centrifugal force chem/phys chemical engineering chess chromatography class participation climate change clinical experience community service constitutional law consulting cover letters curriculum dementia demonstrated interest dimensional analysis distance learning econometrics electric engineering electricity and magnetism escape velocity evolution executive function freewriting genomics harmonics health policy history of medicine history of science hybrid vehicles hydrophobic effect ideal gas law immunology induction infinite institutional actions integrated reasoning intermolecular forces intern investing investment banking lab reports letter of continued interest linear maps mandarin chinese matrices mba medical physics meiosis microeconomics mitosis mnemonics music