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