OAT General Chemistry and Organic Chemistry Study Guide

The Survey of the Natural Sciences on the Optometry Admission Test (OAT) gives you 30 general chemistry questions and 30 organic chemistry questions back to back, with no calculator. General chemistry rewards mental math fluency and instant stoichiometry and gas law setups. Organic chemistry rewards pattern recognition over memorization: only about 30% of the subtest is individual reaction recall. Here is the high-yield map and drill strategy for both.

Questions 41 through 70 are general chemistry and 71 through 100 are organic chemistry, always in that order. With about 54 seconds per question across the section, chemistry is where your time budget on the Optometry Admission Test lives or dies, because biology runs fast and chemistry does not. This guide covers what to study, how to drill it, and how to pace it. For the biology half of the section, see our OAT biology review.

Where Chemistry Sits in the SNS

The Survey of the Natural Sciences is 100 questions in 90 minutes: 40 biology, 30 general chemistry, 30 organic chemistry. There is no calculator anywhere in this section. The only on-screen calculator on the entire Optometry Admission Test appears in Quantitative Reasoning, which is a different skill set covered in our QR guide.

That one fact shapes everything about how you should train. You are not just learning chemistry. You are learning to do chemistry arithmetic in your head, at speed, under pressure.

General Chemistry: No Calculator, No Excuses

Mental math fluency is tested directly in this subtest. Two skill clusters must be fully automatic:

• Stoichiometry. Mole conversions, limiting reagents, and percent yield should be reflexes, not puzzles. If setting up a proportion takes you 30 seconds, the section owns you.
• Gas laws. PV=nRT and the combined gas law show up constantly. Watch unit consistency: pressure units, volume units, and temperature in Kelvin. Unit errors are the most common way students lose easy points here.

Build the fluency with short daily sets, not marathon sessions. Ten mental-math chemistry problems a day for a month beats a single five-hour weekend grind.

General Chemistry High-Yield Topics

The official general chemistry topic list, with what to prioritize:

• Stoichiometry and general concepts: Mole conversions, limiting reagents, percent yield, density.
• Gases, liquids, solids: PV=nRT, combined gas law, unit consistency.
• Solutions: Molarity, molality, dilution calculations.
• Acids and bases: pH and pOH, strong vs. weak, buffer basics.
• Chemical equilibria: Equilibrium expressions, Le Chatelier's principle.
• Thermodynamics and thermochemistry: Enthalpy, calorimetry, endothermic vs. exothermic.
• Kinetics: Rate laws, reaction order, activation energy.
• Oxidation-reduction: Balancing redox, oxidation numbers, electrochemistry basics.
• Atomic and molecular structure: Electron configuration, bonding, geometry.
• Periodic properties: Trends in size, ionization energy, electronegativity.
• Nuclear reactions: Balancing nuclear equations, decay types.
• Laboratory techniques: Common glassware, separations, safety.

The General Chemistry Problem-Solving Discipline

The highest-leverage habit in general chemistry is identifying the problem type before picking an equation. Read the question, name the type (dilution, gas law, equilibrium shift), and only then reach for a formula. Students who grab equations first waste time solving the wrong problem.

Students consistently report that real-exam calculations are often simpler than practice material. The skill being tested is setup under pressure, not arithmetic heroics. Videos first, then immediate problem sets: watch one concept, drill it the same hour.

Finally, every question is worth the same. Make educated guesses on time-sink questions, mark them, and return if time allows. Two correct two-minute answers beat one three-minute answer.

Organic Chemistry: Pattern Recognition Over Memorization

Organic chemistry has a reputation for endless memorization that the exam does not actually deserve. Only about 30% of the subtest is individual reaction recall, and named reactions are a small fraction of that. The rest is concepts applied to molecules you have never seen: stability rankings, mechanism logic, and spectroscopy.

So train your eye, not just your memory. When you see a new molecule, you should immediately scan for the same features every time: functional groups, resonance options, stereocenters, leaving groups. That scan is the pattern, and it is learnable in weeks.

Organic Chemistry High-Yield Conceptual Topics

These are the conceptual items students consistently under-train:

• Aromaticity. Count the pi electrons, check the ring rules.
• Resonance. Draw the contributors, rank their stability.
• Carbocation and radical stability. Substitution patterns and resonance effects.
• Acidity rankings. Know what stabilizes the conjugate base.
• Leaving-group quality. Weak bases leave; everything follows from that.
• Stereochemistry. R/S configuration, E/Z alkene geometry, and spotting meso compounds.
• Spectroscopy. IR stretch regions plus C-NMR and H-NMR interpretation: how many signals, what the shifts suggest.

The Mechanisms That Matter

Deep arrow-pushing is rarely required on the Optometry Admission Test, but you must know the core mechanisms cold: what starts them, what intermediate forms, what conditions favor them, and what product results.

• SN1: Favored by stable carbocation and weak nucleophile. Classic trap: carbocation rearrangements.
• SN2: Favored by strong nucleophile, unhindered carbon. Classic trap: backside attack inverts configuration.
• E1: Conditions similar to SN1. Classic trap: competes with SN1 for the same substrate.
• E2: Favored by strong base. Classic trap: Zaitsev product vs. bulky-base exception.
• Radical halogenation: Favored by light or heat initiation. Classic trap: radical stability drives selectivity.
• Addition reactions: Favored by alkenes and alkynes. Classic trap: Markovnikov vs. anti-Markovnikov orientation.

Know the reagents and products for the standard named reactions, but do not burn weeks memorizing exotic transformations. The exam rewards the fundamentals executed fast.

The Reaction Sheet Drill Method

The organic chemistry drill that students praise most:

1. Run reaction sheets forward. Starting material plus reagent, predict the product.
2. Run them backward. Blank the reagent and fill it in from the starting material and product. Backward fluency is what synthesis-style questions test.
3. Convert to flashcards. Every reaction you miss becomes a card. Space the deck across weeks.

Ten minutes of reaction sheets daily beats three hours on Sunday. Repetition across the whole study window is what makes recognition instant on test day.

The June 2026 Organic Chemistry Spec Update

An organic chemistry specification update is anticipated in June 2026. This is not a major content change: it introduces simpler, more intuitive topic names and a more comprehensive subtopic list, organized around mechanisms, combined mechanisms, reaction coordinate diagrams, and one-step reactions.

The content itself is stable, so your preparation does not change. Just confirm your materials reference the specifications in effect on your test date. We break down exactly what changed and what did not in our guide to the OAT organic chemistry changes.

Our Recommendation

General chemistry is a speed exam in disguise: automate stoichiometry and gas laws, identify problem types fast, and guess smart on time sinks. Organic chemistry is a pattern exam: drill the conceptual rankings and run reaction sheets forward and backward until recognition is instant. Two skills, two drills, one combined score that carries your Total Science. A prep platform with detailed explanations and adaptive quizzes can speed up the pattern recognition, but the real work is just daily reps with a whiteboard and a stopwatch.

That is the entire game.