How To Prepare for the ACS Organic Chemistry Exam

If organic chemistry isn’t already difficult enough, many schools or professors add to the nightmare by offering the ACS exam in place of (or in addition to) your orgo final exam. The ACS exam is a standardized exam administered by professors who don’t want to write their own final or who seek a standardized means of testing.

If you ask my students, they’ll tell you that it’s like an Organic Chemistry SAT or ACT, created to torture you just a bit more before escaping what may very well be your most difficult undergraduate science course.

And if you’re not taking the ACS?
Well, this article still applies, even if your final exam contains only some multiple choice questions (or maybe none at all).

And regardless of who writes the exam, the ACS or your professor, having a proper strategy for tackling multiple choice questions will make finals week that much less stressful for you. 

Let’s face it. Multiple choice style questions are different and, dare I say, MORE difficult than open-ended reaction, mechanism, or synthesis type questions.

Before we delve into strategy, I strongly urge you to acquire the ACS Organic Chemistry Official Guide. Sooner rather than later. Buy it for practice throughout the semester, rather than for last minute exam review.

What is the ACS Exam for Organic Chemistry?

ACS stands for American Chemical Society. The ACS Examinations Institute creates nationally normed exams for chemistry courses, starting at the high school level and going through the entire undergraduate chemistry curriculum. What’s interesting is that their exams are created by committees of educators who actually (and currently) teach the course. 

Since this discussion is related to organic chemistry, I will focus solely on the ACS Organic Chemistry exam- what it contains and how to prepare for it.

Simply put, the ACS is a standardized test for organic chemistry: 

  • 70 Multiple Choice Questions
  • 110 minutes to complete (That’s less than 2 minutes, at just 1:34, per question!)
  • Tests you on 1 or 2 semesters of undergraduate level organic chemistry

Given the time constraints and sheer volume of information, this is a notoriously difficult exam with the national average (2016 data) at just over 36 / 70 questions. Most professors curve generously so that scoring <60 questions correct can still result in an A.

What is tested on the Orgo ACS Exam?

The ACS is a cumulative exam that will test you on everything you should have learned in the first semester (for Orgo 1 students) or both semesters (for Orgo 2 students). 

I say ‘should have’ because it’s a standardized test covering a standard curriculum.
Most of which your professor should have covered, some of which you may unfortunately have to learn on your own. 

This is just another reason to practice with the ACS guide, to ensure you catch every topic on the test regardless of what was actually taught in your ochem class. 

Some good news?
You are allowed a calculator.

While organic chemistry is mostly reactions and mechanisms, you are allowed to use a calculator on the ACS exam. 
Don’t worry. You may not even need it.
But just in case (optical activity?), have it handy for that one question that requires actual math.

Who takes the ACS Organic Chemistry final?

In working with thousands of orgo students for well over a decade, I typically see 20-40% of my students taking the ACS final exam.
Some students take the ACS exam AS their final exam.
Some professors make students take both the ACS and another written final exam.

What if you don’t know if you’ll be taking the ACS?
Some professors let you know on Day 1.
A small handful surprise their students with this information at the very last minute.

My advice? If your syllabus isn’t clear, ask.
Chances are, if you haven’t heard the term ACS, you’re not taking it.

But even if you’re NOT taking the ACS…

The strategies I share below apply to more than those who are taking this standardized test.
They apply to you if:

  1. You’re taking the ACS as your final exam.
  2. Your professor writes their own multiple choice exam or a mixed format exam, which includes multiple choice questions.
  3. You’re looking to improve your overall test-taking strategy, even for tests without MC questions.

Multiple choice exams, like the ACS, are exams that require you to think on your feet. You have to work quickly and efficiently, while still reasoning through difficult components of multi-step reactions and mechanisms.

In fact, I personally find Multiple Choice (MC) exams to be more difficult than freeform short or long answer exams.

My orgo 1 professor was notorious for his difficult exams, which included at least one or two 20 point multi-step synthesis/retrosynthesis questions.
For context, his school webpage had animated fireballs near his face, back in the early 2000’s when GIFs were not yet popular. 

And yes, despite the difficulty of the exam, partial credit was my friend.
I remember one retrosynthesis question that had at least 8 steps for completion. I had all of the molecules but one. I couldn’t recall that final intermediate.
Instead of leaving it blank and losing points for omission, I invented something that maybe, sorta, kinda could have worked (on another planet). My TA thought that I had made a careless mistake and gave me partial credit.
But between you and me, I had no freakin clue what I needed to reach the final product.

This type of confusion would result in an instant deduction on a multiple choice exam. Multiple choice is black and white- no maybes, no writing explanations for why you chose a certain answer, and no sympathy points or partial credit when you get it wrong.

There’s no wiggle room with multiple choice exams and no way to work around the unknowns. With MC style questions, you have to think EXACTLY how they want you to think.
You have to recognize tricky false answer choices.
And you can sometimes get paralyzed by 2 choices that look very similar. 

So how do you prepare for a multiple choice exam like the ACS?

The first step is understanding how this exam is different.

Say you studied the 3 step mechanism for the SN1 reaction that converts 2-bromo-2-methylpropane to 2-methyl-2-propanol (as taught in this video). 
In a free-response exam, you would start with the reactant, show the arrows that attack, draw every intermediate, and then give your final product.
Your exam is also timed accordingly so that, if you know the reaction, you have enough time to think through the mechanism and draw it all out.
Some professors will even give partial credit for incomplete or partially incorrect drawings.

A multiple choice exam may test you on the very same mechanism with a few key differences.
You’re only tested on one tiny component, a single detail on the reactant, reagent, intermediate, product, or even transition state.
You have limited time to think through the question and certainly no time to draw out the entire mechanism.
And the results are all or nothing.
You either get the question 100% correct or 100% incorrect.
No in-between.

The ACS is NOT a tricky exam.

Hang on… 
Before you x-out of this article in frustration, hear me out.

Yes, I 100% believe that this is a very difficult exam, made even more difficult by the sheer volume of questions and intense time constraints.
But in working with thousands of orgo students for well over a decade and hearing about their exams, I can confidently tell you that, while this is a difficult exam…
The questions themselves are rather straightforward.

Yes, you have to know a LOT of information.
You have to understand it very well.
And you can’t miss the nitty-gritty details.
But if you are well prepared, you will be able to quickly and efficiently work through the questions.
The only thing that could trip you up is lack of proper knowledge, rather than ‘These choices make no sense. How should I know what they want me to choose?”

So how do you study for this exam?

If you approach your MC exam like any other, you’re doomed from the start.
I aced History, Biology, even 3 years of Spanish with simple memorization and regurgitation. 

This doesn’t work for organic chemistry, and this definitely doesn’t work for the ACS.

Instead, you need to approach your studies from a logic-based perspective.
Instead of focusing on the ‘what’, keep asking yourself ‘why’ and ‘how’.
What is most reactive here?
Why do these electrons attack? 
How does this molecule break?

If you can understand the reasoning behind the facts, you will be able to reason your way through difficult questions, even ones that you may not have seen before.

Approaching the Exam on Test Day

Despite the time constraints, I urge you NOT to keep watching the clock. It’s both a distraction and panic-inducing. Instead, give yourself a simple timetable to follow.

With 70 questions in under 2 hours, you need to complete about 38 questions per hour. Let’s build in a slight buffer, and say you need to get through 40 questions per hour, or 10 questions every 15 minutes.

Glance at the clock after every 10 questions and see if you’re on track. 
If you’re moving too quickly, slow down.
We’ve already built in a (5 min) buffer by aiming for 10 questions in 15 minutes.
Make sure you give yourself enough time to actually read the information and reason through the questions.

If you realize you’re moving too slow, make a mental note to speed up and reevaluate your time after the second set of 10 questions.
Your timeline should look something like this: 

Triage. You can’t win em all.

For well-prepared students, the questions are fairly doable in the allotted time.
Until you get stuck.

It’s very easy to fall into the trap of “I need to get this right” and waste precious minutes trying to figure out an answer that you really don’t know.

Give yourself 30 seconds to triage each question.
Ask yourself, “Do I know where to go with this?”
If you feel that spending a few extra seconds will get you the answer, go for it.
But if after a minute, you’re still floundering, which makes you panic and causes you to blank out and waste even more time, was it worth it?

I’ll argue that it wasn’t.
You cannot afford to waste precious minutes on a question you probably won’t get right anyway.
ESPECIALLY if this costs you time that you could have spent on later, potentially EASIER questions.

If you get stuck, give yourself 30 seconds. Then cut your losses.
Don’t leave it blank though because you still have a 25% chance of guessing right.
(And an even higher chance if you follow my POE strategy below.)

Often, students will forget or blank out on a certain topic, only to remember it later on in the exam. Perhaps you forgot a key intermediate for Question 3, but then Question 47 happens to test a similar reaction that triggers your memory.

This forgetfulness is especially true for the early test questions when you’re still rusty and not quite ‘in the zone’ or firing on all cylinders. Once you start to build momentum, you may find that you have improved recall for details that you couldn’t remember at the start of the exam.

Leave time for this by moving past questions you cannot answer initially. Guess an answer. Then mark the question so you know where to come back later. 
And move on!

How to Tackle Multiple Choice Questions

Ever notice that it’s easier to find flaws in other people than it is to find flaws within ourselves?
I have my theories on the why, but perhaps another day.

Because this also works for MC questions, I find it easier to work backwards.
Instead of looking for the right answer, start by identifying and ruling out the incorrect choices.
It’s so much easier to spot what is wrong than to identify what is right.

First thing is the question itself.
Read the question. Look at the answer choices. Choose the right answer.
Actually no!

As soon as you start reviewing the answer choices, your mind will be influenced by what you see, rather than what you think.
So don’t give yourself that distraction!

Instead, read the question and COVER the answer choices.
Process the question, and consider an answer or direction.
If the question is lengthy or confusing, try to reword the question.
Use 5 words or less to consider what they are asking for.

Sometimes the questions are straightforward:
“What is the major product when 1-butene reacts with aqueous sulfuric acid?”

If you studied your alkene reactions, you’ll recognize this as an electrophilic alkene addition reaction that follows Markovnikov’s rule with 2-butanol as the final product.

For questions like this, think of the product first. THEN, look at the answer choices.

Sometimes the direction of the question is not as obvious. 
Take this ACS favorite: “Which of the following is NOT an intermediate in the reaction between…?

For example: “Which of the following is NOT an intermediate in the reaction between methane and chlorine gas at high temperature?”
There’s no way to predict the answer without looking at the choices.

In this case, I still urge you to hold off on looking at the answer choices until you at least have some idea of where the question is going.
You might think, “I know this is a radical halogenation reaction. That means the intermediates must be radicals.”

Now that we have a direction, we can look at the answer choices.

POE – Process Of Elimination

Instead of reading the question and looking for the right answer,
Only to get stuck between 2 similar choices and rip your hair out trying to pick one,
Use the POE approach.

Remember how we’re better at finding flaws? Let’s look for the answer choices that we can very obviously rule out.

This is where I like to look for clues.

In our alkene addition reaction example, we may know the exact product. 
But we can simplify the approach.
First, I know the answer must have one alcohol group.
Rule out all answer choices that have zero or more than one OH group.

Next, I know the answer follows Markovnikov’s rule.
Rule out all choices that have the OH at the wrong position.

This approach works just as well for the radical question. 
Giving you enough information to eliminate 2-3 incorrect choices.

When a question specifies ‘not an intermediate’, I flip the question in my brain.

“Which of the following IS an intermediate?”
And I rule those out.
This leaves me with ONLY the incorrect choice as my correct answer.

With our question above,
I know that every intermediate has a radical.
I expect a Cl radical – rule that choice out.
I expect a methane radical – rule that choice out.

Once you’re down to 2 choices.

Sometimes the obvious eliminations only bring you down to 2 or 3 choices.
When this happens, do a direct comparison.

What’s the difference between choices B and D?
Forget the rest. Forget the similarities.
Instead, zoom in on the specific difference. 
Compare them side-by-side.
And see which one answers your question.

It’s a numbers game.
Having 4 answer choices gives you a 25% chance of guessing the right answer.
Rule out an obvious wrong choice, and you’re up to 33%.
Narrow it down to the final 2, and now you’re at 50%.

It’s easier to dissect 2 choices than 4.
And if you’re completely stuck on those 2, 
At least you still have better odds of guessing.

If you’re really stuck, guess and move on.
Triage. Remember?
Don’t waste an extra few minutes that could be spent answering the final 3 potentially easier questions.

Looking for more in-depth organic chemistry final exam practice? Practice that includes questions, solutions, but most importantly gives step-by-step instructions on how to think about and process questions for your final exam?

This is exactly what my Orgo Final Exam packs are all about. Each one features multiple choice questions, short and long answer questions, solutions and step-by-step video explanations.
Details Here: Organic Chemistry Final Exam Pack

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