Mcat Functional Groups

This can be accomplished in several ways. Generally, chemists turn hydroxyl groups into ketones or aldehydes that become ketals/hemiketals or acetals/hemiacetals. Additionally, hydroxyl groups can be converted into functional groups that are better leaving groups. Mesylate and tosylate reactions convert hydroxyl groups into mesylates or tosylates, which are good leaving groups. These reactions help facilitate substitution or elimination reactions in which an alcohol must be eliminated.

MCAT Mnemonics: 5, 10, 15, 20 Rule

Ken Tao is the MedSchoolCoach expert on MCAT, and will discuss the organic functional groups which are what we call the 5, 10, 15, 20 rule. You’ll learn, specifically, about the pKa of Carboxylic Acid, Phenol, Alcohol, and Alpha Hydrogen used in organic chemistry.

Full Transcription

Welcome back to another episode of MCAT Mnemonic Monday. My name is Ken and I’m an expert with MedSchoolCoach. Today we have an organic chemistry mnemonic for you and it’s on the organic acid functional groups and their pKas. It’s what we call the 5, 10, 15, 20 rule. For the MCAT, you need to know the 4 organic acid functional groups. These are the carboxylic acid, phenol, alcohol, and alpha hydrogen from carbonates. What the 5, 10, 15, 20 rule describes is the pKas of these four organic acid functions.

Remember, pKa is inversely proportional to acidity. So that means the lower the pKa, the more acidic the functional group. So the way the world works is that carboxylic acids have a pKa of about 5. Phenols have a pKa of about 10. Alcohols have a pKa of about 15. And alpha hydrogens off of carbon fuels have a pKa of about 20. That’s it for the mnemonic. And it will be very helpful for you on the MCAT exam.

Ken Tao

Ken is nationally recognized as a premier MCAT mind. He has worked with thousands of undergraduate students as a graduate teaching assistant and MCAT instructor/tutor for the Princeton Review. At Princeton Review, Ken was the only tutor certified in all subjects, was one of the highest rated MCAT tutors ever and was a teacher trainer. Additionally, Ken worked to found Magoosh’s MCAT division. He has written content for dozen’s of MCAT books and guides. He is now the Director of MCAT at MedSchoolCoach

Important Functional Groups for the MCAT: Everything You Need to Know

Learn key MCAT concepts about important functional groups, plus practice questions and answers

(Note: This guide is part of our MCAT Organic Chemistry series.)

Table of Contents

Part 1: Introduction to functional groups

Part 2: Oxygen-containing groups

a) Alcohols

b) Aldehydes and ketones

c) Carboxylic acids

d) Carboxylic acid derivatives

Part 3: Nitrogen-containing groups

a) Amides and amines

b) Imines, and enamines

c) Cyanohydrins

Part 4: Hydrocarbon functional groups

a) Hydrocarbons

b) Amino acid side chains
c) Aromatic compounds

Part 5: Passage-based questions and answers

Part 6: Standalone questions and answers

Part 1: Introduction to functional groups

To gain an understanding of organic chemistry, one must first gain an understanding of functional groups. After all, organic chemistry is all about the study of how molecules interact, and functional groups are collections of atoms that confer certain chemical properties to the molecule.

The sheer variety of functional groups can be overwhelming, but don’t worry if you aren’t familiar with them yet! This guide will review the major functional groups covered on the MCAT. As you work through the guide, it will be most helpful to determine if these functional groups are electrophilic or nucleophilic. (For a review of the function of electrophiles and nucleophiles, be sure to refer to our guide on the fundamentals of organic chemistry.) While the MCAT will rarely test you on nomenclature and molecular structure, general trends in electrophilicity, nucleophilicity, and electronegativity will be the most important information to retain for test day.

At the end of this guide, there are also several AAMC-style practice questions for you to test your knowledge against.

Let’s get started!

Part 2: Oxygen-containing groups

a) Alcohols

Alcohols are molecules that contain a hydroxyl group, or -OH.

There are quite a few important properties that alcoholic functional groups have. One of the most interesting properties is their acidity. Alcohols can serve as weak Bronsted acids, with a pKa between 15 and 20. Though they have a high pKa, alcohols are able to donate their protons in basic solutions. When this occurs, the hydroxyl group can now act as a nucleophile.

Alcohols can also participate in hydrogen bonding. Recall that hydrogen bonding relies on the interactions donated by hydrogens bound to other elements of high electronegativity (including oxygen, nitrogen, and fluorine). Because alcohols possess a hydroxyl group with a hydrogen atom bound to an oxygen atom, they can participate in hydrogen bonding. This is an important property to consider because hydrogen bonding can raise the boiling points of many alcohols.

Alcohols also participate in many important synthesis reactions. Alcohols can be converted into higher-level functional groups through oxidation reactions. There are specific reagents that can create aldehydes, ketones, and even carboxylic acids from an alcohol.

Along with oxidation reactions, alcohols can participate in substitution reactions (Sn1 and Sn2 reactions). In these reactions, the hydroxyl group can serve as a nucleophile, attacking a carbon center and creating a new molecule. Since hydroxyl groups are able to lose a hydrogen ion in basic conditions, these substitution reactions proceed well when occurring in a basic solution.

Alcohols can also partake in protection reactions and mesylate/tosylate reactions. Chemists perform these reactions to ensure the hydroxyl group does not react or interfere during the desired synthesis reaction.

This can be accomplished in several ways. Generally, chemists turn hydroxyl groups into ketones or aldehydes that become ketals/hemiketals or acetals/hemiacetals. Additionally, hydroxyl groups can be converted into functional groups that are better leaving groups. Mesylate and tosylate reactions convert hydroxyl groups into mesylates or tosylates, which are good leaving groups. These reactions help facilitate substitution or elimination reactions in which an alcohol must be eliminated.

There is a specific nomenclature used to describe alcohols. To do so, determine the name of the alkane body (more on this later). Then, remove the –e ending. A suffix of –ol is added at the end of the name. A number describing which carbon the hydroxyl group is bound to in the longest chain is added as a prefix. Naming alcohols is as simple as that!