Isomers Mcat

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Isomers for the MCAT: Everything You Need to Know

Learn key MCAT concepts about isomers, plus practice questions and answers

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

Table of Contents

Part 1: Introduction to isomers

Part 2: Structural isomers

Part 3: Chirality

a) Chiral centers

b) R, S configuration

c) E, Z configuration

d) Diastereomers and enantiomers

e) Conformational isomers

Part 4: In biological systems

a) Amino acids

b) Carbohydrates

c) Boat and chair conformations

Part 5: High-yield terms

Part 6: Passage-based questions and answers

Part 7: Standalone questions and answers

Part 1: Introduction to isomers

Isomers are compounds with the same chemical formula but different arrangements of atoms. Often, different isomers will behave differently. This is especially important in considering how chemicals react with one another. For instance, it is important to keep isomers in mind when creating drugs so that the chemical interacts with the body as desired–without any lethal side effects.

This study guide will take you on a tour of the different types of isomers, along with examples and naming conventions. Throughout this guide, several key terms are highlighted in bold. At the end of this guide, there are also several MCAT-style practice questions for you to test your knowledge against.

Let’s get started!

Part 2: Structural isomers

Recall that covalent bonds form when one or more electron pairs are shared between atoms. Covalent bonds arrange atoms in space and influence the overall geometry of molecules. (For more information on this topic, be sure to refer to our guide on bonds and interactions.)

Hence, covalent bonds are crucial in any discussion of isomers, because isomers arise from different spatial connectivities of atoms in three-dimensional space.

Chemical structures should always be considered in their three-dimensional configurations. In other words: the bonding of individual atoms within a molecule must be taken into account. Structural isomers arise from forming covalent bonds in different arrangements despite having the same number and types of atoms. As a result, structural isomers have different structures in three-dimensional space due to the unique arrangements of atoms by covalent bonds.

Let’s compare two molecules with the formula C₄H₁₀: butane and isobutane. Both butane and isobutane have four carbons and ten hydrogens, but the arrangement of individual atoms within the molecule varies.

MCAT Basics: Isomers

This episode reviews three common types of isomers that you are likely to see on the MCAT: 1) structural isomers, 2) geometric isomers, and 3) stereoisomers. I define each type of isomer, give a common example, and discuss applications that you may see.

Please email me if you have any comments or concerns: [email protected]

Thanks for listening!

Sam Smith

Sam completed his Bachelors of Science in Chemical and Biological Engineering at the University of Colorado Boulder. Following his graduation, he worked at the National Institutes of Health Vaccine Research Center studying HIV. Meanwhile, with a microphone in his garage, Sam founded the MCAT Basics podcast. The podcast has grown to become the top rated MCAT podcast on iTunes. In addition to podcasting, Sam enjoys the outdoors, sports, and his friends and family.