Fundamentals of Organic Chemistry for the DAT
/Learn key DAT concepts about the fundamentals of organic chemistry, plus practice questions and answers
Learn the fundamentals of organic chemistry for the dat
Table of Contents
Part 1: Introduction to the fundamentals of organic chemistry
Part 2: Mechanism notation
a) Depicting molecules
b) Arrows
Part 3: Nucleophiles and electrophiles
a) Overview of functional groups
b) Nucleophilic substitution reactions
c) Elimination reactions
Part 4: High-yield terms
Part 5: Questions and answers
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Part 1: Introduction to the fundamentals of organic chemistry
Organic chemistry can be an overwhelming subject on the DAT. There are many reactions to memorize, mechanisms to understand, and products to predict. A solid understanding of the fundamentals of organic chemistry will help the other sections make more sense and become easier to grasp.
This guide will focus on some of these fundamental concepts, such as notation and identifying electrophiles and nucleophiles. As you study this guide, pay attention to any bolded terms. These are high-yield terms that may show up on your DAT. Also, be sure to answer the DAT-style practice questions at the end.
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Part 2: Mechanism notation
a) Depicting molecules
Molecules in organic chemistry usually start from a hydrocarbon backbone. This means that molecules are made up of connected carbon and hydrogen atoms. Functional groups or other substituents are added to the hydrocarbon backbone to create more complex molecules.
There are multiple ways to depict molecules in organic chemistry. One method of depiction is using the structural formula. Pentane is a hydrocarbon with the molecular formula of C5H12. Its written structural formula is CH3CH2CH2CH2CH3. This formula can be condensed to CH3(CH2)3CH3. The structural formula may also be depicted with lines showing the bonds between molecules, such as in the following figure:
FIGURE 1: PENTANE STRUCTURAL FORMULA
Another way of visualizing molecules is line structure. In line structure, carbon atoms are represented by the end point of a line. Carbon atoms are also found where lines are connected. Hydrogen atoms are not shown in line structures, but are implied in order to complete carbon’s octet. Here is pentane’s line structure:
FIGURE 2: PENTANE LINE STRUCTURE
The DAT will use each of these methods to depict molecules, and you should be able to convert a line structure to its written or visual structural formula, and vice versa. This is especially important when answering questions about specific reactions. You may have memorized the line structure of each reaction, but a DAT question could show the reaction as a written formula. Be prepared by practicing converting between these structures so you don’t get tripped up on the actual exam, even if you memorized the correct content.
b) Arrows
FIGURE 3: A HEMIACETAL-PRODUCING REACTION
The image above depicts a reaction that yields a new product. It involves the interaction of an aldehyde-bearing molecule with a hydrogen ion and alcohol, resulting in the formation of a hemiacetal. (See organic chemistry guide “functional groups” for more details.)
Each molecule in the figure is connected by equilibrium arrows. Equilibrium arrows are 2 half arrows, one pointing left and the other right, that signify the reversibility of the reaction. This means that every phase of the reaction can transition forwards or backwards with equal likelihood. It's important to note that equilibrium arrows may not always be of equal length, as they correspond to the probability of the organic reaction proceeding in that direction.
Mechanisms are written representations of chemical reactions that portray bond formation and cleavage between atoms. Typically, mechanisms employ arrows to signify electron movement. These arrows usually begin at a specific electron pair and point towards the targeted bond or atom. When two electrons are involved, double-headed arrows are used.
Returning to the illustrated mechanism, you can see the electron flow between each step. In the initial stage, valence electrons originating from the oxygen atom initiate the reaction by attacking the hydrogen ion. In the second step, two double arrows are depicted. The first double arrow arises from the valence electrons in the alcohol group's oxygen, attacking the carbon atom. The second double arrow illustrates the transfer of electrons from the carbon-oxygen double bond to the oxygen atom. In the third step, electrons shift from the oxygen-hydrogen bond to the oxygen, freeing a hydrogen ion. It's worth noting that drawing double arrows in the opposite direction (from a source lacking electrons) is incorrect; the arrows extend from the electron source to their target.
Arrows in mechanisms can be either double-headed or single-headed, each with distinct meanings.
FIGURE 4: LIGHT-MEDIATED REACTION OF A BROMINE MOLECULE SPLITTING INTO TWO IONS
In the organic reaction above, a single bromine molecule (Br2) undergoes a cleavage, yielding two bromine ions (Br-). This reaction is catalyzed by light, with the notation "hv" signifying high-energy light responsible for bond breakage. Unlike the previous mechanism, this one employs single-headed arrows.
Single-headed arrows also represent electron movement and extend from the electron source to the target. In this instance, electrons originate within a single bond and are directed toward each bromine atom.
Single-headed arrows depict the movement of a single electron, not an electron pair. In the example, when the initial bromine molecule is broken, each bromine ion receives a single electron instead of a pair of electrons.
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