Organic Chemistry Cheat Sheet

The core ideas of Organic Chemistry distilled into a single, scannable reference — perfect for review or quick lookup.

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Quick Reference

Functional Groups

Specific groupings of atoms within molecules that have predictable chemical behavior regardless of the rest of the molecule. They are the key to classifying organic compounds and predicting their reactivity, solubility, and physical properties.

Reaction Mechanisms

Detailed, step-by-step descriptions of how bonds break and form during a chemical reaction, including the movement of electron pairs shown with curved arrows. Understanding mechanisms allows chemists to predict products, stereochemistry, and side reactions.

Stereochemistry

The study of the three-dimensional arrangement of atoms in molecules and how spatial orientation affects chemical and physical properties. Molecules with the same connectivity but different spatial arrangements (stereoisomers) can have dramatically different biological activities.

Nucleophilic Substitution

A class of reactions in which a nucleophile (electron-rich species) replaces a leaving group on an electrophilic carbon. The two main pathways, SN1 and SN2, differ in kinetics, stereochemical outcomes, and substrate preferences.

Electrophilic Addition

A reaction in which an electrophile adds to a carbon-carbon double or triple bond, breaking the pi bond and forming two new sigma bonds. This is the most characteristic reaction type for alkenes and alkynes.

Aromaticity

A property of cyclic, planar, fully conjugated molecules that possess a special stability arising from the delocalization of pi electrons according to Huckel's rule ($4n+2$ pi electrons). Aromatic compounds resist addition reactions and instead undergo electrophilic aromatic substitution.

Carbonyl Chemistry

The chemistry of compounds containing the C=O (carbonyl) group, including aldehydes, ketones, carboxylic acids, esters, and amides. The polarized carbonyl bond makes the carbon electrophilic and the oxygen nucleophilic, driving a rich variety of addition and substitution reactions.

Polymers and Macromolecules

Large molecules composed of repeating structural units (monomers) connected by covalent bonds through polymerization reactions. Organic polymers range from synthetic plastics like polyethylene and nylon to biological macromolecules such as proteins, nucleic acids, and polysaccharides.

Spectroscopic Identification

The use of instrumental techniques such as infrared spectroscopy (IR), nuclear magnetic resonance (NMR), and mass spectrometry (MS) to determine the structure of organic molecules. Each method provides complementary information about functional groups, connectivity, and molecular formula.

Retrosynthetic Analysis

A problem-solving strategy for planning organic syntheses by working backward from the target molecule to simpler, commercially available starting materials. Developed by E. J. Corey, it involves identifying strategic bond disconnections and the corresponding forward reactions.

Key Terms at a Glance

Alkane:A saturated hydrocarbon containing only carbon-carbon single bonds, with the general formula $\text{C}_n\text{H}_{2n+2}$ for acyclic alkanes. They are relatively unreactive and serve as the parent chain for IUPAC naming of more complex molecules.

Alkene:An unsaturated hydrocarbon containing at least one carbon-carbon double bond ($\text{C}=\text{C}$), with the general formula $\text{C}_n\text{H}_{2n}$ for acyclic monoenes. Alkenes undergo addition reactions, including hydrogenation, halogenation, and hydration.

Alkyne:An unsaturated hydrocarbon containing at least one carbon-carbon triple bond, with the general formula $\text{C}_n\text{H}_{2n-2}$. Terminal alkynes have a weakly acidic hydrogen that can be removed by strong bases to form acetylide anions useful in synthesis.

Carbonyl group:A functional group consisting of a carbon atom double-bonded to an oxygen atom ($\text{C}=\text{O}$). It is the defining group in aldehydes, ketones, carboxylic acids, esters, amides, and other compound classes, and is central to much of organic reactivity.

Chirality:The geometric property of a molecule that makes it non-superimposable on its mirror image, analogous to left and right hands. Chirality most commonly arises from a tetrahedral carbon bonded to four different substituents.

Enantiomer:One of a pair of stereoisomers that are non-superimposable mirror images of each other. Enantiomers have identical physical properties (melting point, boiling point, solubility) except for the direction in which they rotate plane-polarized light.

Diastereomer:Stereoisomers that are not mirror images of each other. Unlike enantiomers, diastereomers can have different physical properties such as melting points and solubilities, making them separable by conventional techniques.

Nucleophile:An electron-rich chemical species that donates an electron pair to an electrophilic atom to form a new covalent bond. Common nucleophiles include hydroxide, cyanide, amines, and carbanions.

Electrophile:An electron-poor chemical species that accepts an electron pair from a nucleophile to form a new covalent bond. Examples include protons (H+), carbocations, and Lewis acids like BF3 and AlCl3.

Carbocation:A positively charged ion in which a carbon atom bears only three bonds and an empty p orbital. Carbocation stability increases with substitution (tertiary > secondary > primary) due to hyperconjugation and inductive electron donation.

Leaving group:An atom or group of atoms that departs with a pair of electrons during a substitution or elimination reaction. Good leaving groups are weak bases that can stabilize the negative charge, such as halides (Cl-, Br-, I-) and tosylates.

Resonance:The delocalization of electrons in a molecule represented by two or more Lewis structures (resonance contributors) that differ only in the placement of electrons. The actual structure is a weighted average (hybrid) of all resonance forms.

Conjugation:The overlap of p orbitals across alternating single and multiple bonds, allowing electron delocalization across the system. Conjugation stabilizes molecules, affects UV absorption, and is a prerequisite for aromaticity.

Isomer:Molecules that share the same molecular formula but differ in the arrangement of atoms. Constitutional (structural) isomers differ in connectivity, while stereoisomers have the same connectivity but different spatial arrangements.

Ester:An organic compound derived from a carboxylic acid and an alcohol, containing the functional group $-\text{COO}-$. Esters are commonly formed by Fischer esterification and are responsible for many fruity aromas and flavors in nature.

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