Organic Chemistry Glossary

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.

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.

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.

An organic compound containing a carbonyl group bonded to a nitrogen atom ($-\text{CONR}_2$). The amide bond (peptide bond) is the linkage between amino acids in proteins and is stabilized by resonance, giving it partial double-bond character.

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.

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.

A substance that increases the rate of a chemical reaction by lowering the activation energy without being consumed. In organic chemistry, catalysts include acids, bases, transition metals (e.g., Pd, Pt), and enzymes.

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.

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.

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.

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.

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.

A resonance-stabilized anion formed by deprotonation of the alpha-carbon adjacent to a carbonyl group. Enolates are versatile nucleophiles used in carbon-carbon bond-forming reactions such as the aldol condensation and Claisen condensation.

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.

The shift of electron density along a chain of sigma bonds caused by the electronegativity of substituents. Electron-withdrawing groups (e.g., halogens) create a negative inductive effect (-I), while electron-donating groups (e.g., alkyl groups) create a positive inductive effect (+I).

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.

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.

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.

In organic chemistry, oxidation generally involves the gain of oxygen, loss of hydrogen, or loss of electrons from a carbon atom. Common oxidation sequences include alcohol to aldehyde to carboxylic acid, and alkene to diol.

A large molecule composed of many repeating structural units (monomers) joined by covalent bonds. Polymers can be natural (proteins, DNA, cellulose) or synthetic (polyethylene, nylon, Teflon) and are classified by their polymerization mechanism.

An equal mixture of both enantiomers of a chiral compound, resulting in no net optical rotation. Racemic mixtures are often produced in reactions that create a new stereocenter without chiral influence and are denoted with the prefix (±) or 'rac.'

In organic chemistry, reduction generally involves the gain of hydrogen, loss of oxygen, or gain of electrons at a carbon atom. Common reducing agents include lithium aluminum hydride ($\text{LiAlH}_4$) for carbonyls and catalytic hydrogenation ($\text{H}_2$/Pd) for alkenes.

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.

The base-catalyzed hydrolysis of an ester (or fat/oil) to produce an alcohol and a carboxylate salt (soap). This irreversible reaction is driven by the formation of the resonance-stabilized carboxylate anion.

The slowing or prevention of a chemical reaction caused by the physical bulk of substituents near the reaction site. Steric effects are crucial in determining whether substitution or elimination occurs and in controlling stereoselectivity.