Chapter 17: Aromatic Compounds Vocabulary

Vocabulary flashcards identifying definitions, nomenclature rules, structural properties, reactions, and spectroscopy features of aromatic compounds based on Chapter 17 notes.

Arenes (Aromatic Compounds)

A class of unsaturated hydrocarbons containing a benzene ring or related aromatic structural unit.

Phenyl Group

A benzene ring attached as a substituent on a larger parent chain, commonly represented as $\text{Ph}$ or by the symbol $\phi$.

Xylene

The common name for dimethylbenzene derivatives, which occur as ortho-xylene ($1,2$-dimethylbenzene), meta-xylene ($1,3$-dimethylbenzene), and para-xylene ($1,4$-dimethylbenzene).

Ortho, Meta, and Para (o-, m-, p-)

Locant descriptors used to specify the substitution patterns on disubstituted benzene rings, denoting $1,2$-disubstituted (ortho), $1,3$-disubstituted (meta), and $1,4$-disubstituted (para) positions.

Kekul Structure

A structural proposal for benzene made by August Kekul in 1866 featuring a six-membered ring with alternating single and double carbon-carbon bonds.

Hckel's Rule

A rule stating that a planar, fully conjugated cyclic molecule is aromatic if it contains an odd number of electron pairs or $4n + 2$ total $\pi$ electrons, where $n = 0, 1, 2, 3, 4, ...$.

Antiaromatic Compound

A compound possessing a fully conjugated planar ring with overlapping p orbitals containing $4n$ total $\pi$ electrons (an even number of electron pairs), resulting in severe electronic instability.

Nonaromatic Compound

A compound that fails the criteria for aromaticity or antiaromaticity because it lacks a fully conjugated continuous ring of p orbitals or lacks a planar conformation.

Tub-Shaped Conformation

The nonplanar conformational shape adopted by cyclooctatetraene that breaks continuous p orbital overlap and allows it to exist as a stable nonaromatic system rather than an unstable antiaromatic system.

Frost Circle

A central geometric method used to derive relative molecular orbital energy levels of a conjugated ring system by inscribing its polygon into a circle with one vertex pointing directly downward.

Annulenes

Completely conjugated monocyclic hydrocarbons named by indicating the ring size in brackets, such as [6]annulene, [10]annulene, and [14]annulene.

Cyclopentadienyl Anion

An aromatic carbanion containing a five-membered ring with $6\,\pi$ electrons delocalized over all five carbon atoms, whose stability gives cyclopentadiene a lower $pK_a$ of $16$.

Tropylium Cation

An aromatic carbocation composed of a seven-membered carbon ring containing $6\,\pi$ electrons and an empty p orbital.

Pyridine and Pyrrole

Aromatic heterocycles containing nitrogen; in pyridine, the lone pair occupies an $sp^2$ orbital orthogonal to the $\pi$ system, whereas in pyrrole, the lone pair resides in a p orbital to complete the $6\,\pi$ aromatic system.

Polycyclic Aromatic Hydrocarbons (PAHs)

Molecules composed of multiple fused benzene rings, such as naphthalene, anthracene, and phenanthrene.

Benzylic Position

The carbon atom directly attached to an aromatic benzene ring.

Chromic Acid Oxidation (Benzylic)

An oxidation reaction using $\text{Na}_2\text{Cr}_2\text{O}_7$, $\text{H}_2\text{SO}_4$, and $\text{H}_2\text{O}$ that converts alkyl side chains with at least one benzylic hydrogen into benzoic acid.

Birch Reduction

A reaction using sodium metal ($\text{Na}$) in liquid ammonia ($\text{NH}_3$) and methanol ($\text{CH}_3\text{OH}$) that partially reduces an aromatic ring into a non-conjugated $1,4$-cyclohexadiene.

Graphite

An allotrope of carbon consisting of layers of sheets made from fused aromatic carbon rings.

Buckyballs

Spherical fullerenes ($\text{C}_{60}$) formed from interlocking aromatic rings.

Nanotubes

Cylindrical fullerenes made of rolled sheets of carbon atoms with applications in conductive plastics, molecular electronics, and energy storage.