Benzene and Its Derivatives Flashcards

Vocabulary flashcards covering the discovery, structure, hybridization, resonance, stability, and aromaticity rules of benzene.

Benzene

An organic chemical compound with the molecular formula $C_6H_6$, existing as a colorless, highly flammable liquid with a sweet smell.

Bicarburet of hydrogen

The original name given to benzene by Michael Faraday in 1825 after isolating it from compressed illuminating gas produced by pyrolyzing whale oil.

Eilhardt Mitscherlich

The German chemist who synthesized benzene in 1834 by heating benzoic acid with calcium oxide and determined its molecular formula to be $C_6H_6$.

Kekule's structure for benzene

A cyclic planar structure proposed in 1865 consisting of six carbon atoms with alternating double and single bonds, where each carbon is bonded to one hydrogen atom.

Ladenburg's prism formula

A proposed benzene structure with six carbon atoms positioned at the corners of a prism without double bonds, which failed to explain addition reactions like the formation of benzene hexachloride ($BHC; C_6H_6Cl_6$).

Linus Pauling

The American chemist who suggested in 1931 that benzene possesses a single structure that is a resonance hybrid of two Kekule structures.

Heat of hydrogenation

The quantity of heat evolved when one mole of an unsaturated compound is hydrogenated.

Resonance energy of benzene

The stability gained by benzene ($36\,\text{kcal/mol}$ or $152\,\text{kJ/mol}$), resulting in a lower heat of hydrogenation than the theoretical value calculated for three isolated double bonds ($85.8\,\text{kcal/mol}$).

Benzene C-C bond length

The uniform C-C bond length in benzene of $1.40\,\text{\AA}$, which is intermediate between a C-C single bond ($1.54\,\text{\AA}$) and a C=C double bond ($1.34\,\text{\AA}$).

Delocalized \pi electrons

Electrons in benzene that are not localized between alternating double bonds but are spread out over the entire system in a ring-shaped molecular orbital.

Resonance in benzene

The depiction of actual benzene as a hybrid of two equivalent Kekule structures (I and II) that differ only in the arrangement of electrons.

Hückel's Rule

A theory proposed in 1931 by Erich Hückel stating that a cyclic, planar, completely conjugated molecule is aromatic if it contains $(4n + 2)\,\pi$ electrons, where $n$ is a non-negative integer.

Aromatic compound

A cyclic, planar, completely conjugated compound containing $(4n + 2)\,\pi$ electrons that exhibits unusual stability and prefers substitution over addition reactions.

Antiaromatic compound

A cyclic, planar, completely conjugated compound containing $4n\,\pi$ electrons (e.g., $4, 8, 12, 16\dots$), making it unusually unstable.

Nonaromatic compound

A compound that fails to meet at least one of the four requirements necessary to be considered aromatic or antiaromatic.

Cyclobutadiene

An antiaromatic compound containing $4\,\pi$ electrons that is unusually unstable and only stable below $-100\,^\circ\text{C}$.

Cyclooctatetraene

A non-aromatic 8-membered ring molecule that adopts a tub-like shape to prevent adjacent p-orbitals from overlapping, thereby escaping anti-aromaticity.