Aromatic Chemistry and Arenes

A set of vocabulary flashcards covering the structure, bonding, stability, and reactions of arenes as described in the lecture notes.

Arenes

Hydrocarbons based on benzene, $C_6H_6$, which are also known as aromatic compounds.

Delocalisation

A state where electrons are spread over more than two atoms; in benzene, the sixth electron of each carbon atom is in a p-orbital that overlaps to form a region of electron density above and below the ring.

Aromatic stability

The unusual stability of benzene and its derivatives resulting from the delocalised electron system.

$$0.140\,nm$$

The length of each carbon-carbon bond in benzene, which is intermediate between the length of a $C-C$ single bond ($0.154\,nm$) and a $C=C$ double bond ($0.134\,nm$).

Cyclohexa-1,3,5-triene

The hypothetical non-delocalised benzene structure with alternating double and single bonds; it is predicted to have a hydrogenation enthalpy of $-360\,kJ\,mol^{-1}$.

$$152\,kJ\,mol^{-1}$$

The delocalisation energy of benzene, representing how much more stable benzene is compared to the hypothetical cyclohexa-1,3,5-triene.

Friedrich August von Kekulé

The chemist who in 1865 suggested that benzene's structure was based on a ring of carbon atoms with alternating double and single bonds after a dream of whirling snakes.

Electrophile

A species with a positive charge, either as a positive ion or the positive end of a dipole, which is attracted to areas of high electron density.

Nitronium ion

The electrophile $NO_2^+$ (also called the nitryl cation) generated by the reaction of concentrated sulfuric acid and concentrated nitric acid.

TNT

Short for trinitrotoluene ($2,4,6\text{-trinitrotoluene}$), a high explosive made by nitrating methylbenzene (toluene).

Electron-releasing groups

Substituents like $-CH_3$, $-OCH_3$, $-OH$, and $-NH_2$ that make the benzene ring more susceptible to electrophilic substitution and direct further substitution to the $2$, $4$, and $6$ positions.

Electron-withdrawing groups

Substituents like $-NO_2$ and $-COCl$ that make the benzene ring less susceptible to electrophilic substitution and direct further substitution to the $3$ and $5$ positions.

Friedel-Crafts acylation

An electrophilic substitution reaction where an acyl group ($RCO$) is added to an aromatic ring using an aluminium chloride ($AlCl_3$) catalyst.

Aluminium chloride ($AlCl_3$)

A catalyst used in Friedel-Crafts acylation that accepts a lone pair from the chlorine atom of an acyl chloride to form the $RCO^+$ electrophile.