Treatment of an alcohol or phenol with benzyl chloride in the presence of a base such as triethylamine or pyridine results in the formation of benzyl ethers.

• Benzylic ethers are useful because they can act as protective groups for the —OH groups of alcohols and phenols, as shown in the image attached.

Aromatic compounds include benzene and its derivatives.

• Aromatic molecules are extremely stable, making them unreactive to reagents that target other unsaturated species such as alkenes and alkynes.

• Aromaticity refers to the unique stability of benzene and its derivatives, and arene refers to aromatic hydrocarbons.

• August Kekulé claimed that benzene is made up of six carbon atoms arranged in a ring, with one hydrogen atom connected to each.

The ring's six carbon atoms are comparable, and the carbon-carbon bond lengths are all halfway between a single and a double bond.

• It is wrong to consider of benzene as having static alternating single and double bonds since this would incorrectly anticipate alternating longer and shorter bonds.

The ring's carbon atoms are all sp2 hybridized.

• Each carbon atom in the ring forms s bonds by overlapping sp2-sp2 with two neighboring carbon atoms and sp2-1s with a hydrogen atom.

• Each carbon atom also possesses a single unhybridized 2p orbital with a single electron. Six p molecular orbitals are formed when six 2p orbitals overlap.

• In terms of energy, these molecular orbitals are grouped in a 1:2:2:1 arrangement.

The six p electrons fill the three p-bonding molecular orbitals, all of which are lower in energy than the six isolated 2p orbitals, which explains why the benzene p system is so unreactive.

The lowest-lying full molecular orbital contains two torus-shaped lobes, one above and one below the plane of the ring, underlining the p system's delocalized character.

• The remaining two full molecular orbitals each contain one node, emphasizing that the bond order between carbon atoms is halfway between a double and a single bond.

Benzene is best represented as a resonance hybrid comprised of two resonance forms with the double bond positions inverted.

• For ease of understanding, benzene is frequently shown as a single contributing structure or as a hexagon with a circle drawn on the interior.

The difference in energy between a resonance hybrid and the most stable hypothetical contributing structure in which electron density is confined is referred to as resonance energy.

The aromatic properties of benzene are not shared by all cyclic hydrocarbons with alternating double bonds.

• Erich Hückel defined a set of aromaticity criteria using molecular orbital simulations.

The molecule must have a cyclic structure.

• Each atom in the ring must have a 2p orbital (there can be no sp3 hybridized atoms in the ring).

• The molecule must be planar, or nearly so, in order for the 2p orbitals to overlap.

• In the aromatic p system, there must be (4n 1 2) p electrons, where n is a positive integer (0, 1, 2, 3, 4, 5,... ) for a total of 2, 6, 10, 14,... p electrons.

Some hydrocarbons are classified as antiaromatic because they are substantially less stable (more reactive) than an acyclic analog with the same molecular formula.

The inscribed polygon approach may be used to anticipate the arrangement of molecular orbitals observed on a molecular orbital energy map (Frost circles).

• The geometry of the polygon under consideration (for example, a hexagon for benzene) is drawn in a ring with one vertex down, and the relative energies of the molecular orbitals are shown by the polygon vertices that contact the circle.

• A horizontal line is drawn through the figure's center.

Bonding molecular orbitals are located below the line, nonbonding molecular orbitals (if present) are located on the line, and antibonding molecular orbitals are located above the line.

• An annulene is a cyclic hydrocarbon with constantly overlapping 2p orbitals. It is called by multiplying the number of atoms in the

• In a heterocyclic compound, the ring contains more than one kind of atom. If the Hückel conditions are fulfilled, some heterocycles can be aromatic.

• Aromatic heterocycles, such as indoles, purines, and pyrimidines, abound in nature.

The presence of lone pairs of electrons in the aromatic p system is an essential metric to monitor in aromatic heterocycles.

The lone pair of electrons on nitrogen in pyridine (C5H5N) is in a sp2 hybrid orbital that is perpendicular to the aromatic six p electron system's six 2p orbitals.

• This lone pair is not a member of the aromatic p system and is free to interact with other species.

Several of the simplest benzene derivatives, such as toluene, cumene, styrene, xylene, phenol, aniline, benzoic acid, and anisole, are still known by their common names in the IUPAC system.

• If their distinctive functional groups are present on a benzene derivative, these common names are utilized as the parent name.

The benzene ring is identified as a substituent on a parent chain in compounds with various functional groups.

• The three potential constitutional isomers for benzene rings with two substituents are designated ortho (1,2-substitution), meta (1,3-substitution), and para (1,4-substitution), and are abbreviated as o, m, and p, respectively.

• It is also allowed to use numerals as locators to name these species (such as 1,2- or 1,3-).

When one of the substituents has a unique name (for example, NH2 indicates that the molecule is an aniline), the molecule is called after that parent molecule, and the key group is assigned the number 1.

• Polynuclear aromatic hydrocarbons (PAHs) have several benzene rings.

• If none of the groups have a unique name, the substituents are given alphabetically, followed by the word benzene. 1-chloro-4-ethylbenzene and p-chloroethylbenzene, for example, are both valid names for the same chemical.

• A hydroxyl group linked to a benzene ring is the distinguishing property of phenols.

Because the negative charge of the phenoxide anion is substantially delocalized within the aromatic ring as suggested by resonance contributing structures, phenols (pKa approximately 10) are more acidic than simple alcohols.

Ring substituents that lead to increased stability of the phenoxide anion enhance phenol acidity, whereas substituents that destabilize the phenoxide anion lower phenol acidity.

• According to the inductive effect, electron-withdrawing groups (more electronegative than sp2 hybridized carbon) like halogens stabilize a phenoxide anion by absorbing some of the negative charge, making a phenol more acidic, whereas electron-releasing groups (less electronegative than sp2 hybridized carbon) like alkyl groups destabilize a phenoxide anion.