Chapter 21 - Benzene and the Concept of Aromaticity

Erich Hückel

________ defined a set of aromaticity criteria using molecular orbital simulations.

August Kekulé

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

annulene

A(n) ________ is a cyclic hydrocarbon with constantly overlapping 2p orbitals.

Benzene

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

hydroxyl group

A(n) ________ linked to a benzene ring is the distinguishing property of phenols.

Polynuclear aromatic hydrocarbons

________ (PAHs) have several benzene rings.

aromatic properties of benzene

The ________ are not shared by all cyclic hydrocarbons with alternating double bonds.

single contributing

For ease of understanding, benzene is frequently shown as a(n) ________ structure or as a hexagon with a circle drawn on the interior.

stable hypothetical contributing

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

phenoxide anion

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

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.

benzene ring

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

molecular orbitals

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

phenoxide anion

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

carbon atoms

The ring's ________ are all sp2 hybridized.

carbon atom

Each ________ also possesses a single unhybridized 2p orbital with a single electron.