Ch 14

An aromatic six-carbon ring with the molecular formula C6H6 ; each carbon atom is sp2 hybridized with one p orbital that contains one electron. Also called [6]annulene.

A nonaromatic compound such as an alkane, cycloalkane, alkene, alkyne, or one of their derivatives

A planar cyclic conjugated system that is stabilized by electron delocalization

 The C6H5- group; obtained by removing a hydrogen atom from benzene, C6H6 . Abbreviated Ph- or φ- .

The C6H5CH2- group; obtained by removing a hydrogen atom from the methyl group of toluene, C6H5CH3 . Abbreviated Bn-

Having a 1,2 relationship on a benzene ring.

Having a 1,3 relationship on a benzene ring.

Having a 1,4 relationship on a benzene ring.

Replacement of a hydrogen on a benzene ring by a strong electrophile.

The extra stability of a molecule that has resonance contributors, since the energy of the actual molecule is lower than the energy that is estimated for any of its resonance structures.

The energy of stabilization that represents the difference in energy between the actual molecule or ion and that calculated for any resonance structure; this lower energy state arises from delocalization of electrons, and it results in resonance stabilization.

The number of chemical bonds between a pair of atoms, which is an index of bond strength. In molecular orbital theory, bond order is defined as the difference between the number of bonding electrons and the number of antibonding electrons, divided by two. For example, the bond order for a carbon-carbon bond is 1 for ethane, 2 for ethene, 3 for ethyne, and 1.5 for benzene.

Computer generated structure that uses color to show the relative distribution of electron density at the Van der Waals surface of a molecule or ion; violet and blue show electron-poor regions that have a partial positive charge (δ+); green and yellow show regions of normal electron density with almost no charge; orange and red show electron-rich regions that have a partial negative charge (δ─). Also called map of electrostatic potential.

A rule stating that planar monocyclic rings with (4n + 2) delocalized pi electrons will be aromatic; Hückel numbers include 2, 6, 10, 14, 18, 22, 26, 30, . . .

Monocyclic hydrocarbon characterized by a completely conjugated system of double bonds, which may or may not be aromatic. The ring size of an annulene is represented by a number in brackets. For example, benzene is [6]annulene, and 1,3,5,7-cyclooctatetraene is [8]annulene.

A planar cyclic conjugated system that is stabilized by electron delocalization; its pi electron energy is less than that of a corresponding open-chain compound; it has a large resonance energy; it reacts by substitution rather than addition; in the lH NMR spectrum, protons exterior to the ring are deshielded.

 A planar cyclic conjugated ion that is stabilized by electron delocalization, and its pi electron energy is less than that of a corresponding open-chain ion

A planar cyclic conjugated system that is destabilized by electron delocalization, and its pi electron energy is greater than that of a corresponding open-chain compound.

A cyclic conjugated system (usually not planar) whose pi electron energy is the same as that of the corresponding open-chain compound.

 A class of aromatic compounds whose molecules have two or more benzene rings fused together. Also called polycyclic benzenoid aromatic hydrocarbons.

An aromatic compound that does not contain any benzene rings, such as azulene.

 A class of aromatic compounds with an even number of carbon atoms, which form a cage-like fused-ring polycyclic system with twelve five-membered rings and the rest six-membered rings. For example, [60]fullerene has the geometry of a truncated icosahedron and is called buckminsterfullerene.

A form of elemental carbon composed of a cylindrical cluster of carbon atoms

A cyclic compound that has an element other than carbon in an aromatic ring; the most common heteroatoms are N, O and S