chem241 - aromaticity

conjugated systems

• aromatic systems

• non-aromatic system

• anti-aromatic systems

aromatic systems

• D-cyclic

• at least 1 p-orbital (conjugated system)

• planar

• 4n + 2 π e^- (n → integer)

huckle rules

needs:

• cyclic

• conjugate

• planar (all sp²)

• 4n + 2 π e^-s

  • n = 1, 4 × 1 + 2 = 6

frost diagram (FD)

non-aromatic → no frost circle

• frost circle method predicts E level of molecular orbitals of planar cyclic arrangements of idential atoms ONLY

  • usually all carbons

  • aromatic

• always 1 single MO that is ↓ in E than all the rest

• if there is an even # atoms, there is also a single MO that is ↑ in E then all the rest

• all the molecular orbitals come in degenerate pairs except for lowest E

FD 3 membered ring

FD 4 membered ring

FD 5 membered ring

FD 6 membered ring

FD 7 membered ring

FD 8 membered ring

aromatic nomenclature

• monosubstituted benzene

• disubstituted benzene

• trisubstituted benzene

monosubstituted benzene

have specific (common) names

disubstituted benzene

need to know parent compound + use ortho, meta, & para to designate substitution position on ring

trisubstituted benzene

start by giving C that contains parent group #1 & following regular IUPAC rules

monosubstituted benzene list

• aniline

• phenol

• anisole

• toluene

• styrene

• chloro/bromo benzene

• benzaldehyde

• acetophenone

• benzoic acid

• nitrobenzene

• cyanobenzene

• benzenesulfonic acid

• pyridine

aniline

monosubstituted

phenol

monosubstituted

anisole

monosubstituted

tolulene

monosubstituted

styrene

monosubstituted

chlorobenzene

monosubstituted

bromobenzene

monosubstituted

benzaldehyde

monosubstituted

acetophenone

monosubstituted

benzoic acid

monosubstituted

nitrobenzene

monosubstituted

• nitro group

cyanobenzene

monosubstituted

• cyano group

benzenesulfonic acid

monosubstituted

pyradine

monosubstituted

disubstituted benzene list

• ortho—

• meta—

• para—

  • meta-methyl phenol

  • 3,5-dibromophenol

  • 5-bromo-2-chlorophenol

benzene substituent groups

• amino

• hydroxy

• methoxy

• methyl

• vinyl

• acetyl

• carboxy

• nitro

amino group

hyroxy group

methoxy group

methyl group

vinyl group

acetyl group

caboxy group

nitro group

phenyl group

• benzene is substituent