aming Aromatic Compounds (Benzene as the Parent) If the the alkyl chain is smaller than the ring use the ring as the parent Monosubstituted benzenes are named the same way as other hydrocarbons using benzene as the parent name
Aromatic Compounds C 3 C 3 C 3 C 3 C 3 3 C C 3 Common ame benzene C 3 toluene ortho-xylene meta-xylene C 3 para-xylene cumene IUPAC methylbenzene 1,2-dimethylbenzene 1,3-dimethylbenzene 1,4-dimethylbenzene isopropylbenzene Other aromatic compounds: O Cl 2 OMe SO 3 O 2 C C 2 phenol chlorobenzene aniline anisole benzene sulfonic acid nitrobenzene styrene C 2 O O O O O C 3 benzylalcohol or phenylmethanol benzaldehyde benzoic acid acetophenone biphenyl
More Aromatic Compounds Polycyclic Aromatic Compounds 7 8 1 2 2 1 9 8 7 3 4 5 6 7 8 6 5 4 3 3 4 10 5 6 2 1 10 9 naphthalene anthracene phenanthrene 2,4,5,6,10-pentamethylphenanthrene eterocyclic Aromatic Compounds O furan pyrrole pyridine pyrimidine indole purine
aming Aromatic Compounds (Disubstituted Benzenes) Relative positions on a benzene ring ipso- carbon 1 ortho- (o) on adjacent carbons (1,2) meta- (m) separated by one carbon (1,3) para- (p) separated by two carbons (1,4)
aming Aromatic Compounds (Benzenes with More Substituents) Choose numbers for the lowest possible values List groups alphabetically (hyphenated between) numbers Common names, such as toluene can serve as root name (as in TT)
aming Aromatic Compounds (Benzene as a Substituent) If the the alkyl chain is larger than the ring use it as the parent When a benzene ring is a substituent, the term phenyl is used (for C 6 5 ) You may also see Ph or φ or C 6 5 Remember that benzyl refers to C 6 5 C 2
Structure of Benzene All its C-C bonds are the same length (1.39 ) between length of normal single and double bonds Electron density in all six C-C bonds is identical Structure is planar
Stability of Benzene (eats of ydrogenation) 2, Pd Δ exp = 28.6 kcal/mol 2, Pd 2, i 175 C 180 atm Δ est = 57.2 kcal/mol Δ exp = 55.5 kcal/mol = 1.7 kcal resonance energy Δ est = 85.8 kcal/mol Δ exp = 49.8 kcal/mol = 36 kcal resonance energy 2, Pd Δ est = 85.8 kcal/mol Δ exp = 80.6 kcal/mol = 5.2 kcal resonance energy
Aromaticity and the 4n + 2 Rule 1 monocyclic cmp (i.e. don't look at anthracene, etc) 2 All atoms in the ring must have a p-orbital (sp 2 atoms) 3 The p-orbitals must overlap...the cmp must be flat and the overlap unbroken 4 π-cloud must contain 4n+2 electrons (ückel's Rule) n = 0,1,2,3,4,5... Therefore, compounds with 2,6,10,14,18 electrons will be aromatic ALL the rules must be followed to be aromatic! uge energy advantage to being aromatic! sp 3
Antiaromatic Compounds 1 monocyclic cmp (i.e. don't look at anthracene, etc) 2 All atoms in the ring must have a p-orbital (sp 2 atoms) 3 The p-orbitals must overlap...the cmp must be flat and the overlap unbroken 4 π-cloud must contain 4n electrons n = 0,1,2,3,4,5... Therefore, compounds with 4,8,12,16,20 electrons will be antiaromatic ALL the rules must be followed to be antiaromatic! Basically, nature avoids...use to explain why stuff doesn't happen X
Aromatic Ions
A eterocycle is a cyclic compound that contains an atom or atoms other than carbon Aromatic eterocycles
More Aromatic eterocycles O Furan Thiophene
Special Cases Pay Attention! O O X C 3 3 C
Special Compounds With 4n π Electrons 4π electrons antiaromatic Exists @ 4 K
Cool Aromatic Compounds azulene Aromatic compounds composed smaller rings other than benzene are called nonbenzenoid aromatic compounds
What is Aromaticity? MO Description of Benzene
Frost Diagrams 1. Inscribe the ring in a concentric circle with one of the points down 2. Draw energy levels at each of the intersections between the circle and the ring 3. Cut circle in half 4. Fill the levels with π electrons starting at the bottom and working your way up 6 π e non-bond MO's bonding MO's
Why 4n+2? Aromatic B B Antiaromatic or onaromatic B B
Reactions at the Benzylic Carbon and Reductions of Aromatic Compounds Oxidation with 2CrO4 or KMnO4 (o Mechanism) Free radical reactions (Review Mechanism) S1, S2, E1, E2 (Review Mechanisms) ydrogenation (o arrow pushing Mechanism) Birch reduction with EWG and EDG 24