《有机化学》课程PPT教学课件（Organic Chemistry, William A. Price, Ph.D. PPT, La Salle University, L.G.WADE, JR., 8th Edition）Benzene and Aromaticity（2011）

Benzene and Aromaticity 1.397A H H 20° H 120°

Benzene and Aromaticity

Bonding in Benzene all C-C bond double bond lengths 1.397 A 1.34A single bond 1.48A resonance representation bond order =1 butadiene combined representation

Bonding in Benzene

Proposed Benzene Structures Dewar benzene Lade nburg be nze ne Kekule be nze ne

Proposed Benzene Structures Dewar benzene Ladenburg benzene Kekule benzene

C.H reacts with Br2 to form one isomer of CHsBr Br Br2,cat. Br2,cat 12-1,3-&1,4-dibromo +HBr Kekule benzene C6H6 Br2.caluqueCHBr Br cat 3 unique C 6H4Br2 (+HBr) (+HBr) Lade nburg be nze ne C6H6

C6H6 reacts with Br2 to form one isomer of C6H5Br Ladenburg benzene Kekule benzene Br2 , cat. 1 unique C 6H5Br Br2, cat. 3 unique C 6H4Br2 (+ HBr) (+ HBr) C6H6 C6H6 Br2, cat. Br Br2, cat. 1,2- 1,3- & 1,4-dibromo + HBr

Other Conjugated Hydrocarbon Rings Annulenes cyclobutadiene benzene cyclooctatetraene [4]annulene [6]annulene [8]annulene cyclodecapentaene [10]annulene

Other Conjugated Hydrocarbon Rings Annulenes

AHyd Data Illustrates Stability ----(-85.8 predicted) (-57.2 predicted) 36 kcal resonance energy energy 1.8 keal resonance energy -57.4 kcal -55.4 keal -49.8 keal -28.6 keal energy

DHhyd Data Illustrates Stability

Benzene Representations 1.397A 120° H 120°

Benzene Representations

Molecular Orbitals of Benzene 6 y4* y3

Molecular Orbitals of Benzene + + + + + + + + + + + + + + + + + + + - - - - - + - - - - - - -             * * *

all antibonding node node node antibonding π考 node node T2 bonding node 不3 all bonding

M.O.'s of Cyclobutadiene Ψ3

M.O.’s of Cyclobutadiene + + + + + + _ _ + _ + + _ _ 1 3 1 4