Sec 1 Structure Physical Properties Each carbon contributes a p orbital Six p orbitals overlap to give cyclic p system; 合的共轭体系（环状π电子流） Six p electrons delocalized throughout p system高度离域（无单双键之分） High electron density above and below plane of ring平面结构，键角为1200，Planar
Sec 1 Structure & Physical Properties ❖Each carbon contributes a p orbital ❖Six p orbitals overlap to give cyclic p system;闭 合的共轭体系(环状电子流) ❖Six p electrons delocalized throughout p system 高度离域(无单双键之分) ❖High electron density above and below plane of ring 平面结构，键角为1200 ，Planar
Sec 1 Structure Physical Properties The conjugated system in the benzene ring results in the formation of a continuous -cloud,above and below the plane of the ring. An electrostatic potential map of benzene showing enhanced electron density above and below the ring plane
Sec 1 Structure & Physical Properties
Sec 1 Structure Physical Properties 140pm 146pm 140pm 140pm 微微米 140p 134pm 140pm 140pm 芳香性
Sec 1 Structure & Physical Properties 芳香性 140 pm 140 pm 140 pm 140 pm 140 pm 140 pm 146 pm 134 pm 微微米
Unusual Reactions Alkene KMno>diol (addition) -Benzene KMnO4->no reaction. Alkene Br2/CCl4>dibromide (addition) -Benzene Br2/CCl4->no reaction. With FeCl3 catalyst,Br2 reacts with benzene to form bromobenzene HBr (substitution!). -Double bonds remain
Unusual Reactions ❖Alkene + KMnO4 → diol (addition) ◼Benzene + KMnO4 → no reaction. ❖Alkene + Br2/CCl4 → dibromide (addition) ◼Benzene + Br2/CCl4 → no reaction. ❖With FeCl3 catalyst, Br2 reacts with benzene to form bromobenzene + HBr (substitution!). ◼Double bonds remain
Sec 1 Structure Physical Properties Unusual Stability -Hydrogenation of just one double bond in benzene is endothermic! -Benzene is 150 kJ/mol(36 kcal/mol)more stable than might be expected for,“cyclohexatriene” (-359 predicted) 151kJ (-240 predicted) resonance energy energy 8kJ resonance energy -240 kJ/mol -232 kJ/mol -208 kJ/mol -120 kJ/mol energy
Sec 1 Structure & Physical Properties ❖Unusual Stability ◼Hydrogenation of just one double bond in benzene is endothermic! ◼Benzene is 150 kJ/mol (36 kcal/mol) more stable than might be expected for “cyclohexatriene