有机化学英文课件：CH4-arenes1.pptVIP

Benzyl Cation 600 1 Phenyl vs. Methyl C6H6 + Br2 No Reaction C6H6 + HBr No Reaction C6H6 + Br2 Fe C6H5Br + HBr Substitution Reaction - NOT Addition RESONANCE ENERGY 120 231 208 152 3x120 Heats of Hydrogenation KJ/mole Oxidation of Alkylbenzenes KMnO4 Na2Cr2O7 H2SO4 Aromatic Character (Aromaticity) 1) Chemical properties : Aromatics have tendency to undergo substitution reaction rather than addition or oxidation reaction. 2) Structural speciality: they all have cyclic conjugated system. 3) If the number of π–electrons in a cyclic conjugated system follows 4n+2 rule (n=0, 1, 2, 3) and all the atoms in the system are in the same plane. The system is an aromatic system. Other AROMATIC systems? Hückel’s Rule Planar, (mono)cyclic, conjugated, polyenes (4 n + 2) electrons n = 0,1, 2, 3 .... Counting Electrons p Electrons Charge 0 + 1 none 2 - (4 n + 2) Hückel’s Rule n Electrons 0 1 2 2 6 10 Look for systems with 2, 6, 10 pi electrons. + + + 2 electrons Aromatic Cation 4 pi electrons Not Aromatic How many pi electrons? To be aromatic how many electrons go here? 2 electrons - + H+ Acidic Proton pKa = 16 Cyclopentadienide Anion Aromatic: 6 pi electrons - - - - - - How many pi electrons? 6 Aromatic Chapter 4 Aromatic Compounds Chapter 4 Aromatic Compounds Arenes Chapter 4 Aliphatic Aromatic alkanes, alkenes, alkynes... benzene, naphthalene, pyridine Types of Organic Compounds BENZENE C6H6 How many structural isomers of C6H6 are possible? 217 structures Benzene 120o 120o Kekulé Resonance Structures Summary: Electron Density Kekulé Structures for Naphthalene Kekulé Structures for Phenanthrene What is the name of this substance? graphite Graphite Buckminsterfullerene 1967年加拿大蒙特婁世界博覽會上的美國館，建築物高60公尺 Diamond 1 Benzene as substituent (phenyl group, ph-) Nomenclature 2-Methyl-2-phenylhexane Triphenylmethane Phenylethene 2. Benzene is considered as the parent compound. chlorobenzene bromobenzene nitrobenzene 3.The substituent and the benzene ring togeth