2008有机化学复习(第一期)2008有机化学复习(第一学期)2008有机化学复习(第一学期)2008有机化学复习(第一学期).ppt

Benzenes Alchohs 1. Benezne Reactions of Arenes The reactivity issues of arenes can be separated into two types of reactions:? Reactions of electrophiles directly on the aromatic ring Reactions of the substituents (since the neighbouring aromatic group influences its reactivity). The reactivity issues on the aromatic ring can be separated into two types of reactions:? 1. One mode of chemical reactivity involves the ring itself as a functional group and includes: Reduction: Catalytic hydrogenation Electrophilic aromatic substitution: The most important reaction type of benzene and its derivatives 2. The reactions encompasses those in which the aryl group acts as a substituent and affects the reactivity o functional unit to which it is attached Reactions of the Benzylic position Benzylic C-H can easily be radically halogenated since the benzylic radical is resonance stabilized. Benzylic C-H bonds of alkyl benzenes can be oxidized to give benzoic(苯甲酸)acids Benzylic halides readily undergo nucleophilic substitution reactions even with weak nucleophiles. Benzylic halides or alcohols readily eliminate to give conjugated alkenes. Electrophilic Aromatic Substitution Mechanistic Principles of Electrophilic Aromatic Substitution Step 1: Step 2: The relative rates of attack at various positions in toluene: The relative rates of attack at various positions in trifluoromethylbenzene: 实验事实表明： 一个致活基使苯环所有位置活化。而由于该基团对于其邻，对位的活化高于其间位，故表现出对邻，对位的定位作用。 一个致钝基使苯环所有位置钝化，包括其间位。由于其对邻，对位的钝化作用更强，使之表现出间位的定位效应。 因此，邻，对位定位效应和间位定位效应都是同样地形成：任一基团（无论是致活或致钝），对其邻，对位的影响最强。 Halogenation X2/Fe Nitration HNO3/H2SO4 Sulfonation H2SO4 Fridel-Craft Alkylation RX/AlCl3 C+: R C3 Rearrangement Acylation RCOX/AlCl3 Alkylation = Acylation then reduction Example: Multiple Substituent Effects The directing effects of substituents reinforce each other. In case in which the directing effects of individual substituents oppose each other, i