CHM 234| Aromatic compound (cont.) and Aromatic Reactions
CHM 234| Aromatic compound (cont.) and Aromatic Reactions CHM 234
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This 10 page Class Notes was uploaded by Alvin Notetaker on Sunday March 27, 2016. The Class Notes belongs to CHM 234 at Arizona State University taught by Pillai in Fall 2015. Since its upload, it has received 9 views. For similar materials see General Organic Chemistry II in Chemistry at Arizona State University.
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Date Created: 03/27/16
Aromatic compounds (cont.) Antiaromatic Similar to to aromatics’ criteria, but it needs even number of pi electrons pair. Aromatic compound other than Benzene Nonaromatic Compounds A compound that lacks a continuous systems of p orbitals. Example : Annulenes ring system that are fully conjugated.  Annulenes Nonaromatic Aromatic Antiaromatic 4n+2 4n Example: Aromatic Antiaromatic Antiaromatic Nonaromatic Example: Nonaromatic Aromatic Antiaromatic Aromatic ion Some ring carry formal charge Aromatic Heterocycles Heteroatoms are other atoms that are within the ring other than C or H. Polycyclic Aromatic Compounds More than one ring system together. Reactions of Benzylic Position A carbon that is attached to a benzene ring is benzylic Oxidation The benzylic position needs at least one proton. Free Radical Bromination Substitution Reactions of Benzylic Halides Elimination Reactions Reduction of Aromatic Moiety Hydrogenation Benzene can be reduced only in a forceful manner. (At 100 atm and 150 °C) Chapter 19 Aromatic Substitution Reactions Introduction Halogenation with benzene doesn’t work. To make a substitution, a lewis acid must be introduce. Halogenation This reaction uses mostly bromine and chlorine. This reaction requires a lewis acid catalyst. Lewis acid compound use: FeCl 3and AlCl 3 Mechanism: With iodine, CuCl is needed for this type of reaction. 2 Sulfonation Fuming H 2 4consist of sulfuric acid and SO3gas. Mechanism: Depending on the concentration of the sulfuric acid: Concentrated = forward reaction Diluted = reverse reaction Nitration A mixture of sulfuric acid and nitric acid Mechanism: Reduction a Nitro Substituent Reagent : H , Pt 2 Fe, HCl Sn, HCl Nitro group to an amine group FriedelCrafts Alkylation Mechanism: As for primary halide, they cannot convert into a carbocation since primary halide are very high in energy. So, they undergo h ydride shift. FriedelCrafts Alkylation Limitation 1. Halide must be attached to a sp 3 hybridized carbon. 2. Polyalkylation can occur. ● More than one substituents can form on the benzene 3. Some substituted aromatic rings are too deactivated to react. ● Substituents that withdraws electrons. This is called deactivation. FriedelCrafts Acylation Forms carboncarbon bond Mechanism: ● Acylium ion, RC +=O, is stabilized by resonance. Clemmensen Reaction Activating Group Substituents that are good electron donating group like nitration reaction. Deactivation Group Substituents that are good electron withdrawing group like nitration reaction. Nitro group is a good withdrawing group. The ortho and para formation created a two positive partial charge next to each other which will create an unstable bonding. So, only meta is the most stable of the three formation. So, for major products: Donating group = ortho and para products Withdrawing group = meta products
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