CHEM 3153 1nd EditionExam # 2 Study GuideLecture 10 (February 4)In-Class QuestionShow a plausible mechanism for the following reaction:Step 1: Making the super electrophileStep 2: Nucleophilic attack by benzene- Draw out two hydrogens around π bond for personal clarity.- The intermediate drawn is resonance stabilized.o Also called arenium ion.o Know how to draw resonance structures!! Do not draw them in mechanism.Step 3: Regeneration of aromaticity- Regeneration of aromaticity is favored over addition of Br2 because aromaticity makes the product more stable.- Can also add chlorine in this fashion (seen below).o Cl2 + AlCl3- Other groups can be added to the aromatic ring as well.Integrated Example:1. Which two molecules will react together first?CH3Cl and AlCl3 in order to make the super electrophile.2. Show the mechanism for the first step of the reaction.Chlorine attacks aluminum’s lone pairs.3. Assign formal charges in the molecule produce in question two.Chlorine donates its lone pairs to aluminum, so it gets a positive formal charge and aluminum gets a negative formal charge.4. Show the mechanism for the second step of the reaction.Now that the carbon attached to the chlorine has a partial positive charge, benzene wants to attack it. Carbon will give its e-’s to the chlorine.5. Show the formal charge on the intermediate.Now that the π bond has given up some of its ed, the carbon next to the carbon holding the methyl will have a positive charge.6. Show the mechanism for the last step of the reaction.Friedel Crafts Alkylation (FC Alkylation)- This is the addition of an alkyl group to a benzene ring.- Ex:- Thisis a mechanism for methyl halides (CH3X) and ethyl halides (CH3CH3X)Step 1: Making the super electrophileIn the next step, the carbon group will leave. In its configuration, the positive charge will end upon a secondary carbocation. We can leave positive charges on secondary and tertiary carbocations, but not primary. If that happens, we will get hyperconjugation.Steps 2 and 3 are the same as the previous mechanism, but will be outlined below.Step 2: Nucleophilic attack by benzeneStep 3: Regeneration of aromaticity- FC alkylation can lead to problems of polyalkylationo This is adding many alkyl groups- Ex:- The aromatic ring is nucleophilic.- The alkyl groups are e- donating.- The aromatic ring becomes more e- rich after alkyl group is added.o Better nucleophile = more reactive.Lecture 11 (February 9)In-Class QuestionThe Friedel Crafts Alkylation reaction can only be performed with 1° alkyl halides if they are either methyl or ethyl halides. The use of other 1° alkyl halides can be problematic.Ex: Using a mechanism, explain how the major product is formed in this reaction.Step 1: Making the super electrophileStep 2: Attack by benzeneStep 3: Regeneration of aromaticity- Due to this problem and polyalkylation problem with the FC alkylation, a variation on this reaction can be employed that is more selective.o We will introduce an acyl group as a synthetic precursor to the alkyl group.o Ex: Introducing, the Friedel Crafts Acylation ReactionIntegrated Question:1. Which two molecules react together first?Molecules B and C because benzene won’t attack unless it is a super electrophile.2. Show the mechanism for the first step of the reaction.The chlorine attacks the aluminum with its lone pairs.3. Assign the FC in the molecule produced in question 2.The chlorine donated its e-’s, so it has a positive formal charge. The aluminum received e-’s fromthe chlorine, so it has a negative formal charge.4. Propose a plausible mechanism to obtain the super electrophile.It’s time to boot off the chlorine as it is a good leaving group. To replace the lost electrons, oxygen will donate some of its electrons to make a triple bond.5. Show mechanism for the next step of the reaction.Don’t automatically assume that the atom that has a positive formal charge will be attacked. The π bond will attack the less electronegative atom; the carbon in this case. Oxygen is pulling away ed from the carbon. It will receive its electrons back after the attack.6. Show the mechanism for the last step of the reaction.Now that there’s a positive charge on the benzene ring, electrons need to be donated to restorearomaticity. A hydrogen is removed by the bond between chlorine and aluminum. The electrons then form the pi bond.Another Electrophilic Aromatic Substitution ReactionNitration of Benzene- You need to practice this reaction.- Know the structures of HNO3 and H2SO4- Know how NO2 is made!!o Called the nitronium ion; it’s the super electrophileStep 1: Making the super electrophileStep 2: Reaction with benzene- Think about electronegativity.o Oxygen is more EN than nitrogen. So the π bond attacks the nitrogen.Step 3: Regeneration of aromaticityLecture 12 (February 11)In-Class Question:Propose a mechanism for the following reaction and give the product.- Treat H3PO4 as H+Step 1: Making the super electrophileStep 2: Reaction with benzeneStep 3: Regeneration of aromaticitySulfonation of BenzeneEx: Fuming H2SO4- Mixture of H2SO4 and SO3 gas.- SO3 is a super electrophileo Sulfur is very e- poor due to nature of the S-O π bond.o Since sulfur uses its 3p orbital and oxygen use its 2p orbital to form the π bond, there isn’t very good overlap.o It behaves more like S+---O- instead of S==Oo So the S is very e- poor.Step 1: Attack by benzeneStep 2: Regeneration of aromaticityStep 3: Proton transfer- Reaction is reversible!o Add H2O and H2SO4o Follows principle of microscopic reversibility.o Know the mechanism (lined out below).Step 1: Proton transferStep 2: Break aromaticityStep 3: Regenerate aromaticity Useful Post-EAS Modification of SubstituentsAcyl-Alkyl- Good for after FC acylations.Nitro-Amino- Can be used after nitration reactions.Alkyl-CarboxylSulfonyl-Hydrogen- This is the reverse of fuming (sulfonation of benzene).- Mechanism shown above.Substituents Can Affect Reactivity of Benzene RingTwo types of groups on aromaticity rings:1. Activating groups: gives ed2. Deactivating groups: takes away edActivating Groups: Electron Donating Groups- Donate ed to the ring.o Make aromatic ring more reactive (nucleophilic).Integrated Question:1. Which of the following compounds have e- donating groups attached to their aromatic ring?A, B, and F. Reasons are below:A: alkyl groups are e- donating (hyperconjugation)B: lone pairs next to ring are involved in resonance; they donate their