This chemistry question involves key chemical concepts and calculations. The detailed solution below walks through each step, from identifying the reaction type to computing the final answer.
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Step 1: Mechanism for 1.1 - Friedel-Crafts Acylation This is a Friedel-Crafts acylation reaction. Benzene reacts with acetic anhydride in the presence of a Lewis acid catalyst (AlCl_3) to form acetophenone. 1. Formation of the acylium ion electrophile: The Lewis acid (AlCl_3) reacts with acetic anhydride to generate a highly electrophilic acylium ion. (CH_3CO)_2O + AlCl_3 & CH_3CO^+ + CH_3COOAlCl_3^- \\ [width=0.9]1.1_step1.png 2. Electrophilic attack on the aromatic ring: The benzene ring, acting as a nucleophile, attacks the acylium ion. This forms a resonance-stabilized arenium ion (or -complex). [width=0.9]1.1_step2.png 3. Deprotonation and restoration of aromaticity: A base (e.g., AlCl_4^- or CH_3COOAlCl_3^-) abstracts a proton from the carbon bearing the acyl group, restoring aromaticity and forming the product, acetophenone. The AlCl_3 catalyst is regenerated. [width=0.9]1.1_step3.png Step 2: Resonance contributors for arenium ions and directing effects for 1.2 For each molecule, we will consider the attack of Br^+ (from Br_2/FeBr_3) at the ortho, meta, and para positions and draw the resonance structures of the resulting arenium ions. The position that leads to the most stable arenium ion (often by delocalizing the positive charge onto the substituent or an adjacent atom with a lone pair) will be the preferred site of attack. a) Phenol (–OH group) The hydroxyl group (–OH) is a strong activating group and an ortho/para director due to the lone pair on oxygen that can stabilize the positive charge in the arenium ion. Ortho attack: [width=0.9]1.2a_ortho.png This arenium ion has a resonance structure where the positive charge is directly on the carbon bearing the hydroxyl group, which is stabilized by the lone pair on oxygen. Meta attack: [width=0.9]1.2a_meta.png The positive charge is never directly on the carbon bearing the hydroxyl group. Para attack: [width=0.9]1.2a_para.png Similar to ortho attack, this arenium ion has a resonance structure where the positive charge is directly on the carbon bearing the hydroxyl group, which is stabilized by the lone pair on oxygen. Conclusion for Phenol: Both ortho and para attacks lead to more stable arenium ions because the positive charge can be delocalized onto the oxygen atom, forming an additional resonance structure. Therefore, the –OH group is an ortho/para director. b) N,N-dimethylbenzamide (–CON(CH_3)_2 group) The N,N-dimethylamide group (–CON(CH_3)_2) is a deactivating group and a meta director. The carbonyl group withdraws electron density from the ring, and the nitrogen's lone pair is delocalized into the carbonyl, not primarily into the ring. Ortho attack: [width=0.9]1.2b_ortho.png This arenium ion has a resonance structure where the positive charge is adjacent to the carbonyl carbon, which is electron-withdrawing, making this structure less stable. Meta attack: [width=0.9]1.2b_meta.png The positive charge is never directly adjacent to the carbonyl carbon. Para attack: [width=0.9]1.2b_para.png Similar to ortho attack, this arenium ion has a resonance structure where the positive charge is adjacent to the carbonyl carbon, making this structure less stable. Conclusion for N,N-dimethylbenzamide: The meta attack avoids placing a positive charge directly adjacent to the electron-withdrawing carbonyl carbon, which would be highly destabilizing. Therefore, the –CON(CH_3)_2 group is a meta director. c) Acetanilide (–NHCOCH_3 group) The acetamido group (–NHCOCH_3) is a moderate activating group and an ortho/para director. The lone pair on the nitrogen can donate electron density to the ring, but it is also delocalized into the carbonyl group, making it a weaker activator than an amino group. Ortho attack: [width=0.9]1.2c_ortho.png This arenium ion has a resonance structure where the positive charge is directly on the carbon bearing the acetamido group, which is stabilized by the lone pair on nitrogen. Meta attack: [width=0.9]1.2c_meta.png The positive charge is never directly on the carbon bearing the acetamido group. Para attack: [width=0.9]1.2c_para.png Similar to ortho attack, this arenium ion has a resonance structure where the positive charge is directly on the carbon bearing the acetamido group, which is stabilized by the lone pair on nitrogen. Conclusion for Acetanilide: Both ortho and para attacks lead to more stable arenium ions because the positive charge can be delocalized onto the nitrogen atom, forming an additional resonance structure. Therefore, the –NHCOCH_3 group is an ortho/para director. Step 3: Ranking substituents for 1.3 The influence on electrophilic aromatic substitution reactions depends on whether the substituent is activating or deactivating, and its strength. Activating groups increase the rate of reaction, while deactivating groups decrease it. a) -F, -CF_3, -NO_2 • -F (Fluoro): Weakly deactivating, ortho/para director (due to lone pair resonance). • -CF_3 (Trifluoromethyl): Strongly deactivating, meta director (due to inductive withdrawal). • -NO_2 (Nitro): Strongly deactivating, meta director (due to resonance and inductive withdrawal). Comparing -CF_3 and -NO_2, the nitro group is generally a stronger deactivator. Order of decreasing influence (most activating/least deactivating to most deactivating): -F > -CF_3 > -NO_2 b) -OH, -OCH_3, -F • -OH (Hydroxyl): Strongly activating, ortho/para director. • -OCH_3 (Methoxy): Strongly activating, ortho/para director. • -F (Fluoro): Weakly deactivating, ortho/para director. Comparing -OH and -OCH_3: -OH is slightly more activating than -OCH_3 because the oxygen in -OH is less sterically hindered and its lone pair is more available for resonance donation to the ring. Order of decreasing influence: -OH > -OCH_3 > -F c) -OH, -CH_2CH_3, -NO_2 • -OH (Hydroxyl): Strongly activating, ortho/para director. • -CH_2CH_3 (Ethyl): Weakly activating, ortho/para director (due to hyperconjugation). • -NO_2 (Nitro): Strongly deactivating, meta director. Order of decreasing influence: -OH > -CH_2CH_3 > -NO_2 Step 4: Mechanism for 1.4 - Friedel-Crafts Alkylation This is a Friedel-Crafts alkylation reaction. Benzene reacts with 2-chloro-2-methylbutane in the presence of a Lewis acid catalyst (AlCl_3) to form 2-methyl-2-phenylbutane. 1. Formation of the carbocation electrophile: The Lewis acid (AlCl_3) reacts with 2-chloro-2-methylbutane to generate a tertiary carbocation. This carbocation is already tertiary and therefore stable, so no rearrangement occurs. [width=0.9]1.4_step1.png 2. Electrophilic attack on the aromatic ring: The benzene ring, acting as a nucleophile, attacks the carbocation. This forms a resonance-stabilized arenium ion (or -complex). [width=0.9]1.4_step2.png 3. Deprotonation and restoration of aromaticity: A base (e.g., AlCl_4^-) abstracts a proton from the carbon bearing the alkyl group, restoring aromaticity and forming the product, 2-methyl-2-phenylbutane. The AlCl_3 catalyst is regenerated. [width=0.9]1.4_step3.png Step 5: Explanation of Friedel-Crafts limitations for 1.5 a) Aniline with acyl chloride and AlCl_3 Reason for not working: Aniline (NH_2) is a strong Lewis base. It reacts with the Lewis acid catalyst (AlCl_3) to form an acid-base complex. This complexation converts the strongly activating amino group into a strongly deactivating group (e.g., -NH_2^+-AlCl_3^-), which is too deactivating for Friedel-Crafts acylation to occur. Other expected product: The acid-base complex between aniline and AlCl_3. [width=0.9]1.5a_product.png b) Benzoic acid with acyl chloride and AlCl_3 Reason for not working: Benzoic acid contains a carboxylic acid group (–COOH), which is a strong electron-withdrawing group. Strong electron-withdrawing groups deactivate the benzene ring significantly, making it unreactive towards electrophilic aromatic substitution reactions like Friedel-Crafts acylation. Other expected product: No reaction or extremely poor yield of a meta-substituted product. [width=0.9]1.5b_product.png c) Benzene with 1-chloropropane and AlCl_3 Reason for not working as expected (to give n-propylbenzene): Friedel-Crafts alkylation with primary alkyl halides often leads to carbocation rearrangements. The primary carbocation formed from 1-chloropropane is unstable and will rearrange via a hydride shift to form a more stable secondary carbocation. This results in the formation of isopropylbenzene as the major product, not n-propylbenzene. Other expected product: Isopropylbenzene. [width=0.9]1.5c_product.png Step 6: Synthetic sequence and reagents for 1.6 a) Synthesis of 3-chlorophenol from benzene To synthesize 3-chlorophenol from benzene, we need to introduce a hydroxyl group and a chlorine atom in a meta relationship. Since both -OH and -Cl are ortho/para directors, a direct approach is difficult. A common strategy is to use a nitro group (a meta director) to control regioselectivity, then convert it to the desired functional group. 1. Nitration of benzene: Introduces a meta-directing group. Benzene HNO_3, H_2SO_4 Nitrobenzene 2. Chlorination of nitrobenzene: The nitro group directs chlorine to the meta position. Nitrobenzene Cl_2, FeCl_3 1-chloro-3-nitrobenzene 3. Reduction of nitro group: Converts the nitro group to an amino group. 1-chloro-3-nitrobenzene Sn, HCl or H_2, Pd/C 3-chloroaniline 4. Diazotization: Converts the amino group to a diazonium salt. 3-chloroaniline NaNO_2, HCl, 0-5^ 3-chlorobenzenediazonium chloride 5. Hydrolysis of diazonium salt: Replaces the diazonium group with a hydroxyl group. 3-chlorobenzenediazonium chloride H_2O, warm 3-chlorophenol The synthetic sequence is: Benzene HNO_3, H_2SO_4 Nitrobenzene Cl_2, FeCl_3 1-chloro-3-nitrobenzene Sn, HCl 3-chloroaniline NaNO_2, HCl 3-chlorobenzenediazonium chloride H_2O, warm 3-chlorophenol b) Reagents for transformations (a-e) (a) Benzene to Acetophenone: This is a Friedel-Crafts acylation. Reagents: CH_3COCl, AlCl_3 (or (CH_3CO)_2O, AlCl_3) (b) Acetophenone to 3-chloroacetophenone: Acetophenone has a carbonyl group, which is a meta-director. Chlorination will occur at the meta* position. Reagents: Cl_2, FeCl_3 (c) 3-chloroacetophenone to 1-chloro-3-ethylbenzene: This involves the reduction of a ketone to an alkane. Reagents: Zn(Hg), HCl, heat (Clemmensen reduction) or N_2H_4, KOH, heat (Wolff-Kishner reduction) (d) 1-chloro-3-ethylbenzene to 1-bromo-3-chloro-5-ethylbenzene: The starting material is 1-chloro-3-ethylbenzene. The ethyl group is an ortho/para director and activating. The chloro group is an ortho/para director and deactivating. The ethyl group is a stronger director. Direct electrophilic bromination of 1-chloro-3-ethylbenzene would primarily occur at the position para to the ethyl group (position 4), which is also para to the chloro group, leading to 1-bromo-3-chloro-4-ethylbenzene. The product shown, 1-bromo-3-chloro-5-ethylbenzene, has bromine at position 5, which is meta to both the ethyl and chloro groups. This position is the least activated and would not be the major product of direct electrophilic bromination. Therefore, this transformation is not achievable by simple electrophilic aromatic substitution reagents. If the question implies a direct bromination, there might be an error in the product structure. Assuming the question requires reagents for the shown transformation, it is not possible with simple reagents. Reagents: Not achievable by simple electrophilic substitution (If a reagent must be provided, and assuming a typo in the product structure to 1-bromo-3-chloro-4-ethylbenzene, then Br_2, FeBr_3 would be used.) (e) 1-bromo-3-chloro-5-ethylbenzene-2-sulfonic acid to 1-bromo-3-chloro-5-ethylbenzene: This is a desulfonation reaction, where the sulfonic acid group is removed. Reagents: H_2SO_4, H_2O, heat (dilute sulfuric acid and heat) Step 7: Mechanism for 2.1 - Diazonium Coupling Reaction This is an electrophilic aromatic substitution reaction where the benzenediazonium ion acts as an electrophile and N,N-dimethylaniline acts as a highly activated nucleophile. The dimethylamino group is a strong activating and ortho/para-directing group. The para position is attacked due to less steric hindrance. 1. Electrophilic attack: The highly activated aromatic ring of N,N-dimethylaniline attacks the terminal nitrogen of the benzenediazonium ion at the para position. This forms a resonance-stabilized arenium ion. [width=0.9]2.1_step1.png 2. Deprotonation and restoration of aromaticity: A base (e.g., solvent or another molecule of N,N-dimethylaniline) abstracts a proton from the para position of the arenium ion, restoring aromaticity and forming the final product, p-(dimethylamino)azobenzene. [width=0.9]2.1_step2.png Step 8: Mechanisms for 2.2 a) Benzyne Reaction for 2-bromo-1,3-dimethylbenzene The reaction conditions (NaNH_2 in NH_3) are characteristic of a benzyne (elimination-addition) mechanism for aryl halides. This mechanism requires an ortho hydrogen atom relative to the leaving group (bromine) for the initial deprotonation step. Upon examining the given reactant, 2-bromo-1,3-dimethylbenzene, the bromine atom is at position 2. The ortho positions (positions 1 and 3) are both substituted with methyl groups (CH_3), meaning there are no hydrogen atoms available at these positions for abstraction by the strong base (NH_2^-). Therefore, the benzyne mechanism is not possible for 2-bromo-1,3-dimethylbenzene. No reaction via the benzyne pathway will occur. The benzyne mechanism is not possible for 2-bromo-1,3-dimethylbenzene because there are no ortho hydrogens available for deprotonation. b) Nucleophilic Aromatic Substitution (SNAr) for 2-chloro-3-carboxy-4-nitrobenzene This is a nucleophilic aromatic substitution reaction. The chlorine atom is replaced by a methoxy group. The presence of the strong electron-withdrawing nitro (NO_2) group para to the leaving group (Cl) and the carboxylic acid (COOH) group ortho to the leaving group activates the ring towards SNAr. 1. Nucleophilic attack: The methoxide ion (MeO^-) acts as a nucleophile and attacks the carbon bearing the chlorine atom. This forms a resonance-stabilized Meisenheimer complex (an anionic -complex). The negative charge is delocalized into the electron-withdrawing nitro group. [width=0.9]2.2b_step1.png 2. Expulsion of leaving group: The chloride ion (Cl^-) is then expelled, restoring aromaticity and forming the final product, 2-methoxy-3-carboxy-4-nitrobenzene. [width=0.9]2.2b_step2.png c) Diazotization and Hydrolysis for 3-methylaniline This reaction proceeds in two main parts: Part 1: Diazotization (formation of the arenediazonium salt) 1. Formation of nitrosonium ion: Nitrous acid (HNO_2) is generated in situ from NaNO_2 and HCl. HNO_2 is then protonated and loses water to form the electrophilic nitrosonium ion (NO^+). NaNO_2 + HCl & HNO_2 + NaCl \\ HNO_2 + H^+ & H_2NO_2^+ \\ H_2NO_2^+ & NO^+ + H_2O \\ 2. Attack of aniline on nitrosonium ion and formation of diazonium ion: The nitrogen of 3-methylaniline attacks the nitrosonium ion, followed by a series of proton transfers and tautomerization, leading to the formation of the 3-methylbenzenediazonium ion. [width=0.9]2.2c_diazotization.png Part 2: Hydrolysis (replacement of the diazonium group with a hydroxyl group) 1. Loss of nitrogen gas: When the arenediazonium ion is warmed in the presence of water, the diazonium group (N_2^+) departs as stable nitrogen gas (N_2), forming an aryl cation. [width=0.9]2.2c_hydrolysis_step1.png 2. Nucleophilic attack by water and deprotonation: Water then acts as a nucleophile, attacking the aryl cation. Subsequent deprotonation yields the 3-methylphenol product. [width=0.9]2.2c_hydrolysis_step2.png 3 done, 2 left today. You're making progress.