RI Arenes Remedial

Name: ………………………………………. ( ) Class: ……………. Date: ……………. Raffles Institution Year 6 H2 Chemistry 2025 Set A T1W8 – Arenes Notes: ⎯ Pre-ChemFocus Activity ⎯ • Familiarise yourself with the following mechanism: Electrophilic substitution of arenes • To view infopack at IVY > C2025 – H2 CHEMISTRY > Pages > [ChemFocus] T1W8 Arenes > FIRST VIDEO ONLY • • • •

Self-Check Questions 1 Suggest the major organic product(s) formed from the following reactions. (Refer to the Data Booklet for directing effects) (a) (b) (c) (d) (e) Check your answers at IVY > C2025 – H2 CHEMISTRY > Pages > [ChemFocus] T1W8 Arenes > Remaining videos

2 The nitration of benzene requires concentrated nitric acid and concentrated sulfuric acid, heated to 55 °C. Explain whether the nitration of chlorobenzene requires a temperature greater than, equal to, or less than 55 °C. ……………………………………………………………………………………………….…….. …………………………………………………………………………………….……………..[1] 3 Methylbenzene undergoes nitration to form a mixture of 1-methyl-2-nitrobenzene and 1-methyl-4-nitrobenzene. (a) A description of the reaction mechanism producing 1-methyl-4-nitrobenzene is illustrated below. Correct the mechanism by annotating on the figure below. (b) Explain why 1-methyl-4-nitrobenzene was produced in greater amount compared to 1-methyl-2-nitrobenzene. ………………………………………………………………………………………………. …………………………………………………………………………………….………[1]

Tutorial Discussion Questions (to complete before Chemfocus session) 1a State the reagents and conditions needed in each of the following schemes. Draw the structure of the intermediate organic compound in each case. (Hint: consider the directing effects of the group(s) already bonded to the benzene ring.) (i) Reagents and conditions Step 1: …………………………………………………………………………………… Step 2: …………………………………………………………………………………… (ii) Reagents and conditions Step 1: …………………………………………………………………………………… Step 2: …………………………………………………………………………………… (iii) Reagents and conditions Step 1: …………………………………………………………………………………… Step 2: …………………………………………………………………………………… Step 1 Step 2 Br NO2

2a (i) Draw the mechanism of the reaction to form compound A from benzene, showing any intermediates, and movement of electron pairs by using curly arrows. A [2] (ii) Draw the major product formed when compound A reacts with BrCl in the presence of a Lewis acid catalyst. Explain your answer Major product: ……………………………………………………………………………………………….. ……………………………………………………………………………………………..[2] CH3O

Tutorial Practice Questions (to be attempted IN CLASS) 1b [RI 2001 Promos/C3] Compound A has a molecular formula of C 9H8. When reacted with cold acidified potassium manganate(VII), compound A forms B, C9H10O2. However, when the mixture is further heated, compound C, C8H6O4, is formed. Mononitration of C gives a mixture of products. C can also be synthesised via the following reaction scheme. [10] Information Deductions Compound A has a molecular formula of C9H8. When reacted with cold acidified potassium manganate(VII), compound A forms B, C9H10O2. A has __________ which underwent ______ ___________, forming a _______. However, when the mixture is further heated, compound C, C8H6O4, is formed. A has ___ ______ _______ which underwent ______ ________ ___________, giving 2 ______ groups. C could be: or or Mononitration of C gives a mixture of products. C must be or as nitration of will only give 1 nitrated product. –CH3 is a ____-directing group. C is: A is: B is:

2b AlCl3 acts as a Lewis acid catalyst for electrophilic substitution of the benzene ring. Describe the mechanism of the reaction above. [3]

Self-Check Questions 1 (a) CH3 conc HNO3, conc H2SO4, 30oC CH3 NO2 CH3 NO2 (b) FeBr3, Br2 NO2 NO2 Br (c) AlCl3 , O CH3CH2Cl O (d) AlCl3 , O ClBr Br O Br O (e) KMnO4(aq), H2SO4(aq), heat COOH COOH 2 The chloro -substituent is electron withdrawing , causing the benzene ring to be more electron poor / less electron rich . Hence, the benzene ring is less susceptible to electrophilic attack, hence a higher temperature is needed for reaction to occur.

3 (a) Electrophilic substitution NO2 NO2H NO2H NO2 H2SO4 2H2SO4 + HNO 3 NO 2 + + 2HSO 4 - + H 2O HSO4 - slow fast (b) The –CH3 group poses steric hindrance to the approach of the electrophile at the 2-position during the reaction. Hence, substitution by –NO2 at the 2-position with respect to –CH3 occurs less than the 4-position.

Set A Tutorial Discussion Questions (to complete before Chemfocus session) 1a (i) Intermediate: NO2 Step 1: concentrated HNO3, concentrated H2SO4, 30 °C Step 2: Br2, AlBr3 (ii) Intermediate: Cl Step 1: Cl2, AlCl3 Step 2: CH2CHCH2Cl, AlCl3 (iii) Intermediate: Final product: Br HO NO2 Step 1: CH2CHCH2Cl, AlCl3 Step 2: concentrated HNO3, concentrated H2SO4, 30 °C 2a (i) O C CH3 Cl AlCl3 O C+ CH3 AlCl4 - Electrophilic substitution O C+ CH3 slow H CH3 O H CH3 O AlCl4 - fast O AlCl3 HCl