Reaction Mechanism Exercise # 4

Exercise # 4 1. [Subjective Type Questions] In each of the following pairs of species which species is better leaving group : (a) OH and H2O (b) OH and F (c) Br and F 2. 3. 4. 5. and Label each of the following solvent as Protic or Aprotic (a) Tetrahydrofuran (b) Acetonitrile (c) Acetic acid (e) DMSO (f) Formamide (g) Cyclohexane (d) Acetone (h) Ammonia Which of the following are non-polar solvent ? (a) DMS (b) CCl4 (e) Ethyl alcohol (f) Dimethylacetamide (c) CHCl3 (g) Benzene (d) Acetone (h) Tetrahydrofuran Which of the followings are electrophile ? – (a) CN (b) H+ (c) Br+ (d) AlCl3 (e) BH3 (g) NH3 (h)   (d) (CH3)3 N (e) :CH2 (f) Which of the followings are nucleophille ? (a) HS– 6. (d) (b) BF3 (c) C2 H5 – OH Arrange the given species in decreasing order of their nucleophilicity : (a) H2O (b) 7. Which compound in the following couples will react faster in SN1 reaction and why ? (a) 1-Bromopentane or 2-Bromopentane (b) 1-Bromo-2-methylbutane or 2-Bromo-2-methylbutane. 8. What effect do you expect due to following changes in SN1 reaction of (CH3)3CBr with CH3OH ? (a) The concentration of (CH3)3CBr is doubled and that of CH3OH is halved. (b) The concentration of both (CH3)3CBr and CH3OH are tripled. 9.  A + B A and B are two structural isomeric products of this reaction. Identify each. Which is predominant ? REACTION MECHANISM 10. Explain the order of the rate of esterification of the following acid with MeOH : CH3COOH > MeCH2COOH > Me2CHCOOH > Me3CCOOH 11. What will be the major product of the following reaction ? + CH3OH  (a) (b) CH3– –OC2H5 + H2O  12. Write the correct reactivity order with NaOH for the following compounds. 13. Write the product of the following reaction with proper stereochemistry. CH3 OH   Products 14. Arrange the compounds of each set in order of reactivity towards SN2 displacement. (a) 2-Bromo-2-methylbutane, 1-Bromopentane, 2-Bromopentane (b) 1-Bromo-3-methylbutane, 2-Bromo-2-methylbutane, 2-Bromo-3-methylbutane 15. What will be the major product of the following reaction ? NaOH    PCl (a) CH –CH–CH–CH   5  (b)  3 3 OH 16. H H3C CH3 H I Arrange the following in decreasing order of their reactivity with an electrophile. (I) (II) (III) (IV) NO2 17. DMSO CH3 Cl Complete the following reactions : O (a) + (CH3)3C-Cl  (b) AlCl3 C + Cl AlCl3   18. Give the major product of monobromination of following compounds. (a) 19. (b) (c) (d) Give the products in following reactions : Cl O2N CH3 – SNa    (a) NO2 NaOH    (b)   NO2 20. Complete the following reaction. ( i) PhMgBr (a) Ph–CHO    (b) (ii ) H2 O HCN   21. How many compounds out of following will give secondary alcohol on treatment with Grignard reagent. (a) Ph–CO–CH3 (b) Ph–CHO (c) HCHO (d) CH3CH2CHO 22. Give products of reaction when 2-Methylbut-2-ene react with HBr in presence and absence of peroxide. Cl2   X (major product) + Y (minor product) h 23. Give structure of X & Y. 24. What will be order of reactivity of following compounds towards ionic addition of HBr ? CH3 | Ph  C  CH  CH3 CH3  CH  CH  CH3 III I Ph | Ph  C  CH  CH3 IV 25. Give the product formed when But-1-yne reacts with two moles of Br2. 26. Give the product formed when But-1-yne reacts with two moles of HBr in prensence of peroxide. 27. Arrange the following alcohol in increasing order of reactivity towards acid catalyzed dehydration. (I) 28. (II) (III) What would be the major product in the following reaction ? OH OH (a) conc.H2SO4 (b) conc.H2SO4 REACTION MECHANISM 29. What would be the major product in the following reaction ? CH3 alc.KOH F 30. Give major product and classifiy the mechanism in the following reactions. alc.KOH (a) Conc. NaOH (c) 31. (b) Arrange the following alkyl halide in increasing order of reactivity towards alcoholic KOH. CH3 (I) 32. CH3 (II) CH3–C–CH2CH3 (III) CH3–C–CH2CH3 Br Cl What is the major product of dehydrohalogenation when following compounds are treated with alcoholic KOH. Br Cl (a) CH3–C–CH2–CH3 CH3 (c) CH3–CH–CH2–Br (b) CH3 CH3 33. ‘X’ is a smallest optically active alkanol. On dehydration it can form Y number of alkenes (including stereoisomers). On reaction with Lucas reagent it forms Z number of alkyl halides (including stereoisomers). Identify the numbers Y and Z. 34. 3, 3-Dimethylbutan-2-ol loses a mole of water in the presence of concentrated sulphuric acid to give tetramethylethylene as a major product. Suggest a suitable mechanism. 35. Predict the major products (including stereochemistry) when R–2–Butanol reacts with the following reagents. (a) PBr3 (b) SOCI2 / (c) Lucas reagent (d) TsCI / pyridine, then NaI + KOH + MeOH  Product , Identify the product. 36. Cl – CH2 – CH2 – CH2 – 37. The order of nucleophilicity in a period does not depend on nature of solvent whether it is protic or aprotic but the order of nucleophilicity in a group is different in polar protic and polar aprotic solvent. Explain. 38. Write the product of the following reaction : (a) (b) CH3–CH2–CH2–CH2–Br (c) 39. (a) Optically active 2-Bromobutane undergoes recemization on treatment with a solution of KBr.Give a mechanism for this racemization. (b) In contrast, optically active 2-Butanol does not recemize on treatment with a solution of KOH. Explain why a reaction like that in part (a) does not occur. (c) Optically active 2-Butanol racemizes in dilute acid. Propose a mechanism for this racemization. 40. Identify the reactants / products in following reactions :  (P + Q) (a) conc. HI    (X + Y) (b) 41. (c) HI (conc.)  W  excess (d) HI (conc.)  (CH3)2CHI + CH3CH2CH2I Z  excess + CH3I When ethyl bromide is added to potassium t-butoxide, the product is ethyl t-butyl ether. CH3 CH2 – Br ethyl bromide + (CH3 )3 C – OK potassium t butoxide  (CH3 )3 C – O – CH2 CH3 ethyl t butyl either (a) What happens to the reaction rate if the concentration of ethyl bromide is doubled? (b) What happens to the rate if the concentration of potassium t-butoxide is tripled and the concentration of ethyl bromide is doubled? (c) What happens, if the temperature is raised? 42. When (R)-2-bromobutane is heated with water, the SN1 substitution proceeds twice as fast as the SN2. Calculate the approximate enantiomeric excess and the specific rotation expected for the product. The specific rotation of (R)-2 butanol is –13.5o. 43. In 80% ethanol at 55ºC Isopropyl bromide react with hydroxide according to the following kinetic equation. where the rate is expressed as moles per litre per second. rate = 4.7 × 10–5 (RX) (OH–) + 0.24 × 10–5 (RX) What percentage of isopropyl bromide react with SN1 mechanism when [OH–] conc is 5 molar 44. The alkene (X) produced by solvolysis of 3-chloro-3-methylpentane, is more in quantity than the alkene (Y) produced by solvolysis of 3-chloro-3-ethylpentane. Explain and also write the structure of X and Y. 45. Which reacts faster (a) Ph CH2 Br (b) PhCH2 – CH2 Br (c) Ph CH2 – CH2 – Cl 46. and and and Ph CMe2 Br (H2O – C2H5OH) Ph CMe2 Br (Na – Acetone) Ph CMe2 Br (KOH + C2H5OH) What is the effect of increasing solvent polarity over the reactions   (a) CH3 – Cl + NH3  CH3 NH3 Cl 47.   (b) Me3 S + OH  Me – OH + Me2S + KNH2   Product , Identify the product.