UNIVERSITY OF KWAZULU-NATAL, HOWARD COLLEGE, CHEM 241 : APPLIED ORGANIC CHEMISTRY FOR CHEMICAL ENGINEERS JUNE 2006 EXAMINATION MODEL ANSWERS

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1 School of Chemistry, UNIVERSITY F KWAZULU-NATAL, WARD CLLEGE, CEM 241 : APPLIED RGANIC CEMISTRY FR CEMICAL ENGINEERS JUNE 2006 EXAMINATIN MDEL ANSWERS QUESTIN NE 1.1 Give four reasons why benzene is aromatic. It is cyclic It is has uninterrupted cyclic cloud of π e- above and below the ring. It is planar and each ring atom has unhybridised p orbital. It has an odd number of π e- pairs it satisfies the (4n + 2) π e- rule. ½ mark each. (2) 1.2 Draw resonance forms of cyclopentadienyl anion. (1) cyclopentadienyl anion 1/2 mk 1/2 mk 2

2 School of Chemistry, UNIVERSITY F KWAZULU-NATAL, WARD CLLEGE, CEM 241 : APPLIED RGANIC CEMISTRY FR CEMICAL ENGINEERS JUNE 2006 EXAMINATIN MDEL ANSWERS 1.3 Which ion in each of the following pairs is more stable? Give your reasons. (2) or or is more stable because it is aromatic - it has one π electron pair (it obeys the [4n + 2]π e - rule) { for correct choice and 1.5 for correct reason} is more stable because it is aromatic - it has three π electron pairs (it obeys the [4n + 2]π e - rule) { for correct choice and 1.5 for correct reason} 1.4 Draw structures of the following compounds. m chlorotoluene 4 Bromo -2-chlorophenol c) o Iodobenzene sulphonic acid d) 2,5 Dinitrobenzaldelyde (4) 3

3 School of Chemistry, UNIVERSITY F KWAZULU-NATAL, WARD CLLEGE, CEM 241 : APPLIED RGANIC CEMISTRY FR CEMICAL ENGINEERS JUNE 2006 EXAMINATIN MDEL ANSWERS C 3 Cl c) S 3 I d) Cl C N 2 Br 2 N 4

4 School of Chemistry, UNIVERSITY F KWAZULU-NATAL, WARD CLLEGE, CEM 241 : APPLIED RGANIC CEMISTRY FR CEMICAL ENGINEERS JUNE 2006 EXAMINATIN MDEL ANSWERS QUESTIN NE (Continued) 1.5 Complete the following reactions. Provide answers for A F. (9) I 2 / N 3 A B AlCl 3 c) C + Cl d) C 3 C3C2Cl/ AlCl3 D Cl e) N 2 Br 2 /Fe E f) F S 3 5

5 School of Chemistry, UNIVERSITY F KWAZULU-NATAL, WARD CLLEGE, CEM 241 : APPLIED RGANIC CEMISTRY FR CEMICAL ENGINEERS JUNE 2006 EXAMINATIN MDEL ANSWERS A = I B = Cl 2 mks C 3 C = Cl 2 /FeCl 3 D = 2 mks N 2 C 2 C 3 E = Br 2 mks F = S 3 / 2 S 4 6

6 School of Chemistry, UNIVERSITY F KWAZULU-NATAL, WARD CLLEGE, CEM 241 : APPLIED RGANIC CEMISTRY FR CEMICAL ENGINEERS JUNE 2006 EXAMINATIN MDEL ANSWERS QUESTIN NE (Continued) 1.6 Give a detailed mechanism for the following reactions (6) C 3 C 3 N 3 / 2 S 4 N 2 + C 3 CC 3 2 S 4 Δ 3 C C 3 N 2 S 3 2 N S 3 2 N N 2 + C 3 C 3 C 3 + N N - S 3 N [25] 7

7 School of Chemistry, UNIVERSITY F KWAZULU-NATAL, WARD CLLEGE, CEM 241 : APPLIED RGANIC CEMISTRY FR CEMICAL ENGINEERS JUNE 2006 EXAMINATIN MDEL ANSWERS QUESTIN TW 2.1 Write a structure for each of the following compounds. (5) Phenyl acetate N-Benzylethanamide c) Propanoic anhydride d) Benzoyl chloride e) Cyclohexanone 3 C 3 C N 2 mks c) d) Cl e) 8

8 School of Chemistry, UNIVERSITY F KWAZULU-NATAL, WARD CLLEGE, CEM 241 : APPLIED RGANIC CEMISTRY FR CEMICAL ENGINEERS JUNE 2006 EXAMINATIN MDEL ANSWERS QUESTIN TW (Continued) 2.2 Write structures for the products of the following reactions. + 3 C Cl 3 C (6) 3 C C 3 + C 3 C 2 c) C3 C 2 C C 2 C 3 + C 3 N 2 d) C 3 C + C 3 (excess) + 3 C Cl + 3 C 3 C C 3 + C 3 C 2 + c) C3 C 2 C C 2 C 3 + C 3 N 2 d) C 3 C + C 3 (excess) + N C 3 C 2 9

9 School of Chemistry, UNIVERSITY F KWAZULU-NATAL, WARD CLLEGE, CEM 241 : APPLIED RGANIC CEMISTRY FR CEMICAL ENGINEERS JUNE 2006 EXAMINATIN MDEL ANSWERS QUESTIN TW (Continued) 2.3 Give a detailed mechanism for each of the following reactions. Reaction of acetyl chloride with water to form acetic acid. (4) Reaction of methyl ethanoate with water in the presence acid. 3 C Cl 3 C Cl 3 C Cl - (4) 3 C + 2 1mk C 3 10

10 School of Chemistry, UNIVERSITY F KWAZULU-NATAL, WARD CLLEGE, CEM 241 : APPLIED RGANIC CEMISTRY FR CEMICAL ENGINEERS JUNE 2006 EXAMINATIN MDEL ANSWERS QUESTIN TW (Continued) 2.4 Give the product of the following reactions. (A catalytic amount of acid is present in each reaction.) Cyclopentanone + ethylamine Propanal + ethylamine c) cyclopentanone + diethylamine d) cyclohexanone + ethanol (6) NEt N Et Et C 2 C 3 c) N Et d) [25] 11

11 School of Chemistry, UNIVERSITY F KWAZULU-NATAL, WARD CLLEGE, CEM 241 : APPLIED RGANIC CEMISTRY FR CEMICAL ENGINEERS JUNE 2006 EXAMINATIN MDEL ANSWERS QUESTIN TREE 3.1 Give the products of the following reactions. Indicate whether each reaction is an oxidation or reduction. (9) C 3 C 2 C 2 C 2 C 2 Na 2 Cr S 4 C C 2 KMn 4 -, heat c) C 3 C 2 C 2 CCl d) C 3 C 2 C 2 CNC 3 2 /Pd-C 1. LiAl 4 e) Peracid 2. 2 oxidation C 2 NC 3 oxidation reduction reduction oxidation f) C 3 C 2 C 2 C CC , -78 o C C 3 C 2 oxidation 3.2 Give an example of each of the following named reactions using a chemical equation. Baeyer-Villiger oxidation Swern oxidation c) zonolysis 12 (6)

12 School of Chemistry, UNIVERSITY F KWAZULU-NATAL, WARD CLLEGE, CEM 241 : APPLIED RGANIC CEMISTRY FR CEMICAL ENGINEERS JUNE 2006 EXAMINATIN MDEL ANSWERS [15] Baeyer-Villiger oxidation: Aldehyde RC 2 Acid 2 mks Ketone RC 2 Ester Swern oxidation: Primary alcohol 1. DMS, Cl 2 C 2 2. Et 3 N Aldehyde 2 mks c) Wolff-Kshner reduction: Ketone 1. N /eat Alkane 2 mks QUESTIN FUR 4.1 Which peak would be more intense in the mass spectrum of the following compounds? 3-methylpentane 2-methyl pentane c) 2-hexanol (3) C 4 9 = m/z 57 C 3 7 = m/z 43 c) C 5 11 = m/z 71 13

13 School of Chemistry, UNIVERSITY F KWAZULU-NATAL, WARD CLLEGE, CEM 241 : APPLIED RGANIC CEMISTRY FR CEMICAL ENGINEERS JUNE 2006 EXAMINATIN MDEL ANSWERS QUESTIN FUR (Continued) 4.2 Using curved arrows, show the principal fragment that would be observed in the mass spectrum of each of the following compounds. C 3 (C 2 ) 3 C 2 C 3 C 2 C 2 C 2 C 3 (6) -e 1.5 mk C + i - e iii ii i + C 3 iii ii + C 3 C 2 3 C + C 3 C 2 C 2 14

14 School of Chemistry, UNIVERSITY F KWAZULU-NATAL, WARD CLLEGE, CEM 241 : APPLIED RGANIC CEMISTRY FR CEMICAL ENGINEERS JUNE 2006 EXAMINATIN MDEL ANSWERS 4.3 Indicate which of the following compounds has a vibration that is infrared Inactive or active? Acetone active 2 inactive c) 2 active d) ethane active (2) 4.4 A UV spectrum of acetone shows two λ max at 195nm (ε = 9000) and 274nm (ε = 13.6). What electronic transitions are responsible for the two λ max s? (i) λ max at 195 nm: (ii) λ max at 274 nm: π to π n to π (2) [13] QUESTIN FIVE 15

15 School of Chemistry, UNIVERSITY F KWAZULU-NATAL, WARD CLLEGE, CEM 241 : APPLIED RGANIC CEMISTRY FR CEMICAL ENGINEERS JUNE 2006 EXAMINATIN MDEL ANSWERS 5.1 ow many signals would you expect to see in the 1 NMR spectrum of each of the following compounds? C 3 C 2 C 2 C 3 Cl c) 2-pentanone 2 signals 2 mks 3 signals 2 mks c) 4 signals 2 mks (6) 5.2 A signal has been reported to occur at 600z downfield from TMS in an NMR spectrometer? What is the chemical shift of the signal? What would its chemical shift be in an instrument operating at 100Mz? 2.0 ppm 2.0 ppm (3) 5.3 Indicate the number of signals and the multiplicity of each signal in the 16

16 School of Chemistry, UNIVERSITY F KWAZULU-NATAL, WARD CLLEGE, CEM 241 : APPLIED RGANIC CEMISTRY FR CEMICAL ENGINEERS JUNE 2006 EXAMINATIN MDEL ANSWERS 1 NMR spectrum of 1-bromo-3-iodopropane C 4 (3) 1 signal, triplet Br 1 signal; multiplet I 1 signal; triplet 2 mks C 4 1 signal, singlet [10] QUESTIN SIX 6.1 What is a polymer? (1) A polymer is a large molecule made by linking together repeating units of small molecules called monomer. [ ] 6.2 What are the two major classes of synthetic polymers? (2) (i) Addition polymer ( chain-growth polymer) [] (ii) Codensation polymer ( step-growth polymer) [ ] 6.3 The repeating unit of a polymer is called? (0.5) Monomer [ 0.5] 17

17 School of Chemistry, UNIVERSITY F KWAZULU-NATAL, WARD CLLEGE, CEM 241 : APPLIED RGANIC CEMISTRY FR CEMICAL ENGINEERS JUNE 2006 EXAMINATIN MDEL ANSWERS 6.4 What are the three stages of radical polymerization? (i) Chain initiation [ ] (ii) Chain propagation [ ] (iii) Chain termination [ ] (1.5) 6.5 What is a synthetic rubber? A synthetic rubber is a polymer of dienes other than isoprene ( 2-methyl-1,3- butadiene) (2) 6.6 Give the structure of neoprene. (2) Cl Cl n > 5000 [10] END 18