PEPERIKSAAN IJAZAH SARJANA MUDA SAINS EXAMINATION FOR THE DEGREE OF BACHELOR OF SCIENCE SCES1220 : KIMIA ORGANIK I ORGANIC CHEMISTRY I

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1 UNIVERSITI MALAYA UNIVERSITY OF MALAYA PEPERIKSAAN IJAZAH SARJANA MUDA SAINS EXAMINATION FOR THE DEGREE OF BACHELOR OF SCIENCE SESI AKADEMIK 2010/2011 : SEMESTER 1 ACADEMIC SESSION 2010/2011 : SEMESTER 1 SCES1220 : KIMIA ORGANIK I ORGANIC CHEMISTRY I November/ Disember 2010 November/ December 2010 MASA : 2 jam TIME : 2 hours ARAHAN KEPADA CALON : INSTRUCTIONS TO CANDIDATES : Jawab mana-mana EMPAT (4) soalan sahaja. Answer any FOUR (4) questions. (Kertas ini mengandungi 5 soalan dalam 7 halaman yang dicetak) (This question paper consists of 5 questions on 7 printed pages)

2 SCES1220/02 1. (a) (i) Sebatian yang manakah mempunyai tenaga pemutusan ikatan karbon-klorin yang lebih kecil, CH3Cl atau (CH3)3CCl? Terangkan jawapan anda. Which compound has the smaller bond dissociation energy for its carbon-chlorine bond, CH3Cl or (CH3)3CCl? Explain your answer. (ii) Lukiskan hasil monoklorin apabila 2,2,4-trimetilpentana mengalami tindak balas pengklorinan radikal bebas. Draw monochlorinated product(s) when 2,2,4-trimethylpentane is subjected to free radical chlorination. (iii) Apabila radikal bromin bertindak balas dengan 1-butena (CH3CH2CH=CH2), atom hidrogen yang diabstrakkan adalah yang boleh menghasilkan struktur radikal yang distabilkan oleh resonan. Lukis struktur resonan utama bagi radikal ini. When Br radical reacts with 1-butene (CH3CH2CH=CH2), the hydrogen atom which is abstracted is the one which produces a resonance stabilized radical. Draw the major resonance structure of this radical. (iv) Lukiskan hasil terbentuk apabila alkuna H-C C-CH 2 CH 2 -C C-CH 3 ditindak balaskan dengan O 3 diikuti dengan H 2 O. Draw the product(s) formed when the alkyne H-C C-CH 2 CH 2 -C C- CH 3 is treated with O 3 followed by H 2 O.

3 SCES1220/03 (b) Pertimbangkan tindak balas berikut. Sebatian manakah yang dijangkakan merupakan satu-satunya hasil atau hasil utama yang terbentuk? Terangkan jawapan anda dengan menulis mekanisme tindak balas lengkap. Consider the following reactions. Which compound is expected to be either the only product or the major product formed? Justify your answers by writing complete reaction mechanisms. (15 markah/ marks)

4 SCES1220/04 2. (a) Beri hasil utama, bahan pemula atau reagen untuk tindak balas berikut. Di mana berkenaan, tunjukkan stereokimia bahan pemula atau hasil. Give the major product(s), starting material(s) or reagent(s) for the following reactions. Where appropriate, indicate the stereochemistry of the starting material(s) or product(s). (b) Tuliskan mekanisme lengkap bagi menjelaskan hasil yang terbentuk dalam setiap tindak balas berikut. Write complete mechanisms to illustrate the product(s) formed in each of the following reactions. (15 markah/ marks)

5 SCES1220/05 3. Tunjukkan bagaimana EMPAT (4) daripada penukaran berikut dapat dilakukan. Tulis semua reagen yang digunakan dan perantaraan yang terlibat. Show how FOUR (4) of the following transformations can be carried out. Write all reagents used and intermediates involved. (25 markah/ marks) 4. (a) (i) Melihat pada ikatan C 1 C 2 bagi sebatian 1-kloropropana, lukis unjuran Newman bagi konformasi yang paling stabil dan yang paling tidak stabil. Terangkan kemungkinan interaksi molekul yang bertanggungjawab bagi konformasi yang paling tidak stabil. Sighting along the C 1 C 2 bond of 1-chloropropane, draw Newman projection of the most stable and the least stable conformation. Descibe the probable molecular interaction(s) responsible for the least stable conformation.

6 SCES1220/06 (ii) Berapakah bilangan interaksi gerhana H - H yang wujud dalam etana dan siklopropana? How many H H eclipsing interactions are present in ethane and cyclopropane? (iii) Lukiskan struktur dan ramalkan dengan memberi keterangan kestabilan relatif cis-1,2-dimetilsiklopropana dan trans-1,2- dimetilsiklopropana. Draw the structure and predict with explanations the relative stability of cis-1,2-dimethylcyclopropane and trans-1,2- dimethylcyclopropane. (iv) Lukiskan konformasi kerusi yang mungkin bagi cis-1-tert-butil-4- klorosikloheksana dan ramalkan, dengan memberi penjelasan, kestabilan relatifnya. Draw the possible chair conformations of cis-1-tert-butyl-4- chlorocyclohexane and predict, with explanations, their relative stability. (12 markah/ marks) (b) (i) Lukiskan formula perspektif dan unjuran Fischer bagi setiap sebatian berikut: Draw a perspective formula and a Fischer projection for each of the following compounds: (I) (II) (2S,3R)-3-chloro-2-pentanol (R)-1,2-dibromobutane (ii) Putaran tentu bagi (R)-(+)-gliseraldehid adalah +8.7 o. Jika putaran tentu yang dicerap bagi campuran larutan (R)- gliseraldehid and (S)- gliseraldehid adalah +1.4 o, apakah peratusan gliseraldehid yang hadir sebagai R enantiomer? The specific rotation of (R)-(+)-glyceraldehyde is +8.7 o. If the observed specific rotation of a solution of a mixture of (R)- glyceraldehyde and (S)-glyceraldehyde is +1.4 o, what percentage of the glyceraldehydes is present as the R enantiomer? (iii) Berikan penjelasan mekanisme bagi tindak balas berikut. Give the mechanistic explanation for the following reaction. (S)-2-bromobutane + HO - (S)-2-bromobutanol + (R)-2-bromobutanol 50% 50% (13 markah/ marks)

7 SCES1220/07 5. (a) Jelaskan peraturan bagi melukis struktur resonan. Lukiskan struktur resonan bagi setiap sebatian berikut. Susunkan sebatian berikut mengikut penurunan sumbangan struktur hibrid. Explain the rules for drawing resonance contributing structures. Draw the resonance structures for each of the following compounds. Arrange the structures in order of decreasing contribution to the hybrid. (b) Bincangkan mekanisme bagi tindak balas berikut: Discuss the reaction mechanisms for the following reactions: (c) Susunkan sebatian berikut mengikut penurunan kereaktifan terhadap penukargantian elektrofilik. Jelaskan jawapan anda. Arrange the following compounds, in order of decreasing reactivity towards electrophilic substitution. Explain your answer. Benzene, fenol, toluene, nitrobenzene, bromobenzena benzene, phenol, toluene, nitrobenzene, bromobenzene TAMAT END (5 markah/ marks)