(Kertas soalan ini mengandungi 4 soalan dalam 10 halaman yang bercetak) (This question paper consists of 4 questions on 10 printed pages)

Transcription

1 UNIVERSITI MALAYA UNIVERSITY OF MALAYA PEPERIKSAAN IJAZAH SARJANA MUDA SAINS EXAMINATION FOR THE DEGREE OF BACHELOR OF SCIENCE PEPERIKSAAN IJAZAH SARJANA MUDA SAINS DENGAN PENDIDIKAN EXAMINATION FOR THE DEGREE OF BACHELOR OF SCIENCE WITH EDUCATION SESI AKADEMIK 2016/2017 ACADEMIC SESSION 2016/2017 : SEMESTER I : SEMESTER I SCES3120 : KIMIA ORGANIK III ORGANIC CHEMISTRY III Dis 2016/Jan 2017 Dec 2016/Jan 2017 Masa: 3 jam Time: 3 hours ARAHAN KEPADA CALON: INSTRUCTIONS TO CANDIDATES: Jawab semua soalan. Answer all question. (Kertas soalan ini mengandungi 4 soalan dalam 10 halaman yang bercetak) (This question paper consists of 4 questions on 10 printed pages)

2 1. Pengolahan 2- metilsikloheksanon dengan LDA pada suhu - 78 o C membentuk enolat A dan B. Treatment of 2-methylcyclohexanone with LDA at - 78 o C gives enolates A and B. (a) Lukis struktur enolat terbentuk dan nyatakan stereokimia terlibat. Jelaskan jawapan anda. Draw the enolates formed and indicate the stereochemistry involved. Explain your answer. (b) (c) Kawalan kinetik enolat A bertindak balas dengan benzaldehid membentuk dua hasil berisomer yang mungkin. Lukis stuktur kedua-dua stereoisomer and jelaskan jawapan anda. Kinectically controlled enolate reacts with benzaldehyde gives two possible isomeric products. Draw the stuctures of both isomers and explain your answer Lukis mekanisme bagi pembentukan hasil di (b). Draw mechanism for the formation of the product in (b). (14 markah/marks) 2. (a) 5-Metil-3-etoksisikloheks-2-enon bertindak balas dengan MeMgI diikuti dengan H + membentuk 3,5-dimetilsikloheks-2-enon. Jelaskan pembentukan hasil melalui laluan penambahan 1,4- dan 1, Methyl-3-ethoxycyclohex-2-enone reacts with MeMgI followed by H + to give 3,5-dimethylcyclohex-2-enone. Explain the formation of product via 1,4- and 1-2 addition pathways. (b) Dalam mana-mana tindak balas pengalkilan yang melibatkan enolat sebagai perantara, jelaskan kenapa pengalkilan-o merupakan hasil utama apabila In any alkylation reaction that involves enolate as intermediate, explain why O- alkylation is the major product when (i) K + diguna mengantikan Li + K + is used instead of Li + (ii) DMSO menggantikan etanol DMSO is used instead of ethanol (16 markah/marks) 2/10

3 3. (a) (i) (ii) Berikan semua reagen yang tertinggal dalam turutan tindak balas di atas yang membawa kepada (8) suatu bahantara utama dalam sintesis prostaglandin asimetrik Provide all missing reagents in the above sequence of reactions leading to (8)- a key intermediate in an efficient asymmetric synthesis of a prostaglandin. Tunjukkan mekanisme tindak balas enantioselective Diels Alder. Draw out a mechanism for the enantioselective Diels Alder reaction (2) to (3). 3/10

4 (iii) Tunjukkan mekanisme bagi penukaran samada (3) kepada (4) ATAU (5) kepada (6) Draw out reaction mechanisms for either transformation (3) to (4) OR (5) to (6). (iv) Tunjukkan mekanisme lengkap bagi tindak balas iodolactonisation (7) kepada (8). Anda mesti menggunakan sepenuhnya lukisan konframasi 3- demensional. Draw out a detailed mechanism for the iodolactonisation reaction (7) to (8). You must make full use of 3-dimensional conformation drawings. (11 markah/marks) Jawab samada 3 (b) atau 3 (c) Answer either 3(b) or 3(c) 3. (b) (i) Secara ringkas tunjukkan langkah-langkah yang diperlukan penyediaan Alpine Borane daripada siklooto-1,5-diene (9). Briefly describe the steps required for the preparation of the Alpine Borane from cycloocta-1,5-diene (9). (ii) Tunjukkan mekanisme penurunan enantioselektif bagi (10) kepada (11) mengunakan Alpine Borane. Draw out a mechanism for the enantioselective reduction of (10) to (11) by means of the Alpine Borane. (6 markah/marks) 4/10

5 Atau (c) Or (c) 3. (c) Berikan penjelasan bagi pemerhatian berikut. Provide an explanation for the following observations. (6 markah/marks) 5/10

6 3. (d) Kenalpasti hasil-hasil D, E, F dan G dan jelaskan jawapan anda. Tunjukkan mekanisme tindak balas lengkap bagi penukaran (i), (ii) dan (iii). Identify the products (D), (E), (F) and (G) and give reasons for your answer. Draw out detailed reaction mechanisms for all transformations (i), (ii) and (iii).( Note: DIPT is Diisopropyl Tartrate). (6 markah/marks) 6/10

7 3. (e) (i) Kenalpasti reagen-reagen H ke L. Identify all missing reagents H to L. (ii) Lukiskan mekanisme lengkap bagi langkah (14) ke (15) dan (15) ke (16). Lukiskan konformasi 3-demensi akan diperlukan bagi langkah Diels Alder (15) ke (16). Draw out detailed mechanisms for steps (14) to (15) and (15) to (16). 3- dimensional conformational drawings will be required for the Diels Alder step (15) to (16). (12 markah/marks) 7/10

8 4. (a) Jawab soalan (i) dan (ii) Answer questions (i) or (ii). (i) Molekul trans-3,4-dimethylcyclobutene seperti ditunjukkan di bawah boleh terbuka secara konrotatori bagi menghasilkan samada (2E,4E)-hexa-2,4- diene atau (2Z,4Z)-hexa-2,4-diene. Terangkan mengapa kedua-dua hasil ini adalah dibenarkan secara simetri, dan terangkan mengenai fakta bahawa hanya isomer 2E,4E sahaja yang diperolehi. Trans-3,4-dimethylcyclobutene as shown below can open by two conrotatory paths to give either (2E,4E)-hexa-2,4-diene or (2Z,4Z)-hexa-2,4-diene. Explain why both products are symmetry-allowed, and then account for the fact that only the 2E,4E isomer is obtained in practice. trans-3,4-dimethylcyclobutene (ii) Lukiskan hasil daripada pengsiklikan konrotatori dan disrotatori (2Z,4Z,6Z)-octa-2,4,6-triene seperti ditunjukkan di bawah. Di antara keduanya, yang manakah yang dijangkakan akan dilalui oleh tindak balas termal? Draw the products you would expect from conrotatory and disrotatory cyclization of (2Z,4Z,6Z)-octa-2,4,6- triene as below. Which of the two paths would you expect the thermal reaction to follow? (2Z,4Z,6Z)-octa-2,4,6-triene (8 markah/marks) (a) Jawab soalan (i) dan samada (ii) atau (iii). Answer question (i) and either question (ii) or (iii). (i) Takrifkan kesan isotop kinetic primer. Cadangkan penerangan mekanisme bagi nilai k H /k D =1 bagi tindak balas penukargantian aromatic berikut. 8/10

9 Define primary kinetic isotope effect. Propose the mechanistic explanation of the value of k H /k D =1 for the following aromatic substitution reaction. (10 markah/marks) (ii) Gambarkan ayat di bawah dengan menggunakan rajah tenaga: Kesan isotop kinetic berpunca dari tenaga titik sifar yang berbeza bagi ikatan C-H dan C-D. Illustrate the following statement with an energy diagram: Kinetic isotope effects originate in different zero point energies for C-H and C-D bonds. (5 markah/marks) (iii) Berdasarkan gambarajah di bawah, jelaskan sebutan kawalan kinetik dan termodinamik. Based on the following diagram, explain the terms kinetic and thermodynamic product control. (5 markah/marks) 9/10

10 (b) Plot Hammett bagi hidrolisis bermangkinan asid untuk X-C 6 H 4 CO 2 Et dan X-C 6 H 4 CO 2 Me ditunjukkan di bawah. Cadangkan mekanisme tindak balas yang boleh menerangkan plot Hammett yang diperhatikan. The Hammett plots for acid-catalyzed hydrolysis of X-C 6 H 4 CO 2 Et and X- C 6 H 4 CO 2 Me are shown below. Suggest reaction mechanisms which can explain the observed Hammett plots. (12 markah/marks) TAMAT END 10/10