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REAKSI ELIMINASI

REAKSI ELIMINASI. PELEPASAN MOLEKUL YZ DARI ATOM-ATOM C BERDAMPINGAN DLM SUATU MOLEKUL PEREAKSI. DEHIDROHALOGENASI DAN DEHIDRASI. DEHIDROHALOGENASI ALKIL HALIDA. PELEPASAN/ PENARIKAN HX DARI ATOM-2 C BERDAMPINGAN DLM SEBUAH ALKIL HALIDA DILAKUKAN DG BASA KUAT

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REAKSI ELIMINASI

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  1. REAKSI ELIMINASI PELEPASAN MOLEKUL YZ DARI ATOM-ATOM C BERDAMPINGAN DLM SUATU MOLEKUL PEREAKSI. DEHIDROHALOGENASI DAN DEHIDRASI

  2. DEHIDROHALOGENASI ALKIL HALIDA • PELEPASAN/ PENARIKAN HX DARI ATOM-2 C BERDAMPINGAN DLM SEBUAH ALKIL HALIDA • DILAKUKAN DG BASA KUAT • MISALNYA: CH3ONa, C2H5ONa DAN (CH3)3COK

  3. CONTOH DEHIDROBROMINASI ALKIL BROMIDA

  4. DEHIDRASI ALKOHOL • PELEPASAN/ PENARIKAN H2O DARI ATOM-2 C BERDAMPINGAN DLM SEBUAH ALKOHOL • DILAKUKAN DG ASAM KUAT • MISALNYA: H2SO4 DAN H3PO4

  5. MEKANIME REAKSI ELIMINASI • REAKSI ELIMINASI BIMOLEKULER (E2) r = k [R-X].[:B-] r = k [CH3CHBrCH3].[C2H5O-] • REAKSI ELIMINASI UNIMOLEKULER (E1) r = k [R-X] r = k [(CH3)3C-Cl]

  6.  REAKSI E2 • DEHIDROBROMINASI ISOPROPIL BROMIDA DG LARUTAN NATRIUM ETOKSIDA DLM ETANOL

  7. MEKANISME REAKSI E2 • BASA MENYERANG AT. H  DARI ARAH BERLAWANAN DG X (Br) • AT . X (Br)  PERGI DR ARAH BERLAWANAN DG BASA SBG ION X- (Br-) • AT-2 C  DAN  MEMBENTUK IKATAN RANGKAP MENGHASILKAN ALKENA

  8. REAKSI E1 • DEHIDROBROMINASI t-BUTIL BROMIDA DG LARUTAN NATRIUM ETOKSIDA DLM ETANOL

  9. MEKANISME REAKSI E1 • ALKIL HALIDA MENGALAMI IONISASI MENGHASILKAN ION KARBONIUM • BASA MENYERANG AT. H  • AT C  MEMBENTUK IKATAN RANGKAP DENGAN AT. C  MENGHASILKAN ALKENA

  10. KOMPETISI SN2 DAN E2 PD HALIDA 3o KENAIKAN T TERJADI REAKSI E2

  11. KERUAHAN BASA PEREAKSI • KERUAHAN BASA PEREAKSI MENDORONG REAKSI ELIMINASI

  12. KEBASAAN • BASA LEMAH SPT Cl-, CH3COO-, Br-, I- MENDORONG SN2 • BASA KUAT: C2H5O-, OH-, NH2- MENDORONG E2

  13. KOMPETISI SN2 DAN E2 • REAKSI SN2 MELIBATKAN BASA LEMAH, BASA SEDERHANA DLM PELARUT POLAR, DAN SUHU RENDAH • REAKSI E2 MELIBATKAN BASA KUAT, BASA MERUAH, DLM PELARUT POLAR, DAN SUHU TINGGI.

  14. BAGAIMANA KOMPETISI SN1 DAN E1 • REAKSI E1 MELIBATKAN KARBOKATION STABIL, BASA LEMAH, PELARUT POLAR DAN SUHU TINGGI • REAKSI SN1 MELIBATKAN KARBOKATION STABIL, BASA LEMAH, PELARUT POLAR DAN SUHU RENDAH

  15.   ATURAN ZAITSEV • DEHIDROBROMINASI 2-BROMO-2-METILBUTANA DG NATRIUM ETOKSIDA • REAKSI ELIMINASI TERJADI DG MEMBERIKAN ALKENA YG LEBIH TERSUBSTITUSI.

  16. BUKTI LAIN ATURAN ZAITSEV • DEHIDROKLORINASI NEOMENTIL KLORIDA DAN MENTIL KLORIDA DG NATRIUM ETOKSIDA

  17.   ANTI ZAITSEV • DEHIDROBROMINASI 2-BROMO-2-METILBUTANA DG KALIUM t-BUTOKSIDA • ELIMINASI DG BASA MERUAH MEMBERIKAN ALKENA YG KURANG TERSUBSTITUSI.

  18. BAGAIMANA KOMPETISI SN1 DAN E1 • REAKSI E1 MELIBATKAN KARBOKATION STABIL, BASA LEMAH, PELARUT POLAR DAN SUHU TINGGI • REAKSI SN1 MELIBATKAN KARBOKATION STABIL, BASA LEMAH, PELARUT POLAR DAN SUHU RENDAH

  19. PROBLEM 1 • WHEN CIS -1-BROMO-4-tert-BUTYLCYCLOHEXANE IS TREATED WITH SODIUM ETHOXIDE IN ETHANOL, IT REACT RAPIDLY. THE PRODUCT IS 4-tert-BUTYLCYCLOHEXENE. UNDER THE SAME CONDITIONS, TRANS-1-BROMO-4-tert-BUTYLCYCLOHEXANE REACTS VERY SLOWLY. WRITE CONFORMATIONAL STRUCTURE AND EXPLAIN THE DIFFERENCE IN REACTIVITY OF THIS CIS-TRANS ISOMERS.

  20. REAKSINYA

  21. JAWAB PROBLEM 1 • PD ISOMER CIS TERDAPAT 2 AT H  DG POSISI AKSIAL, BEGITU JUGA Br BERADA PD POSISI AKSIAL SHG REAKSI E2 BERLANGSUNG LEBIH CEPAT. • PD ISOMER TRANS BAIK AT H  MAUPUN Br YG AKAN BEREAKSI DLM POSISI EQUATORIAL, SEHG MENYEBABKAN REAKSI E2 SANGAT LAMBAT (SULIT).

  22. REAKSINYA

  23. PROBLEM 2 • A). When cis-1-bromo-2-methylcyclohexane undergoes an E2 reaction, two product (cycloalkenes) are formed. What are these two cycloalkenes, and which would you expect to be the major product? Write conformational structures showing how each is formed. • B) When trans-1-bromo-2-methylcyclohexane reacts in an E2 reaction, only one cycloalkene is formed. What is this product? Write conformational structures showing why is the only product.

  24. KESIMPULAN

  25. A BIOLOGICAL NUCLEOPHILIC SUBSTITUTION REACTION: BIOLOGICAL METHYLATION • THE CELLS OF LIVING ORGANISMS SYNTHESIZE MANY OF THE COMPOUNDS THEY NEED FROM SMALLER MOLECULES. • A NUMBER OF REACTIONS TAKE PLACE IN THE CELLS OF PLANTS AND ANIMALS THAT INVOLVE THE TRANSFER OF A METHYL GROUP FROM AN AMINO ACID CALLED METHIONINE TO SOME OTHER COMPOUND.

  26. SOME OF THE COMPOUNDS THAT GET THEIR METHYL GROUP FROM METHIONINE

  27. METHYL TRANSFER MECHANISM

  28. BIOSYNTHESIS OF CHOLINE

  29. DEHIDRASI ALKOHOL • PELEPASAN H2O DR ALKOHOL-2 MELALUI PEMANASAN DG ASAM KUAT • ASAM BRONSTED: H2SO4 DAN H3PO4 ASAM LEWIS: ALUMINA (Al2O3) DLM INDUSTRI • REAKSI DEHIDRASI ALKOHOL MENUNJUKKAN BBP KARAKTERISTIK PENTING.

  30. KONDISI REAKSI • ALKOHOL PRIMER MEMERLUKAN ASAM PEKAT DAN SUHU TINGGI

  31. CAMPURAN ALKENA • BBP ALKOHOL TERDEHIDRASI MEMBERIKAN HASIL CAMPURAN ALKENA • MENGIKUTI ATURAN ZAITZEV

  32. PENATAAN ULANG • BBP ALKOHOL 1o DAN 2o MENGALAMI PENATAAN ULANG SELAMA DEHIDRASI

  33. MEKANISME UMUM DEHIDRASI ALKOHOL TERKATALISIS ASAM • MENGIKUTI MEKANISME E1

  34. MEKANISME PENATAAN ULANG • PENATAAN ULANG SELAMA DEHIDRASI DARI 3,3-DIMETIL-2-BUTANOL

  35. FINAL PRODUCT

  36. BEBERAPA PERGESERAN DLM PENATAAN ULANG ION KARBONIUM

  37. DEBROMINATION OF VICINAL DIBROMIDES • VIC-DIBROMIDES UNDERGO THE LOSS OF A MOLECULE OF BROMINE (Br2)WHEN THEY ARE TREATED WITH A SOLUTION OF SODIUM IODIDE IN ACETON OR MIXTURE OF ZINC DUST IN ETHANOL. • DEBROMINATION BY SODIUM IODIDE TAKE PLACE BY AN E2 MECHANISM.

  38. THE MECHANISM OF DEBROMINATION

  39. PROBLEM 1 • Although ethyl bromide and isobutyl bromide are both primary halides, ethyl bromide undergoes SN2 reactions more than ten times faster than isobutyl bromide. When each compound is treated with a strong base (CH3CH2O-), isobutyl bromide gives a greater yield of elimination products than substitution products, whereas with ethyl bromide this behavior is reversed. What factor accounts for these results?

  40. PROBLEM 2 • Consider the reaction of I- with CH3CH2Cl. (a). Would you expect the reaction to be SN1 or SN2? The rate constant for the reaction at 60o is 5x10-5 liter mole-1 sec-1. (b). What is the reaction rate if [I-] = 0.1 mole liter-1 and [CH3CH2Cl] = 0.1 mole liter-1? (c). If [I-] = 0.1 mole liter-1 and [CH3CH2Cl] = 0.2 mole liter-1? (d). If [I-] = 0.2 mole liter-1 and [CH3CH2Cl] = 0.1 mole liter-1? (e). If [I-] = 0.2 mole liter-1 and [CH3CH2Cl] = 0.2 mole liter-1?

  41. PROBLEM 3 • When tert-butyl bromide undergoes SN1 hydrolisis, adding a “common ion” (i.e NaBr) to the aqueous solution has no effect on the rate. On the other hand when (C6H5)2CHBr undergoes SN1 hydrolisis, adding NaBr retards the reaction. Given that the (C6H5)2CH+cation is known to be much more stable than the (CH3)3C+ cation, provide an explanation for the different behavior of the two compounds.

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