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Nucleophilic Substitution

Nucleophilic Substitution. Functional Group Transformation By Nucleophilic Substitution. –. –. : X. Y :. Nucleophilic Substitution. +. R. +. Y. R. X. nucleophile is a Lewis base (electron-pair donor) often negatively charged and used as Na + or K + salt

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Nucleophilic Substitution

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  1. Nucleophilic Substitution

  2. Functional Group Transformation By Nucleophilic Substitution

  3. – – : X Y : Nucleophilic Substitution + R + Y R X • nucleophile is a Lewis base (electron-pair donor) • often negatively charged and used as Na+ or K+ salt • substrate is usually an alkylhalide

  4. X C C Nucleophilic Substitution Substrate cannot be an a vinylic halide or an aryl halide, except under certain conditions X

  5. – .. R X R' O: .. .. – + R' R : X O .. Examples of Nucleophilic Substitution Alkoxide ion as the nucleophile + gives an ether

  6. Example (CH3)2CHCH2ONa + CH3CH2Br Isobutyl alcohol (CH3)2CHCH2OCH2CH3 + NaBr Ethyl isobutyl ether (66%)

  7. O R X O Examples of Nucleophilic Substitution Carboxylate ion as the nucleophile – .. + R'C O: .. gives an ester .. – + R'C R : X O ..

  8. O O Example + CH3(CH2)16C OK CH3CH2I acetone, water + CH3(CH2)16C KI O CH2CH3 Ethyl octadecanoate (95%)

  9. – .. R X H S: .. .. – + H R : X S .. Examples of Nucleophilic Substitution Hydrogen sulfide ion as the nucleophile + gives a thiol

  10. Example KSH + CH3CH(CH2)6CH3 Br ethanol, water + KBr CH3CH(CH2)6CH3 SH 2-Nonanethiol (74%)

  11. : : N R X C : N C Examples of Nucleophilic Substitution Cyanide ion as the nucleophile – + gives a nitrile – + R : X

  12. Br CN Example NaCN + DMSO + NaCN Cyclopentyl cyanide (70%)

  13. + – – : : N N N R X .. .. – : N N N .. .. Examples of Nucleophilic Substitution Azide ion as the nucleophile + gives an alkyl azide + – + R : X

  14. Example NaN3 + CH3CH2CH2CH2CH2I 2-Propanol-water CH3CH2CH2CH2CH2N3 + NaI Pentyl azide (52%)

  15. .. : : I R X .. .. : I .. Examples of Nucleophilic Substitution Iodide ion as the nucleophile – + gives an alkyl iodide – + R : X

  16. + NaI CH3CHCH3 Br Example acetone + NaBr CH3CHCH3 NaI is soluble in acetone; NaCl and NaBr are not soluble in acetone. I 63%

  17. Relative Reactivity of Halide Leaving Groups

  18. Generalization • Reactivity of halide leaving groups in nucleophilic substitution is the same as for elimination. most reactive RI RBr RCl RF least reactive

  19. Problem A single organic product was obtained when 1-bromo-3-chloropropane was allowed to react with one molar equivalent of sodium cyanide in aqueous ethanol. What was this product? • Br is a better leaving group than Cl BrCH2CH2CH2Cl + NaCN

  20. : N C CH2CH2CH2Cl + NaBr Problem A single organic product was obtained when 1-bromo-3-chloropropane was allowed to react with one molar equivalent of sodium cyanide in aqueous ethanol. What was this product? BrCH2CH2CH2Cl + NaCN

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