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REACTIONS OF AlDEHYDES AND KETONES

REACTIONS OF AlDEHYDES AND KETONES. L.O.: Outline the mechanism for nucleophilic addition reaction of aldehydes and ketones with hydrides.

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REACTIONS OF AlDEHYDES AND KETONES

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  1. REACTIONS OF AlDEHYDES AND KETONES L.O.: Outline the mechanism for nucleophilic addition reaction of aldehydes and ketones with hydrides.

  2. Nucleophile: is a atom or groups of atoms attracted to an electron-deficient centre, where it donates a pair of electrons to form a new covalent bond A curly arrow is a symbol used in reaction mechanisms to show the movement of an electron pair in the braking or forming of a covalent bond

  3. Mechanism: Reduction of an aldehyde by nucleophilic addition

  4. The reduction of an aldehyde You get exactly the same organic product whether you use lithium tetrahydridoaluminate or sodium tetrahydridoborate. For example, with ethanal you get ethanol: Reduction of an aldehyde leads to a primary alcohol.

  5. Reaction summary: Reduction: Sodium borohydride (NaBH4) is a reducing agent. It provides a source of hydrogen and also allows hydrogen to act as a nucleophile by creating H-. It can be represented by [H].

  6. Many reducing agents will reduce ketones and aldehydes to alcohols. NaBH4 (sodium tetrahydroborate(III) ) generates the nucleophile H-, the hydride ion. Write the mechanism of the reaction of a ketone/aldehyde with H-.

  7. Will NaBH4 react with an alkene? NO! H- is repelled by the electron density of C=C. CH2 = CHCHO + 2[H] ———> CH2 =CHCH2OH

  8. CARBONYL COMPOUNDS - REDUCTION ExampleWhat are the products when Compound X is reduced? COMPOUND X H2 NaBH4

  9. CARBONYL COMPOUNDS - REDUCTION ExampleWhat are the products when Compound X is reduced? COMPOUND X H2 NaBH4 C=O is polar so is attacked by the nucleophilic H¯ C=C is non-polar so is not attacked by the nucleophilic H¯

  10. Page 43, Q5

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