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Organic Mechanism 5

Organic Mechanism 5. Nucleophilic Addition. Carbonyl Group. The carbonyl group Although we will consider aldehydes and ketones, C=O group is also present in carboxylic acids and esters. C = O /. butanal. methylpropanal. hexan-3-one. C = O. δ+. δ-. Carbonyl Group.

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Organic Mechanism 5

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  1. Organic Mechanism 5 Nucleophilic Addition

  2. Carbonyl Group • The carbonyl group • Although we will consider aldehydes and ketones, C=O group is also present in carboxylic acids and esters \ C = O / butanal methylpropanal hexan-3-one

  3. C = O δ+ δ- Carbonyl Group • The carbonyl group is a centre of high electron density due to the presence of the double bond C=O • The C=O bond is polar because oxygen is more electronegative then carbon

  4. Type of Reaction • The type of reaction undergone by carbonyl groups in aldehydes and ketones is ADDITION due to the C=O double bond • Addition reactions involve two molecules combining to form one product

  5. Type of Reaction • The polarity of C=O means it is susceptible to attack by a NUCLEOPHILE on the δ+C • Nucleophiles are species which donate a lone pair of electrons, resulting in the formation of a new covalent bond

  6. Nucleophilic Addition • The reagent for this reaction is hydrogen cyanide in the presence of potassium cyanide • The purpose of the potassium cyanide is to produce CN– which acts as a catalyst • Hydrogen cyanide is a polar molecule KCN  K+ + :CN– δ+ δ- H  CN

  7. CH3 C = O H Mechanism 1 • The electron pair on the CN– is attracted to δ+C resulting in the formation of a new CC bond • One of the C=O bonds breaks heterolytically and the two electrons move to the O:– δ+ δ- :CN–

  8. CH3 O:– C HCN Mechanism 2 δ+ δ- H  CN The intermediate rapidly reacts, the electron pair on the O:– is attracted to δ+H resulting in the formation of a new OH bond The HCN bond breaks heterolytically and the :CN– ion is reformed

  9. CH3 OH C HCN Mechanism 3 • The product is always a hydroxynitrile • In this case using ethanal the product is 2-hydroxypropanenitrile CH3CH(OH)CN

  10. Mechanism 4 • This reaction is very important as a synthetic route because it involves CC bond formation and increases the length of the carbon chain • The :CN– ion is reformed so can be classed as a catalyst for this reaction • The overall reaction being the addition of hydrogen cyanide to ethanal CH3CHO + HCN  CH3CH(OH)CN

  11. Synthetic Route1 • The nitrile group is readily hydrolysed by refluxing with aqueous hydrochloric acid. • This converts the nitrile to a carboxylic acid CH3CH(OH)CN + 2H2O CH3CH(OH)COOH + NH3

  12. Synthetic Route 2 • The nitrile group can be reduced using sodium in ethanol. • This converts the nitrile to an amine CH3CH(OH)CN + 2[H] CH3CH(OH)CH2NH2

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