2444-101711

2444-101711 - EXAM Avg. Stnd. Dev. 68.6 / 100 18.1 2 2 Weak...

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EXAM 2 Avg. 68.6 / 100 Stnd. Dev. 18.1
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Weak Nucleophiles: water 2 • The fact that 6 is isolated from this reaction, and there is no product, clearly indicates that if addition of water occurs, 36 is unstable and the equilibrium lies far to the left as the reaction is written. • The hydronium ion is the conjugate acid of water when water reacts with an acid, H + . In 36 , the stable molecule water is released as 6 is regenerated, so the water unit in 36 is a good leaving group . • The reaction of water gives a product ( 36 ) that is unstable and water is considered to be a weak nucleophile. In general, a neutral nucleophile such as water will add to a carbonyl to give a charged species and the reaction is reversible for most ketones and aldehydes, but not all . mechanism of carbonyl hydration mechanism of carbonyl hydration O Me Me 1 O Me Me H O Me Me H Me O- H Me O 4 H H Me O- H Me O H 5 + H + -H + OH 2 H +
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Hydrates 3 • If the carbon attached to the carbonyl carbon (the ! -carbon) has strong electron withdrawing groups on it, and particularly if there are no hydrogen atoms on the ! -carbon adjacent to the carbon bearing the two OH units, the hydrate may be isolated. • Chloral ( 40 ) is a common name for trichloroethanal (trichloroacetaldehyde is also used as a common name) and it reacts with water to form a stable hydrate, 41 . • Hydrate 41 ( chloral hydrate chloral hydrate ) is stable because there are no ! -hydrogen atoms to lose, and the chlorine atoms withdraw electrons from the carbon, which in turn withdraws electrons from the C-O units. • Hydrate 41 has no protons on the ! -carbon, so enol formation is not possible. C Cl Cl Cl C O H Cl C Cl Cl C OH OH H 40 41 H 2 O
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Weak Nucleophiles: alcohols 4 • Initial reaction of ethanol with butanal ( 20 ) leads to the acyl addition product, oxonium ion 42 , analogous to the reaction of water and acetone that gave 36 . • The ethanol unit [C-O(H)Et
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This note was uploaded on 02/25/2012 for the course CHEM 244 taught by Professor Jardin,j during the Fall '08 term at UConn.

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2444-101711 - EXAM Avg. Stnd. Dev. 68.6 / 100 18.1 2 2 Weak...

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