12_all_ - 12.1 One method for assigning an oxidation state...

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12.1 One method for assigning an oxidation state to a carbon atom of an organic compound is to base that assignment on the groups attached to the carbon; a bond to hydrogen for (anything less electronegative than carbon) make it –1, a bond to oxygen, nitrogen, or halogen (or to anything more electronegative than carbon) make it +1, and a bond to another carbon makers it to 0. Thus the carbon of methane is assigned an oxidation state of –4, and that of carbon dioxide, +4. (a) Use this method to assign oxidation states to the carbon atoms of methanol, formic acid, and formaldehyde. (b) Arrange the compounds methane, carbon dioxide, methanol, formic acid, and formaldehyde in order of increasing oxidation states. (c) What change in oxidation state accompanies the reaction, methanol formaldehyde? (d) Is this an oxidation or a reduction? (e) When H 2 CrO 4 acts an oxidizing agent in this reaction, the chromium of H 2 CrO 4 becomes Cr3+. What change in oxidation state does chromium undergo? (a) Oxidation states to the carbon atoms of methanol –2, formic acid +2, formaldehyde 0. (b) Methane, methanol, formaldehyde, formic acid, and carbon dioxide. (c) Oxidation states to the carbon atoms from methanol –2 to formaldehyde. (d) An oxidation. (e) Oxidation state of chromium form +6 to +3. 12.2 (a) Use the method described in the preceding to assign oxidation states to each carbon of ethanol and to each carbon of acetaldehyde. (b) What do these numbers reveal about the site of oxidation when ethanol is oxidized to acetaldehyde? (c) Repeat this proceduce for the oxidation of acetaldehyde to acetic acid. (a) H 3 C H 2 C OH -3 0; H 3 C C O H +1; (b) It reveals that the carbon of methyl has no oxidation state changed, but the carbon of CH 2 OH has been oxidized. (c) H 3 C C O H H 3 C C O +3; It reveals that the carbon of methyl has no oxidation state changed, but the carbon of OH C O has been oxidized.
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12.3 (a) Although we have described the hydrogenation of an alkene as an addition reaction, organic chemists often refer to it as a “reduction.” Refer to the method described in Problem 12.1 and explain. (b) Make similar comments about this reaction: H 3 CC H O + HH Ni CH 3 CH 2 OH Answer: During the addition reaction, the oxidation state of the carbonyl carbon changes from +1 to –1, it means that this carbon is reduced. 12.4 Which reducing agent, LiAlH 4 or NaBH 4 , would you use to carry out the following transformations? (a) H 3 C C O OH H 3 C C H 2 OH (b) C O OH CH C H 2 OH O OH H 3 C H 3 C (c) C O OCH 3 CH CO C H 3 O OH H H O (a) LiAlH 4 (b) LiAlH 4 (c) NaBH 4 12.5 Show how each of the following transformations could be accomplished. (a) CH 2 OH PCC CH 2 Cl 2 CHO (b) CH 2 OH COOH KMnO 4 H 3 O OH COOH (c) PBr 3 Br 1, Mg 2, CO 2 3. H 3 O +
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(d) O 3 Zn / H 2 O HCCH 2 CH 2 CH 2 CH O O 1. 2. 12.6 Write equations similar to the above for the reaction that take place when phenyl-lithium is threated with (a) water and (b) ethanol. Designate the stronger and weaker acids and strong and weaker bases.
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This note was uploaded on 02/23/2010 for the course CHEM 101 taught by Professor Smith during the Spring '10 term at Duke.

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12_all_ - 12.1 One method for assigning an oxidation state...

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