Organic Chemistry : Help with Reduction

Study concepts, example questions & explanations for Organic Chemistry

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Example Questions

Example Question #11 : Oxidation Reduction Reactions

In general, the reduction of a ketone to an alcohol can be accomplished by all of the following except one. Which one will not reduce a ketone?

Possible Answers:

Hydride nucleophile 

Correct answer:

Explanation:

 is the only option that will not reduce a ketone to an alcohol, simply because it is not a reducing agent like the other four—it is an oxidizing agent. The addition of oxygens to a ketone will not yield an alcohol (oxidation). The addition of hydrogen to a ketone will yield an alcohol (reduction). The other answer options are reducing agents that would facilitate this reaction.

Example Question #12 : Oxidation Reduction Reactions

In which of the following reactions is sodium reduced?

Possible Answers:

Conversion sodium chloride to sodium sulfide

Both of these reduce sodium

None of these reduce sodium

Conversion of sodium chloride to sodium bromide

Correct answer:

None of these reduce sodium

Explanation:

Reduction involves gain of electrons whereas oxidation involves loss of electrons. In reduction, the oxidation number becomes more negative (due to gain of electrons) whereas in oxidation, the oxidation number becomes more positive. Sodium is an alkali metal, found on the first column of the periodic table. Every atom in this column has one valence electron; therefore, to complete its octet every alkali metal will lose an electron and will have an oxidation number of . It is very hard to oxidize and reduce these metals because of its desire to maintain octet; therefore, sodium can never be reduced or oxidized (it will always have an oxidation number of ).

Example Question #13 : Oxidation Reduction Reactions

A molecule undergoing oxidation __________ protons and a molecule undergoing reduction __________ protons.

Possible Answers:

gains . . . loses

loses . . . does not lose

does not lose . . . does not lose

loses . . . gains

Correct answer:

does not lose . . . does not lose

Explanation:

Oxidation and reduction involve loss and gain of electrons, respectively. It does not involve loss or gain of protons. Recall that the identity of an atom is changed when the amount of protons change; therefore, it is very hard to change the amount of protons. Only few reactions (such as nuclear decay reactions) can change the number of protons and alter the identity of an atom.

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