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Example Questions
Example Question #3 : Help With Acid Base Reactions
Rank the given molecules in order of increasing pKa.
I, II, V, IV, III
III, I, IV, V, II
II, V, IV, I, III
III, II, V, I, IV
IV, II, V, I, III
II, V, IV, I, III
Recall that the stronger an acid, the lower the pKa.
II (two fluorine atoms really close to has largest inductive effect, so bond is most weakened, and pKa is lowest)
V (one fluorine really close to has strong inductive effect)
I (one fluorine a little further away from has weaker inductive effect)
IV (no inductive effect)
III (alcohols are much less acidic than carboxylic acids, and it has the highest pKa of all)
Example Question #6 : Help With Acid Base Reactions
Which side (left or right) of the following reaction is favored and why?
Left side, because the of is lower than the of 2-butanol.
Right side, because the of is lower than the of 2-butanol.
Left side, because the of is higher than the of 2-butanol.
Right side, because the of is higher than the of 2-butanol.
Right side, because the of is lower than the of 2-butanol.
The side of the reaction that is favored will have the acid with the higher , because the reaction goes (strong acid + strong base weak acid + weak base).
Example Question #1 : Help With Radical Reactions
Which reagent must be used with hydrobromic acid to convert 1-hexene to 1-bromohexane?
A peroxide
None of these
A peroxide
The double bond in 1-hexene is across carbons one and two. Just adding HBr would put the bromine on carbon 2 because the bromine is more stable on the more highly subtituted carbon. If you want to put the bromine on the less substituted carbon (generating 1-bromohexane), you must carry out the reaction in the presence of peroxides. The mechanism involves a free radical on the secondary carbon and a bromine addition on the primary carbon.
Example Question #2 : Help With Radical Reactions
Which site would the reagent N-Bromosuccinimide (NBS) be most likely to attack?
The most substituted atom is most likely to be attacked, as a radical intermediate would be created. The radical intermediate would be most stable on the most substituted carbon.
Example Question #3 : Help With Radical Reactions
Which of the following reagents would create the product for the reaction below?
and and , AIBN (azobisisobutyronitrile)
only
, AIBN (azobisisobutyronitrile) only
, hv only
, hv and , AIBN (azobisisobutyronitrile)
, hv and , AIBN (azobisisobutyronitrile)
The radical reaction would create the anti-Markovnikov product shown and both , hv and , AIBN (azobisisobutyronitrile) effectively cause radical reactions. The bromine would then be substituted with the group.
Example Question #3 : Help With Radical Reactions
Which of these steps in a free-radical halogenation of an alkene will not generate a radical molecule?
None of these steps
Initiation
Termination
All of these steps
Propagation
Termination
Termination is the only step that does not generate a radical product. The termination step ends the reaction by bringing together two radical molecules to produce a stable non-radical product.
Example Question #4 : Help With Radical Reactions
Classify the type of reaction given.
Heterolytic bond breaking
Rearrangement reaction
Homolytic bond breaking
Substitution reaction
Homolytic bond breaking
Homolytic bond breaking occurs when a molecule breaks up to form two or more new products. In the reaction given, molecular chlorine forms two radicals in which one electron stays with each fragment formed.
Example Question #1 : Other Reactions
Which of the following is not capable of oxidizing a secondary alcohol to a ketone?
Lithium aluminum hydride
, , acetone
Pyridinium chlorochromate (PCC)
All of these answers can oxidize secondary alcohols to ketones
Lithium aluminum hydride
Lithium aluminum hydride is correct because it is a reducing agent, and is therefore not capable of oxidizing secondary alcohols. Instead, LAH could be used to perform the reverse reaction, reducing a ketone to an alcohol. The other answer choices are oxidizing agents.
Example Question #1 : Help With Oxidation Reduction Reactions
In the following equation, which element is reduced?
Manganese, iodine, and oxygen are all oxidized.
In an oxidation-reduction (redox) reaction, reduction and oxidation both occur. Thus, not all of the elements can be oxidized, and not all of them can be reduced. In this equation, the oxidation number of oxygen is . Multiplying that by the number of oxygen atoms (), the overall charge on oxygen is . has an overall charge, so the oxidation number on must combine with to form . Thus, the oxidation number of at the beginning of the reaction is . The iodine at the beginning of the reaction has an oxidation number of , as seen by the negative superscript.
At the end of the reaction, has an oxidation number of , as seen by the positive superscript. Iodine has an oxidation number of (there is no charge on the ).
Thus, went from having an oxidation number of to one of . Iodine went from having an oxidation number of to one of . Oxidation occurs when electrons are lost (the number becomes more positive), and reduction occurs when electrons are gained (the number becomes more negative). Because the oxidation number of iodine became more positive, iodine was oxidized. Because the oxidation number of manganese became more negative (less positive), manganese was reduced.
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