Organic Chemistry : Organic Concepts

Study concepts, example questions & explanations for Organic Chemistry

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Example Questions

Example Question #1 : Help With Acid Base Reactions


 

Which of the following sets of bases are listed from most basic to least basic?

Possible Answers:

Correct answer:

Explanation:

The correct ranking from most basic to least basic is:

The best bases are negatively charged, and the worst bases are positively charged (acidic). The stronger the base, the weaker (more stable) it's conjugate acid. An alkane is a very stable conjugate acid, which tells us that is the most basic of the set.

We know based on charge alone, that is more basic than but less basic than or .

We know that is more basic because the electronegativity of  is less than that of . This means the lone pair of electrons on are held less tightly and more likely to pick up a proton.

Example Question #1 : Help With Acid Base Reactions

Which of the following sets of acids are correctly listed from most to least acidic?

Possible Answers:

Correct answer:

Explanation:

Remember that the strongest acids have the weakest conjugate bases.  is more acidic than  because iodine has a larger atomic radius than bromine. , , and  are strong acids and should be at the beginning of the list. Alkanes are not acidic. Acetic acid is a weak acid (pKa =4-5).

Example Question #1 : Help With Acid Base Reactions

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Rank the given molecules in order of increasing pKa.

Possible Answers:

I, II, V, IV, III

III, I, IV, V, II

IV, II, V, I, III

II, V, IV, I, III

III, II, V, I, IV

Correct answer:

II, V, IV, I, III

Explanation:

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 #156 : Organic Chemistry

Which side (left or right) of the following reaction is favored and why?

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Possible Answers:

Right side, because the  of  is lower than the  of 2-butanol.

Right side, because the  of  is higher than the  of 2-butanol.

Left side, because the  of  is lower than the  of 2-butanol.

Left side, because the  of  is higher than the  of 2-butanol.

Correct answer:

Right side, because the  of  is lower than the  of 2-butanol.

Explanation:

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 #61 : Reactions Types

Which reagent must be used with hydrobromic acid to convert 1-hexene to 1-bromohexane?

Possible Answers:

None of these

A peroxide

Correct answer:

A peroxide

Explanation:

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 #62 : Reactions Types

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Which site would the reagent N-Bromosuccinimide (NBS) be most likely to attack?

Possible Answers:

Correct answer:

Explanation:

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 #61 : Reactions Types

Which of the following reagents would create the product for the reaction below?

Screen shot 2015 10 24 at 10.14.31 am

Possible Answers:

, AIBN (azobisisobutyronitrile) only

 and and , AIBN (azobisisobutyronitrile)

, hv and , AIBN (azobisisobutyronitrile)

 only

, hv only

Correct answer:

, hv and , AIBN (azobisisobutyronitrile)

Explanation:

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 #63 : Reactions Types

Which of these steps in a free-radical halogenation of an alkene will not generate a radical molecule?

Possible Answers:

All of these steps

Propagation

None of these steps

Termination

Initiation

Correct answer:

Termination

Explanation:

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 #64 : Reactions Types

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Classify the type of reaction given.

Possible Answers:

Substitution reaction

Homolytic bond breaking

Heterolytic bond breaking

Rearrangement reaction

Correct answer:

Homolytic bond breaking

Explanation:

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 : Help With Oxidation Reduction Reactions

Which of the following is not capable of oxidizing a secondary alcohol to a ketone?

Possible Answers:

Pyridinium chlorochromate (PCC)

Lithium aluminum hydride

, , acetone

All of these answers can oxidize secondary alcohols to ketones

Correct answer:

Lithium aluminum hydride

Explanation:

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.

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