Organic Chemistry : Organic Concepts

Study concepts, example questions & explanations for Organic Chemistry

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Example Questions

Example Question #8 : Help With Substitution Reactions

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Which reagent(s) are required to carry out the given reaction?

Possible Answers:

 

Correct answer:

 

Explanation:

This problem involves the synthesis of a Grignard reagent. Grignard reagents are easily created in the presence of halo-alkanes by adding magnesium in an inert solvent (in this case ). Once we have created our Gringard, it can readily attack a carbonyl. In this case, our Grignard attacks carbon dioxide to create our desired product.

Example Question #6 : Help With Substitution Reactions

Which of the following statements is true regarding an  reaction?

Possible Answers:

The nucleophile that is substituted forms a pi bond with the electrophile

All of these

An  reaction is best carried out in a protic solvent, such as water or ethanol

The configuration at the site of the leaving group becomes inverted

Correct answer:

An  reaction is best carried out in a protic solvent, such as water or ethanol

Explanation:

An  reaction is most efficiently carried out in a protic solvent. An inverted configuration site is characteristic of an  reaction and the substituted nucleophile does not form a pi bond in an  reaction.

Example Question #21 : Reactions Types

Sn1 problemSn1 product

By which of the following mechanisms does the given reaction take place?

Possible Answers:

Correct answer:

Explanation:

In this question, we're given the reactant and product as well as the reagent being used in the reaction, and we're being asked to identify which reaction mechanism will correctly lead us from reactant to product.

To begin, it's important to notice that the reactant contains a tertiary bromine and the product contains a methoxy group in place of where the bromine was. Thus, we can conclude that a substitution reaction has taken place. If an elimination reaction had taken place, then there would have been a double bond in the product.

Now we need to identify which kind of substitution has occurred. Since the leaving group is attached to a tertiary carbon, we know that a stable carbocation will be generated upon dissociation. Therefore, we would expect this to be an  reaction.

Example Question #11 : Help With Substitution Reactions

A solvolysis reaction occurs when dimethyl bromoethane is placed in methanol.

What is the final product?

Possible Answers:

2-methoxy-2-methylpropane

2-ethoxy-3-propanoic acid

3-isoproxy-1-butanol

3-methoxy-2-ethylbutane

Correct answer:

2-methoxy-2-methylpropane

Explanation:

A solvolysis reaction is simply an  reaction where the solvent acts as a nucleophile.

In this case, we start with a tertiary alkyl halide. Bromine, a stellar leaving group, leaves the substrate and leaves a carbocation intermediate. The methanol is then free to attack the carbon chain at the site of the carbocation to form an ether. The correct answer is 2-methoxy-2-methylpropane.

Example Question #12 : Help With Substitution Reactions

Which of the following reagents would convert 2-butanol into 2-bromobutane?

Possible Answers:

Correct answer:

Explanation:

The correct answer is .

Alcohol is a horrible leaving group.  is often employed to convert an alcohol group into a bromine group so that additional substitution and elimination reactions can ensue.

Example Question #13 : Help With Substitution Reactions

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Possible Answers:

II only

I only

I and II

III only

Correct answer:

II only

Explanation:

Cyanide is a weak base and a good nucleophile, and the solvent is aprotic; therefore, the  product is favored. This involves 100% inversion of stereochemistry; therefore II is favored.

Example Question #14 : Help With Substitution Reactions

Question 10

Which of these molecules would undergo a faster SN2 reaction?

Possible Answers:

2-iodobutane

3-iodo-1-butene

Neither would undergo the reaction.

They would react at the same rate.  

Correct answer:

3-iodo-1-butene

Explanation:

The double bond in 3-iodo-1-butene would stabilize the transition state through resonance. This would make the transition state lower in energy due to its increased stability. Thus, the reaction would be faster as reactions with lower activation energies proceed at faster rates. 

Example Question #15 : Help With Substitution Reactions

Question 10

Would this reaction proceed through an SN1 or SN2 mechanism?

Possible Answers:

SN2

Both

Neither

 SN1

Correct answer:

 SN1

Explanation:

This reaction would use an  SN1 mechanism because the leaving group, bromine, is on a tertiary carbon, which is a carbon attached to three other carbon atoms. The bulk of these methyl groups would make SN2 impossible, but it would make the carbocation produced by an  SN1 reaction very stable. The methyl group would lead to hyperconjugation, which is a type of resonance that stabilizes transition states. 

Example Question #16 : Help With Substitution Reactions

Screen shot 2016 02 21 at 6.39.54 am

Classify the type of reaction given.

Possible Answers:

Rearrangement

Substitution

Elimination

Addition

Correct answer:

Substitution

Explanation:

A substitution reaction is a chemical reaction that occurs when the reactants exchange atoms to form new products. In the reaction given the chloride in chloromethane  is substituted for the hydroxide in sodium hydroxide to form methanol. Also the hydroxide in sodium hydroxide is substituted for the chloride in chloromethane to form sodium chloride.

Example Question #17 : Help With Substitution Reactions

Screen shot 2016 02 22 at 11.06.36 am

 Classify the type of reaction given.

Possible Answers:

Catalytic

Substitution

Addition

Elimination

Correct answer:

Substitution

Explanation:

A substitution reaction is a chemical reaction that occurs when the reactants exchange atoms to form new products. In the reaction given the chloride and hydroxyl groups in water and 2-chloro-2-methylpropane are exchanged in the reactants to form two new products.

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