Organic Chemistry : Help with Alkene Synthesis

Study concepts, example questions & explanations for Organic Chemistry

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Example Questions

Example Question #5 : Hydrocarbon Products

Untitled

What is the IUPAC name of the given diene?

Possible Answers:

5-chloro-3,6-dimethyl-1,5-heptadiene

3-chloro-2,5-dimethyl-2,6-heptadiene

None of these answers

3-chloro-2,5-dimethyl-1,5-heptadiene

5-chloro-3,5-dimethyl-1,6-heptadiene

Correct answer:

5-chloro-3,6-dimethyl-1,5-heptadiene

Explanation:

You must begin counting the carbons so that the first functional substituent has the lowest possible number. In this case, C1 is connected to C2 by the double bond, meaning we start counting from the left.

The longest carbon chain is seven carbons so the parent molecule is heptane. With this numbering, there are methyl groups on carbons 3 and 6 and a chlorine on carbon 5.

Substituents are named in alphabetical order and two double bonds result in a diene. Thus, the correct answer is 5-chloro-3,6-dimethyl-1,5-heptadiene.

Example Question #6 : Hydrocarbon Products

Untitled

What is the value of  from Huckel's rule for the given aromatic compound?

Possible Answers:

Correct answer:

Explanation:

Huckel's rule states that an aromatic compound must have  delocalized electrons. The electrons in each double bond are delocalized for this molecule. There are nine double bonds, and thus eighteen delocalized electrons.

If 4n+2=18, then n=4.

Example Question #1 : Help With Alkene Synthesis

Which of the following reagents would convert butanone into 2-butene?

Possible Answers:

1. 

2. Heat/

1. 

2. Heat/

1. 

2. 

Correct answer:

1. 

2. Heat/

Explanation:

Two sets of reagents are required to convert butanone into 2-butene. First, we use  to reduce the butanone into a 2-butanol. Second, we use heat and acid to dehydrate the butanol and yield the final desired product.

1. ; 2. Heat/ may seem like an acceptable answer choice. However, note that the Grignard reagent converts the butanone into a tertiary alcohol, rather than a secondary alcohol as needed.

Example Question #2 : Help With Alkene Synthesis

2-butone is reacted with  to form a product. That product was then heated in acid  to form a final product. What is the final product?

Possible Answers:

None of these

2-butanol

Butane

2-butene

Correct answer:

2-butene

Explanation:

2-butone is a carbonyl compound that can readily be reduced by  into a secondary alcohol, 2-butanol. When 2-butanol is heated in acid, we get dehydration, which leads to 2-butene.

Example Question #6 : Reactions By Product

Noname01

What is the reactant of the given reaction?

Possible Answers:

Noname02

Noname06

Noname03

Noname05

Noname04

Correct answer:

Noname02

Explanation:

This is an addition reaction with 3 products. The unknown reactant reacts with  and gives those three products. Addition reactions begin with double bonded compounds and so these electrons are used to react with some reagent . One needs to work backwards to figure out how something was formed and in this case, there are mechanistic pathways, and one of the pathways involves a hydride shift. These 3 products often exist in different concentrations after the reaction. 

Example Question #4 : Help With Alkene Synthesis

Which of the following reagents can be used to create a E alkene from an alkyne? 

Possible Answers:

None of these

Correct answer:

Explanation:

Metallic sodium in liquid ammonia creates solvated electrons which can convert an alkyne to an E alkene. The same will not happen when sodium is combined with water, where sodium reacts violently to create sodium hydroxide and hydrogen gas. Lindlar's catalyst is a poisoned catalyst used to form alkenes from alkynes, bud results in a Z conformation. Without the poisoned catalyst, an alkane will be formed. 

Example Question #5 : Help With Alkene Synthesis

Screen shot 2015 12 30 at 6.43.54 pm

What is the major product for the reaction given?

Possible Answers:

Screen shot 2015 12 30 at 6.49.04 pm

Screen shot 2015 12 30 at 6.48.56 pm

Screen shot 2015 12 30 at 6.49.10 pm

Screen shot 2015 12 30 at 6.49.00 pm

Correct answer:

Screen shot 2015 12 30 at 6.49.00 pm

Explanation:

The reason this is the major product is because on tertiary alcohols are best dehydrated based on the E1 mechanism below:

Screen shot 2015 12 30 at 7.03.34 pm

Example Question #6 : Help With Alkene Synthesis

Screen shot 2015 12 30 at 7.23.12 pm

What is the major product for the reaction given?

Possible Answers:

Screen shot 2015 12 30 at 7.22.58 pm

Screen shot 2015 12 30 at 7.22.53 pm

Screen shot 2015 12 30 at 7.22.44 pm

Screen shot 2015 12 30 at 7.23.02 pm

Correct answer:

Screen shot 2015 12 30 at 7.22.53 pm

Explanation:

The reason this is the major product is because tertiary alcohols are best dehydrated based on the E1 mechanism below:

Screen shot 2015 12 31 at 11.16.42 am

Example Question #2 : Help With Alkene Synthesis

Screen shot 2015 12 30 at 6.42.35 pm

What is the major product for the reaction given?

Possible Answers:

Screen shot 2015 12 30 at 6.48.40 pm

Screen shot 2015 12 30 at 6.48.53 pm

Screen shot 2015 12 30 at 6.48.49 pm

Screen shot 2015 12 30 at 6.42.50 pm

Correct answer:

Screen shot 2015 12 30 at 6.42.50 pm

Explanation:

Below is the mechanism for the reaction given to form the alkene:

Screen shot 2015 12 31 at 11.21.32 am 

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