Hydrocarbon Reactants - Organic Chemistry

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Question

Which of the following can reduce an alkene to an alkane?

Answer

Neither lithium aluminum hydride, nor sodium borohydride will reduce C–C double bonds.

H2/Raney nickel and H2/Pd can each (individually) reduce an alkene to an alkane. Since both H2/Raney nickel and H2/Pd can reduce the alkene, the answer is both of those reagents. This is a catalytic hydrogenation reaction, and H2/Raney nickel not only reduces C–C double bonds, but also carbonyl compounds.

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Question

Identify the major organic product expected from the acid-catalyzed dehydration of 2-methyl-2-pentanol.

Answer

The initial compound is a five-carbon alkane chain with methyl and hydroxy groups on the second carbon. Dehydration involves the hydrogenation of the hydroxy group. That group then leaves, and a double bond is formed. Zaitsev's rule states that double bonds are more stable on more highly substituted carbons. The double bond forms across carbons two and three.

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Question

If an alkane is reacted with excess in a high temperature environment, what are the products formed?

Answer

Whenever an alkane is reacted with excess oxygen in a high temperature reaction, the reaction is known as combustion. Combustion of an alkane always produces carbon dioxide gas and water vapor.

Therefore the correct answer is: and .

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Question

The stereochemical pathway for the hydrogenation of an alkene with a metal catalyst, such as platinum, occurs via __________.

Answer

Hydrogenation of an alkene with a metal catalyst, such as platinum, occurs via syn addition.

It is important to note the three main types of reactions for alkenes. The first type of reaction is a 2-step mechanism in which the electrophile attacks the carbocation nucleophile. This can yield syn or anti products. The second type of reaction is a 2-step mechanism that forms a bridged carbocation as the intermediate. This can yield only anti products. The third and last type of reaction is a 1-step addition. This can only yield syn products.

An example of the third type of reaction is the addition of a hydrogen with palladium, platinum, or nickel as demonstrated in the picture.

1

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Question

What is(are) the product(s) in the Pd-catalyzed hydrogenation if 1,2-dimethylcyclopentene?

Answer

The product for this hydrogenation is _cis-_1,2-dimethylcyclopentane.

It is important to note the three main types of reactions for alkenes. The first type of reaction is a 2-step mechanism in which the electrophile attacks the carbocation nucleophile. This can yield syn or anti products. The second type of reaction is a 2-step mechanism that forms a bridged carbocation as the intermediate. This can yield only anti products. The third and last type of reaction is a 1-step addition. This can only yield syn products.

The cis product alone forms because the reagents used were hydrogen and a metal catalyst palladium (other common metal catalysts are platinum and nickel). This type of reagent with an alkene will always be a 1-step addition that yields solely syn products. Cis-1,2-dimethylcyclopentane is the only answer that solely indicates syn products.

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Question

Nbs

What reagent will complete this reaction?

Answer

N-bromosuccinimide (NBS) brominates at allylic positions. Br2 will not complete this reaction with the presence of the double bond.

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Question

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Predict the major product of the given reaction.

Answer

Reaction of an alkene with osmium tetroxide results in syn addition of to hydroxyl groups across the double bond, resulting in a 1,2-diol. The correct answer is the option in which hydroxide groups are added to the previously double-bonded carbons on the same side of the ring. The correct answer is compound II.

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Question

reacts with the given molecule to form what final product?

Answer

This is an alkene electrophilic addition reaction. The alkene first attacks the hydrogen on the . The hydrogen always attaches to the last carbon, never the third. This form of regioselectivity is referred to as the Markovnikov rule. This occurs because it creates a secondary carbocation, rather than a primary carbocation intermediate, which is far more stable. The bromine is then free to attack the third, now positively charged carbon.

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Question

What is the major product when 4-bromo-2-pentene reacts with ?

1. Img 0643

2. Img 0644  1

3. Img 0645

Answer

When reacting with alkenes, the reagents add two syn alcohols, meaning that the alcohols face the same way in space. The alcohols can either be configured in the front (wedge) or the back (dash). Therefore, the correct answer is two of these, with the correct products being molecule 1 and molecule 2.

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Question

Each of the following reagents, or sets of reagents, elicit Markovnikov addition to an alkene except __________.

Answer

are the only reagents that do not elicit Markovnikov addition of the available answer choices. Instead, elicits an anti-Markovnikov addition of hydrogen and bromine to an alkene.

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Question

Which of the following show the major product of the addition of hydrobromic acid to 2-methylhex-2-ene?

Answer

This is an addition reaction with being added to an alkene (ionic addition). To reach the correct answer first we need to add the to one of the carbons by using electrons from the double bond. This next step is crucial because the positive charge (carbocation) that forms needs to be in the most substituted position. However, hydride shifts can occur moving a hydrogen atom over to an adjacent carbon to form the most stable carbocation. In this case, the positive charge on the secondary carbon adjacent to the tertiary carbon will first get the positive charge and then a hydride shift will occur amongst those two carbon leading to a more stable tertiary carbocation. Finally, the will attack the carbocation from both sides, and then we will have an alkyl halide. The most stable intermediate (carbocation) produces the greatest quantity of the stable product.

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Question

When reacted with 1 equivalent of , which of these molecules could form multiple products?

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Answer

This is a classic acid catalyzed alkene reaction. Because of resonance, several reactions have multiple products.

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Question

Which of these alkene compounds would react with hydrobromic acid the fastest?

Answer

2-Methyl-2-butene will react the fastest with hydrobromic acid because when it reacts, it will form the most stable carbocation among all of the alkenes listed. This stability allows for the reaction to proceed much quicker than other compounds, therefore it will react the fastest.

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Question

The ozonolysis reaction involves the use of (ozone gas) with alkene molecules. This reaction forms which of the following products?

Answer

The ozonolysis of alkenes forms either ketones or aldehydes. Subsequent reagents can be added to produces alcohols and/or carboxylic acids.

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Question

Which of the followinng sets of addition reactions proceed via syn addition?

Answer

Reactions that proceed by syn addition include hydrogenation, epoxidation, and hydroboration-oxidation. Reactions that proceed by anti addition include halogenation, halohydrin addition and epoxidation followed by ring opening. Syn addition occurs because reagents must approach from only one side of the double bond.

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Question

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Predict the product of the chemical reaction given.

Answer

The reaction given is called a Markovnikov's addition reaction. This is a regiospecific reaction because only one orientation of the reaction occurs. It is an electrophilic addition reaction that involves the reaction of a halogenic acid such as or with an alkene. The hydrogen bonds to the carbon with the less alkyl groups bonded to the organic compound and the halogen ion bonds to the carbon with more alkyl substituents. Therefore the answer is:Screen shot 2015 12 17 at 10.47.24 pm

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Question

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Predict the product of the chemical reaction given.

Answer

The reaction given is called a Markovnikov's addition reaction. This is a regiospecific reaction because only one orientation of the reaction occurs. It is an electrophilic addition reaction that involves the reaction of a halogenic acid such as or with an alkene. The hydrogen bonds to the carbon with the less alkyl groups bonded to the organic compound and the halogen ion bonds to the carbon with more alkyl substituents. Therefore the answer is:Screen shot 2015 12 17 at 11.23.48 pm

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Question

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Which of the following is an intermediate in the hydration of ethylene for the reaction given?

Answer

The reaction mechanism goes through a carbocation intermediate as follows:

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Therefore the answer is the following carbocation intermediate:

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Question

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Which of the following would be the product of the reaction given?

Answer

Molecular chlorine reacts with an alkene in the presence of water to yield a halohydrin product. Below is the mechanism for this reaction:

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Question

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Which of the following would be the product of the reaction given?

Answer

Molecular bromine reacts with an alkene in the presence of water to yield a halohydrin product. Below is the mechanism for this reaction:

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