Reactions
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MCAT Biology › Reactions
Which of the following statements is true concerning the Hofmann elimination reaction?
The least substituted alkene is the major product in the reaction
The ammonium is eliminated following an E1 mechanism
The Zaitsev product is favored in the elimination reaction
The quaternary ammonium salt is a poor leaving group
Explanation
The Hofmann product is the most favored product in a Hofmann elimination reaction. The reaction follows an E2 mechanism, where a quaternary ammonium salt is able to be removed from a hydrocarbon, resulting in an alkene product. This reaction results in the least substituted alkene being the primary product.
Which of the following statements is true concerning the Hofmann elimination reaction?
The least substituted alkene is the major product in the reaction
The ammonium is eliminated following an E1 mechanism
The Zaitsev product is favored in the elimination reaction
The quaternary ammonium salt is a poor leaving group
Explanation
The Hofmann product is the most favored product in a Hofmann elimination reaction. The reaction follows an E2 mechanism, where a quaternary ammonium salt is able to be removed from a hydrocarbon, resulting in an alkene product. This reaction results in the least substituted alkene being the primary product.
Which alcohol will react most rapidly via an SN1 mechanism?
Explanation
Tertiary alcohols react most rapidly via SN1 mechanisms because they form stable tertiary carbocations. Primary and secondary alcohols typically react most rapidly via SN2 mechanisms.
Of the available options, 
Organic reactions can often be classified into two broad categories: substitution and elimination. Substitution reactions substitute one substituent for another. Elimination reactions typically form after the wholesale removal of a substituent, with no replacement. Below are examples of two types of reactions.
Reaction 1:
Reaction 2:
A scientist is studying the rate of reaction 1. He wants to double the rate of the reaction, but is unsure how to increase concentrations of the reactants. Which of the following is true?
Doubling the concentrations of both the hydroxide and the halide will quadruple the reaction rate
Doubling the concentration of the halide only will quadruple the reaction rate
Doubling the concentration of the hydroxide only will quadruple the reaction rate
Neither doubling the concentration of halide, nor doubling the concentration of hydroxide, will quadruple the reaction rate
Reaction rate in this reaction is not determined by concentration
Explanation
Reaction 1 represents an SN2 reaction. The rate limiting step involves both reactants coming together to form a transition state. The rate of this reaction depends on the concentration of both the organic molecule and the nucleophile.
In contrast, reaction 2 is an E1 reaction, in which the rate limiting step is the removal of the leaving group to form a carbocation. In E1 and SN1 reactions, adjusting the concentration of the halide only is enough to affect the rate.
Which alcohol will react most rapidly via an SN1 mechanism?
Explanation
Tertiary alcohols react most rapidly via SN1 mechanisms because they form stable tertiary carbocations. Primary and secondary alcohols typically react most rapidly via SN2 mechanisms.
Of the available options,
Which of the following statements is true concerning the Hofmann elimination reaction?
The least substituted alkene is the major product in the reaction
The ammonium is eliminated following an E1 mechanism
The Zaitsev product is favored in the elimination reaction
The quaternary ammonium salt is a poor leaving group
Explanation
The Hofmann product is the most favored product in a Hofmann elimination reaction. The reaction follows an E2 mechanism, where a quaternary ammonium salt is able to be removed from a hydrocarbon, resulting in an alkene product. This reaction results in the least substituted alkene being the primary product.
Organic reactions can often be classified into two broad categories: substitution and elimination. Substitution reactions substitute one substituent for another. Elimination reactions typically form after the wholesale removal of a substituent, with no replacement. Below are examples of two types of reactions.
Reaction 1:
Reaction 2:
A scientist is studying the rate of reaction 1. He wants to double the rate of the reaction, but is unsure how to increase concentrations of the reactants. Which of the following is true?
Doubling the concentrations of both the hydroxide and the halide will quadruple the reaction rate
Doubling the concentration of the halide only will quadruple the reaction rate
Doubling the concentration of the hydroxide only will quadruple the reaction rate
Neither doubling the concentration of halide, nor doubling the concentration of hydroxide, will quadruple the reaction rate
Reaction rate in this reaction is not determined by concentration
Explanation
Reaction 1 represents an SN2 reaction. The rate limiting step involves both reactants coming together to form a transition state. The rate of this reaction depends on the concentration of both the organic molecule and the nucleophile.
In contrast, reaction 2 is an E1 reaction, in which the rate limiting step is the removal of the leaving group to form a carbocation. In E1 and SN1 reactions, adjusting the concentration of the halide only is enough to affect the rate.
Which alcohol will react most rapidly via an SN1 mechanism?
Explanation
Tertiary alcohols react most rapidly via SN1 mechanisms because they form stable tertiary carbocations. Primary and secondary alcohols typically react most rapidly via SN2 mechanisms.
Of the available options,
Organic reactions can often be classified into two broad categories: substitution and elimination. Substitution reactions substitute one substituent for another. Elimination reactions typically form after the wholesale removal of a substituent, with no replacement. Below are examples of two types of reactions.
Reaction 1:
Reaction 2:
A scientist is studying the rate of reaction 1. He wants to double the rate of the reaction, but is unsure how to increase concentrations of the reactants. Which of the following is true?
Doubling the concentrations of both the hydroxide and the halide will quadruple the reaction rate
Doubling the concentration of the halide only will quadruple the reaction rate
Doubling the concentration of the hydroxide only will quadruple the reaction rate
Neither doubling the concentration of halide, nor doubling the concentration of hydroxide, will quadruple the reaction rate
Reaction rate in this reaction is not determined by concentration
Explanation
Reaction 1 represents an SN2 reaction. The rate limiting step involves both reactants coming together to form a transition state. The rate of this reaction depends on the concentration of both the organic molecule and the nucleophile.
In contrast, reaction 2 is an E1 reaction, in which the rate limiting step is the removal of the leaving group to form a carbocation. In E1 and SN1 reactions, adjusting the concentration of the halide only is enough to affect the rate.
Which of the following reactions is the nucleophile potassium tert-butoxide often used for?
E2
SN1
SN2
E1
Explanation
Tert-butoxide is a large, sterically hindered, strong nucleophile that is often used in E2 reactions. Strong nucleophiles usually undergo the SN2 or E2 pathway, but tert-butoxide is much too large to undergo a substitution reaction.