Question 1

What is the major product of the following reaction?  &#10;A) II&#10;B) IV&#10;C) III&#10;D) I

Accepted Answer

III&#10;

Question 2

If a Claisen condensation reaction is run using methyl propanoate as the reactant, NaOCH₃ is the ideal base. Why is it important to use NaOCH₃ and not NaOCH₂CH₃? A) NaOCH₃ is a weaker base than NaOCH₂CH₃, and this reaction requires a weaker base. B) Transesterfication can occur when esters react, and this transesterfication would result in a mixture of products. C) NaOCH₃ is more soluble than NaOCH₂CH₃ in organic solvents, and this reaction requires a full equivalent of base to proceed. A full equivalent of NaOCH₂CH₃ would not dissolve, so the reaction would not proceed. D) NaOCH₃ is a stronger base than NaOCH₂CH₃, and this reaction requires a stronger base.

Accepted Answer

Transesterification is a concern when using esters in reactions with bases that can also act as nucleophiles. NaOCH3 (sodium methoxide) is preferred over NaOCH2CH3 (sodium ethoxide) to avoid transesterification and ensure a more straightforward reaction pathway.

Question 3

Under basic conditions, the Aldol reaction is reversible, but dehydration is not. What is the reason for this difference in reactivity?&#10;A) The initial Aldol product is an alkoxide, so the reaction is energetically downhill going toward the product.&#10;B) The initial Aldol product is an alkoxide, so the reaction is energetically downhill going toward the starting materials.&#10;C) Water is a stable molecule.&#10;D) The initial Aldol product is an alkoxide, so the reaction is not energetically downhill in either direction.

Accepted Answer

The initial Aldol product is an alkoxide, so the reaction is not energetically downhill in either direction.&#10;

Question 4

In what situation can the yield of a single crossed Aldol product be increased?&#10;A) The electrophilic carbonyl component is relatively unhindered and is used in excess.&#10;B) The nucleophilic carbonyl component is relatively unhindered and is used in excess.&#10;C) The electrophilic carbonyl carbon component is relatively hindered and is used in limited amount.&#10;D) The nucleophilic carbonyl component is relatively hindered and is used in limited amount.

Accepted Answer

Using an excess of the electrophilic carbonyl component, which is relatively unhindered, increases the likelihood of it reacting with the nucleophilic component, thus increasing the yield of the desired crossed Aldol product.

Question 5

A key step in the biosynthesis of glucose involves the reaction of glyceraldehyde 3-phosphate with dihydroxyacetone phosphate to form fructose 1,6-bisphosphate in the presence of an aldolase enzyme. The end product formed from this reaction is

A) a single form of fructose in the cyclic hemiacetal form.
B) a form of critic acid.
C) a single form of fructose in the acyclic form.
D) an equilibrium between an acyclic form of fructose and a cyclic hemiacetal.

Accepted Answer

The reaction described leads to the formation of fructose 1,6-bisphosphate, which can exist in an equilibrium between its acyclic form and a cyclic hemiacetal form. This is due to the nature of the fructose molecule, which can cyclize to form a hemiacetal ring structure, but also exists in an open-chain (acyclic) form.

Question 6

Complete this statement: A major difference between the Aldol condensation and the Claisen condensation reactions is that&#10;A) the Aldol reaction is base catalyzed while the Claisen reaction is acid-catalyzed.&#10;B) the Aldol reaction is base catalyzed while the Claisen reaction requires a full equivalent of base.&#10;C) the Aldol reaction involves substitution while the Claisen reaction involves addition.&#10;D) the Aldol reaction is acid catalyzed while the Claisen reaction is base-catalyzed.

Accepted Answer

The Aldol reaction typically involves base catalysis and can also proceed under acidic conditions, but it does not require a full equivalent of base. In contrast, the Claisen condensation requires a full equivalent of base to deprotonate the ester, making it a stronger nucleophile for the reaction to proceed.

Question 7

The b-hydroxy carbonyl product of an Aldol reaction is oftentimes not the final isolated product; what is the explanation for this result?&#10;A) The hydroxy group reacts with the carbonyl to form a ketal.&#10;B) The hydroxy group is oxidized to a carbonyl.&#10;C) Hydroxide is eliminated via an enolate intermediate.&#10;D) It undergoes elimination, since water is a good leaving group.

Accepted Answer

Hydroxide is eliminated via an enolate intermediate.

Question 8

There are several variations of the Aldol reaction. Which of the following types of reactants leads to only one possible product with the Aldol condensation reaction?&#10;A) Two different aldehydes with a-hydrogens are able to form a single aldol condensation product.&#10;B) Any pair of aldehyde or ketone reactants where one of the reactants has no a-hydrogens will lead to a single aldol product.&#10;C) Two different ketones with a-hydrogens are able to form a single aldol condensation product.&#10;D) Any aldehyde and ketone mixed together can react to form a single condensation product.

Accepted Answer

The key to achieving a single aldol product lies in using a pair of reactants where one has no α-hydrogens. This prevents the formation of multiple products because only the reactant with α-hydrogens can form an enolate ion, which then reacts with the carbonyl carbon of the other reactant, leading to a single aldol product.

Question 9

What is the major product of the following reaction?  &#10;A) IV&#10;B) II&#10;C) III&#10;D) I

Accepted Answer

The answer of What is the major product of the...

Question 10

What is the major product of the following reaction?  &#10;A) II&#10;B) IV&#10;C) I&#10;D) III

Accepted Answer

The answer of What is the major product of the...

Question 11

Which of the following statements about Aldol reactions with either aldehydes or ketones is true?&#10;A) Equilibrium favors the products with aldehydes; equilibrium favors the starting materials with ketones.&#10;B) Equilibrium favors the starting materials with aldehydes; equilibrium favors the products with ketones.&#10;C) Equilibrium favors the starting materials with both aldehydes and ketones.&#10;D) Equilibrium favors the products with both aldehydes and ketones.

Accepted Answer

The answer of Which of the following statements about Aldol...

Question 12

The following reaction is an example of what type of reaction?  &#10;A) Dieckmann condensation&#10;B) Robinson annulation&#10;C) Aldol self-condensation&#10;D) Michael reaction

Accepted Answer

The answer of The following reaction is an example of...

Question 13

Would this crossed Aldol reaction work well? Why or why not?  &#10;A) No, the aldehyde is significantly more acidic, so this enolate cannot be formed selectively.&#10;B) No, the diketone is significantly more acidic, so this enolate cannot be formed selectively.&#10;C) Yes, the diketone is significantly more acidic, so this enolate can be formed selectively.&#10;D) Yes, the aldehyde is significantly more acidic, so this enolate can be formed selectively.

Accepted Answer

The answer of Would this crossed Aldol reaction work well?...

Deck 17: Carbonyl Condensation Reactions