Multiple Choice
In the polymerase chain reaction (PCR), which step is responsible for synthesizing complementary DNA strands?
3. Acids and Bases
Organic Chemistry Reactions
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Which statement about the Diels-Alder reaction is correct?
A
The Diels-Alder reaction is an example of a nucleophilic substitution.
B
The Diels-Alder reaction is a [2+2] cycloaddition.
C
The Diels-Alder reaction forms a six-membered ring.
D
The Diels-Alder reaction requires a radical initiator.
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The Diels-Alder reaction is a type of cycloaddition reaction, specifically a [4+2] cycloaddition, not a [2+2] cycloaddition. This means it involves the interaction of a conjugated diene (4 π electrons) and a dienophile (2 π electrons) to form a cyclic product.
In the Diels-Alder reaction, the diene must be in the s-cis conformation to allow the overlap of π orbitals necessary for the cycloaddition to occur. This is crucial for the formation of the new σ bonds in the cyclic product.
The reaction typically forms a six-membered ring as the product. This is because the combination of the diene and dienophile results in the formation of two new σ bonds, creating a cyclic structure.
The Diels-Alder reaction is a concerted process, meaning that all bond-making and bond-breaking occur simultaneously in a single step without the need for intermediates or radical initiators.
The Diels-Alder reaction is not a nucleophilic substitution; it is a pericyclic reaction involving the cyclic redistribution of bonding electrons. It is characterized by its stereospecificity and ability to form complex cyclic structures efficiently.
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