Textbook Question
Predict the major products of the following reactions.
(d) the tosylate of cyclohexylmethanol + excess NH3
(e) n-butyl tosylate + sodium acetylide, H–C≡C:– +Na
7. Substitution Reactions
SN2 Reaction
4:31 minutesProblem 44a
Textbook Question
Explain why the alkyl halide shown here reacts much more rapidly with guanine than does a primary alkyl halide (such as pentyl chloride).
Verified step by step guidance1
Step 1: Analyze the structure of the alkyl halide provided in the image. The molecule contains two chlorine atoms attached to a tertiary amine group, making it a bifunctional alkyl halide. This structure is significantly different from a primary alkyl halide, such as pentyl chloride, which has only one halogen atom attached to a primary carbon.
Step 2: Consider the reactivity of the alkyl halide. The presence of the tertiary amine group in the molecule increases the electron density around the nitrogen atom, making it more nucleophilic. This nucleophilicity enhances the molecule's ability to react with guanine, which is a nucleophilic base in DNA.
Step 3: Examine the mechanism of the reaction. The alkyl halide undergoes a nucleophilic substitution reaction with guanine. The tertiary amine group stabilizes the intermediate formed during the reaction, facilitating the process and increasing the reaction rate compared to a primary alkyl halide.
Step 4: Compare the steric hindrance. While primary alkyl halides like pentyl chloride have less steric hindrance, the bifunctional alkyl halide shown in the image has a structure that allows for simultaneous interaction with two guanine molecules. This dual reactivity further accelerates the reaction rate.
Step 5: Conclude the explanation. The alkyl halide shown reacts more rapidly with guanine than a primary alkyl halide due to its bifunctional nature, increased nucleophilicity from the tertiary amine group, stabilization of intermediates, and ability to interact with multiple guanine molecules simultaneously.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Nucleophilicity
Nucleophilicity refers to the ability of a nucleophile to donate an electron pair to an electrophile, forming a chemical bond. In this context, guanine acts as a nucleophile due to its electron-rich nitrogen atoms, which can attack the electrophilic carbon in the alkyl halide. The strength of nucleophilicity can vary based on the structure of the nucleophile and the leaving group of the alkyl halide.
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Alkyl Halide Reactivity
Alkyl halides are organic compounds containing a carbon-halogen bond, which can undergo nucleophilic substitution reactions. The reactivity of alkyl halides is influenced by the type of halogen and the structure of the alkyl group. Tertiary alkyl halides react more rapidly than primary ones due to steric hindrance and the stability of the carbocation intermediate formed during the reaction.
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Steric Hindrance
Steric hindrance refers to the prevention of chemical reactions due to the spatial arrangement of atoms within a molecule. In the case of primary alkyl halides, the less crowded environment allows for easier access for nucleophiles. Conversely, more complex alkyl halides, such as the one shown in the image, can provide a more favorable environment for nucleophilic attack due to reduced steric hindrance, leading to faster reaction rates.
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