Determining SN1, SN2, E1, and E2 Reactions: Crash Course Organic Chemistry #23 | Summary and Q&A

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March 4, 2021
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Determining SN1, SN2, E1, and E2 Reactions: Crash Course Organic Chemistry #23

TL;DR

This Crash Course video explains the different types of substitution and elimination reactions in organic chemistry and how nucleophiles transform substrates.

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Questions & Answers

Q: What are some examples of nucleophiles and what reactions do they favor?

Nucleophiles can be strong or weak and can favor substitution (SN) or elimination (E) reactions. Strong nucleophiles and strong bases, such as alkoxides, tend to favor E2 reactions. Weak nucleophiles and strong bases, like acetylide anions, favor E2 reactions. Weak nucleophiles and weak bases, such as water or alcohols, usually favor SN1 or E1 reactions. Strong nucleophiles and weak bases, like alkyl halides or azides, usually favor SN2 reactions.

Q: How does steric hindrance affect substitution and elimination reactions?

Steric hindrance refers to the hindrance or blocking of nucleophiles or bases due to bulky substituents on the substrate. Bulky substrates, such as tertiary substrates, have more steric hindrance, making them unable to undergo SN2 reactions. However, steric hindrance also affects the selectivity of elimination reactions, such as E2. Bulky bases may preferentially abstract a proton from a less substituted carbon, resulting in the formation of a less substituted alkene.

Q: What role do reaction conditions play in determining the type of reaction?

The reaction conditions, including solvent, temperature, and the strength of the nucleophile/base, can influence the outcome of the reaction. Polar, protic solvents tend to favor SN1 and E1 reactions, while polar, aprotic solvents can enhance the nucleophilicity of weak nucleophiles and favor SN2 reactions. Higher temperatures generally favor elimination reactions over substitution reactions.

Q: What is Zaitsev's rule, and how does it apply to elimination reactions?

Zaitsev's rule states that in elimination reactions, the major product is the most substituted alkene. This rule is based on the principle that the more substituted alkene is more stable due to hyperconjugation and dispersion forces. However, Zaitsev's rule may have exceptions when bulky bases are involved, resulting in the formation of less substituted alkenes.

Summary & Key Takeaways

  • Organic chemicals can be compared to characters in an adventure game, and the substrate is the protagonist. Different substrates can undergo various transformations through substitution and elimination reactions.

  • There are four major types of substitution and elimination reactions: SN1, SN2, E1, and E2.

  • The type of reaction and the resulting product depend on the substrate, the nucleophile, and the surrounding reaction conditions.

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