E/Z Alkenes, Electrophilic Addition, & Carbocations: Crash Course Organic Chemistry #14 | Summary and Q&A

TL;DR

This Crash Course Organic Chemistry video explains alkene nomenclature, Markovnikov's rule, and how carbocation rearrangements affect reactions.

Key Insights

• 💙 Isoprene, emitted by trees, contributes to the blue haze observed in the Blue Mountains.
• 🤨 Alkenes have rigid double bonds due to the cost of breaking the pi bond.
• 🤪 The E/Z system provides a more precise nomenclature for alkenes than the cis/trans system.
• ⚾ Markovnikov's rule predicts the addition of protons to alkenes based on the stability of carbocations.
• ❓ Carbocations are stabilized by the inductive effect and hyperconjugation.
• 🥺 Some alkene reactions involve carbocation rearrangements through 1,2 shifts, leading to different products.
• ❓ Stability and energy considerations are crucial in understanding organic chemistry reactions.

Transcript

You can review content from Crash Course Organic Chemistry with the Crash Course app, available now for Android and iOS devices. Hi! I’m Deboki Chakravarti and welcome to Crash Course Organic Chemistry! The Australian Blue Mountains and the American Blue Ridge Mountains both get their colorful names from a blue haze that blankets them on hot summer... Read More

Questions & Answers

Q: What is the difference between the E/Z system and the cis/trans system for alkene nomenclature?

While the cis/trans system only works when the double-bonded carbons are attached to two hydrogens and two R-groups, the E/Z system takes into account the priority of groups on each double-bonded carbon, providing a more precise description of the geometric isomers.

Q: How does Markovnikov's rule influence addition reactions involving alkenes?

Markovnikov's rule states that the proton will add to the side of the double bond with more hydrogens. This leads to the formation of a more stable carbocation, and the product is determined by the position of the positive charge.

Q: What factors contribute to the stability of carbocations?

Carbocations are stabilized by the inductive effect, where electron density is spread through sigma bonds, and hyperconjugation, which involves the borrowing of electron density from sigma bonds. The presence of more alkyl groups surrounding the carbocation increases its stability.

Q: When do carbocation rearrangements occur in alkene reactions?

Carbocation rearrangements, such as 1,2-alkyl and 1,2-hydride shifts, occur when there is a possibility to form a more stable carbocation. These rearrangements lead to different reaction products and are influenced by the neighboring groups or atoms.

Summary & Key Takeaways

• Isoprene, a volatile organic compound found in trees, is responsible for the blue haze that covers the Blue Mountains.

• Alkenes are molecules with carbon-carbon double bonds and their pi electrons make them reactive.

• The E/Z system provides a more precise nomenclature for alkenes than the cis/trans system.

• Addition reactions involving alkenes follow Markovnikov's rule, where the proton adds to the side with more hydrogens.

• Carbocations, positively charged carbon atoms, play a crucial role in alkene reactions, and their stability is influenced by factors such as the inductive effect and hyperconjugation.

• Carbocation rearrangements, through 1,2-alkyl and 1,2-hydride shifts, can occur in some reactions, leading to different products.