Entgegen-Zusammen naming scheme for alkenes examples | Organic chemistry | Khan Academy

TL;DR

This video explains how to name molecules with alkene functional groups and determine the positioning of functional groups using the Cahn-Ingold-Prelog priority scheme.

Transcript

Based on what we learned in the last video, let's see if we can name these two molecules here. Let's start with this blue one. So the first thing we notice, it is an alkene. It has a double bond right there. So we can, right from the get go, write that it's going to end with an ene. And then we need to figure out what the longest carbon chain is. A... Read More

Key Insights

• ⏫ Alkenes have a double bond and are named based on the longest carbon chain and the position of the double bond.
• ✋ The Cahn-Ingold-Prelog priority scheme is used to determine the higher priority functional group on each side of the double bond.
• 👥 Z- is used to denote molecules with higher priority functional groups on the same side, while E- is used for molecules with functional groups on opposite sides of the double bond.
• 🫀 The atomic number determines the priority of functional groups in the Cahn-Ingold-Prelog priority scheme.

Questions & Answers

Q: How do you determine the longest carbon chain when naming molecules with alkene functional groups?

To determine the longest carbon chain, identify the chain with the most carbon atoms that includes the double bond. Count the carbons and use the appropriate prefix (e.g., hept for seven carbons) in the name.

Q: How do you start numbering the carbons when identifying the position of the double bond?

Start numbering from the end of the carbon chain that is closest to the double bond. Number the carbons sequentially to determine the position of the double bond in the name.

Q: How do you identify the higher priority functional group using the Cahn-Ingold-Prelog priority scheme?

Compare the atoms directly bonded to the carbons on each side of the double bond. Determine which atom has a higher atomic number. The functional group bonded to the carbon with the higher atomic number takes priority.

Q: What is the significance of determining whether functional groups are zusammen or entgegen?

It helps determine the arrangement of functional groups on either side of the double bond. Zusammen means the higher priority functional groups are on the same side, while entgegen means they are on opposite sides.

Summary & Key Takeaways

• The video demonstrates how to name molecules with alkene functional groups, using the longest carbon chain and the position of the double bond to determine the name.

• It also explains how to identify higher priority functional groups on each side of the double bond using the Cahn-Ingold-Prelog priority scheme.

• The video shows how to determine whether the higher priority functional groups are on the same side (zusammen) or opposite sides (entgegen) of the double bond.