Naming alkenes examples | Alkenes and Alkynes | Organic chemistry | Khan Academy

TL;DR

This video explains how to name alkenes and cycloalkenes in organic chemistry based on the structure and number of carbon atoms.

Transcript

Everything we've named so far has been an alkane. We've seen all single bonds. Let's see if we can expand our repertoire a little bit and do some alkenes. So let's look at this first carbon chain right here. And actually, here I drew out all of the hydrogens just to remind you that everything we were doing before with just the lines, it really was ... Read More

Key Insights

• 📌 Alkenes have double bonds and are named by indicating the location of the bond with a number.
• 💨 Drawing the constituents becomes important when there are multiple ways to arrange the double bonds.
• ⏫ Cycloalkenes are cyclic compounds with double bonds, and the position of the double bond is assumed unless it has other substituents.
• 🪘 Naming alkenes and cycloalkenes involves considering the longest carbon chain and prioritizing the location of the double bond.
• ⏫ Multiple double bonds in a compound are indicated by separating the numbers with commas.
• 🫀 Alkane compounds have only single bonds between carbon atoms.
• ⏫ Double bonds in alkenes make the molecules more rigid and affect their chemical properties.

Questions & Answers

Q: How do you determine if a compound is an alkene or an alkane?

An alkene is a compound with a double bond between two carbon atoms, while an alkane has only single bonds between carbon atoms. A double bond is represented by the suffix "-ene" in the name.

Q: Why is it necessary to draw the constituents when naming alkenes?

Drawing the constituents becomes important when there are multiple ways to arrange the double bonds. The position of the double bond affects the compound's properties, so it needs to be specified in the name.

Q: How do you determine the numbering of carbon atoms in an alkene?

Start numbering from the end nearest to the double bond. The lowest number indicates where the double bond begins, and subsequent numbers are assigned sequentially.

Q: How is the naming different for cycloalkenes?

In cycloalkenes, the position of the double bond is not explicitly mentioned unless there are other substituents on the ring. The double bond is assumed to start at one endpoint, and numbering begins from there.

Summary & Key Takeaways

• Alkenes have double bonds, which make them more rigid and require drawing the constituents to show their arrangement.

• When naming alkenes, start with the longest chain of carbons and indicate the location of the double bond with a number.

• If there are multiple double bonds, use a comma to separate the numbers indicating their locations.

• Cycloalkenes are cyclic compounds with double bonds, and the position of the double bond is not specified unless there are other substituents.