8.3 Nomenclature and Stability of alkenes

What are the four steps for naming alkanes and alkyl halides?

Identify the parent, identify substituents, number the substituents, arrange substituents alphabetically.

How is an alkene parent name different from an alkane?

Replace “ane” with “ene” to show there is a double bond.

When choosing an alkene parent chain, what must the chain include?

The chain must include the π bond.

How do you break a tie between two chains of equal length?

Choose the chain that contains the double bond

What gets numbering priority in alkenes?

The π bond.

From which end do you number an alkene?

From the end closer to the double bond

What did the 2013 IUPAC rule change?

The parent chain is now the longest carbon chain, even if it does not include the double bond

What happens if the longest chain does not include the double bond?

The double bond is named as a substituent (methylene or vinyl group)

How is the position of the double bond indicated?

With a number showing where the π bond starts.

Where is the locant placed according to older (1979) rules?

Before the parent name.

Where may it be placed according to updated IUPAC recommendations (1993+)?

Before the “ene.”

How is stereochemistry shown in alkene names?

By adding (E) or (Z) at the start of the name.

When is the E configuration used?

When the higher-priority groups are on opposite sides.

For cyclic alkenes, where does numbering start?

The double bond defines C1 and C2 automatically.

Do you need to include a number for the double bond in a ring?

No.

What is a diene?

A compound with two double bonds

How are dienes numbered?

Each double bond gets its own number.

What is a 10-carbon chain with three double bonds called?

Decatriene.

What is an 11-carbon chain with four double bonds called?

Undecatetraene.

What are common alkene names recognized by IUPAC?

Ethylene, propylene, and styrene.

What are common substituent names for double-bond units?

Methylene (=CH₂), vinyl (–CH=CH₂), and allyl (–CH₂–CH=CH₂)

What does degree of substitution refer to in alkenes?

Number of alkyl groups attached to the double-bond carbons.

Which is more stable: mono-, di-, tri-, or tetrasubstituted alkenes?

Tetrasubstituted (most stable).

What increases alkene stability?

More alkyl substituents.

Which is more stable: trans or cis?

Trans.

Why is cis less stable?

Steric strain