Alkene and Alkyne Nomenclature

When alkanes contain double or triple bonds, that totally changes the way we name the molecule. 

Concept: How to name alkenes and alkynes 

2m
Video Transcript

Let's go ahead and add a few more functional groups, so now we're going to talk about aklenes, alkynes, and alcohols.
So first let's start off with the pi bonds, with the double bonds and the triple bonds. Alkenes and alkynes are going to be named by adding a modifier. So this is going to be the very first time that we're using a modifier in an IUPAC name, so I'm going to teach you guys how to do this.
What that means is that instead of using the ending -ane, like we always use. It stands for alkane. Instead of using that ending we're going to use, we're going to modify it to either be -ene if it's an alkene or -yne if it's an alkyne. That's why we call it a modifier. It modifies the root name. So now all of the sudden, a hexane becomes a hexyne if it has a triple bond in it. Does that make sense? Cool.
So then let's talk about some important rules here. Alkenes and alkynes are actually going to receive priority in numbering alkanes. This is also going to be the very first time that now when it comes to numbering the chain, we are going to give priority to this group. What that means is that I don't care about the closest substituent, all I care about now is how do I give my double bond or my triple bond the lowest number possible. Isn't that interesting? So now I'm just saying how can I make that number as low as possible. That's all I care about.
Then, finally, this can get tricky because these double bonds go over two carbons, so sometimes it can be tricky what's the location. Is it the first carbon or the second carbon? The location is always assigned to the first double-bonded carbon or triple-bonded carbon.
So what I want to do here is I want to go ahead and name this compound. I want you guys to go ahead and try it first with the rules and then I'll go ahead and I'll give you the name.

Alkenes and alkynes are named as modifiers, meaning we add suffix modifiers to the root chain: 

Double and triple bonds get priority, so try to give them the smallest number possible. 

Alkene and Alkyne Nomenclature Additional Practice Problems

What is the systematic name of this compound?

a) 2-isobutyl-3-mehtylhex-5-ene

b) 5-isobutyl-4-mehtylhex-1-ene

c) 4,5,7-trimethyloct-1-ene

d) 2,4,5-trimethyloct-7-ene

Watch Solution

The IUPAC name for the following molecule is

A)        2,4-dimethyl-5-hexene

B)        3,5,5-triethyl-1-pentene

C)        3,5-dimethyl-1-hexene

Watch Solution

Draw the structure for (R,E)-5-bromo-6-methyloct-4-en-7-yn-4-ol

Watch Solution

Provide a structural formula for the s-cis conformation of (E)-1,3-pentadiene. Note that any correct form of a structural formula is acceptable. Be sure to identify stereoisomers properly.

 

Watch Solution

Please draw or name the corresponding molecular structures. 

(Z)-3-methylhept-3-ene

Watch Solution

Please draw or name the corresponding molecular structures. Indicate stereochemistry (R/S, E/Z) where applicable.

Watch Solution

Applying the correct rules for IUPAC nomenclature, select the correct name for the following compound. Make sure to include correct stereochemistry when appropriate.

A) (R,Z)-3-chloropent-4-en-1-yne

B) (R,Z)-3-chlorohex-2-en-5-yne

C) (S,Z)-3-chlorohex-2-en-5-yne

D) (S,Z)-3-chlorohex-4-en-1-yne

E) (R,Z)-3-chlorohex-4-en-1-yne

Watch Solution

Provide the proper IUPAC name for the structure below.

Watch Solution

Name the following compound using IUPAC nomenclature. Please include all necessary stereochemisty in the name like R/S or E/Z or cis/trans etc. This question is all or nothing, no partial. 

Watch Solution

Provide the missing information (structure, IUPAC name, or substituents) and also indicate the stereochemistry where necessary (i.e. cis, trans)

Watch Solution

Draw the following molecule:

(E)-4,5-dimethyloct-4-ene

Watch Solution

Draw the following molecule:

(Z)-5-methylhex-2-ene

Watch Solution

Name the compound given below.

Watch Solution

Which of the following is the structure for 2,5,5-trimethylhept-3-yne?

A) CH3CH2CH(CH3)C≡CCH2CH(CH3)2

B) CH3CH2C(CH3)2C≡CCH(CH3)2

C) (CH3CH2)2C(CH3)C≡CCH2CH3

D) CH3CH2C(CH3)2C≡CC(CH3)3

E) CH3CH2CH2CH(CH3)C≡CC(CH3)3

 

Watch Solution

Draw (E)-5-methyl-5-heptene-1-yne.

Watch Solution

Which of the following is the correct IUPAC name for the following compound?

a) 4-ethyl-1,3-dimethyl-3-pentene

b) 2-ethyl-1,1,3-trimethylbutene

c) 3-ethyl-2,4-dimethyl-2-pentene

d) 2,4-dimethylhexene

Watch Solution

Give the IUPAC name for the following molecule:

a) 2-chloro-1,4-dimethylcyclohex-4-ene

b) 1-chloro-3,6-dimethylcyclohex-3-ene

c) 3-chloro-2,4-dimethylcyclohexene

d) 5-chloro-1,4-dimethylcyclohexene

Watch Solution