Naming Alkenes and Alkynes (rules) Download

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Naming Alkenes and Alkynes
STEP 1: Name the main chain. Find the longest continuous chain of carbons containing the double or triple bond.
The names of alkenes end with –ene, and the names of alkynes end with -yne. When there is more than one multiple
bond, use numerical prefixes (diene, diyne, triene, triyne, etc.)
CH 3
CH 2
CH 2
CH
CH 3
CH 2
CH 2
CH 3
CH 2
C
CH 3
CH 2
CH
CH 2
C
C
CH 3
Name as hexyne - a six C chain
containing a double bond
Name as p entene - a f ive C chain
containing a double bond
CH 3
CH 2
CH 2
CH 2
C
CH3
CH 3
CH 2
CH 2
CH
CH3
CH 2
not as a heptene - the double bond is not
contained on the seve C chain.
Name as hexene - a six C chain
containing a double bond...
STEP 2: Number the carbon atoms in the main chain. Begin at the end nearer the multiple bond. If the multiple
bond is at the same distance from both ends, begin numbering at the end nearer the first branch point.
CH 3
CH 3
CH3 CH 2 CH 2 CH CH CH 3
4
6
5
3
2
1
This end is closer to the double bond.
CH 3 C
C
CH2 CH 2 CH 2 CH
CH 3
CH 3 CH CH CH CH 2 CH 3
1
2
3
4
5
6
2
6
7
8
1
4
5
3
Both ends are at the same distance
The lef t end is closer to the triple bond.
f rom the double bond, but this is closer
to the branch.
The double-bond carbon atoms in substituted cycloalkenes are numbered 1 and 2 so as to give the first substituent the
3
lowest number:
Do not begin here.
CH3
2
4
1
6
1
5
6
If we start here the brach
gets the lowest possible number
CH3
5
2
4
3
STEP 3: Write the full name. Assign numbers to the branching substituents, and list the substituents alphabetically.
Indicate the position of the multiple bond(s) in the chain by giving the number of the first multiple-bonded carbon. If
more than one multiple bond is present, identify the position of each multiple bond and use the appropriate ending
diene, triene, tetraene, and so forth.
6
CH3
CH3
5
CH2
4
CH2
CH
3
2
1-pentene or
pent-1-ene
CH2
CH3
6
1
CH2
5
CH 3
CH3 C
1
2
Reyes C
3
CH2 CH2 CH 2
4
5
6
CH
7
7-methyl-2-octyne or
7-methyloct-2-yne
CH2
C
4
3
2-hexyne or
hex-2-yne
C
2
CH 2
1
C
2
CH
3
CH2
CH2
CH3
1
3
C
CH3
CH2
2
CH
1
CH 3
CH2
3-propyl-2-hexene or
3-propylhex-2-ene
CH 2 CH 3
CH 3
8
4
5
3
CH2
4
2-ethyl-1,3-butadiene or
2-ethylbuta-1,3-diene
2
CH 3
4
1
5
6
4-methylcyclohexene
Assigning Priority
What happens when double and triple bonds appear in the same molecule?
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Alkenes and alkynes are considered to have equal priority.
In a molecule with both a double and a triple bond, whichever is closer to the end of the chain determines
the direction of numbering.
In the case where each would have the same position number, the double bond takes the lower number.
In the name, “ene” comes before “yne” because of alphabetization.
1
2
3
4
5
CH
C
CH
CH
CH 3
pent-3-en-1-yne
("yne" closer to end of chain)
10
8
9
7
5
4
3
2
1
CH
C
CH 2
CH
CH 2
pent-1-en-4-yne
("ene" goes f irst in the alphabet and
takes priority over "yne")
6
4
5
2
3
1
deca-5,7-dien-1,3-diyne
•
Reyes Notice how in the names the last letter of the “—ene” ending is dropped to let people know that the
molecule has more functional groups (triple bonds in the examples above).