1. Alkynes, Alkenes, and Benzene rings
Nomenclature II
Alkynes, Alkenes, and Benzene rings

2. Simple Names- Linear Alkynes
Alkynes have the suffix -yne
First, find the longest linear chain by numbering carbons.
This gets the –yne suffix.
The p-bond numbering is represented by the first numbered carbon attached to the p-bond. Use the lowest number. 7 6 5 4 3 2 1 1 2 3 4 5 6 7 3-
heptyne

3. Simple Names- Linear Alkenes
The carbon carbon double bond cannot be rotated.
As a result, two diastereomers are possible.
A diastereomer is a compound with same connectivity,
But different interatom distances.
Same substituent on same side of double bond - cis
Same substituent on opposite side of double bond - trans H
H’s are on same side
H’s are on opposite side
is not the same compound as
cis
trans

4. Simple Names- Linear Alkenes
Alkenes have the suffix -ene
First, find the longest linear chain by numbering carbons.
This gets the –ene suffix.
The p-bond numbering is represented by the first numbered carbon attached to the p-bond. Use the lowest number.
The cis/trans label is placed in front of the name to distinguish between the two diastereomers. 1 2 3 4 5 6 7 8 9 9 8 7 6 5 4 3 2 1
trans- 2-
nonene
cis-2-nonene

5. Simplest Alkene: Ethylene 2C’s
Ethene/ethylene suffix or vinyl prefix. F Br
bromoethylene or
vinylbromide F
1,1-difluoroethylene Br Cl
cis 2-bromo-1-chloroethylene or
cis 1-bromo-2-chloroethylene

6. Tri and Tetrasubstituted Alkenes
The cis and trans prefix really should only be used with disubstituted alkenes.
When three or four nonhydrogen substituents are attached to an alkene, the E or Z system should be used.
E is short for entgegen (German for opposite).
Z is short for zusammen (German for together). H
Z is for Zee Zame Zide
cis-2-pentene
or Z-2-pentene
trans-2-pentene
or E-2-pentene

7. Assigning E/Z
Divide the molecule in half, by cutting perpendicular to the C=C bond.
Assign priority 1 or 2 on each side of the C=C bond by atomic number of the atom directly attached to the alkene.
6>1 1 2
If there is a tie, then list the atoms directly attached to the atom attached to the alkene. Find the atom with the highest atomic number in each set. If there still is a tie, look at the next highest number. Keep repeating the process until there is a difference.
Draw a dashed line along the alkene. If the 1’s are on the Zee Zame Zide, then it is a Z alkene, otherwise it is an E alkene.
CHH E
6>1 1 2
6=6 H
HHH
E-3-methyl-2-pentene

8. Exam Level Questions:
Assign E/Z to the following alkenes. Some molecules have more than one alkene that need E/Z assignment. Some alkenes cannot be assigned. You do not need to name the molecule itself. 3. 1. 2. Z 4. E E Z Z
(Carbon carbon double bonds count as two bonds to carbon)
CCH
CHH
CCC 5. 6. 7. E Z E E

9. Benzene Benzene is a special type of molecule called an aromatic ring.
Even though it contains p bonds, it really is not an alkene as it is immune to many reactions that alkenes are susceptible. There are some special names that relate to the benzene ring.

10. phenylchloride (PhCl)
Naming Benzene Rings
There are two ways to name a benzene ring:
Benzene (if it is main part of molecule)
or phenyl prefix if it is a side chain.
bromobenzene or
phenylbromide (PhBr)
chlorobenzene or
phenylchloride (PhCl)
fluorobenzene or
phenylfluoride (PhF)
iodobenzene or
phenyliodide (PhI)
Benzyl prefix: A phenyl group attached to a CH2
benzyl bromide
benzyl chloride
benzyl fluoride
benzyl iodide

11. Exam Level Questions: Draw the following: trans-3-heptene Z-3-heptene
E-2-phenyl-2-butene
E-3-methyl-4-isopropyl-2-octene
1-benzyl-1-bromoethylene
triphenylmethane