Chemistry Reference
In-Depth Information
OLEFINS
=
=
• Nomenclature: CH
CHCH
CH
CH
CH
CHCH
2
2
3
3
3
1-butylene
2-butylene
1-butene
2-butene
• Multiple double bonds
CH
=
CHCH
=
CH
2
2
1,3-butadiene or just “butadiene”
• Geometrical isomers
H
H
H
Cl
CC
CC
Cl
Cl
Cl
H
cis-1,2-dichloroethylene
trans-1,2-dichloroethylene
In naming olefins, the prefix number indicates the lower numbered carbon
atom involved in the double bond, numbering from one end of the molecule.
Two or more double bonds in one molecule are possible with the number of
double bonds indicated by “di-” for two double bonds, “tri-” for three, “tetra”
for four, etc. before the “-ene” ending (e.g., butadiene).
Buta
- means four
carbons and
indicates the presence of two double bonds.
Because a double bond between two carbons prevents the carbons from
rotating, isomers involving the atoms bonded to the carbons are possible, as
shown above with dichloroethylene. Such isomers are called
diene
geometrical
isomers,
discussed previously. When the
substiuent groups are on the same side of the molecule, the compound is
designated the “
in contrast to the
structural isomers
-” isomer. When the substituent groups are on the opposite
side, the compound is the “
cis
-
isomers have the same molecular formula, but differ in certain physical and
chemical properties. For example,
trans
-” isomer. Like all isomers,
cis-
and
trans
cis
-1,2-dichloroethylene boils at 60
°
C
whereas
trans
-1,2-dichloroethylene boils at 48
°
C.
