Untitled - Kelly Walsh High School

310 CHEMISTRY FOR THE UTTERLY CONFUSED
In the above example this gives: 5-ethyl-2,2-dimethylnonane
a. ethyl before methyl (alphabetical prefixes are ignored)
b. two methyl groups = dimethyl
c. three branches = three numbers
We separate numbers from other numbers by commas, and we separate numbers
from letters by a dash.
Alkenes are hydrocarbons that have at least one carbon-to-carbon double
bond, while alkynes have a carbon-to-carbon triple bond. Alkenes have the
general formula of C nH 2n while the alkynes have the general formula of C nH 2n2.
Cyclic alkenes and alkynes would have two less hydrogen atoms. Aromatic
hydrocarbons are usually ring systems of alternating double and single bonds.
Benzene, C 6H 6, is a very common aromatic hydrocarbon. The presence of a
double or triple bond make these hydrocarbons unsaturated, that is they do not
have the maximum number of bonds to other atoms.
Benzene, C 6H 6, is the best-known aromatic compound. It consists of a ring of
six carbon atoms. One way of representing the structure is to alternate single
and double bonds about the ring as shown in the leftmost diagram in the following
figure. The center structure is a resonance form of the first structure.
The presence of resonance stabilizes the structure by delocalizing the electrons.
Resonance makes all the carbon-carbon bonds equal instead of some single and
some double. The structure at the far right in the following diagram is a common
representation of benzene to indicate the presence of resonance along
with the equality of all carbon-carbon bonds.
H
H
C
C
H
C
C
H
C
C
H
H
H
H
C
C
H
C
C
H
C
C
H
H
H
H C H
=
C C
C C
H C H
The nomenclature of alkenes and alkynes is very similar to that of the alkanes
with two major differences. (1) The longest carbon chain must contain the double
or triple bond and number the chain from the end closest to the
double/triple bond. A number indicates the position of the double/triple bond.
H