Chemistry 30
Organic Chemistry
NOTES
I. Organic Chemistry
Definition


Organic compounds are those obtained from living
organisms. Inorganic compounds are those obtained
from minerals.
Organic Chemistry is the study of molecular
compounds of carbon (except oxides and carbonates).
Of the approximately 10 million compounds
discovered, 90% are molecular compounds of carbon.
Carbon is unique because it can form 4 bonds (4
bonding electrons), and can form chains, rings,
spheres, and can form combinations of single, double,
and triple bonds.
I. Organic Chemistry
Hydrocarbons

Hydrocarbons can be divided into two
main categories


Aliphatics
Aromatics
II. Aliphatics
1.
Alkanes: CnH2n+2
Carbon – Carbon single bonds
II. Aliphatics - Alkanes
These are compounds composed of carbon and
hydrogen whose carbon – carbon bonds are all
single bonds (saturated). Hydrocarbons
containing carbon – carbon double or triple
bonds are said to be unsaturated.
Alkanes in which the carbon atoms form long
“strings” or chains are called normal, straight
chain, or unbranched hydrocarbons.
2. Types of Formulas
a) Molecular formula
Example: C2H6
b) Expanded molecular formula
Example: CH3CH3
c) Structural formula
Example:
d) Condensed structural formula
Example:
e) Line Structural formula
Example:
H3C
CH3
3. Structural Isomers
Hydrocarbons can have the same number of atoms
but are arranged differently; these are called
structural isomers.
Example: C4H10 can be written as
normal
or
branched
H
H
H
H
H
H
H
C
H
C
H
C
H
C
H
C
H
H
H
H
H
C
C
C
C
H
H
H
H
H
C
H
H
H
4. Nomenclature (Naming) of Alkanes
a) normal alkanes: each is named according to the
stem plus the ending -ane.
Stem Prefix
# of Carbons
Formula
Name
meth
1
CH4
methane
eth
2
C2H6
prop
3
C3H8
but
4
C4H10
ethane
propane
butane
pent
5
C5H12
hex
6
C6H14
hept
7
C7H16
oct
8
C8H18
non
9
C9H20
dec
10
C H
pentane
hexane
heptane
octane
nonane
decane
Each of these names can have an “n” in
front to indicate normal

Example: n-butane

b) Branched alkanes: follow these steps
i.
ii.
iii.
iv.
v.
Find the longest continuous chain
Number the carbon atoms starting at the end closest
to the branch (if more than one branch is present, start
at the side that will result in the lowest numbers)
When alkane groups appear as branches, they are
named by dropping the –ane and adding –yl. For
example methane becomes methyl. These are called
alkyl groups and branches.
Name the branch first, indicating its number, then a
hyphen followed by the stem name.
The branches are listed in alphabetical order and the
prefixes di-, tri-, etc. are used to indicate multiple,
identical branches.
c. Examples:
i.
ii.
Heptane H
H
H
H
H
H
H
H
C
C
C
C
C
C
C
H
H
H
H
H
H
H
3 - methylheptane
H
H
H
H
H
H
H
H
H
C
C
C
C
C
C
C
H
H
H
H
H
H
H
C
H
H
H
iii. 2, 4 – dimethylheptane
H
H
H
H
H
H
C
C
C
H
H
H
C
H
H
C
H
H
H
H
C
C
C
C
H
H
H
H
H
iv. 3-ethyl-4,7-dimethyldecane
H3C
CH3
CH2 CH
H2C
CH
CH3
CH3
CH2 CH2 CH
CH2 CH2 CH3
v. n-butane
H3C
CH2
CH2
CH3
vi. 2,3 – dimethylbutane
CH3
H3C
CH
CH
CH3
CH3
vii. Draw all 5 structural isomers of C6H14
H3C
CH2 CH2 CH2 CH2 CH3
H3C
H3C
CH
CH3
CH2 CH2 CH2 CH2 CH3
CH2 CH2 CH3
vii. Draw all 5 structural isomers of C6H14
CH3
H3C
CH2 CH
CH2 CH3
CH3
H3C
CH
CH3
CH
CH3
vii. Draw all 5 structural isomers of C6H14
CH3
H3C
C
CH3
CH2 CH3
5. Drawing Structural Diagrams from Names
Start with the number of carbons in the
longest continuous chain, then add
branches where needed.
6. Cyclic Alkanes: CnH2n
Carbon atoms can form rings. The simplest is
cyclopropane. These bonds are unusually weak
or strained so it is more reactive than normal
propane. The same rules apply for naming but
the prefix cyclo- is added.
Example:
CH2
cyclopropane: C3H6
H2C
CH2
More examples:
Cyclobutane: C4H8
H2C
CH2
H2C
CH2
1-ethyl-2-propylcyclobutane
CH2 CH3
H2C
CH
H2C
CH
CH2 CH2 CH3
Properties of Alkanes

Physical Properties







Nonpolar results in London Dispersion Forces
C1 – C4: gases (cooking, heating)
C5 – C16: liquids (camping fuel, auto gas)
C16 > wax like solids
Fairly unreactive because saturated bonds are
strong (good for plastics, lubricants)
Refining: physically separating HC mixtures (coal
and natural gas)
Petroleum refining: boil petroleum and separate
on basis of boiling point (fractional distillation)
Properties of Alkanes
Chemical Properties
 Cracking – done to meet extra demand for
smaller alkanes (gasoline C5 – C12)
Thermal cracking – high heat, no oxygen
Catalytic cracking – catalyst used, no oxygen



heat or catalyst
C17H36(s) + H2(g) → C9H20(l) + C8H18(l)

Reforming – converts low grade gasoline
into higher grade, makes synthetic
lubricants and petrochemicals
heat or catalyst

C5H12(l) + C5H12(l) → C10H22(s) + H2(g)
– burning of fuels, incomplete
combustion forms CO(g)
 Combustion
C17H36(s) + O2(g) → CO2(g) + H20(g)
– reactions where one atom
or group substitutes a H atom
 Substitution
CH4 + Cl2 → CH3Cl + HCl