AP
Chemistry
Organic Chemistry
Notes
Chapter 22
All organic chemistry is based upon unique properties of the carbon atom.
Carbon, C, hybridization to 3 sp3 orbitals, carbon can now form 4 bonds,
may be single, or in combination of double (sp2) or triple bonds (sp). Carbon
forms very strong bonds with many non-metal atoms, H, O, Cl, N.
Note: silicon and germanium are in the same family and form 4 bonds,
but the bond energy is low, so weak bonds are formed. This severely
restricts their chemistry.
I. Hydrocarbons
4 categories: alkanes, alkenes, alkynes, and aromatic compounds
1. Alkanes: carbon atoms are bonded to each other with single bonds.
Each C has 4 bonds (sp3 hybrid). Bonds are directed to
corners of a tetrahedron (bond angles of 109.5o). Chains are
"zig-zag". The general rule for writing formulas is 2n+2.
Where n represents the number of carbons and 2n+2 equals
the number of hydrogens.
methane (1C), ethane (2C's), propane (3C's), butane (4C's), pentane (5C's),
hexane (6C's), heptane (7C's), octane (8C's), nonane(9C's), decane(10C's)
Isomerization- same molecular formula, but different structure. Also creates
different properties for the molecule. The number of possible
isomers increases rapidly as the length of the chain increases.
n-butane
2-methyl propane (iso-butane)
**When adding carbon "groups" to the main chain, add the ending yl. e.g.
methyl, ethyl, propyl, butyl. These are called substituents.
n-hexane
2n+2
2(6)+2=14
Therefore it is
C6H14
2-methyl pentane
3-methyl pentane
2,3-dimethylbutane
2,2-dimethyl butane (not 3,3dimethyl butane)
Alkanes, straight or branched chains, all have an exterior which is mostly
hydrogen atoms. Surface of one molecule is quite like any other. No well-defined
+ or - center, so they are non-polar. Soluble in each other and in other non-polar
solvents. (not soluble in water, which is very polar).
Alkanes are rather unreactive chemically. Principle reaction is burning in air
(combustion reaction). Also are involved in substitution reactions.
Cycloalkanes: molecular formula has 2 less H atoms than straight chain (2n).
cyclohexane
cyclobutane
cyclopropane
2. Alkenes (unsaturated hydrocarbon, olefin) contains one double bond.
Made by cracking an alkane (heating long-chain alkane in
presence of catalyst). This causes (among other things) a
double bond to form, and the elimination of two H's. General
rule: 2n, creates at least one pi bond. Has sp2 hybridization on
the double bond.
No rotation about the double bond, this leads to the formation of geometric
isomers.
cis-2-butene
trans-2-butene
The presence of the double bond makes alkenes more reactive than alkanes.
Also can polymerize.
3. Alkynes contain 1 triple bond. General rule, 2n-2, sp hybridization
around the triple bond.
acetylene
ethyne
1-butyne
The presence of the triple bond makes these very reactive.
4. Aromatic
hydrocarbons-all involve the molecule benzene C6H6.
Aromatic compounds are very stable. The double bonds in benzene are
delocalized (creates resonance). Benzene molecules are very carcinogenic.
ortho-dichloro
benzene
meta-dichloro
benzene
para-dichloro
benzene
note: each benzene still has H's at each
C without a chlorine
5. Types of Reactions of Alkanes and Alkenes
A.
Substitution: characteristic of single bonds (alkanes).
+ Br2
B.
+ HBr
Addition: characteristic of double bond (alkenes).
+ Br2
Note: no byproduct.
Addition reactions are a good test for a double bond. A diatomic bromine
solution of carbon tetrachloride is reacted with the suspected compound. If a
double bond is present, red color (from Br2) will quickly fade.
II. Hydrocarbon Derivatives
1. Alcohols contain the hydroxide group, OH, substituted for hydrogen.
Suffix is -ol.
methyl alcohol
ethyl alcohol
propyl alcohol
isopropyl alcohol
methanol
ethanol
propanol
2-propanol
General formula R-OH, where R is an alkyl group. Hydrogen bonding in the -OH
group causes alcohols to have a high boiling point.
a.
Can be formed by oxidation (addition of oxygen, removal of H on both).
+O2
Oxidizing a hydrocarbon gives an alcohol.
b.
Can be formed by reduction (addition of hydrogen, removal of oxygen,
or both)
+H2
This process is used for about 80% of industrial ethanol production.
Methanol-present in liquid distillate from heating wood and oxygen, "wood
alcohol", deadly and causes blinding.
2. Ethers
dimethyl ether
-oxygen singly bonded to two carbon atoms.
ethyl methyl ether
diethyl ether (anesthetic)
General formula R-O-R'
Diethyl ether-anesthetic, good solvent. Vapors highly flammable.
3. Aldehydes have carbonyl group (
) bonded to at least one
hydrogen atom. Add the suffix -al.
formaldehyde
acetaldehyde
propionaldehyde
methanal
ethanal
propanal
General formula:
The boiling point for aldehydes is lower than the corresponding alcohol's, since
there is no hydrogen bonding. The boiling point is much higher than
corresponding saturated hydrocarbons, since
bond is highly polar.
Produced by oxidizing an alcohol with a terminal -OH group. Reduction is the
opposite process.
4. Ketones have a carbonyl on the interior of the chain. Oxidation of an
alcohol with non-terminal -OH. Suffix is an -one ending.
+
2-propanol +
+ H2O
O2
oxygen
2-propanone
acetone
dimethyl ketone
+ water
General formula:
5. Acids
contain a carboxyl group,
suffix is an -ioc ending.
,general form,
+ O2
ethanol +
oxygen
+ H2O
acetic acid
(vinegar)
+ water
formic acid
propionic acid
butyric acid
from "formica" (ants)
acetic acid
(rancid butter)
methanoic acid
ethanoic acid
propanioc acid
,
Organic acids ionize by:
+ H+
-Most are weak acids.
-As the length of the chain increases, organic acids become less soluble in water
and more soluble in non-polar solvents (remember that the -OH creates high
polarity).
6. Esters are produced by a reaction between an acid and an alcohol.
+
acetic acid
+
+ H2 O
methanol
methyl acetate**
+ water
**Note: the alcohol residue comes first, then the acid.
-Most esters have a very pleasant odor.
+
salicylic acid
+
+ H2O
methyl alcohol
methyl salicylate
(wintergreen)
+ water
7. Nitrogen Functional Groups
A. Amines are derivatives of ammonia in which one or more N-H
bonds have been replaced with a N-C bond. The name
amine represents the -NH2 functional group.
Primary amine
Secondary amine
Tertiary amine
B. Amides have a carbonyl group and an amine (pronounced a-mids).
Add -amide suffix.
C. Amino Acids are organic acids with a amine group directly next to
the carboxyl group.
D. Nitro
are a NO2 group. Nitro- prefix.
E. Nitrile a carbon triple bonded to a nitrogen. Add -nitrile suffix.
III. Miscellaneous
1. Soaps
Animal and vegetable fats are esters made of
a.
b.
Long-chain organic acids (fatty acids)
Various alcohols, glycerol (glycerin) is the most common. Glycerol is
a triol.
Reacting a fat with NaOH splits the fat into glycerin and the sodium salt of the
fatty acid. This sodium salt is the soap.
+ 3 NaOH
fat
+ sodium hydroxide
+
glycerol
3
+
3 soap
Soap cleans because:
a.
b.
Long chain hydrocarbon has a good solvent action on other hydrocarbons.
end has a high water solubility.
Soaps from 'scum" in hard water. "Scum" is a precipitates of the Ca2+ and Mg2+
of the soap. Detergents contain poly phosphorus ions, which tie up the Ca2+ and
Mg2+ ions so the detergent can do its work.
2. Aspirin
+
salicylic acid
+
+ H2O
acetic acid
acetyl salicylic acid
(aspirin)
+ water