Download Organic Notes #5 - RX`ns - Winston Knoll Collegiate

Properties of Different Functional Groups
Boiling Points - As the carbon chain gets longer, the mass of the molecule increases
which results in stronger van der Waal’s forces and consequently higher boiling points.
When branching occurs the molecules are more spherical which results in less contact,
weaker van der Waal’s, and lower boiling points.
Alcohols follow a similar pattern, however have higher boiling points over all due to
increased attraction from the hydrogen bonding between molecules.
Solubility in Water - Is determined by the polarity of the molecule from the presence
of functional groups and on the chain length. Shorter chains of most functional groups
are soluble. Longer chains much less so.
Compounds with non-polar functional groups such as alkenes and alkynes are not
soluble.
Acidity and Basicity - Most organic compounds do not show acid base behavior,
because they do not readily donate or accept protons.
Two significant exceptions are:
Carboxylic acids (CH3COOH) are weak acids because they will donate a proton.
Amines (containing a lone pair of e- on the nitrogen) are weak bases because they will
accept a proton.
Reactions of Hydrocarbons
Alkanes (saturated molecules with single bonds) are generally unreactive under normal
conditions (room temperature and pressure). This is due to the fact that all bonds are
single. This makes them useful as solvents and lubricants.
Alkenes and alkynes (unsaturated molecules with multiple bonds) are generally more
reactive.
Combustion - when a hydrocarbon combines with oxygen in an exothermic reaction.
Incomplete combustion occurs when the amount of oxygen is limited and the reacting
temperature is relatively low. Carbon monoxide is produced and the oxidation state of
carbon is +2.
CH4 + 3/2O2 ➩ CO + 2H2O
Complete combustion occurs when there is an excess amount of oxygen, and the
reacting temperature is relatively high. Carbon dioxide is produced and the oxidation
state of carbon is +4.
CH4 + 2O2 ➩ CO2 + 2H2O
Cracking - when larger hydrocarbons (10-16 carbons) are broken into smaller
hydrocarbons. This process is used in the petroleum industry to create a larger number
of molecules suitable for gasoline.
Substitution - when one or more hydrogen of the hydrocarbon is replaced by some
other element or group.
Substitution of alkanes with halides is a common example:
CH4 + Br2 ➩ CH3Br + HBr
Addition - when an element or group is added to the double or triple bond changing
the bond from unsaturated to saturated.
CH2=CH2 + Br2 ➩ CH2Br-CH2Br
This type of reaction can occur with any bromine (bromination), hydrogen
(hydrogenation), hydrogen halides and water (hydration) which requires an acid
catalyst.
Addition Polymerization - the formation of polymers (giant molecules) from joining
simple molecules into long chains.
Another type of addition reaction is the addition polymerization of small alkenes. The
double bond is “opened” allowing for the alkene to form two more bonds with similar
molecules to create a long repetitive chain of indefinite length.
CH2=CH2 ➩
H H
C-C
H H
H H
C-C
H H
+
H H
H H H H
C-C È C-C-C-C
H H
H H H H
Condensation (Dehydration)-two smaller molecules are linked to create a larger
molecule. This is made possible by the removal of a hydrogen form one molecule and
a hydroxide from the other which creates water.
Esters are made this way by reacting a carboxylic acid and an alcohol.
O
RCOH
carboxylic acid
O
+
HOR
⇄
alcohol
RCOR
+
H 2O
ester
water is removed
Esters are responsible for many pleasant fragrances such as those found in fruit.
Condensation reactions can also be used to create polymers. These reactions produce
compounds like polyesters and polyamides. These are often called synthetic polymers
because they have been produced in a lab. Dacron, nylon and Teflon are just a few
examples of polymers created using this process.
Natural polymers are seen when peptides and proteins are formed from amino acids.
Dehydration of alcohols are also possible. The removal of the hydroxyl from one
carbon and the hydrogen from another carbon creates an alkene and water.
Oxidation -the conversion of an alcohol to a carboxylic acid or a ketone.
Primary alcohols are converted to carboxylic acids because the hydroxide is located on
the end of the molecule.
Secondary alcohols become ketones because the hydroxide will convert to a carbonyl
in the interior of the molecule.
Tertiary alcohols are very stable and do not react.