Download Carbon Compounds. Organic Molecules.

Lecture 23
Carbon Compounds.
Chapter 12.1  12.9
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Carbon Bonds
Structural Formulas
Unsaturated Hydrocarbons
Functional Groups
Carbon
Carbon forms far more compounds than any other element.
Carbon compounds are the basis of life.
Part of chemistry describing carbon compounds is called
organic chemistry.
Carbon is element #6. The main isotope is 126C.
The inner electronic shell is closed, the outer one is
halffull (contains 4 electrons out of 8 permitted).
The outer electrons are attracted to the nucleus by the
effective charge of +4.
The attractive force is sufficient to keep all 4 outer e, but is
not enough to accept another 4 to fill the shell.
Forming Carbon Compounds
Carbon forms covalent bonds, sharing 4 pairs of electrons.
A carbon atom can form bonds with other carbon atoms
too.
Diamond, a crystalline form of carbon, is the hardest
mineral.
Carbon compounds are mostly nonelectrolytes.
Their reaction rates are usually slow.
Carbon easily connects with hydrogen and oxygen.
Due to the presence of oxygen, many carbon compounds
are unstable at high temperatures.
Alkanes
The simplest organic compounds contain only C and H.
They are called alkanes.
They include methane (CH4), ethane (C2H6), propane
(C3H8), and butane (C4H10), widely used fuels.
Alkane molecules have single covalent bonds between
their carbon atoms.
Natural gas and petroleum consists mainly of alkanes.
Natural gas includes the lowest alkanes, while petroleum
includes higher alkanes.
Petroleum
Petroleum (crude oil) can be separated into different
alkanes according their boiling points.
Fractional distillation is the process in which crude oil is
heated and its vapors are condensed at progressively
higher temperatures.
Gasoline is the most valuable product of crude oil.
However, its content in most petroleums is low.
To increase its concentration, its is cracked.
C16H34  C8H18 + C8H16  cracking reaction
Petroleum
The second procedure of enriching crude oil in gasoline is
polymerization.
C3H8 + C4H8 C7H16  polymerization reaction
Octane rating of gasoline is a measure of the tendency to
prevent engine knocking.
The simplest alkanes have the lowest rating, while more
complicated, branched-chain, hydrocarbons the highest.
Alkane molecules are nonpolar and insoluble in water.
This leads the formation of thin layers of oil from spills on
the water surface.
Structural Formulas
A structural formula shows the covalent bonds between the
atoms in a molecule.
Structural formulas show how the carbon atoms are
linked together.
A carbon atom always forms four bonds.
For the simplest hydrocarbons there is only one way to
connect the atoms together.
More complicated ones can be arranged differently.
Compounds with the same molecular formulas, but
different structural ones, are called isomers.
Unsaturated Hydrocarbons
Carbon atoms can be connected by double and even triple
bonds.
HCCH
 acetylene
Compounds with multiple bonds are much more reactive
than the alkanes.
They can add other atoms to their molecules and are
called unsaturated.
Compounds with single carbon bonds are called saturated.
Benzene
Benzene, C6H6, is a clear liquid which is not mixed with
water and has a strong odor.
It is widely used as a solvent and in making more complex
organic compounds.
The six C atoms are arranged in a flat hexagonal ring.
Six electrons are shared by the entire ring (delocalized).
Compounds that contain a ring of six C atoms are called
aromatic.
Those without ring structures are called aliphatic.
Hydrocarbon Groups
Compounds that contain other elements besides C and H
are regarded as derivatives of hydrocarbons.
The groups of C and H that appear in hydrocarbon
derivatives are named from the hydrocarbons.
Examples: methyl group (CH3), ethyl group (C2H5).
CH3Cl  methyl chloride.
Functional Groups. Alcohols.
The chemical behavior of many organic compounds is
largely determined by the presence of certain atom
groups, called functional groups.
Alcohols contain OH groups, which make them slightly
polar and soluble in water.
The ethanol (C2H5OH) can be produced by fermentation.
C6H12O6  2C2H5OH + 2CO2
Mendeleev’s Doctoral Thesis: “On the Combinations of
Water with Alcohol”.
40% is the best concentration of alcohol.
Functional Groups.
Aldehydes and Ketones.
Aldehydes and ketones contain the carbonyl group.
The group is in the end of aldehyde molecules and inside
ketone molecules, between two other C atoms.
The double bond between C and O is highly polar, and
aldehydes and ketones are soluble in water.
Oxidation of ethanol in the liver produces acetaldehyde.
The most familiar ketone is called acetone.
Functional Groups. Organic Acids.
Organic acids contain the carboxyl group (COOH).
Since the H atom is loosely attached to the molecule, it
can be taken out to produce an H+ ion.
Most organic acids are weak.
Examples: formic acid (insect bites), acetic acid (vinegar),
citric acid (citrus fruits), acetylsalicylic acid (aspirin).
Esters is a result of the reaction of alcohols (organic
hydroxides) with organic acids.
Esters are analogous to inorganic salts, but not
electrolytes.
Summary
Carbon produces the largest amount of
compounds, including the base for living
organisms.
Carbon forms covalent bonds which can be either
single or multiple.
Organic molecules are best represented by
structural formulas.