Simple Organic Compounds
Organic chemistry is the branch of chemistry
that studies carbon compounds. This field is very important since
carbon compounds are all around us—they make up a wide array of common
substances such as plastics, oil, gasoline, and alcohols and are
also a part of many of the foods we eat, such as proteins, carbohydrates,
One reason that there are so many carbon compounds is
because of carbon’s unique ability for bonding. Recall the electron
structure of carbon:
Carbon has four valence electrons, and these electrons
can hybridize into sp3, sp2,
and sp atomic orbitals. This enables carbon to
join with other elements and be involved in single, double, and
triple bonds. Organic compounds that contain only carbon and hydrogen
are called hydrocarbons.
Some general properties of organic compounds are
They usually have low melting points.
usually are nonpolar (unless they bear functional groups).
are usually nonconductors of electricity.
can exist in solid, liquid, and gaseous form. Compounds with:
- 1–4 carbons tend to be gases at room temperature; butane and propane are among
the lightest hydrocarbons and are used for fuel
- 5–10 carbons tend to be in the liquid state at room temperature;
compounds that fall in this size range are used to make gasoline
- 12–18 carbons make up jet fuels and kerosene
- More than 18 carbons tend to be solids at room temperature
Organic compounds can exist as polymers,
in which many repeating units (called monomers) make
up a larger molecule. Amino acids are monomers of proteins when
amino acids are bonded in a chain, they make a polypeptide or protein. Starches are
polymers of the monomer glucose. Plastics are polymers
of organic molecules extracted from crude oil. Some common examples
- Polyethylene—Many ethenes strung
together with covalent bonds (ethylene is another name for ethene);
shopping bags and plastic bottles are made of polyethylene.
- Polypropylene—Many propenes strung together;
glues and carpets are made of polypropylene.
- Polystyrene—A clear, hard, brittle polymer
used in CD cases; if you blow carbon dioxide into it during manufacture
and you get the soft, opaque, foamy polymer used in a coffee cup.
Common Functional Groups
Functional groups are atoms or groups of
atoms attached to an organic compound that impart characteristic
shapes and chemical properties to the compound. There are a few functional
groups that you should be able to recognize for the SAT II Chemistry
Hydroxyl group, —OH: Compounds that contain
an —OH group are considered alcohols. An example of
an alcohol, ethanol, is shown below:
acid group, —COOH: In a carboxyl group, the carbon is doubly bonded
to one oxygen and singly bonded to an OH group. An example of an organic
compound containing a carboxyl group, trichloroethanoic acid, is shown
group, –NH2: An amino
group contains a nitrogen and two hydrogens. In organic chemistry,
an R, like the one in the diagram below, is often used as a shorthand
notation to signify the rest of the molecule. This notation is generally
used when only a specific part of the molecule is being discussed.
Naming Organic Compounds
Take this opportunity to look through Appendix II, Chemical
Formulas Review, if you need a refresher on how to name organic
compounds. It might come in handy on test day.
Isomers are compounds that have the same
number and kinds of atoms but have different structures—meaning
that the atoms are arranged differently in the molecule. Generally
the number of isomers increases dramatically as the number of carbon
atoms increases because there are more options for molecular structure.
Different carbon skeletons (one or more bonds
differ). An example is C4H10:
functional groups. An example is C2H6O:
positions of functional groups. An example is C3H7NH2.
Don’t worry about memorizing all of the names of these
compounds. They are only included to show that isomers are completely
different compounds, with different names.
Simple Organic Reactions
You will be expected to be familiar with a few simple,
common organic reactions for the SAT II Chemistry exam, so we’ll
go through them briefly now. Let’s start with combustion reactions. Combustion
reactions are reactions that occur between oxygen and hydrocarbons,
There are two main types of combustion reactions—complete and incomplete.
Complete combustion occurs when excess oxygen
is present; this type of reaction produces carbon dioxide and water.
CH4 + 2O2CO2 + 2H2O
Incomplete combustion occurs when a limited
amount of oxygen is present, and the products of incomplete combustion
are often difficult to determine. There may be carbon monoxide,
carbon, and water or some mixture of all of these. When cooking
outdoors on a grill, you often are left with pure carbon (soot)
on utensils. Space heaters and automobiles often undergo incomplete
combustion and produce deadly carbon monoxide (CO) gas. Here’s the
reaction for an incomplete combustion:
2CH4 + 3O22CO + 4H2O
Another common organic reaction is called an addition
reaction. In an addition reaction, two reactants join
to form a single product:
H2C = CH2 +
Finally, we have the substitution reactions. In a substitution
reaction, one group replaces another group on the main carbon
chain. The atom that’s most commonly replaced in a substitution
reaction is hydrogen. One common example of this is halogenation,
which is the addition of a halide—remember, group 7A on the periodic
CH4 + Cl2CH3Cl + HCl