Organic Families and Their Functional Groups

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Such a huge number of organic compounds requires organization. They are sorted into organic families defined by functional groups. Functional groups are small structural units within molecules at which most of the compound's chemical reactions occur.
For example, two of the most important families are the alcohols and the carboxylic acids. Their functional groups, the alcohol group and the carboxyl group, respectively, distinguishes them from the rest of the other types of organic compounds.
-OH
alcohol group
 CH3OH
methanol (methyl alcohol)
-COOH
carboxyl group
 CH3COOH
acetic acid (ethanoic acid)
Important Families of Organic Compounds
Symbolism shown below that you may not understand will be explained later in this topic
Hydrocarbons
Only C and H present
Alkanes
Only single bonds
Alkenes
Double bond(s) between two carbons
Alkynes
Triple bond(s) between two carbons
Aromatic
Benzene ring
Alcohols
R-OH
Ethers
R-O-R'
Aldehydes
R-CHO
Ketones
R-CO-R'
Carboxylic Acids
R-COOH
Esters
R-COO-R'
Amines
RNH2, RNHR', or RNR'R''
Amides
R-CON-R'R''
R, R', and R'' represent hydrocarbon groups (alkyl groups)
The type of properties associated with a compound is different depending on the family it is in. For example, the alkanes have just C-C and C-H single bonds. Since C and H are so alike in electronegativity, they are least able to attract ions or polar molecules, and least able to interact with them. The significance of this will be explained later.

Condensed Structures

To save space and time, condensed structures may be used to simplify the drawing and writing of structural formulas of organic compounds. C-H bonds are understood, and CH3 means that three hydrogen atoms are bonded to a carbon atom. For example:
CH3 is understood to be 
  H
  |
H-C-
  |
  H
CH3CH2OH is understood to be 
  H H
  | |
H-C-C-O-H
  | |
  H H
CH3OCH2 is understood to be 
  H   H
  |   |
H-C-O-C-H
  |   |
  H   H

Functional Groups and Polar Reactants

When a polar group of atoms, like the OH group or NH group are attached to a carbon, the molecule has a polar site. It may undergo chemical reactions when it attracts polar and ionic reactants, but it will usually be near this functional group. This is why compounds with the same functional group have similar chemical properties, or kinds of reactions. For example, in the amine group, both methylamine and ethylamine give the same kinds of reactions.
CH3NH2 + HCl ==> CH3NH3+ + Cl-
methylamine + hydrogen chloride ==> methylammonium ion + chloride ion

CH3CH2NH2 + HCl ==> CH3CH2NH3+ + Cl-
ethylamine + hydrogen chloride ==> ethylammonium ion + chloride ion

Only the NH2 group of the amines change in the previous two reactions, and it changes the same way in both.

The Symbol R in Structural Formulas

The symbol R, stands for the word radical, and in organic chemistry, represents alkane-like groups. It is sometimes used to simplify equations or to summarize them. For example, to summarize the two equations in the previous sections, you may write:
RNH2 + HCl ==> RHN3 + Cl-

The R takes care of any alkane group that you may substitute in. It takes care of all the equations, including methylamine, ethylamine, propylamine, butylamine, etc. It gives a simpler view of how one group, not just the individual compound, changes into another and how each group affects its properties.
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