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Organic chemistry and Biological chemistry for Health Sciences
59-191
Lecture 6
Saturated compounds:
When the molecules have only single bonds, the compound is called a saturated
compound.
Atoms in the molecule directly holds as many other atoms as they can.
F. example
Each carbon in ethyl alcohol directly holds four atoms
Unsaturated compounds:
Molecules with double and triple bonds are called unsaturated compound.
Can add certain substances, like hydrogen, to their double or triple bonds
Cyclic compounds:
Arrangement of three or more carbon atoms into a closed cycle is called a carbon ring.
Molecules with a carbon ring are called ring compounds or cyclic compounds.
F.example
Cyclohexane is a ring of six carbons
Cyclopropane- ring of three carbons (important anesthetic)
Cyclic compounds can have double bonds and those have to be shown in the structure as
any other double bonds.
Cyclic compounds can also carry substituents
F.example
Ethylcyclohexane
Heterocyclic compounds:
Cyclic compounds with ring atoms other than carbon is called heterocyclic compounds.
Example:
Tetrahydropyran
Other atoms can be O, N, or S.
Simple polygons can be used to represent the ring of cyclic compounds.
F.example
Cyclobutane can be represented by a square. Each line in the square is a carbon-carbon
single bond and there is a CH2 group in each corner of the square.
Polygons like the hexagon for cyclohexane can be used to represent rings provided that
we understand the following rules:
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Carbon occurs in each corner unless O or N (or another multivalent atom) explicitly
written at a corner
A line connecting two corners is a covalent bond between adjacent ring atoms
Remaining bonds, as required by the covalence of the atom, are understood to hold H
atoms
Double bonds are always explicitly shown
Free rotation is not possible about single bonds in a cyclic compound. Single bond has to
be broken in a cyclic compound to get the same kind of flex as you observed in pentane.
Isomer:
Compounds that have identical molecular formulas but different structures are called
isomers of each other, and the existence of isomers is a phenomenon called isomerism.
There are several kinds of isomers.
Constitutional isomer:
They have the same molecular formula but differ in basic atom-to-atom connectivities.
F.example:
There are three constitutional isomers of C5H12, for example, pentane, 2-methylbutane
and 2,2-dimethylpropane.
The larger the number of carbon atoms per molecule, the larger is the number of isomers.
F. example
C8H18 has 18, C10H22 has 75 and C20H42 has 366,619.
Often isomers have very different properties.
F.example
Ethyl alcohol and dimethyl ether is constitutional isomers.
They are radically different compounds
 Ethyl alcohol is a liquid at room temperature but dimethyl ether is a gas.

Ethyl alcohol reacts with sodium; dimethyl alcohol does not.
Since isomers have very different properties structural formula is nearly always used
rather than the molecular formula for organic compounds.
Only structures show the organization of atoms in the molecule
To recognize two structures as identical molecules or as isomers or something else is very
important.
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Functional groups:
Regions of molecules that have nonmetal atoms other than C and H or that have double
or triple bonds are specific sites in organic molecules that chemicals most often attack.
These small structural units are called functional groups, because they are the
chemically functioning group of the molecule.
Sections of molecules consisting only of carbon and hydrogen and only single bonds are
called non-functional groups
Each functional group defines an organic family
Many organic compounds irrespective of their carbon chain length can be grouped
together in a family provided that they have the same functional group
Because all these compounds have the same functional group, they exhibit the same kind
of reactions.
So when one of these reactions is learned, it applies to all members of the family.
Using a family formula often summarizes a particular reaction for an organic family.
All alcohols, for example can be symbolized by R-OH, where R stands for a carbon chain
(or ring), one whatever length or branching (or ring size).
F.example
All alcohols react with sodium metal as follows
2R-OH + 2 Na  2R-ONa + H2
2CH3CH2OH + 2 Na  2 CH3CH2-ONa + H2
N.B. this reaction changes only the –OH group of the reaction.
Dimethyl ether that is the structural isomer of ethyl alcohol cannot give the same reaction
with sodium.
Thus the functional group in dimethyl ether is not the same as that in ethyl alcohol.
Another important organic family is that of the carboxylic acids. All their molecules have
the carboxyl group, which makes all its compounds weak acids
All molecules with the carboxyl group give the same reaction, so we can represent
literally thousands of reactions by a simple equation.
Amino acids that are the building block of protein is an example of substances with more
than one functional groups. It contains both amino (-NH2) and carboxyl (-COOH) group.
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Glycine, amino acid, is able to both neutralize strong acids (by the -NH2 group) and bases
(by the –COOH group).
ALKANES AND CYCLOHEXANES:
Hydrocarbons:

Are made from only C and H.

Covalent bond between the carbon atoms can be single, double or triple.

Carbon skeleton can be chains or rings.
Hydrocarbons can be classified in two major groups:

Aliphatic hydrocarbon (no benzene ring)

Aromatic hydrocarbon (contain benzene ring)
Aliphatic hydrocarbons can be divided in three different groups as follows:

Alkanes

Alkenes

Alkynes
Alkane:
Saturated hydrocarbons (only single bonds)
Alkenes:
Hydrocarbons with one or more carbon-carbon double bonds, whether the skeletons are
chains or rings.
Alkynes:
Hydrocarbon with one or more carbon-carbon triple bonds.
N.B. It is possible for a molecule to have both double and triple bonds.