organic chemistry - suli-pharma.comorganic chemistry alkanes • alkanes: are saturated hydrocarbons...
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Organic Chemistry
Alkanes
• Alkanes: are saturated hydrocarbons (paraffin) that is
contain only carbon and hydrogen bonded together through
carbon-hydrogen and carbon-carbon single bonds. They are
either straight- chain or branched-chain hydrocarbons, with
general formula CnH2n+2
o All hydrocarbons are nonpolar molecules. As a result they
are not water soluble but are soluble in nonpolar organic
solvents.
o they have relatively low melting points and boiling points
and are generally less dense than water.
o The longer the hydrocarbon chain (greater the molecular
weight), the higher the melting and boiling points and the
greater the density (see next slide).
Molecules having the same molecular formula but different
arrangements of atoms are called structural or constitutional
isomers.
Physical Properties of Alkanes
Carbon atoms are classified according to the number of
other carbon atoms to which they are attached.
Primary carbon (1ᵒ) is directly bonded to one other carbon.
Secondary carbon(2ᵒ) is bonded to two other carbon atoms.
Tertiary carbon (3ᵒ) is bonded to three other carbon atoms
Quaternary carbon (4ᵒ) is bounded to four carbon atoms.
If there is a competition between two chains of equal length,
then choose the chain with the greater number of substituents.
o Substituents are the groups connected to the parent chain:
Example: Identify and name the parent in each of the
following compounds:
Answers:
a) parent= hexane
2. Identify and Name the Substituents.
Substituents are named with the same terminology used
for naming parents; only we add the letters (yl).
Alkane – 1H = Alkyl substituent
e.g.
Methane – H= methyl
CH4-H = -CH3
Alkane alkyl group
Ethane Ethyl group
3. Number the parent chain and assign a locant to each
substituent:
o If one substituent is present, it should be assigned the lower
possible number.
o When multiple substituents are present, assign numbers so that
the first substituent receives the lower number.
o If there is a tri, then the second locant should be as low as possible:
o When a substituent appears more than once in a compound, a prefix
is used to identify how many times that substituent appears in the
compound (di = 2, tri = 3, tetra = 4, penta = 5, and hexa = 6).
For example, the compound above would be called
• 2,3,6-trimethylheptane.
Notice that a hyphen (-) is used to separate numbers from letters,
while commas are used to separate two numbers from each other.
4. Arrange the substituents alphabetically:
Once all substituents have been identified and assigned
the proper locants, they are placed in alphabetical order.
Ex/ Provide a systematic name for the following compound:
Many common names persist in organic chemistry, despite
IUPAC rules, e.g.
Compound ‘common’ name IUPAC name
H3CC
CH3
O
HC
H
O
H3CC
OH
O
H3CO
CH3
Acetone Propanone
Formaldehyde Methanal
Acetic acid Ethanoic acid
Dimethylether Methoxymethane
• Benzene (C6H6) is the simplest aromatic hydrocarbon.
• All C—C bond lengths are equal.
• The resonance description of benzene consists of two
equivalent Lewis structures, each with three double bonds
that alternate with three single bonds.
Benzene
• In benzene, the actual bond length (1.39 Å) is intermediate
between the carbon—carbon single bond (1.53 Å) and the
carbon—carbon double bond (1.34 Å).
Many mono substituted benzenes have common names which you must also learn.
Common Names of Benzene Derivatives
OH OCH3NH2CH3
phenol toluene aniline anisole
C
H
CH2 C
O
CH3
C
O
HC
O
OH
styrene acetophenone benzaldehyde benzoic acid
Methyl phenyl ether
Common Aromatic Compounds
4-Hydroxy-3-methoxybenzaldehyde 2-Acetoxybenzoic acid
2-(Acetyloxy)benzoic acid
2-(4-Isobutylphenyl)propanoic acid