ORGANIC CHEMISTRY
STRUCTURE AND FORMULAE OF CARBON COMPOUNDS
MEISHA MEEKS
Look at the following sets of images. In each image A and B are related and the same
relationship exists between C and D. Determine the correct image for D in each set.
1.
2.
3.
OBJECTIVES
• Discuss the ability of carbon to form branched and
unbranched compounds with single, double and triple bonds
• Distinguish between aliphatic and aromatic compounds
• Explain the terms functional group and homologous series
• Describe the types of formulae
• Determine the empirical and molecular formulae from
combustion analysis data
• Apply IUPAC nomenclature to the naming of organic
compounds
Formation of Organic Compounds
• Organic compounds are a large class of compounds containing
carbon
• Typically these compounds will also contain hydrogen, oxygen,
nitrogen and sulfur
• Compounds containing carbon and hydrogen only are known as
hydrocarbons
• Carbon forms these compound because of its ability to catenate
•
•
Catenation is the ability of an element to form long chain-like structures with itself
Carbon is able to form single, double and triple bonds with itself which gives rise to
the formation straight-chain and ring structures
• Carbon is tetravalent, having 4 electrons available for co-valent
bonding and is therefore able to form single, double and triple
bonds with other elements
Organic Compounds
•
Branched vs. Unbranched
•
Single, Double and Triple Bonds
CH3 – CH2 – OH
CH3-CH2 - C=O
H
CH3 - C≡N
•
Aliphatic vs. Aromatic
CH3 –CH2CH=CH2
•
Cyclic Compounds
Homologous Series
Property
•
•
Characteristic
Example
Functional group
• atom or group of
atoms within a
molecule that is
responsible the
chemical properties
of the molecule
Molecular Mass
neighbouring members differ by 14 units
which corresponds to a –CH2 unit
Series: Alkane
Methane R.M.M. – 16;
Ethane R.M.M. - 30
General Formula
All members have the same general
formula
Series: Alkene
General Formula: CnH2n
Chemical Properties
All members have the same chemical
properties because they have the same
functional group
Series: Alkane
All alkanes do not react with Cl or Br in the
dark.
Homologous series
• group of organic
compounds that
have similar
characteristics
Physical Properties
Physical properties of members vary in
regular pattern generally corresponding
with an increase in molecular mass
Series: Alkane
B.P. of methane: -161oC
B.P. of ethane: -88oC
B.P. of propane:-42oC
Preparation
All members of the group can be
prepared by the same method
Series: Alcohol
All alcohols can be prepared from hydration
of the corresponding alkene.
Homologous Series
COMBUSTION ANALYSIS
• The process of burning a unknown compound in excess oxygen
• The products are analysed to determine the empirical and/or molecular
formulae of the unknown
• Organic compounds on combustion will produce CO2 and H2O
• If other elements (apart from C, H or O) are present then other products will
be formed
•
Eg. N producing NO2
• All the C in the organic compound will form CO2 and
all the H will form H2O
• Determination of O is done by subtracting the masses of C and H from the
total mass of the compound
Types of Formulae
•
General Formula
•
•
•
Empirical Formula
•
•
•
simplest whole number ratio of atoms each element present in a molecule
eg. ethene: CH2
Molecular Formula
•
•
•
simplest algebraic formula for members of a homologous series
eg. Alkenes: CnH2n
the actual whole number ratio of atoms of each element present in a
molecule
eg. ethene: C2H4
Structural Formula
•
•
•
shows the manner in which atoms are bonded together in a molecule
displayed: shows the positioning of atoms and the bonds between them
condensed: does not show the bonds between atoms
IUPAC NOMENCLATURE
1.
2.
3.
4.
Determine the longest continuous carbon chain (parent chain).
Identify the functional groups present.
Determine the carbon atom to which the functional group is attached.
Number the carbons in the parent chain giving the carbon attached to the functional group the lowest
number.
5. Identify any side-chains present and assign them the number of the carbon in the parent chain to which
they are attached.
a. If there are 2 or more of the same type of side chain attach the corresponding prefix (i.e. 2-di, 3-tri,
etc.) followed by the numbers for each side-chain group
b. Side-chains are to be arranged in alphabetical order
6. The name begins with the numbers of the side-chains; followed by the names of the side-chains; then
the number and prefix of the parent chain; then the name of the functional group including the number
carbon to which it is attached.
7. Numbers are always separated by commas and numbers are separated from words by dashes. Words are
joined together
IUPAC NOMENCLATURE
IUPAC NOMENCLATURE
IUPAC NOMENCLATURE