Bonding of Carbon. Hydrocarbons. Constitutional Isomerism and Branched-Chain Alkanes. Uses of Alkanes and Cycloalkanes. Substitution Reactions of Alkanes. Geometric Isomerism. Addition Reactions of Alkenes. Substitution Reactions of Aromatic Hydrocarbons.

1. Naming Organic Compounds I
Dr. K. Shahzad Baig
Memorial University of Newfoundland
(MUN)
Canada
Petrucci, et al. 2011. General Chemistry: Principles and Modern Applications. Pearson Canada Inc., Toronto, Ontario.
Tro, N.J. 2010. Principles of Chemistry. : a molecular approach. Pearson Education, Inc.

2. The Bonding of Carbon
Because carbon is in Group 4A
Carbon forms single, double, and triple bonds to achieve a filled octet.
Therefore, the possible bonding combinations for carbon are as follows
Carbon has ability to bond with other carbon atoms to form chains and rings of various
lengths.

3. Hydrocarbons
The simplest organic compounds are hydrocarbons, containing only C and H
Hydrocarbons can be separated into three main groups:
1. Saturated hydrocarbons contain only single bonds between the carbon atoms.
Saturated hydrocarbon molecules can be cyclic or acyclic.
A cyclic hydrocarbon is one in which a chain of carbon atoms has formed a ring.
2. Unsaturated hydrocarbons are hydrocarbons that contain double or triple bonds
between carbon atoms.
3. Aromatic hydrocarbons are hydrocarbons that contain benzene rings or similar
features.

4. Alkanes and Cycloalkanes
the structural formula does not convey information about the
3D arrangement of the atoms. To do this, you would need to
draw the 3D formula depicting the molecular geometry

5. The Alkane Series
the general formula CnH2n+2.
For n = 1, methane, CH4; C1H2x1+ 2
for n = 2, ethane, C2H6; C2H2x2+ 2
for n = 3, propane, C3H8; C3H2x3+ 2
The alkanes constitute a homologous series, which is a series of
compounds in which one compound differs from a preceding one
by a fixed group of atoms.

6. Number Prefix
1 metha
2 etha
3 propa
4 buta
5 penta
6 hexa
7 hepta
8 octa
9 nona
10 deca
11 undeca
12 dodeca

7. Constitutional Isomerism and Branched-Chain Alkanes
In addition to the straight-chain alkanes, branched-chain alkanes
are possible. For example, isobutane (or 2-methylpropane) has the
structure

8. Butane and isobutane are constitutional (or structural) isomers,
Isomers, are compounds with the same molecular formula but different structural
formulas.
Because these isomers have different structures, they have different properties. For
example, isobutane boils at −12°C, whereas butane boils at 0°C.
The number of constitutional isomers rapidly increases with the number of carbons in the
series.
For example, there are :
3 for C5H12 , pentanes
5 of C6H14 (hexanes), and
75 of C10H22 (decanes).

9. Cycloalkanes
The general
formula for cyclic
cycloalkanes is
CnH2n.

10. Sources and Uses of Alkanes and Cycloalkanes
Fossil fuels (natural gas, petroleum, and coal) are the principal sources of all types of
organic chemicals.
Natural gas is a mixture of low molecular- weight hydrocarbons made up primarily of
methane, CH4,with lesser amounts of ethane, C2H6; propane, C3H8; and butane, C4H10.
Petroleum, or crude oil, is the raw material extracted from a well. It is a mixture of alkanes
and cycloalkanes with small amounts of aromatic hydrocarbons.
The composition of petroleum is not consistent; it is dependent on geologic location and
the organic matter present during oil formation.
Because fossil fuels are extracted is separated these mixtures into various components
by distillation’
The separated fractions include as gasoline (C5 to C12) and kerosene (C12 to C15) etc.

11. Reactions of Alkanes with Oxygen
alkanes, probably, are not reactive molecules at normal temperatures
For example, a propane gas grill uses the reaction
The large negative ΔH ° value for this reaction and all hydrocarbon reactions with
oxygen demonstrates why we rely on these molecules to meet our energy needs.

12. Substitution Reactions of Alkanes
Under the right conditions, alkanes can react with other molecules.
Reaction with Cl2, for example, requires light (indicated by hv) or heat.
A substitution reaction is a reaction in which a part of the reacting molecule is substituted for
an H atom on a hydrocarbon or hydrocarbon group.
All of the H atoms of an alkane may undergo substitution, leading to a mixture of products

13. The CCl4 product can be reacted with HF in the presence of a SbCl5 catalyst to produce
trichlorofluoromethane, CCl3F, also known as CFC-11.
This compound is one of a number of chlorofluorocarbons (CFCs) used as a refrigerant,
till 1970s.
Recent refrigerants that do not contribute to ozone destruction include hydrofluorocarbons
(HFCs), such as CF3CH2F, which do not contain chlorine atoms. These HFCs are now
used to replace CFCs

14. Alkenes
Alkenes have the general formula CnH2n and contain a carbon–carbon double bond
Alkenes are unsaturated hydrocarbons. Because they contain C–C multiple bonds, they
are typically much more reactive than alkanes.
Under the proper conditions, molecular hydrogen can be added to an alkene or alkyne to
produce a saturated compound in a process called catalytic hydrogenation.
For example, ethylene adds hydrogen to give ethane.
Another example is manufacturing of margarine

15. Alkenes and Geometric Isomerism
In ethylene and other alkenes, all of the atoms connected to the two carbon atoms of the
double bond lie in a single plane. This is due to the need for maximum overlap of 2p
orbitals on the carbon atoms to form a pi (p) bond.
For rotation to occur, a significant amount of energy must be supplied to break the p bond,
so rotation does not normally occur.
This inability to rotate gives rise to geometric isomers in certain alkenes. Geometric
isomers are isomers in which the atoms are joined to one another in the same way but differ
because some atoms occupy different relative positions in space.
For example, 2-butene, C4H8, has two geometric
isomers, called cis-2-butene and trans-2-butene

16. Oxidation Reactions of Alkenes
Unsaturated hydrocarbons can also be partially oxidized under relatively mild
conditions.
For example, when aqueous potassium permanganate, KMnO4(aq), is added to an
alkene (or alkyne), the purple color of KMnO4 fades and a brown precipitate of
manganese dioxide forms

17. Addition Reactions of Alkenes
Alkenes are more reactive than alkanes because of the presence of the double bond
An addition reaction is a reaction in which parts of a reactant are added to each carbon
atom of a carbon–carbon double bond, which converts to a carbon–carbon single bond.
Unsymmetrical reagents, such as HCl and HBr, add to unsymmetrical alkenes
to give two products that are constitutional isomers. For example

18. Markownikoff’s rule is a generalization that states that the major product formed by
the addition of an unsymmetrical reagent such as HCl, HBr, or HOH is the one obtained
when the H atom of the reagent adds to the carbon atom of the multiple bond that
already has the greater number of hydrogen atoms attached to it.
In the preceding example, the H atom of HBr should add preferentially to carbon atom
1, which has two hydrogen atoms attached to it.
Experimentally, the major product then is 2-bromopropane.

19. Alkynes
Alkynes are unsaturated hydrocarbons containing a carbon–carbon triple bond.
The general formula is CnH2n−2. The simplest alkyne is acetylene (ethyne), a linear
molecule.
Acetylene burns with oxygen in the oxyacetylene torch to give a very hot flame
(about 3000°C). Acetylene is produced commercially from methane
Acetylene is also prepared from calcium carbide, CaC2. Calcium carbide is obtained
by heating calcium oxide and coke (carbon) in an electric furnace:
The carbide ion, C2
2−, is strongly basic and reacts with water to produce acetylene

20. The alkynes, like the alkenes, undergo addition reactions, usually adding two
molecules of the reagent for each C ≡ C bond. The major product is the isomer
predicted by Markownikoff’s rule,

21. Aromatic Hydrocarbons
Aromatic hydrocarbons usually contain benzene rings:
six-membered rings of carbon atoms with alternating
carbon–carbon single and carbon–carbon double bonds.
The electronic structure of benzene can be represented
by resonance formulas
This electronic structure can also be described
using molecular orbitals

22. Two condensed formulas for benzene are
In this description, p molecular orbitals encompass the entire
carbon-atom ring, and the p electrons are said to be delocalized.
Delocalization of p electrons means that the double bonds in
benzene do not behave as isolated double bonds.
Benzene rings also exist in the pain
relievers
acetylsalicylic acid (aspirin),
acetaminophen (Tylenol),

23. Substitution Reactions of Aromatic Hydrocarbons
Benzene does not undergo an addition reaction with Br2. The usual reactions of
benzene are substitution reactions.
For example,