It clarifies basics to organic chemistry

1. GROUP ONE
alkanes and alkenes
KABUUKA RICHARD VU- BPC- 2307-0724-DAY
KAWALYA STEVEN VU- BPC -2307- 0639-DAY
KAWALYA TREVOR VU-BPC-2307-0250-DAY
WEGOSASA EVERLYN VU- BPC-2307-0432-DAY

2. Organic compounds
• Organic compounds are the
compounds that contain the
element carbon.
• Catenation is the ability of atoms
of the same element to join
together forming short or long
chains and rings as in organic
componds.

3. Hydrocarbons
• Hydrocarbons are organic compounds
composed of the elements carbon and
hydrogen only.
• There subdivided into two groups, based on
the type of bonding between carbon atoms;
• Saturated Hydrocarbons are those
compounds of carbon and hydrogen
containing only carbon-carbon single bonds.
Examples; Alkanes
• Unsaturated Hydrocarbons are those
compounds of carbon and hydrogen
possessing one or more multiple bonds
(double or triple bonds) between carbon
atoms. Examples; Alkenes, alkynes and
aromatic hydrocarbons

4. Structure of Hydrocarbons
Detailed structure; is a formula that shows all the bonds and atoms.
Condensed structure; shows shorter structure

5. Classification of organic compounds.
The functional group is the part of a molecule or a
compound that determines the its chemical properties
and some of the physical properties of a compound.

6. Different ways in which an organic
compound can be displayed
:
● Molecular formula- actual number of atoms of
each element in a molecule.
● Structural formula - shows the structure carbon
by carbon with hydrogens and functional groups
attached.
● Skeletal formula - only shows the bonds on the
carbon skeleton. The carbon and hydrogen atoms
are not shown but any functional groups are. It can
be used to simplify large complicated structures.
● Displayed formula – shows how all the atoms
are arranged and every bond between them.

7. SOME OF ALIPHATIC COMPOUNDS

8. ALKANES
Homologous series is a group of compounds
with the same functional groups with
successive members differing by -CH2
Alkanes are saturated hydrocarbons.
They have one C-C single bond between carbon
atoms

9. Physical properties of alkanes
• At room temperature the first four alkanes;
methane to butane are gases
• C5 H12 to C17 H36 are liquids
• The rest above are solids at room temperature.
• Alkanes are non pollar; soluble in organic solvents
like benzene, toulene, ether and CCl4. They are
insoluble in water which is polar.
• The density, boling point and melting point
increases with increase in number of carbon
atoms

11. Nomenclature of Alkanes
In naming alkanes we use International Union of Pure and Applied
Chemistry (IUPAC) system;
Prefix - indicating number of carbon atoms in the main/parent chain
of the molecule.
Suffix – “ane” indicates the functional group in the molecule is an
alkane

12. Alkyl radicals are obtained by removing one hydrogen atom from
the corresponding alkanes. Their general formula is CnH2n+1, where
n = 1, 2, 3 . . . .
The names of alkyl radicals are derived from the names of the
corresponding parent alkanes by changing the suffix –ane to -yl.

13. IUPAC system of naming Alkanes
Ex1. 3-methyl, 4-ethyl heptane,
Ex3. 4-bromo-3,5-dichloro-3,4,6-trimethyl octane

14. Name: 3-fluoro-2,2,4,5-tetramethyl heptane
Name:

15. Isomerism Of Alkanes
• Isomer are different compounds that share
the same molecular formula.
• The straight-chain and branched chain
represent isomers alkanes

17. Preparation of alkanes
• Industrially, alkanes are prepared by fractional
distillation of petroleum.
• Laboratory preparation of alkanes
• 1. Hydrogenation with Ni catalyst at 200oC or
heated Pt.
•

18. 2. Decarboxylation reaction.
Heating sodium salt of an organic acid with soda
lime

19. 3.Wurtz reaction;
Halo alkanes are reacted with sodium under dry ether/heated
nickle to form alkanes. It leads to formation of symmetrical
alkane having even number of carbon atoms.

20. 4. Heating sodium salt of an organic acid with soda lime
Mixture of sodium hydroxide and calcium oxide; the reaction
brings about the removal of the carboxylate group from the
sodium salt of the carboxylic acid. This type of reaction is called
decarboxylation.

21. Chemical properties of alkanes
• 1.Combustion Rxn; Alkanes burn in plenty of O2
forming CO2 and water with liberation of heat
energy

22. 2.Elimination reactions; this is the removal of
molecules from a saturated compound to form
an unsaturated product.

23. 3. Substitution Reaction
• This is a reaction that involves the replacement of
one atom or a group of atoms by another atom
or group of atoms. Eg. Halogenation of alkanes
• This reaction involves reacting of halogens F2, Cl2,
Br2 or I2 with alkanes, it proceeds in presence of
heat or sunlight. This type of reaction is called
photochemical reaction.
• The reaction of alkanes with Cl2 and Br2 proceeds
in a sequence of steps. For example, Consider the
photochemical reaction of CH4 with Cl2
(chlorination)

24. Halogenation of methane

27. Cycloalkanes
• These are saturated hydro carbons in which carbon
atoms form closed rings
• The general formula is CnH2n where n>=3
• Cyclopentane cyclobutane cyclopentane

28. Preparation of Cyclohalkanes
By Perkin`s Method:
Vicinal dihalide reacts with
diester of dicarboxylic acid
followed by hydrolysis and
heated.
By Wislicenus pyrolysis
method: divalent metal salts
of dicarboxylic acids heated
followed by reduced with
Zn/Hg.HCl from cycloalkenes
By Freund Rxn: Elimination
of terminal halogen atoms
from dihalides with Na or
Zn dust

29. contn
Reduction of cyclic ketone: The
Wolff-kishner carbonyl reduction is
used to convert carbonyl groups
directly to methylene group.
Hydrazone is heated with carbonyl
Cpd in presence of an alkali and a
metal catalyst
From aromatic Cpds: Catalytic
reduction of benzene and its
delivatives.
Use of Carbenes: Are unstable
intermediates in which C has a
pair of unshared electrons. Are
neutral species with no formal
charge, (methylene :CH2

30. Chemical Reactions of Cycloalkanes
Addition Rxn:
Cycloalkanes are inert at
room temp.
Cyclopropane forms
additional products with
ring forms
Substitution Rxn: In
diffused light,
cyclopropane reacts with
Cl2 to give substitution
product
Oxidation: Cycloalkanes
Are oxidised by alkaline
KMnO4 to dicaboxylic
acids involving ring
fusions

31. Application of alkanes
• Used as detergents to solubize fats for use in treatment of
asthma, psoriasis, atopic dermatitis and inflammatory
diseases
• Alkanes with high number of carbons are used as anti-
corrosive agents: .nonane and hexadecane are used in
diesel, kerosene and aviation fuel.
• Versatile alkanes are used as carrier gases in gas
chromatography, an essential analytical technique in
pharmaceutical research and quality control.
• Alkanes like hexane and heptane used as nonpolar solvents
in the pharmaceutical industry essential for the extraction
of natural products and the formulation of various drug
products,
• Alkyl halides are useful solvents in refigerants, insectcides
and herbicides.

32. Alkenes
• These are unsaturated hydro
carbons with with a carbon
to carbon double bond as
their functional group C=C.
• They are also known as
olefins. They have a
homologous series
represented by the general
formula CnH2n; n=2,3,4…

33. Physical
properties
• At room temperature alkenes
containing 2-4 are gases
• Those having 5 to 17 carbons
are liquids
• Those having 18 carbons and
above are solids
• Alkenes are non polar;
insoluble in pollar solvents
like water, but soluble in non
polar solvents like ether,
benzene, toulene and CCl4

34. Homologous series of alkenes and
physical constants

35. Nomenclature of alkenes
• The IUPAC names (International Union of Applied and Pure
Chemistry). of alkenes are obtained by using the prefixes to
indicate number of carbon atoms in the molecule and adding
the suffix ‘-ene’ that indicates the presence of a double bond.

36. Continuation
• 1. Select the longest continuous chain of carbon
atoms in the molecule that includes the double
bond as a parent structure. Its name will be the
same as the alkene containing the same number
of carbon atoms.
• 2. Number the carbon atoms starting from one
end to the other in such a way that the carbon
atom preceding the double bond takes the lowest
possible number and indicate the position of the
double bond by this number in the name.

38. Isomerism in Alkenes
• Alkenes containing two and three carbon atoms
have only one possible structure. Alkenes
containing four or more carbon atoms exhibit
isomerism. Alkenes show the following three
types of isomerism:
• 1. Chain isomerism: This is due to the difference
in the arrangement of the carbon atoms in the
longest continuous carbon chain.
• 2. Position isomerism: This is due to the
difference in the position of the double bond in
the carbon chain.

39. Compounds (a) and (b) represent the position isomers of
pentene
(c) and (d) are position isomers of methylbutene, (a),
(c) and (e) are the chain isomers, while all these compounds are
the isomers of C5H12.

40. 3. Geometrical isomerism. This results from the difference in the
relative spatial arrangement of atoms or groups about the double
bond. This isomerism exists because free rotation about the double
bond is not possible.
To differentiate geometrical isomers, we use the prefix ‘cis’ if two
similar groups are on the same side of the double bond and ‘trans’
when the two similar groups are on opposite sides of it; ‘cis’ means
the same and ‘trans’ means across. Consider the following geometrical
isomers of 2-pentene;

41. Preparation of
Alkenes
• Alkenes are mainly obtained
during fractional distillation of
petroleum when the process
called cracking is carried out.
• In the laboratory, alkenes can
be prepared by the following
methods:

42. 1. Dehydrohalogenation of alkyl halides with a base (KOH).
This occurs by means removal of hydrogen and a halogen atom
from adjacent carbons.
When alkyl halides are heated with strong bases NaOH or KOH,
they generate alkenes.
Alkyl halides are compounds of an alkyl group and a halogen
such as CH3Cl and CH3 – CH2 – Br.

43. 2. Dehydration of alcohols
Dehydration of alcohols when heated with
strong acids H2SO4 , H3PO4 acid at 85oC or
alumina (Al2O3 ) as a catalyst at 350oC.
This reaction generates an alkene and water

45. Chemical properties
of Alkenes
• Alkenes are unsaturated
hydrocarbons containing double
bond (a strong bond and a weak
bond) between the two carbon
atoms.
• They are more reactive than
alkanes, because the weak
bond can be used for further
reaction.

46. 1. Combustion reaction
Alkenes burn in oxygen with a luminous flame
to form carbon dioxide and water.

47. 2. Addition reaction
• .The addition occurs at the carbon-carbon double
bond.
• a Addition of halogens (halogenation): When a
halogen molecule, X2 , (where, X2 = Cl2 or Br2 ) is added
to alkenes, the product is a dihaloalkane.
• If bromine water (bromine in CCl4 ) is added to alkenes,
the reddish brown colour of Br2 in CCl4 will disappear.
• This is due to the addition of bromine (Br2 ) across the
double bond. So, Br2 in CCl4 is used to detect
unsaturation (presence of multiple bond) in a
compound.

48. General addition reaction:

49. B) Hydrogenation
. Addition of hydrogen molecule to alkenes in the
presence of a nickel or platinum catalyst yields
alkanes.

50. c. Addition of hydrogen halides, HX
Hydrohalogenation: Addition of hydrogen halide (HCl, HBr
or HI) to alkenes leads to the formation of alkyl halides.
The product of the reaction can be predicted by
Markovnikov’srule;
• It states that “when an alkene reacts with a hydrogen
halide to give an alkyl halide, the hydrogen adds to the
carbon atom of the double bond that has the greater
number of hydrogen atoms,
• And the halogen to the carbon that has the fewer
number of hydrogen atoms”. The same is true when an
alkene reacts with water in an addition reaction to form
an alcohol.

52. Anti-Markovnkov Rxn
• It is possible to obtain Anti-Markovnkov products when
HBr is added to alkenes in presence of free radical
initiators like peroxides H2O2, ROOR.
• Initiation: O-O bond is weak, In presence of
heat/sunlight its easily cleaved to generate alkoxy
radicals, .OR and .OR which then abstracts HX.
• Propagation: Halogen radical is electron deficient and
electrophilic. The radical adds to double bond,
generating a carbon centered radical. This radical the
abstracts hydrogen from a molecule of H-X, giving a
product and another halogen radicle.

54. Hydration Of Alkenes
• D) Addition of water: When alkenes are
hydrated in the presence of an acid catalyst,
they produce alcohols, in accordance with
Markovnikov’s rule.

55. Mechanism of synthesis

56. Oxidation of Alkenes
• E) Oxidation of alkenes: with cold alkaline
potassium permanganate solution (KMnO4 )
forms diols or glycols(compounds containing two
hydroxyl groups).
• Alkaline KMnO4 solution is also used as
aqualitative test for the identification of
unsaturation in a compound.
• The solution is called Baeyer’s reagent. In the
presence of unsaturated hydrocarbons, the
purple colour of alkaline KMnO4 solution gets
decolorised and a brown precipitate is formed

57. Oxidation reaction with alkaline KMnO4
In acidified KMnO4 or KCr2O6, oxidizes the dihydroxy
compound so produced in the reaction or
carboxylic acid. Mechanism occurs as below;

59. Polymerization of Alkenes
• F) Polymerization (self-addition) of alkenes:
• Polymerization is the union of small molecules called
monomers to form a large molecule called a polymer.
• Alkenes monomers in presence of O2 are linked to form
polymetric material without loss of material, known as
addition or chain-growth polymerization.

60. Polymerization Of Halo-alkenes
Vinyl Chloride is
synthesized in
presence of peroxide
catalyst to form
Polyvinyl Chloride
(PVC)
Teflon is a
synthesized from
tetrafluoroethene
monomers

61. Cycloalkenes
• Cycloalkenes are unsaturated cyclic
hydrocarbons. The carbon atoms are linked in
such a manner as to form a closed chain or a ring
structure.
• They contain a double bond between carbon
atoms and are represented by the general
formula Cn H2n–2, where n should be equal to or
greater than 3. They are isomeric with alkynes.
• They are named by prefixing “cyclo” to the name
of alkenes containing the same number of carbon
atoms.

62. The given structures show some examples of cycloalkenes.

63. Methods for formation of cycloalkenes
From cyclic alcohols; they are dehydrated
under mild conditions. The loss of water
from cyclic alcohols gives a cyclic-alkene
By Birch reduction: The Rxn proceeds via
one-electron transmision mechanism.
The 1,4 reduction of aromatic Cpds to the
corresponding uncongugated cyclohexadiens
by alkali metals dissolved in liquid ammonia
in presence of alcohol.
By Diel-Alder reduction: Addition of
conjugated diene and alkene leads to a
cycloalkene. In this Rxn, participating bonds
are broken and new are simultaneously
formed.
Electric Reaction: Conjugated double-bond
system can be cyclized in a reversible rxn
either by heating or using photolysis to for
cycloalkene

64. SUMMARISED REACTIONS OF CYCLOALKENES IN SUMMERY

65. Uses of Ethene (Ethylene)
• Ethene is used in the production of
ethanol, and polymers such as
polyethene, polyvinylchloride (PVC),
polystyrene and teflon.
• Used in the production of 1,2-ethanediol,
which is used as an antifreeze material;
and for the preservation as well as
artificial ripening of fruits.
• Drug synthesis: used as starting materials
in the synthesis of pharmaceutical drugs.
Tetracyclins, steroids,

66. REFRENCES
• Kamal K.B., Girdhar J., Vipin C.J., (2017)
Organic chemistry I, Uttarakhand Open
University, Haldwani, Nainital, 263139, Issue
978-93-8574054-1.
• Shaik R.V., Applieed Organic Chemistry (Part-
B), AASTU-ETHIOPIA, Dept, Of Industrial
Chemistry, Chapter 4.
• Introduction to Organic Chemistry, Unit 1.