1. 1
Course Code: CHM 203
Course Title: Organic Chemistry II
Number of Units: 2 Units
Course Duration: Two hours per week
Course Details:
Lecturer: Miss Adedo, K.O (B Sc., M Sc)
E-mail: adetoks4u@yahoo.com
Office Location: Islam Block
Course Content:
Stereochemistry
Methane, energy of activation and free radicals Substitution reactions in alkanes
Functional Group chemistry
Electrophilic and Nucleophilic Substitution Reaction
Aromaticity
Various organic Reactions, e.g addition of free radicals, elimination reactions

2. 2
Lecture Notes
SUBSTITUTION REACTION OF ALKANE
Alkane has been found to undergo substitution reaction, i.e replacement of hydrogen with a
functional group. This substitution reaction can be transformed to other organic compounds
through a reaction that occur at the site of the functional group. It is important to note that the
C―H bond of an alkane is not polar; hence alkane does not react with nucleophylic or
electrophylic reagents. Equally alkane is not a bronsted acid or bases and is inert to them too.
However, alkane requires some reagents and reaction conditions suitable for substitution of
hydrogen atom by a functional group.
Halogenation Reaction of Alkane
The oldest known substitution reaction of alkane is chlorination. This occur in the presence of
UV or bright sun light, hence it is an example of photo-chemical reactions.
R―H + Cl2 ―→ R―Cl + HCl [R can be benzene, aliphatic (alkyl) or cyclic (aryl) group.
Dumas was the first scientist to observe that chlorine and alkane could react to form alkyl
halide and HCl. Both Cl2 and Br2 substitute halogen for hydrogen in compound containing
C―H bond. The reactions are initiated by either heat or irradiation with UV light and or
visible light.
Fluorination also occurs with alkane but some substitution reaction must be initiated with
light at low temperature.
The halogenation reactions of alkane occur via substitution reaction. Note that the order of
reactivity of halogenations with alkane is F > Cl > Br while iodine undergoes little or no
reaction. Because each hydrogen is subjected to substitution by a halogen, all possible

3. 3
isomeric monohalides are obtained in the halogenation reaction. These isomeric products are
based on the number of equivalent hydrogen positions on the alkane that is undergoing this
reaction.
There are three kinds of equivalent hydrogen namely: primary hydrogen (e.g CH3), secondary
hydrogen (e.g CH2) and tertiary hydrogen (e.g CH). It is equally important to note that the
possible kinds of equivalent hydrogen can as well be used to determine the possible number
of isomers that a particular alkane can have.
For instance, fluorination of n-butane in the presence of UV light at low temperature gives
the following isomeric product.
UV (-800C)
CH3CH2CH2CH3 + F2 ――――→ CH2CH2CH2CH3 + CH3CHCH2CH3 + HF
Low temp. │ (60% yield) │ (40% yield)
F F
The isomeric halides obtained from different equivalent hydrogen position are often
separated by fractional distillation using an efficient distillation column and a high
refluxation within the column.
It has been observed experimentally that isomeric halides obtained do not correspond directly
to the relative number of chemically equivalent hydrogen at each chemically different
position.
For instance in the chlorination of propane in the presence of UV light at 3000C gave the
following isomeric and percentage yields.
CH3CH2CH3 + Cl2 ――→ CH2CH2CH3 + CH3CHCH3
│ │
Cl Cl
Propane has six equivalent primary positions and only two equivalent secondary positions, if
chlorination was purely statistical, one would expect a ratio of 75% to 25%, but what is
observed experimentally is a ratio of 50% to 50%.

4. 4
Relative Reactivity in the Halogenation of Alkane
Halogenation of alkane as earlier discussed does not give the isomeric primary, secondary
and tertiary monohalide in statistical yield. The observed ratio of the product indicates a
difference in the reactivities of primary, secondary and tertiary positions. The ratio of the
observed yield to the predicted yield of 2-chloro propane divided by the ratio the observed to
the predicted yield of 1-chloro propane represent the difference in reactivity for chlorination
at secondary positions compared to the primary position. This ratio is called relative
reactivity (R.R).
R.R at secondary position =
% (2− 𝑐ℎ𝑙𝑜𝑟𝑜 𝑝𝑟𝑜𝑝𝑎𝑛𝑒)𝑜𝑏𝑠. % (2 − 𝑐ℎ𝑙𝑜𝑟𝑜 𝑝𝑟𝑜𝑝𝑎𝑛𝑒)𝑝𝑟𝑒
⁄
% (1 − 𝑐ℎ𝑙𝑜𝑟𝑜 𝑝𝑟𝑜𝑝𝑎𝑛𝑒)𝑜𝑏𝑠. % (1− 𝑐ℎ𝑙𝑜𝑟𝑜𝑝𝑟𝑜𝑝𝑎𝑛𝑒)
⁄ 𝑝𝑟𝑒
R. R at secondary position =
50 25
⁄
50 75
⁄
= 3.0
This relative reactivity of 3.0 indicates that hydrogen in the secondary position of propane are
3 times more reactive than are the hydrogens of the primary positions towards chlorination at
3000C.
R. R at primary position =
% (1 − 𝑐ℎ𝑙𝑜𝑟𝑜 𝑝𝑟𝑜𝑝𝑎𝑛𝑒)𝑜𝑏𝑠. % (1 − 𝑐ℎ𝑙𝑜𝑟𝑜 𝑝𝑟𝑜𝑝𝑎𝑛𝑒)𝑝𝑟𝑒
⁄
% (2− 𝑐ℎ𝑙𝑜𝑟𝑜 𝑝𝑟𝑜𝑝𝑎𝑛𝑒)𝑜𝑏𝑠. % (2− 𝑐ℎ𝑙𝑜𝑟𝑜𝑝𝑟𝑜𝑝𝑎𝑛𝑒)
⁄ 𝑝𝑟𝑒
R. R at primary position =
50 75
⁄
50 25
⁄
= 0.334%
Equally a hydrogen on a tertiary hydrogen position is 4.5 time more reactive toward
chlorination at 3000C than a hydrogen at primary position.
In summary, the relative reactivities of hydrogen toward chlorination at 3000C follow the
order 30 > 20 > 10

5. 5
All chlorination reactions performed in the gas phase at 3000C have the same order of relative
reactivity.
Mechanism of Halogenation Reaction of Alkane
CH4 + Cl2 ―→ CH3Cl +HCl
 Chain Initiation step
UV
Cl2 ―→ Cl. +Cl.
UV
CH4 ―→ CH3
. + H.
 Chain Propagating step
Cl. + CH4 ―→ CH3
. + HCl
CH3 + Cl2 ―→ CH3―Cl + Cl.
 Chain terminating Stage
Cl. + Cl. ―→ Cl2
CH3
. + H. ―→ CH4
The free radical mechanism for halogenation reactions are in three steps and it occur in chain
generally called Free Radical Reaction Chain Mechanism.
It begins with an initiation step which involves cleavage of the weakest covalent bond in the
system to form radicals. Radicals are species formed through homolytical process.

6. 6
The association of a small portion of initiator molecules start with a sequence of self
propagating reactions that are known as Propagating step.
Chemical Properties of Free Radicals
Radical Coupling
CH3
. + CH3
. ―→ CH3
. .CH3 → CH3―CH3
Abstraction of Atom
CH3
. + A.―.
B → CH3―A + B.
Radical Addition
CH3
. + H2C = CH2 → CH3
. + CH2
.― .CH2 → CH3― CH2 ― CH2
.
Bond Dissociation Energy and Free Radicals
Free radicals are formed through homolytical cleavage of covalent bond. Energy required for
the homolytic cleavage of two atoms is known as Bond Dissociation Energy [BDE].
The lower the BDE, the less the energy required to form homolytic cleavage. For instance,
less energy is required to form Br―Br bond which is 46Kcal/mol than Cl―Cl bond which is
58Kcal/mol. Equally more energy is required to break or cleave C―H bond in methane
which is 102Kcal/mol than in C2H6 which is 97Kcal/mol.
Application of Bond Dissociation Energy [BDE]
Bond Dissociation Energy [BDE] allows us to estimate the possibility of the pathway by
which certain chemical reaction occur. For instance in the chlorination of methane to form
chloro methane and hydrogen chloride.

7. 7
CH4 + Cl2 ―→ CH3Cl +HCl
The BDE value enables us to know which bond is broken first or preferentially.
E.g. UV
Cl2 ―→ Cl. +Cl.
UV
CH4 ―→ CH3
.
+ H.
BDE also allows a prediction of the probability of subsequent reaction pathway. E.g. reaction
of chlorine atom or radicals.
Cl. + CH4 ―→ CH3
. + HCl
Since BDE is characterised by the release of energy, hence reaction of chlorine radical with
propane is exothermic. This is shown below:
CH3CH2CH3 + Cl
.
→ CH3CH2CH2
.
+ HCl
Bond broken = CH3CH2CH2―H, BDE = 97Kcal/mol
Bond formed = H―Cl, BDE = 103Kcal/mol
∆H = ΣBDE(Bond broken) - ΣBDE(Bond formed)
∆H = 97-103
∆H = -6Kcal/mol
Relative Stability of Radicals
The order of radical stability follows the order of relative reactivity in the halogenation of
alkane. For instance hydrogen abstraction from a tertiary position is favoured over that of
primary position.

8. 8
Hence tertiary alkyl radical is more stable than secondary alkyl radical. Likewise, formation
of a secondary alkyl radical by hydrogen abstraction from a secondary position is favoured
over formation of the less stable primary radical by hydrogen abstraction in the primary
position.
Equally it has been experimentally observed that the more resonance structure that can be
written, the more stable the radical is. 30 > 20 > 10
Also, note that phenyl radical is more stable than ethyl radical, due to the presence of more
double bonds.
STEREOCHEMISTRY
Stereochemistry is a sub discipline of chemistry that involves the study of the relative spatial
arrangement of atoms that form the structure of molecules. Stereochemistry also known as 3
dimensionality chemistry focuses on stereo isomers and spans the entire spectrum of organic,
inorganic, biological, physical and especially supra molecular chemistry.
Stereo isomers are compounds with the same chemical formula but which have different 3-
dimensional structures because of the different ways the atoms of the molecule are arranged
or oriented in space.
Enantiomers are stereo isomers which are not super imposable on a mirror image. They are
optically active.
Stereo chemistry on Tetrahedral Carbon
Stereochemistry refers to the arrangement in space of atoms of organic compounds. The
hands are not identical, they are mirror images. For instance compound CHXYZ cannot be

9. 9
super imposed on its mirror image and it represent a special kind of stereo isomer called
Enantiomer.
Enantiomer is from the greek word ‘enantio’ meaning opposite. Enantiomers are related to
each other just as right hand is related to left hand. It results whenever a tetrahedral carbon is
bonded to four different substituents.
For example, 2-hydroxyl propanoic acid also called Lactic acid.
H │ H
│ │ │
H3C―C―COOH │ HOOC―C―CH3
│ │ │
OH │ OH
Mirror
Lactic acid has no plane of symmetry and it is chiral, the central carbon is the chiral centre.
Compounds that are not identical to their mirror images and thus exist in two enantiometric
form are said to be chiral.
Chirality is a term that describe the spatial arrangement of atoms that is non-super imposable
on its mirror image. Such an object has no symmetry elements of the second kind. If the
object is super imposable on its mirror image, the object is described as being achiral.
A plane of symmetry is an imaginary line that cut through an object or molecule, so that one-
half of the object is an exact mirror images of the exact other half.
POLY FUNCTIONAL CHEMISTRY
Amino acids are the building blocks of life molecules called PROTEIN. All amino acids exist
as α-amino acids. α-amino acids are naturally occurring carboxylic acids with an amino group
attached to the α-carbon atom [carbon containing COOH]

10. 10
General formula of amino acid is shown below:
H
│
R―C―COOH
│
NH2
Where R can be hydrogen or alkyl group. When R is hydrogen, we have glycine.
H
│
H―C―COOH
│
NH2
Amino as a base
 Action with acid such as HCl
H H
│ │
H―C―COOH + HCl → H―C―COOH
│ │
NH2 NH2 (Glycine hydrochloride salt)
 Acetylation of Glycine
H H
│ │
H―C―COOH + CH3COCl → CH3CO―N―C―COOH
│ │ │
NH2 H NH2 (N-acetylglycine)
 Action with Nitrous acid
H H
│ │
H―C―COOH + HNO2→ H―C―COOH
│ │
NH2 OH (Hydroxyl acetic acid)
Amino as an Acid
 Action with Base
H H

11. 11
│ │
H―C―COOH + NaOH→ H―C―COONa + H2O
│ │
NH2 NH2 (Sodium glycine)
 Action with Ethanol
H H
│ │
H―C―COOH + CH3CH2OH→ H―C―COOCH2CH3
│ │
NH2 NH2 (Ethyl glycine)
Amino Acid as both Acid and Base
 It forms internal salt
H H
│ │
H―C―COOH ↔ H―C―COO-
│ │
NH2 NH3 (Zwitter ion)
 Formation of Amides
 Amino acids form both cyclic and linear amides with themselves.
NH2 HOCO NH―CO
̸ Heat ⁄
H―C―H + C―H ――→ H―C―H H―C―H + 2H2O
⁄ │ ̸
COOH H NH2 CO―NH
 Amide is the carbanide of amine
H H H
│ │ │
H―C―CO―OH + H―NH― C ―CO―OH + H―NH―C―COOH
│ │ │
NH2 H H
│
│
˅
H H H
│ │ │
H―C―CO ―NH― C ―CO― NH―C―COOH
│ │ │
NH2 H H
The linear amide is called peptides which lead to the formation of proteins.

12. 12
AROMATICITY
Aromatic compounds are compounds containing benzene ring or closely related ring. These
compounds are cyclic generally containing 5, 6 or 7 membered rings. Aromaticity implies
that the Pi-electrons are delocalized over the entire ring system and they are stabilized by the
pie-electron delocalization called RESONANCE. For instance, Benzene is represented by the
Kekule structure.
Properties of Aromatic Compounds
 They undergo substitution reaction rather than addition reaction with polar reagents
such as HNO3, H2SO4 and Br2. The unsaturated bonds in the ring are preserved in this
reaction.
 They posses unique NMR spectra.
 They are resistant to oxidation by aqueous potassium permanganate or nitric acid.
 Thermal stability: The heat of hydrogenation and combustion is usually less than
expected.
 They obey Huckel’s (4n+2) 𝜋 electrons rule, where n = number of rings.
 They are flat or near flat molecules
 They are cyclic, cloud of de-localised 𝜋 −electrons are above and below the plain of
the molecules.
Resonance Structure of Benzene
Benzene- a colourless compound with boiling point of 80o C was first isolated by Michael
Faraday in1825 from the oily residue collected in the Illumin along gas lines of London. The
molecular formula of benzene is C6H6, which suggest that benzene is an unsaturated
hydrocarbon. Thus, chemists believe that it should be able to undergo electrovalent addition
reaction such as hydrogenation, halogenations and reaction with halogen acids. Benzene is a
hybrid of two equal energy (Kekule) structures, differing only in the location of the double

13. 13
bond. In the structure of Benzene, the six bond angles are equal (1200), hybridization is sp2
and planar from x-ray analysis. The bonding in benzene is a multicenter bonding or
delocalized bonding. The pie (𝜋) electrons in the benzene is delocalized and not restricted to
either multicenter bonding or delocalized bonding on any carbon atom.
Benzene is a molecule with high pie (π) electron density and so electrophilic reaction is
expected.
The two canonical forms exist. The implication of the parameter highlighted above is an
indication that the double bonds in benzene are unlike that found in alkene. Also experiment
has shown that benzene does not undergo addition reaction, expected in the C=C double bond
in alkene. For comparison, a saturated alkane of six carbon atoms has the molecular formula
C6H14 and saturated cycloalkane of six carbon atom has molecular formula of C6H12 while
benzene has a molecular formula of C6H6. Considering benzene’s high degree of
unsaturation, it is expected that it will be highly reactive and to exhibit reactions
characteristics of alkenes and alkynes. However, this is not so, as benzene does not undergo
addition, oxidation and reduction reactions, characteristics of alkenes and alkynes. For

14. 14
instance, it does not decolorizes bromine water, nor oxidized by potassium per manganate
(KMnO4) or Chromic acid (CrO3) under conditions that readily oxidizes alkenes and alkynes.
Rather, benzene undergoes substitution reaction just like alkanes.
Structures of Benzene
Kekule’s model;
In 1865, Kekule a London chemist worked seriously on the structure of Benzene. He
proposed that the six carbon atoms of benzene are arranged in a six membered ring with
hydrogen attached to each carbon. To maintain the then established tetravalency of carbon,
Kekule further proposed that the ring contains three double bonds that shift back and forth so
rapidly that the two forms cannot be separated. The model above is called Kekule’s structure.
The Kekule’s structure was found to be consistent with many experimental observations.
Bonding in Benzene
Each carbon atom is sp2 hybridized and its sigma bonded to two other carbon atoms and one
hydrogen atom. These sigma bonds comprised the skeleton of the molecule. Each carbon
atom has one electron in a p-orbital at right angle to the plane of the ring. These p-orbitals
overlap equally with each of the two adjacent p-orbital to form a pie-electron system parallel
to, above and below the plane of the ring. The six 𝜋-electrons are associated with six carbon
atoms. They are therefore more delocalized and this accounts for the great stability and large
resonance energy of aromatic rings.
Calculating the Resonance Energy
The observed heat of combustion of benzene is -3301.6KJ/mol. Theoretical values are
calculated for C6H6 by adding the contributions from each bond obtained experimentally for
other compounds. E.g C=C is -492.5KJ/mol, C-C is -206.3KJ/mol and -225.9KJ/mol for C-H.
These data can be used to calculate the heat of combustion for benzene. The difference

15. 15
between this value and the experimental value gives the resonance energy. For example, in
benzene, there are; 6 C-H bonds, 3 C-C bonds, 3 C=C bonds.
6 C-C bonds = (6x -225.9) KJ/mol = -1355.4KJ/mol
3 C-C bonds = (3x -206.3) KJ/mol = - 618.9 KJ/mol
3 C=C bonds = (3x -492.5) KJ/mol = -1477.5KJ/mol
Calculated value = Total ΔHc = -3451.8KJ/mol
Experimental value = - 3301.6KJ/mol
Difference = 150.2KJ/mol
This difference is the resonance energy of benzene. Hence, the resonance energy is
150.2KJ/mol.
For an organic compound to be aromatic, it must be cyclic, planar, possess delocalized pie-
electrons and obey Huckel’s rule of 4n+2= Π –electrons.
Aromaticity and Huckel’s rule
Huckel’s rule (1931) for aromaticity states that if the number of pie-electrons is equal to
4n+2, where n equals the number of rings, the compound is aromatic. This rule applies to C-
containing monocyclic ring in which each carbon is capable of being sp2 hybridized to
provide a p-orbital for extended pie-bonding. The rule has been extended to unsaturated
heterocyclic compounds and fused ring compounds.
ELECTROPHILIC AND NUCLEOPHILIC SUBSTITUTION REACTION
Electrophilic substitution reactions are chemical reactions in which an electrophile displaces
a group in a compound. Electrophilic aromatic substitution is characteristic of aromatic
compounds and is an important way of introducing functional groups onto benzene rings.
The other main reaction type is electrophilic aliphatic substitution.
Electrophilic Aromatic Substitution

16. 16
In electrophilic substitution in aromatic compounds, an atom appended to the aromatic ring,
usually hydrogen, is replaced by an electrophile. The most important reactions of this type
that take place are aromatic nitration, aromatic halogenation, aromatic sulfonation and
acylation and alkylating Friedel-Crafts reactions.
Electrophilic Aliphatic Substitution
In electrophilic substitution in aliphatic compounds, an electrophile displaces a functional
group. This reaction is similar to nucleophilic aliphatic substitution where the reactant is a
nucleophile rather than an electrophile. The two electrophilic reaction mechanisms, SE1 and
SE2 (Substitution Electrophilic), are also similar to the nucleophile counterparts SN1 and SN2.
In the SE1 course of action the substrate first ionizes into a carbanion and a positively charged
organic residue. The carbanion then quickly recombines with the electrophile. The SE2
reaction mechanism has a single transition state in which the old bond and the newly formed
bond are both present.
Electrophilic aliphatic substitution reactions are:
 Nitrosation
 Ketone halogenation
 Keto-enol tautomerism
 aliphatic diazonium coupling
 carbene insertion into C-H bonds
Mechanism of Electrophilic Substitution Reaction in Benzene

17. 17
Resonance hybrid:
In order to restore the resonance structure of benzene ring, a proton (H+) is expelled by a
base (Y-) rather than addition of a nucleophile (as in alkene).
Electrophilic substitution reaction involves 2 steps:
a. Electrophilic attack on the benzene ring by an electrophile leads to the formation of a
carbonium ion. The positive charge of this carbonium ion is distributed over the whole
molecule, particularly on the first and third carbon position relative to the carbon atom
bearing the electrophile.
b. The expulsion of an H+ from the carbonium ion leads to the formation of a substituted
benzene.

18. 18
Electrophilic Substitution Reaction in Benzene
1. Nitration
This is the attachment of nitrogen dioxide (NO2) to the benzene. The equal mixture of
concentrated sulphuric acid and nitric acid at 550-600C generates nitronium ions (NO2+).
The Reaction: HNO3 + H2SO4 → NO2+ + H3O+ + 2HSO4
Mechanism of Nitration
2. Sulphonation
This is the introduction of sulphuric acid group (SO3H) to benzene. Concentrated sulphuric
acid containing sulphur trioxide is added to the benzene.
Stage 1: Generation of electrophile:
2H2SO4 ↔ SO3
- + H3O+ + HSO4-
Stage 2: Formation of Hydride

19. 19
3. Halogenation
This is the introduction of halogen to benzene for halogenations.
Benzene Chlorination
4. Friedal – Craft Alkylation
This the reaction of benzene with alkyl halides (RCl) to form alkyl benzene or arene in he
presence of AlCl3 as catalyst
5. Friedal – Craft Acylation
This is the reaction of benzene with acyl halide or alkanol halide with anhydrous AlCl3 as a
catalyst.

20. 20
Nucleophilic Substitution Reactions
Nucleophilic substitution reaction is an important class of reactions that allow the
interconversion of functional groups, for example R-OH to R-Br. It is a fundamental class of
reaction in which an electron, nucleophile selectively bonds with or attacks the positive or
partially positive charge of an atom or a group of atoms called the leaving group; the positive
or partially positive atom is referred to as an electrophile. The most general form for the
reaction may be given as:
Nu: + R-LG → R-Nu + LG:
The electron pair (:) from the nucleophile (Nu) attacks the substrate (R-LG) forming a new
bond, while the leaving group (LG) departs with an electron pair (LG:). The principal product
in this case is R-Nu. The nucleophile may be electrically neutral or negatively charged,
whereas the substrate is typically neutral or positively charged.
An example of nucleophilic substitution is the hydrolysis of an alkyl bromide, R-Br, under
alkaline conditions, where the attacking nucleophile is the OH− and the leaving group is Br-.
R-Br + OH− → R-OH + Br−

21. 21
Nucleophilic substitution reactions are commonplace in organic chemistry, and they can be
broadly categorised as taking place at a saturated aliphatic carbon or at (less often) a saturated
aromatic or other unsaturated carbon centre.
Nucleophilic Substitution at Saturated Carbon Centres
A nucleophile (Nu) is the electron rich specie that will react with an electron poor species.
There are two fundamental mechanisms in these substitution reactions, depending on the
relative timing of these events. They include:
 Bond breaking from the leaving group to form a carbocation (SN1 reaction)
 Simultaneous bond formation to the nucleophile and bond breaking (SN2 reaction)
S stands for chemical substitution, N stands for nucleophilic, and the number represents the
kinetic order of the reaction.
SN1 Mechanism
SN1 indicates a substitution, nucleophilic, unimolecular reaction, described by the expression
rate = k [R-LG]
This pathway is a multi-step process with the following characteristics:
Step 1: Rate determining (slow) loss of the leaving group, LG, to generate a carbocation
intermediate, then
Step 2: Rapid attack of a nucleophile on the electrophilic carbocation to form a new bond
SN2 Mechanism
In the SN2 reaction mechanism, the addition of the nucleophile and the elimination of leaving
group take place simultaneously. SN2 occurs where the central carbon atom is easily
accessible to the nucleophile. By contrast the SN1 reaction involves two steps. SN1 reactions

22. 22
tend to be important when the central carbon atom of the substrate is surrounded by bulky
groups, both because such groups interfere sterically with the SN2 reaction and because a
highly substituted carbon forms a stable carbocation.
Nucleophilic substitution reactions
There are many reactions in organic chemistry that involve this type of mechanism. Common
examples include
 Organic reductions with hydrides, for example
R-X → R-H using LiAlH4 (SN2)
 Hydrolysis reactions such as
R-Br + OH− → R-OH + Br− (SN2) or
R-Br + H2O → R-OH + HBr (SN1)
 Williamson ether synthesis
R-Br + OR'− → R-OR' + Br− (SN2)
Nucleophilic Substitution at Unsaturated Carbon Centres
Nucleophilic substitution via the SN1 or SN2 mechanism does not generally occur with vinyl
or aryl halides or related compounds. Under certain conditions nucleophilic substitutions may
occur, via other mechanisms such as those described in the nucleophilic aromatic substitution
article.
When the substitution occurs at the carbonyl group, the acyl group may undergo nucleophilic
acyl substitution. This is the normal mode of substitution with carboxylic acid derivatives
such as acyl chlorides, esters and amides.
Physical Properties of Organic Compounds
An organic compound is any member of a large class of gaseous, liquid, or solid chemical
compounds whose molecules contain carbon. Chemically, most organic compounds can be

23. 23
divided among hydrocarbons, oxygen-containing compounds, nitrogen-containing
compounds, sulfur-containing compounds, organohalides, phosphorus-containing
compounds, or combinations of these kinds of compounds. Virtually all organic compounds
contain hydrogen and have at least one C–H bond. The simplest organic compounds and
those easiest to understand, are those that contain only hydrogen and carbon, they are called
HYDROCARBONS They are used to illustrate some of the most fundamental points of
organic chemistry, including organic formulas, structures, and names.
The three-dimensional shape of a molecule, that is, its molecular geometry, is particularly
important in organic chemistry. This is because it’s molecular geometry determines, in part,
the properties of an organic molecule, particularly its interactions with biological systems and
how it is metabolized by organisms.
The physical properties of organic compounds include the following: melting point, boiling
point, density, formula and refractive index.
One of the most revealing of all physical properties for a chemical substance is its boiling
point. Boiling point reflects the strength of the intermolecular attractive forces that hold the
molecules of a substance together in a condensed phase, and as such, it is useful to compare
the boiling points for related compounds to see how structural differences account for the
differences in intermolecular attractions. After briefly reviewing the nature of intermolecular
attractive forces, this page will examine trends in boiling points for various groups of
compounds to help the reader understand how size, shape, and functional group polarity
affect boiling point.

24. 24
References
Bola O; Wole, F. and Jide, A. 2003Basic Organic Chemistry, Panaf Publishing, Inc.
Clayden, G., Waren and Wothers, 2000. Organic Chemistry, Oxford University
Press.
Manaham, S. E. 2001. Fundamentalsof Environmental Chemistry. Second Edition, 396-406
Boca Raton CRC Press LLC