HSSC Second year Chemistry course slides for Federal Board Pakistan, lectures by Dr. Raja Hashim Ali (also available on Youtube as a series of video lectures).

1. Dr. Hashim Ali
Post-Doc Uppsala University, Sweden.
PhD Computational Biology, KTH, Stockholm, Sweden.
Chapter 19 - Aldehydes and ketones

2. • Explain nomenclature and structure of aldehydes and ketones.
• Discuss the preparation of aldehydes and ketones by ozonolysis of alkene,
hydration of alkynes, oxidation of alcohols and Friedal Craft’s acylation of
armatics.
• Describe reactivity of aldehydes and ketones and their comparison.
• Describe acid and base catalyzed nucleophilic addition reaction of aldehydes
and ketones.
• Discuss the chemistry of aldehydes and ketones by their reduction to
hydrocarbons, alcohols, by using carbon nucleophiles, nitrogen nucleophiles,
oxygen nucleophiles.
• Describe oxidation reactions of aldehydes and ketones.
• Describe isomerism in aldehydes and ketones.
After completing this lesson, you will be able to

3. Chapter Overview - Sections
• Introduction
• Nomenclature
• Physical properties
• Structure
• Preparation
• Reactivity
• Reactions
Chapter Overview - Sections

4. Dr. Hashim Ali
Post-Doc Uppsala University, Sweden.
PhD Computational Biology, KTH, Stockholm, Sweden.
19.0 – Introduction to aldehydes and ketones

5. S
O
C
X
Hydrogen atom
Carbon atom
Oxygen atom
Sulphur atom
Halogens atom
Single bond
R
Double bond
Triple bond
Hydrocarbon chain
(alkyl chain)
N Nitrogen atom
H
15.7.3 – Color scheme for elements

6. Alkyne
C CR R
XR
Ethyne/Acetylene
CH3CH3  C2H6
Bromoethane/Ethylbromide/Monobromoethane
CH3CH2Br  C2H5Br
Halide
15.7.4 – Common functional groups

7. Amide
Ethylamine/Ethanamine/Acetamine
CH3CH2O  C2H7N
Ethylamide/Ethanamide/Acetamide
CH3CONH2  C2H5ON
N R
H
H
C O
N
H
R
H
Amine
15.7.4 – Common functional groups - Nitrogen containing groups

8. • Industrial and household cleaners.
• Anesthetics:
o CHCl3 (commonly called chloroform) used
originally as a general anesthetic but it is toxic
and carcinogenic.
o CF3CHClBr is a mixed halide sold as
Halothane®
• Freons are used as refrigerants and foaming
agents.
o Freons can harm the ozone layer so they have
been replaced by low-boiling hydrocarbons or
carbon dioxide.
• Pesticides such as DDT are extremely toxic
to insects but not as toxic to mammals.
o Haloalkanes can not be destroyed by bacteria so
they accumulate in the soil to a level which can
be toxic to mammals, especially humans.
17.0.1 - Introduction - Alkyl halides in daily life

9. • Polyamides, a major reactant in the production
of nylon, is produced by reaction of di-acid
chloride with di-amines.
• Proteins like silk and wool are polyamides.
• Neurotransmitters - a chemical bridge between
neuron cells- are amines. Examples include
Acetylcholine, Dopamine, Norepinephrine and
Serotonin.
• Hormones such as epinephrine (adrenaline)
and flight-or-fight (FOF) are amines.
• Alkaloids - class of nitrogen containing
compounds obtained from plants - are amines.
Examples include nicotine, caffeine, quinine
and opium.
• The Pakistani politics famed medical simulant
ephedrine is also an amine.
17.0.2 - Introduction - Amines in daily life

10. 17.0 - Introduction to alkyl halides and amines

11. Dr. Hashim Ali
Post-Doc Uppsala University, Sweden.
PhD Computational Biology, KTH, Stockholm, Sweden.
17.1 – Alkyl halides

12. • Alkyl halides are compounds in which
one hydrogen atoms in an alkane has
been replaced by halogen atom (fluorine,
chlorine, bromine or iodine).
• They are also known as halogen
derivatives of alkanes.
• They may be mono, di, tri or poly
haloalkanes depending upon the number
of halogen atoms present in the
molecule.
• Monohaloalkanes are called alkyl halides
having general formula R–X.
17.1.1 – Alkyl halides - Introduction
C
H
H
H
C
H
H
X
C
H
H
X
C
H
H
X
X
X
X
trihaloarene
X
XX
trihaloalkane
dihaloarene
monohaloarene
dihaloalkane
monohaloalkane

13. • Alkyl halides fall into different classes
depending on how the halogen atom is
positioned on the chain of carbon atoms.
• There are some chemical differences
between the various types.
o Primary alkyl halide
o Secondary alkyl halide
o Tertiary alkyl halide
17.1.2 – Alkyl halides - Classification
C
H
H
H
C
H
H
ClC
H
H
C
H
H
C
H
H
H
C
H
H
HC
Cl
H
C
H
H
C
CH3
Cl
CH3
C
H
H
HC
H
H
C
H
H
Primary alkyl halide
Primary
carbon
Secondary alkyl halide
Tertiary alkyl halide
Secondary
carbon
Tertiary
carbon

14. • In a primary (1°) alkyl halide, the carbon
which carries the halogen atom is only
attached to one or no other alkyl group.
• Notice that it doesn't matter how
complicated the attached alkyl group is.
• In each case there is only one linkage to
an alkyl group from the CH2 group
holding the halogen.
17.1.2.1 – Alkyl halides - Classification - Primary alkyl halide
C
H
H
H
C
H
H
ClC*
H
H
R–CH2–X
n-propyl chloride
Chloropropane
C
H
H
H
C*
H
H
Cl
ethyl chloride
Chloroethane
H C*
H
H
Cl
methyl chloride
Chloromethane
Primary alkyl halide
*C is primary carbon atom

15. • In a secondary (2°) alkyl halide, the
carbon with the halogen attached is
joined directly to two other alkyl groups,
which may be the same or different.
17.1.2.2 – Alkyl halide - Classification - Secondary alkyl halide
R1–CH2–R2
X
Secondary alkyl halide
C
H
H
H
C*
Cl
H
HC
H
H
iso-propyl chloride
2-Chloropropane
C
H
H
H
C
H
H
HC*
Cl
H
C
H
H
sec-butyl chloride
2-Chlorobutane
*C is secondary carbon atom

16. • In a tertiary (3°) alkyl halide, the
carbon atom holding the halogen is
attached directly to three alkyl
groups, which may be any
combination of same or different.
17.1.2.3 – Alkyl halide - Classification - Tertiary alkyl halide
R1–C*–X
R2
R3
Tertiary alkyl halide
C*
CH3
Cl
CH3
HC
H
H
*C is tertiary carbon atom
t-butyl chloride
2-methyl-2-chloropropane

17. • Alkyl halides are named according
to the following systems.
o Common system of naming.
o IUPAC System of naming.
17.1.3 - Alkyl halide - Nomenclature

18. • This method consists in first writing
the name of alkyl group to which
halogen is attached and then writing
the name of halide ion.
• For secondary alkyl halides, the prefix
sec- and for tertiary alkyl halides, the
prefix ter- or t_is added before the
name of alkyl halides.
• When all the carbons of alkyl group of
primary alkyl halides are in a straight
chain, the prefix n- is used before the
name, which indicates normal.
17.1.3.1 - Alkyl halide - Nomenclature - Common system rules
C
H
H
H
C
H
H
Cl
ethyl chloride
C
CH3
Br
CH3
C
H
H
HC
H
H
C
H
H
n_butyl bromide
C
H
H
H
C
Br
H
HC
H
H
Sec- or iso-propyl
bromide
C
CH3
Cl
CH3
HC
H
H
t_ or ter_butyl chloride

19. • According to this system, alkyl
halides are named as derivatives of
alkanes. The following rules are
observed for this purpose.
• The longest chain bearing halogen is
selected as parent hydrocarbon.
• Prefix halo- i.e. chloro for Cl, bromo
for Br, etc. is used before the name of
hydrocarbon.
• Positional numbers are used to
indicate halogen and other
substituent by the usual methods.
• The names given below are also
accepted by the IUPAC.
17.1.3.2 – Alkyl halide - Nomenclature - IUPAC system rules
C
H
H
H
C
H
CH3
HC
H
Br
C
H
H
2-bromo-3-
methylbutane
What is the main side chain, position of
each carbon and name of compound?
C4
H
H
H
C3
H
CH3
HC2
H
Br
C1
H
H
3-bromo-2-
methylbutane
C1
H
H
H
C2
H
CH3
HC3
H
Br
C4
H
H
H
CH3
HC
Br
C
H
H
2-bromo-propane
H
H
HC
Cl
C
H
H
Ethyl chloride
H
CH3
HC
Br
C
H
H
iso-propyl bromide
CH3C
CH3
H
Br
C
H
H
ter-butyl bromide

20. • The polar bond creates
a molecular dipole that
raises the melting
points and boiling
points compared to
alkanes.
• Also, the boiling points
of a given alkyl group
halide increase in the
following order.
o n-alkyl halide > sec-
alkyl halide > ter-alkyl
halide.
17.1.4 – Alkyl halides - Physical properties
Name Structure Boiling
points (K)
N-butyl bromide CH3–CH2–CH2–CH2–Br 375
Sec-butyl
bromide
CH3–CH2–CH–CH3
364
Ter-butyl
bromide
CH3–C–CH3
346
Br
Br
–
CH3
–
–

21. • The alkyl halide functional group consists of an
sp3 hybridized C atom bonded to a halogen (X),
via sigma bond.
• As discussed earlier, as you go down the
periodic table,
o C–X bond is longer
o C–X bond is weaker
o Which means that the organic halides with
Fluorine have the shortest bond length, strongest
bonds and most dipole moment as compared to
similar organic halides of chlorine, bromine and
iodine.
• Due to the difference in electronegativity and
polarizability of the halogen, the carbon
halogen bonds are typically quite polar with:
o Slight positive on carbon.
o Slight negative on halogen.
17.1.5 – Alkyl halides - Structure
Halomethane
Bond
length
(pm)
Bond strength Dipole
moment
(D)
(kj/m
ol)
(kcal/
mol)
CH3F 139 452 108 1.85
CH3Cl 178 351 84 1.87
CH3Br 193 293 70 1.81
CH3I 214 234 56 1.62

22. • Alkyl halides are prepared by
o reactions of alcohols with hydrogen
halide,
o reactions of alcohols with other
halogenating agents (SOCl2, PX3 and
PX5).
o halogenation of alkanes.
17.1.6 – Alkyl halides - Preparation

23. • Alcohols may be converted to the corresponding alkyl halides by the action
of halogen acid in the presence of ZnCl2, which acts as a catalyst.
17.1.6.1 – Alkyl halides - Preparation - Reaction of alcohols with
hydrogen halides
CH3CH2–OH+ HX CH3CH2–X + H2O
Ethyl halide
ZnCl2

24. • Alcohols (ROH) react with
thionyl chloride (SOCl2) in
pyridine as a solvent to give
alkyl chlorides.
• This is the best method
because HCl and SO2 escape
leaving behind the pure
product.
• Phosphorous trihalides or
phosphorous pentahalides
react with alcohols to form
alkyl halides.
17.1.6.2 – Alkyl halides - Preparation - Reaction of alcohols with
other halogenating agents (SOCl2, PX3 and PX5)
ROH + SOCl2 R–Cl + SO2 + HCl
Alkyl chloride
3CH3–CH2–OH + PBr3 3CH3–CH2–Br + H3PO3
Ethyl bromideEthyl alcohol
CH3–CH2–OH + PCl5 CH3–CH2–Cl + POCl3 + HCl
Ethyl chlorideEthyl alcohol

25. • By the action of chlorine or bromine,
alkanes are converted into alkyl halides.
This reaction takes place in the presence of
diffused sunlight or ultraviolet light.
• This method does not give pure alkyl
halides as halogen derivatives containing
two or more halogen atoms are also
formed along with alkyl halides.
• The detail mechanism of this reaction has
already been discussed in radical chain
mechanism in chapter 16 under title
“reaction of methane with bromine”.
17.1.6.3 - Alkyl halides - Preparation - Halogenation of alkanes

26. • There are two main factors which
control the reactivity of alkyl halides.
o Bond polarity of C-X bond.
o Bond energy of C-X bond.
17.1.7 – Alkyl halides - Reactivity

27. • The molecule of alkyl halide is polarized
due to the greater electronegativity of
halogen compared to C.
• Hence carbon acquires partial positive
whereas halogens acquires partial
negative.
• Halogen becomes nucleophilic in
character, which can be replaced by
another nucleophilic on the basis of
bond polarity reactivity of alkyl halides
decreases in the following order.
17.1.7.1 – Alkyl halides - Reactivity - Bond polarity
Atom Electronegativity
F 4.0
Cl 3.0
Br 2.8
I 2.5
H 2.1
C 2.5
R–F > R–Cl > R-Br > R-I

28. • Experiments have shown that the bond
energy of the C-X bond is the main
factor which decides the reactivity of
alkyl halides and not the polarity of the
molecule.
• As you go down the periodic table,
o C–X bond is longer.
o C–X bond is weaker.
• A study of bond energies of C-X bond
shows that C-F bond is the strongest .
So the overall order of reactivity of
alkyl halides is:
• In fact, the C-F bond is so strong that
alkyl fluorides do not react under
ordinary conditions.
17.1.7.2 – Alkyl halides - Reactivity - Bond energy
R–F > R–Cl > R-Br > R-I
Halometha
ne
Bond
length
(pm)
Bond strength Dipole
moment
(D)
kJ/mol Kcal/
mol
CH3F 139 452 108 1.85
CH3Cl 178 351 84 1.87
CH3Br 193 293 70 1.81
CH3I 214 234 56 1.62

29. • General Introduction - What does the term nucleophilic substitution imply?
• A nucleophile is electron rich species that will react with an electron poor
species.
• A substitution implies that one group replaces another.
• Nucleophilic substitution reactions occur when an electron rich species, the
nucleophile reacts with an electrophilic C atom attached to an electronegative
group (important), the leaving group, that can be displaced as shown by the
general scheme.
• A leaving group is a molecular fragment that departs with a pair of electrons in
heterolytic bond cleavage.
• Leaving groups can be anions or neutral molecules, but in either case it is
crucial that the leaving group be able to stabilize the additional electron density
that results from bond heterolysis.
• Heterolysis is the process of cleaving a covalent bond where one previously
bonded species takes both original bonding electrons from the other species.
• During heterolytic bond cleavage of a neutral molecule, a cation and an anion
will be generated.
• Most commonly the more electronegative atom keeps the pair of electrons
becoming anionic while the more electropositive atom becomes cationic.
• The electrophilic C can be recognized by looking for the polar sigma bond due
to the presence of an electronegative substituent (esp. C-Cl, C-Br and C-I).
17.1.8.1.0.1 – Alkyl halides - Reactions - Nucleophilic substitution
reactions - Background - General introduction

30. • Nucleophilic substitution reactions are an important class of reactions that
allow the interconversion of functional groups.
• There are two fundamental events in a nucleophilic substitution reaction:
o Formation of the new sigma bond to the nucleophile.
o Breaking of the sigma bond to the leaving group.
• Depending on the relative timing of these events, two different mechanisms
are possible:
o Bond breaking to form a carbocation precedes the formation of the new bond: SN1
reaction.
o Simultaneous bond formation and bond breaking : SN2 reaction.
17.1.8.1.0.1 – Alkyl halides - Reactions - Nucleophilic substitution
reactions - Background - General introduction

31. • The general stability order of simple
alkyl carbocations is: (most stable) 3° >
2° > 1° > methyl (least stable).
• This is because alkyl groups are weakly
electron donating due to
hyperconjugation and inductive effects.
• Resonance effects can further stabilize
carbocations when present.
• Reactions involving carbocations:
o Substitutions via the SN1.
o Eliminations via the E1.
o Additions to alkenes and alkynes.
17.1.8.1.0.2.1 – Alkyl halides - Reactions - Nucleophilic
substitution reactions - Background - Important concepts -
Carbocations and their stability
C
CH3H3C
CH3
C
HH3C
CH3
C
HH3C
H
C
HH
H
> > >
3° 2° 1° methyl
+ + + +

32. • It is species rich in electron and
has an unshared pair of
electrons available for bonding.
• In most cases, it is basic.
• It may be negatively charged or
neutral.
17.1.8.1.0.2.2 – Alkyl halides - Reactions - Nucleophilic
substitution reactions - Background - Important concepts -
Nucleophiles and base
Formula Name of nucleophile
HO- Hydroxide ion
NH2
- Amino group
C2H5O- Ethoxide ion
Cl- Chloride ion
HS- Hydrogen sulphide ion
Br- Bromide ion
SCN- Thio cyanate ion
NH3 Ammonia
H2O Water

33. • The alkyl halide molecule on which a nucleophile attacks is called a
substrate molecule.
• Leaving group is also a nucleophile.
o It departs with an unshared pair of electrons.
o The incoming nucleophile must be stronger than the departing one.
o Cl-, Br-, I-, HSO4
- are good leaving group.
o Poor leaving groups are OH-, OR and NH2
-.
o Iodide ion is a good nucleophile as well as a good leaving group.
17.1.8.1.0.2.3 – Alkyl halides - Reactions - Nucleophilic
substitution reactions - Background - Important concepts -
Substrate and leaving group

34. • What do we mean by this? First we should write the
chemical equations for the two processes.
• These two equations represent Bronsted acid dissociation
and loss of a leaving group in a SN1 type reaction.
• Note the similarity of the two equations: both show
heterolytic cleavage of a sigma bond to create an anion and
a cation.
• For acidity, the more stable A- is, then the more the
equilibrium will favor dissociation, and release of protons
meaning that heterolytic anion is more acidic.
• For the leaving group, the more stable LG- is, the more it
favors leaving.
• Hence factors that stabilize A- also apply to the
stabilization of a LG-.
• Here is a table classifying some common leaving groups
that we will eventually meet.
• But water itself is a good leaving group since it is conjugate
base of H3O+.
17.1.8.1.0.2.3 – Alkyl halides - Reactions - Nucleophilic
substitution reactions - Background - Important concepts -
Substrate and leaving group

35. • It is substitution nucleophilic unimolecular two
step reaction.
• Explanation:
o The substrate R–X first ionizes reversibly into R+ and
X-.
o Then the carbonium ion combines with the attacking
nucleophile to form product.
• Mechanism:
o Since only one molecule is undergoing a change in the
covalency in rate determining step, thus two step
nucleophilic substitution reaction is unimolecular and
is called SN1 reaction.
o The brief mechanistic picture of SN1 reaction is based
upon the following evidences:
• Kinetic evidence.
• Stereo chemical evidence.
17.1.8.1.0.3.1 – Alkyl halides - Reactions - Nucleophilic
substitution reactions - Background - SN1 mechanism -
Introduction and mechanism
R–X R+ + X-
Slow
Step 1:
R+ + Nu- R–Nu
Fast
Step 2:

36. • The rate of an SN1 reaction depends
upon the concentration of alkyl halide
only.
• The change in concentration of
attacking nucleophile has no effect on
the rate.
o Rate = k[R–X]
• It is because the nucleophile combines
with the carbonium ion in the second
step. For the same reason, the rate of an
SN1 reaction does not depend on the
nature of attacking nucleophile.
17.1.8.1.0.3.2 – Alkyl halides - Reactions - Nucleophilic
substitution reactions - Background - SN1 mechanism - Kinetic
evidence
C + X
R1R2
R3
C X
R1
R2
R3
Carbonium ion
+
C
R1R2
R3
C Nu
R1
R2
R3
Nu-
C R1
R2
Nu
R3
Retention of
configuration

37. • Experiments have shown that SN1 reaction occur with partial racemization.
• The extent of partial racemization depends upon several factors including
stability of carbonium ion.
• The carbon atom of carbonium ion is sp2 hybridized and carries one empty p-
orbital.
• The nucleophile can attach itself to the p-orbital either on the right or on the
left side of carbon with equal ease.
• The expected product is a racemic mixture.
• However, the partial racemization suggests a different measure of
attachment, e.g., in case of unstable carbonium ion, the attack of nucleophile
is greater from the side from the side opposite to that of leaving group.
• Thus the side of carbon atom to which the leaving group is attached is
somewhat shielded from the attack of nucleophile.
• The attack of nucleophile occurs more often on the side opposite to the side to
which leaving group is attached, leading to partial inversion of configuration.
• Therefore, the product has some optical activity.
• Step1: Slow loss of the leaving group, LG, to generate a carbocation
intermediate, then
• Step2: Rapid attack of a nucleophile on the electrophilic carbocation to form a
new sigma bond.
17.1.8.1.0.3.3 – Alkyl halides - Reactions - Nucleophilic
substitution reactions - Background - SN1 mechanism - Stereo
chemical evidence
Planar carbonium ion

38. • It is substitution nucleophilic bimolecular
reaction. It occurs in one step.
• Mechanism:
o The attack of nucleophile on carbon and the
departure of the halide ion takes place
simultaneously in single step.
o This is rate-determining step because the bond
breaking and bond making processes occur
simultaneously.
o Since two molecules are undergoing change in
covalency in rate determining step, it is a
bimolecular nucleophilic substitution reaction
which is taking place in one step.
o This mechanistic picture is based on the
following evidences:
17.1.8.1.0.4.1 – Alkyl halides - Reactions - Nucleophilic
substitution reactions - Background - SN2 mechanism -
Introduction and mechanism
Nu- + CH3 – X Nu – CH3 + X-

39. • The rate of an SN2 reaction depends upon
the concentration of nucleophile as well as
the concentration of alkyl halide.
• The rate expression for the reaction can be
written as
• This means that the rate of reaction will be
double if the concentration of any of the
two is doubled, e.g., the rate increases
when one of either OH- or CH3–Br is
increased.
17.1.8.1.0.4.2 – Alkyl halides - Reactions - Nucleophilic
substitution reactions - Background - SN2 mechanism - Kinetic
evidence
Nu-+R–X R–Nu + X-
Rate = K[Nu][R–X]
Where k = specific rate constant
CH3–Br+OH- CH3–Br + Br-

40. • A bimolecular nucleophilic substitution
always occurs with inversion of
configuration.
• The carbon atom in transition state is
sp2-hybridized and is planar.
• The attacking nucleophile and the
leaving groups are present in the
transition state on opposite sides of
electrophilic carbon atom.
17.1.8.1.0.4.3 – Alkyl halides - Reactions - Nucleophilic
substitution reactions - Background - SN2 mechanism - Stereo
chemical evidence

41. 17.1.8.1.0.5 – Alkyl halides - Reactions - Nucleophilic
substitution reactions - Background - SN1 mechanism vs SN2
mechanism
Serial # SN1 SN2
1 It is a two step mechanism It is a one step mechanism
2 First step is slow and the second is
fast.
It has only one step and
that is slow.
3 It is a unimolecular reaction. It is a bimolecular reaction.
4 It is favored in polar solvents. It is favored in non-polar
solvents.
5 Mostly tertiary alkyl halides give
this reaction.
Mostly primary alkyl
halides give this reaction.
6 50% is inversion and 50% retention
of configuration takes place.
100% inversion of
configuration takes place.
7 Rate = K[R–X] Rate = K[Nu][R–X]

42. • Alkyl chlorides, bromides
and iodides are good
substrates for nucleophilic
substitution reactions.
• A variety of nucleophiles
can be used to generate a
range of new functional
groups.
• The diagram reflects some
of the more important
reactions you may
encounter.
17.1.8.1 – Alkyl halides - Reactions - Nucleophilic substitution
reactions

43. • The chemical reaction in which two groups
are eliminated from two adjacent atoms is
called 1,2 elimination reaction.
• Since β-hydrogen is necessary for
eliminations, it is also called β-elimination.
• Β-hydrogen atom in alkyl halides is slightly
acidic due to electron withdrawing effect of
halogen.
• The attacking nucleophile can either attack
α-carbon to give substitution product or β-
hydrogen to give elimination reaction.
• Strong bases such as OH-, OR, NH2 cause
elimination in preferences to substitution.
• Highly polarizable nucleophile and weak
bases such as I-, RS- etc. give substitution
reaction.
17.1.8.2.1 – Alkyl halides - Reactions - 1,2 elimination reactions -
Introduction and explanation

44. • It is a unimolecular two step elimination reactions.
• The substrate undergoes slow ionization in the first step to
form carbonium ion.
• In the second step, the solvent or base pulls off a β-
hydrogen.
• Since only one molecule is undergoing a change in the
covalency in rate determining step, this is a two step
unimolecular elimination reaction.
• The E1 mechanism has been supported by the study of the
reaction.
• It follows first order kinetics in which rate of reaction
depends only on the concentration of substrate.
o Rate = k[R–X]
• The presence of carbonium ion as an intermediate has been
indicated by the presence of more than one kind of
elimination products.
• A relatively less stable carbonium ion rearranges to give
stabler carbonium before giving elimination product.
17.1.8.2.2 – Alkyl halides - Reactions - 1,2 elimination reactions -
E1 mechanism

45. • It is bimolecular one step elimination reaction.
• The attacking base removes a H atom from the β-carbon
simultaneously with the formation of double bond between
Cα and Cβ, and the loss of halide ions.
• This is rate determining step because bond breaking and
bond making processes are taking place simultaneously.
• Since two molecules are undergoing a change in transition
state, it is a bimolecular one step elimination reaction.
• Thus E2 is a one step process in which both the substrate
and the base participate.
• The observed rate law for E2 reaction is
o Rate = K[R–X][B]
• The rate of E2 reaction depends upon the concentration of
substrate and the base, e.g., for the reaction, the rate of
reaction follows second order kinetics.
o Rate = K[CH3CH2Br][OH-]
17.1.8.2.2 – Alkyl halides - Reactions - 1,2 elimination reactions -
E2 mechanism

46. • Though substitution and elimination reaction lead to different products, there is
always a competition between them because of close resemblance in their
mechanism.
• Since substitution is more favorable energetically, it is the dominant reaction in
the substitution-elimination reaction.
• Elimination occurs only in the presence of β-hydrogen whereas substitution does
not require this condition to be satisfied.
• The following factors help to compare these two pathways.
o Structure of substrate
o Nature of base
o The nature of leaving group
o Nature of solvent
o Effect of temperature
17.1.8.3.0 - Alkyl halides - Reactions - Substitution vs.
elimination reactions - Introduction

47. • Crowding within the
substrate favors
elimination over
substitution because
the approach of the
nucleophile to α-
carbon is difficult
for substitution.
• However, the
elimination is
favored because the
removal of β-H
atom by base from
tertiary planar
carbonium ion is
easy.
17.1.8.3.1 – Alkyl halides - Reactions - Substitution vs.
elimination reactions - Structure of substrate
CH3–CH2X + C2H5O-Na+ CH3CH2OC2H5 + CH2 CH2 + NaX
C2H5OH
Substitution = 88% Elimination = 12%
Diethyl ether ethene Sodium
halide
H–C–X + C2H5O-Na+ CH3–C–O–C2H5 + CH3–CH CH2 + NaX
C2H5OH
H
CH3
Substitution = 39% Elimination = 61%
ethyl isopropyl ether propene Sodium
halide
CH3
CH3

48. • When the electron pair donor
is a strong base, e.g., OH-,
OR- etc., the dominant
reaction is E2. The SN2
reaction is a side reaction.
• However when the
nucleophile is weak base like
X-, RS- etc., the main reaction
will be substitution. E2 will
be minor side reaction.
17.1.8.3.2 – Alkyl halides - Reactions - Substitution vs.
elimination reactions - Nature of base
Main product
(Strong
base)
ethene halide
H–C–C–H + O-H CH CH2 + X- + H2O
E2
H
H X
H
Alkyl
halide
β
Main product
(weak
base)
Methyl
propanoate
halideAlkyl
halide
α
H–C–C–H + CH3CO- CH3–CH2–C–O–CH3 + X-
H
H X
H
β α
O O

49. • The role of leaving groups in elimination reactions is similar to that in
substitution reactions.
• In unimolecular reactions it does not affect the mechanism because both the
elimination and substitution products are decided with carbonium ion.
• However, in bimolecular reactions, the nature of product greatly depends
upon the nature of leaving group.
17.1.8.3.3 – Alkyl halides - Reactions - Substitution vs.
elimination reactions - Nature of leaving group
n–C18H37–X + (CH3)3COK nC16H33CH CH2 + nC18H37OC(CH3)3
(CH3)3COH
X = Br 85% 15%
X = OTS 1% 99%
n-octadecyl halide Potassium tertiary
butoxide
n-octadecene Iso-butyl n-
octadecyl ether

50. • Elimination is favored more than substitution by decreasing the solvent
polarity.
• The alcoholic KOH affects elimination while more polar aqueous KOH is
used for substitution.
• E1 is favored by polar solvents like SN1 reaction.
• In non-polar solvents the reaction will follow E2 mechanism.
17.1.8.3.4 – Alkyl halides - Reactions - Substitution vs.
elimination reactions - Nature of solvent

51. • An increase in temperature will favor elimination more than substitution
because substitution reactions require less reorganization of bonds as
compared to elimination
17.1.8.3.5 – Alkyl halides - Reactions - Substitution vs.
elimination reactions - Effect of temperature
CH3–CH–CH3 + NaOH CH3CH CH2 + (CH3)2CHOH + NaBr
H2O
At 45 °C 53% 47%
At 100 °C 64% 36%
iso-propyl bromide Sodium hydroxide propene 2-propanol
Br
Bimolecular

52. 17.1.8.4 – Alkyl halides - Reactions - Substitution vs. elimination
reactions: Which reaction will it be?
Is the substrate primary, secondary or tertiary
Is the leaving group good
AND the solvent have a high
dielectric constant
Is the nucleophile good? Is the nucleophile good?
secondary
No reaction Is the nucleophile
basic?
Is the base
concentration
high?
N
o
Yes
E1 E2
SN1Does the substrate
have a hydrogen on
the adjacent carbon
Yes No
SN1
N
o
Yes
SN2
Yes No
Is the nucleophile
highly basic?
N
o
Does the substrate
have a hydrogen on
the adjacent carbon
Yes
Yes
E2
Slow
SN2
No reaction Or
slow E2 + SN2
Is the nucleophile
highly basic?
Is the substrate
sterically hindered?
N
o
Yes
N
o
Yes
No
Does the substrate
have a hydrogen on
the adjacent carbon
High dielectric
solvent
Slow SN1 + SN2Slow SN2
High dielectric
solvent
N
o
Yes
E2 Is the base
concentration
high?
N
o
Yes
E2E1 + E2
N
o
Yes
N
o
Yes
SN2

53. 17.1.8.5 – Alkyl halides - Reactions - Cheat sheet

54. • What are monohaloalkanes?
• What are primary, secondary and tertiary carbon atoms?
• What is carbonium ion?
• What is leaving group?
• What is sp3 hybridization?
• Define bond polarity.
• Define bond energy.
• What is nucleophile?
• What is electrophile?
• Define inductive effect.
• Define resonating effect.
• What is racemization?
• Define transition state.
17.1.9 - Quick quiz

55. 17.1 - alkyl halides

56. Dr. Hashim Ali
Post-Doc Uppsala University, Sweden.
PhD Computational Biology, KTH, Stockholm, Sweden.
17.2 – Organometallic compounds - Grignards Reagents

57. • Organometallic chemistry is the study of chemical
compounds containing at least one chemical bond
between a carbon atom of an organic compound
and a metal, including alkaline, alkaline earth,
transition metal, and other cases.
• The field of organometallic chemistry combines
aspects of traditional inorganic and organic
chemistry.
• Organometallic compounds are widely used both
stoichiometrically in research and industrial
chemical reactions, as well as in the role of
catalysts to increase the rates of such reactions
(e.g., as in uses of homogeneous catalysis), where
target molecules include polymers,
pharmaceuticals, and many other types of
practical products.
17.2 - Organometallic chemistry

58. • Grignard reactions and reagents were discovered by and are named after the
French chemist François Auguste Victor Grignard, who published it in 1900
and was awarded the 1912 Nobel Prize in Chemistry for this work.
• The Grignard reaction (pronounced /ɡriɲar/) is an organometallic chemical
reaction in which alkyl, vinyl, or aryl-magnesium halides (Grignard
reagents) add to a carbonyl group in an aldehyde or ketone.
• A Grignard reagent has a formula RMgX where X is a halogen, and R is an
alkyl or aryl (based on a benzene ring) group.
• Grignard reagents are similar to organolithium reagents because both are
strong nucleophiles that can form new carbon–carbon bonds.
• For the purposes of this lecture, we shall take R to be an alkyl group.
• A typical Grignard reagent might be CH3CH2MgBr.
17.2.0 - Organometallic chemistry - Grignard reaction and
reagent

59. • Magnesium metal cut into small pieces is
added to a solution of an alkyl halide in
only dry (termed anhydrous) ether.
• The reaction mixture is heated with
electric heater in a round bottom flask
fitted with condenser and other
arrangement to avoid the contact of
moisture or oxygen.
• Alkyl bromide is generally used in the
preparation of Grignard’s reagent because
of its intermediate reactivity. When alkyl
halides are used, the solvent is a high
boiling solvent such as ether.
• Alkyl magnesium halide is separated by
the evaporation of ether.
Alkyl halide
Alkyl magnesium
halide
heat
Ether
+ MgR X RMgX
17.2.1 – Grignard’s reagent - Preparation

60. • Organometallic compounds are
nucleophile because of partial negative
charge on the carbon of alkyl group.
• Carbon atom is more electronegative
than metals such as Mg, Li etc.
• The alkyl group as a whole bears
partial negative charge and organo
metallic compounds act as a source of
nucleophile, e.g., the following
reactions supports the electrophilic
character of organic metallic
compounds.
17.2.2 – Grignard’s reagent - Reactivity
Rδ- Liδ+ Rδ- Mgδ+ X
H3Cδ- Liδ+ H3Cδ- Mgδ+ Br
H3Cδ- Mgδ+ Br + Hδ+ Oδ-H CH4 + Mg
OH
Br

61. • Monohydric alcohols are classified into the following
three families.
o Primary alcohol
o Secondary alcohol
o Tertiary alcohol
• This is done in the following three steps to produce
primary, secondary and tertiary alcohols.
o Reaction with methanal (aldehyde) to form primary
alcohol.
o Reaction with ethanal (aldehyde) to form secondary
alcohol.
o Reaction with propanone (ketone) to form tertiary alcohol.
• These reactions are carried out in the presence of
ether followed by H3O+.
• First two reactions are with aldehydes while third
belongs to ketones.
• The reaction is classified as nucleophilic acyl
substitution followed by nucleophilic addition.
17.2.3.1 – Grignard’s reagent - Reactions - With aldehydes and
ketones
methanal Primary
alcohol
H–C + CH3–Mg–Br CH3–CH2–O–Mg–Br
H
δ+
O
CH3–CH2–OH + Mg
OH
Br
δ-
δ+
H–OH
δ-

62. • Carboxylic esters, R’CO2R’’, react
with two equivalent of
organolithium or Grignard’s
reagents to give tertiary alcohols.
• The tertiary alcohol contains 2
identical alkyl groups.
• The reaction proceeds via a ketone
intermediate which then reacts with
the second equivalent of the
organometallic reagent.
• Since the ketone is more reactive
than the ester, the reaction can not
be used as a preparation of ketones.
17.2.3.1 – Grignard’s reagent - Reactions - With aldehydes and
ketones
ethanal Secondary
alcohol
H–C + CH3–Mg–Br CH3–CH–O–Mg–Br
CH3
δ+
O
CH3–CH–OH + Mg
OH
Br
δ-
δ+
H–OH
δ-
CH3
CH3
propanone Tertiary butyl
alcohol
CH3–C + CH3–Mg–Br CH3–C–O–Mg–Br
CH3
δ+
O
CH3–C–OH + Mg
OH
Br
δ-
δ+
H–OH
δ-
CH3
CH3
CH3
CH3

63. • The nucleophilic C in the organometallic
reagent adds to the electrophilic C in the
polar carbonyl group of the ester.
• Electrons from the C=O move to the
electronegative O creating an
intermediate metal alkoxide complex.
17.2.3.2.1 - Grignard’s reagent - Reactions - Of RMgX or RLi with
an ester - Step1

64. • The tetrahedral intermediate
collapses and displaces the alcohol
portion of the ester as a leaving
group.
• This produces ketone as an
intermediate.
17.2.3.2.2 - Grignard’s reagent - Reactions - Of RMgX or RLi with
an ester - Step2

65. • The nucleophilic C in the organometallic
reagent adds to the electrophilic C in the
polar carbonyl group of the ketone.
• Electrons from the C=O move to the
electronegative O creating an
intermediate metal alkoxide complex.
17.2.3.2.3 – Grignard’s reagent - Reactions - Of RMgX or RLi
with an ester - Step3

66. • This is the work up step, a simple
acid/base reaction.
• Protonation of the alkoxide oxygen
creates the alcohol product from
the intermediate complex.
17.2.3.2.4 – Grignard’s reagent - Reactions - Of RMgX or RLi
with an ester - Step4

67. • This is a nucleophilic addition of RMgX to
carbon dioxide and takes place in two
steps.
• Step1:
o The nucleophilic C in the Grignard’s reagent
adds to the electrophilic C in the polar
carbonyl group.
o Electrons from the C=O move to the
electronegative O creating an intermediate
magnesium carboxylate complex.
• Step2:
o This is the work-up step, a simple acid/base
reaction.
o Protonation of the carboxylate oxygen creates
the carboxylic acid product from the
17.2.3.3 – Grignard’s reagent - Reactions - With carbon dioxide
(carbonation)

68. • What are organometallic compounds?
• Define protonation.
• What is formula of organolithium?
• How does RMgX react with CO2?
• Write the formula of Grignard reagent.
17.2.4 - Quick quiz

69. 17.2 - Organometallic compounds

70. Dr. Hashim Ali
Post-Doc Uppsala University, Sweden.
PhD Computational Biology, KTH, Stockholm, Sweden.
17.3 – Amines

71. 1. The common names of amines are written by adding the suffix ‘-amine’ to the name
of alkyl or aryl radicals.
17.3.1.1 – Amines - Nomenclature - Common system rules
CH3CH2NH2
Ethyl amine
CH3CH2CH2CH2CHNH2
Sec-hexyl amine
CH3
CH3 N H
CH3
Dimethyl amine (a sec-amine)
CH3 N CH3
CH3
Trimethyl amine (a ter-amine)
N
Pyridine(a ter-amine)

72. 2. Aniline, C6H5NH2 containing methyl group on the ring is called Toluidine.
3. If there is some alkyl group substituted in –NH2, its name is represented by writing
N-(alkyl group). It indicates that alkyl group is located on N-atom and not on the
ring.
4. If there are two substituents on N, it is mentioned twice.
17.3.1.1 – Amines - Nomenclature - Common system
NH2
aniline
NH2
o-toluidine
CH3
H3C–N–H
N-methyl-o-toluidine
CH3
N,N-dimethyl-o-toluidine
H3C–N–CH3
CH3

73. 1. In this system, amino group is indicated by a prefix ‘-amino’ followed by the name
of hydrocarbon.
17.3.1.2 – Amines - Nomenclature - IUPAC system
2. The position of amino group is indicated by a number obtained by numbering the
chain of hydrocarbon.
3. Secondary and tertiary amines are named by using a compound prefix that includes
the names of all but the largest alkyl group.
CH3CH2NH2
Amino ethane
CH3–CH2–CH–CH2
2-Aminobutane
–
NH2
CH3–CH2–NH
Methyl amino ethane
–CH3
CH3
CH3–CH2–CH2–CH2–N
Dimethyl amino butane
CH3

74. • The polar nature of the N-H bond (due
to the electronegativity difference of the
two atoms results in the formation of
hydrogen bonds with other amine
molecules.
• The applications of this are:
o High melting and boiling points as
compared to analogous alkanes.
o High solubility in aqueous media.
17.3.2 – Amines - Physical properties
δ+H N:δ-
Intermolecular H-bonding in amines
δ+H Nδ-
HH

75. • In amines, nitrogen atom is sp3 hybridized
and has nearly tetrahedral structure.
• It forms three sigma bonds with its three
sp3-hybrid orbitals while the fourth non-
bonding sp3-hybrid carries a pair of
electrons.
• The non-bonding electron pair is extremely
important in explaining the chemical
behavior of amines because it is responsible
for the basic and nucleophilic properties of
these compounds.
• An amine with three different groups is
optically active.
17.3.3 – Amines - Structure

76. • Amines may act as bases towards
acids and as nucleophiles towards
electrophile.
• They are more basic than alcohols
and ethers and they are also more
nucleophilic, e.g., ether does not
react whereas at the same
temperature amines gives addition
product with CH3–I.
17.3.4 – Amines - Basicity
C2H5OC2H5 + CH3I No reaction
diethyl ether
(C2H5)3N + CH3I [(C2H5)3NCH3]+I-
triethyl amine

77. • Amines can be prepared by the following methods.
o Alkylation of ammonia by alkyl halides.
o Reduction of nitrogen containing functional groups, i.e., reduction of nitriles, nitro
compounds or amides.
17.3.5 – Amines - Preparation

78. • When an alcoholic or aqueous solution of
ammonia is heated with an alkyl halide, a
mixture of prim-, sec-, ter- amines and a
quaternary ammonium salt is obtained.
• The reaction occurs with nucleophilic
displacement of halide by ammonia of
amines.
• This reaction is further alkylated, e.g.,
accompanied by the following reactions.
• At the end of the reaction, addition of
strong alkali such as KOH liberates free
amines from their salts but the quaternary
salts is unaffected.
• The three amines are separated by
fractional distillation.
• Over alkylation can be avoided by using
access of ammonia but the yield is low.
17.3.5.1 – Amines - Preparation - Alkylation of ammonia by alkyl
halide
R–X + 2NH3 R–NH2 + NH+
4X-
Alkyl halide Primary alkyl amine
NH3 + R–X (R–NH3)+X- R–NH2 + HX
Alkyl halide Primary alkyl amine
C2H5–I + NH3 C2H5–NH2 + HI
Ethyl iodide Primary ethyl amine
(C2H5)3N + C2H5I (C2H5)4N+ + I-
Ethyl iodide diethylamine
C2H5–I + C2H5–NH2 C2H5–N–C2H5 + HI
H
Ethyl amine
Ethyl iodide triethylamine
C2H5–I + C2H5–N–C2H5 (C2H5)3N + HI
Diethyl amine
H

79. • Reduction of alkyl or aryl nitriles
gives primary amines.
• The reduction may be brought
about by Lithium aluminum
hydride (LiAlH4) or sodium (Na)
in ethanol (CH3CH2OH).
• Catalytic hydrogenation with Rh-
Al2O3, Pt or Raney nickel may
also be employed to get primary
amines.
17.3.5.2.1 – Amines - Preparation - Reduction of nitrogen
containing groups - Nitriles
CH3CN + 2H2 CH3CH2NH2
Rh. Al2O3
ethane nitrile Primary ethyl amine
Phenylacetonitrile
CH2CN
H2
Ni , 300°C
CH2CH2NH2
Phenethylamine

80. • Nitro compounds on
chemical reduction produce
primary amines.
o Nitroarenes can be reduced
to primary aryl amines.
o Typical reducing agents
include Fe/H+, Sn/H+, or
catalytic hydrogenation (e.g.,
H2/Pd).
o Lithium aluminum hydride
(LiAlH4) is a famous
reducing agent in organic
synthesis that reduces
amides to primary alkyl
amine.
17.3.5.2.2 – Amines - Preparation - Reduction of nitrogen
containing groups - Nitro compounds
Ar – NO2 Ar–NH2
[R]
Nitroarene Primary aryl amine
C6H5NO2 C6H5NH2
Sn + HCl
[H]
4-nitrobenzenamine
NH2
NO2
Fe
H2SO4 , [H]
NH2
NH2
Benzene-1,4-diamine
LiAlH4 + C H C NH2
R NH2
O
H
R
Alkyl Carboxamide Primary alkyl
amine
Lithium aluminum
hydride

81. • An amide on treatment with
Bromine in the presence of KOH
yields primary amines.
• The reaction occurs through
rearrangement (called Hoffman
rearrangement).
17.3.5.2.3 – Amines - Preparation - Reduction of nitrogen
containing groups - Amides
CH3–C–NH2 CH3NH2 + CO2
KOH
O
Br2
Ethanamide Methanamine

82. • Amines are basic and nucleophiles because of
non-bonding pairs of electrons on nitrogen.
• The relative availability of this pair of electron
and the relative stability of corresponding
ammonium ion is responsible for basicity of
different amines.
• Consider the following reactions.
• The strength of a base is expressed in terms of
pkb i.e. pkb = -log kb.
• For ammonia and methyl amine, the pkb
values are PKNH3 = 4.76; PKCH3NH2=3.38.
• Since PKNH3 > PKCH3NH2, methyl amine is a
stronger base than ammonia.
• It can be explained as under.
17.3.6 – Amines - Reactivity
Ammonium cation
NH3 + H+ N+H4
KNH3
CH2–NH2 + H+ CH3–N+H3
KNH3
KCH3NH2
Methyl amine cation

83. • In ammonia, the pair of electrons is attracted by s orbitals
of hydrogen atoms whereas in CH3NH2, sp2–orbital of
carbon pushes electrons towards nitrogen.
• Therefore the pair of electrons on nitrogen is relatively more
available in methyl amine than in ammonia.
• The methyl ammonium ion, CH3-NH3
+, is stabilized due to
electron donating inductive effect of the methyl group.
• On the other hand, NH4
+ ion is not stabilized by hydrogen
atoms.
• Both these factors favor methylamine to a stronger base
than ammonia.
• Higher members show deviation to these arguments.
• It is because the stabilization of a positive ion also depends
upon the extent of solvation, hydrogen bonding and
resonance stabilization.
• Moreover, the availability of non-bonding pair of electrons is
also affected by steric factor in addition to these aspects.
17.3.6 – Amines - Reactivity

84. • The important organic reaction of
amines (nucleophiles) are with the
common electrophiles.
o Alkyl halides via nucleophilic
substitution.
o Aldehydes or ketones via
nucleophilic addition.
o Carboxylic acid derivatives
especially acid chlorides via
nucleophilic acyl substitution.
17.3.7.0 – Amines - Reactions - Overview
R–C–Cl R– C –NR2+ HCl
R2NH
O
base
O
Acid chlorides
R–C–O–C–R R– C –NHR2
R2NH2
O
base
O O
Anhydrides Amide

85. • The transfer of an alkyl group from one
molecule to an amine is called alkylation
of amine or amine alkylation.
• It produces secondary or tertiary amine.
• R2NH2
+ loses a proton with a base to give a
free amine.
• The reaction is called nucleophilic aliphatic
substitution (of the halide), and the reaction
product is a higher substituted amine.
• The method is widely used in the laboratory,
but is less important industrially, where
alkyl halides are not preferred alkylating
agents.
17.3.7.1 – Amines - Reactions - Alkylation by alkyl halides
RNH2 + 2Rδ+–Xδ- [R–N–R]+ + X
Nucleophile Electrophile
––
H
H

86. • Aldehydes and ketones
react with primary amines
to form Schiff’s base.
• A Schiff’s base (named
after Hugo Schiff) is a
compound with the
general structure
o R1R2–C=N–R3 (R3 ≠ H).
17.3.7.2 – Amines - Reactions - primary amines with aldehydes
and ketones
Schiff’s base
Schiff’s base
CH3CH2 NH2 + CH3CHO C2 H5–N CH–CH3
AcetaldehydeEthanamine

87. • When amines react with nitrous acid,
diazonium compounds are formed.
• The diazonium group is rather
unstable. In case of ethyldiazonium
ion, it decomposes at once.
• When the diazonium group is
attached to a benzene ring, the ion is
stabilized to some extent by the
delocalized electron of the ring.
• The benzenediazonium ion is
therefore much more stable than its
aliphatic counterparts.
• Nevertheless, it decomposes readily
above 10 °C.
17.3.7.3 – Amines - Reactions - With nitrous acid and formation
of diazonium salts
diazonium ion
RNH2 + HNO2 R–N+ N + OH- + H2O
diazonium ion
CH3CH2–N+ N N2 + [CH3C+H2]
CH3CH2OH + H+
CH2 CH2 + H+

88. • Define hydration.
• What is the difference between alicyclic and aromatic compounds?
• Define IUPAC.
• Write the equation for the preparation of mustard gas.
• Define polymers.
• What is polymerization?
• What is Markownikov’s rule?
• What are amines?
• Why halogen of vinyl chloride is inert?
17.3.8 - Quick quiz

89. 17.3 - Amines

90. • Sugars, glucose and fructose - naturally occurring carbonyl compounds
o Sugars are sweet tasting soluble carbohydrates.
o Carbohydrates derive their name for the fact that they are composed of carbon,
hydrogen and oxygen with H and O in the ratio 2:1 as in water.
o Monosaccharide such as glucose are usually pentoses or hexoses, i.e., they
contain 5 or 6 carbon atoms in their molecules.
o Disaccharides such as sucrose consist of two monosaccharide molecules joined
by the elimination of a molecule of water.
o Polysaccharides such as starch are made up of many monosaccharide units
joined together.
o Notice that the monosaccharide all have asymmetric molecules. They therefore
exhibit optical isomerism.
Society, Technology and Science

91. • Glucose - An example of aldehyde
o The carbonyl properties possessed by glucose arise from the fact that in addition to
its normal ring form, it can exist as an open chain form.
o The two forms are readily interconverted and about 1% of glucose molecules exist
in open chain form in aqueous solution.
o This form carries an aldehyde group, so glucose has several properties typical of an
aldehyde; it is some times called an aldose.
o Thus in addition to the condensation reaction already mentioned, glucose shows
the reducing properties
Society, Technology and Science

92.  Mono halo derivatives of alkanes are called alkyl halides.
 The general formula for alkyl halides is CnH2n+1X.
 The best method for the preparation of alkyl halides is by the reaction of alcohols with
inorganic halides such as SOCL2, PX3 and PX5.
 Alkyl halides are very reactive class of organic compounds. They undergo nucleophilic
substitution reactions and elimination reaction in the presence of nucleophile or a
base.
 Nucleophilic substitution reactions can take place in two distinct ways. A one step
mechanism is called SN2 while a two step mechanism is called SN1. SN1 reaction show
first order kinetics whereas SN2 reaction show second order kinetics.
 Nucleophilic substitution reactions take place simultaneously with elimination reaction
and often compete with them.
 Elimination of two atoms or groups from adjacent carbon atoms in the presence of a
nucleophile or a base is called elimination reaction. Like nucleophile substitution, β-
elimination reactions also take place in two distinct ways E2 and D1.
Key Points

93.  A nucleophile is an electron rich species that will react with an electron poor species.
 A substitution implies that one group replaces another.
 Grignard reagent can be prepared by adding alkyl halide in a stirred suspension of
magnesium metal in diethyl ether.
 Grignard reagent has a reactive nucleophilic carbon atom which can react with
electrophilic centers to give the products in high yields. Primary, secondary and
tertiary alcohols can be best prepared by reacting Grignard reagent with formaldehyde,
any other aldehydes and ketones respectively.
 The polar nature of the N-H bond (due to the electronegativity difference of the two
atoms) results in the formation of hydrogen bonds with other amine molecules.
 Primary amines R-NH2 or ArNH2 undergo nucleophilic addition with aldehydes or
ketones to give carbinolamines which then dehydrate to give substituted imines.
 Primary alkyl or aryl amines yield diazonium salts.
Key Points

94. 1. In primary alkyl halides, the halogen
atom is attached to a carbon atom
which is further attached to how many
carbon atoms?
a. Two
b. Three.
c. One.
d. Four.
2. SN2 reactions can be best carried out
with:
1. Primary alkyl halides
2. Secondary alkyl halides
3. Tertiary alkyl halides
4. All the three
1. Select the right answer from the choices given
3. For which mechanisms, the first
step involved is the same.
a. E1 and E2.
b. E2 and SN2.
c. E1 and SN2.
d. E1 and SN1.
4. The rate of E1 reaction depends
upon.
1. The concentration of substrate.
2. The concentration of nucleophile.
3. The concentration of substrate as
well as nucleophile.
4. None of the above.

95. 5. Alkyl halides are considered to be very
reactive compounds towards
nucleophiles because
a. They have an electrophilic carbon.
b. They have an electrophilic carbon and a
good leaving group.
c. They have an electrophilic carbon and a
bad leaving group.
d. They have a nucleophilic carbon and a
good leaving group.
6. Which one of the following is not a
nucleophile
a. H2O
b. H2S
c. BF3
d. NH3
1. Select the right answer from the choices given
7. Double bond is formed as a result
of
a. Substitution reactions
b. Elimination reactions
c. Addition reactions
d. Rearrangement reactions
8. Which of the following alkyl
halides can not be formed by direct
reaction of alkanes with halogen
a. RBr
b. RCl
c. RF
d. RI

96. 9. CH3CH2Br on treatment with
alcoholic KOH gives
a. Propanal
b. Propene
c. Propane
d. None of these
10.Grignard’s reagent gives alkane
with
a. Water
b. Ethylamine
c. Ethanol
d. All of the above
1. Select the right answer from the choices given
11. Action of alkyl halides with Na
metal yield
a. Alkanes
b. Alcohols
c. Alkenes
d. Phenols
12.Alkyl halides react with excess of
ammonia to give
a. 1°-amine.
b. 2°-amine.
c. 3°-amine.
d. All of the above.

97. 13. Among the alkyl halides, the
primary alkyl halides always follow
the mechanism
a. SN1
b. SN2
c. SN3
d. SN4
14. Grignard’s reagent on treatment
with chloramines gives
a. Acetamide
b. Primary amine
c. Secondary amine
d. Urea
1. Select the right answer from the choices given
15. Nucleophilic addition of a
primary amine gives
a. Imine
b. Urea
c. Ammonia
d. Nitrobenzene

98. 1. What are primary, secondary and tertiary alkyl halides?
2. Why alkyl iodides can not be prepared by directly heating iodine with
alkene?
3. What are the nucleophilic substitution reactions or SN reaction?
4. Tertiary alkyl halides show SN1 reaction mostly. Why?
5. What are elimination reactions?
6. Which factor decides the reactivity of alkyl halides?
7. What are the diazonium salt?
8. How can nucleophilic addition of a primary amine give an imine?
9. Amines are more basic than analogous alcohols. Why?
10.How tertiary alcohols are obtained from R-Mg-X?
2. Give brief answers to the following questions

99. 1. Discuss the reactivity of alkyl halides.
2. Give three methods for the preparation of alkyl halides.
3. Explain in detail SN1 and SN2 reactions with mechanism.
4. What are the β-elimination reactions? Explain them with detail.
5. How will you convert ethyl chloride to the
i. Ethyl cyanide
ii. Ethanol
iii. Propane
iv. N-butane
v. Tetraethyl lead
6. Discuss the preparation and reactivity of Grignard’s reagent.
7. What are the amines? Give its nomenclature.
8. What are the main features which increase the basicity of amine?
9. Amides are reduced by LiAlH4. Give mechanism.
10. What are the diazonium salts? How can they be prepared? Give their reaction.
3. Give detailed answers to the following questions