GENERAL ORGANIC CHEMISTRY
& ISOMERISM
1. INTRODUCTION M•OI
The making and breaking of bonds usually occurs in several
In 1807, Berzelius proposed the term 'Organic Chemistry' for the discrete steps before transforming into products. The detailed
study ofcompounds derived from natural sources. This was based sequential description of all the steps is called the mechanism
on the theory of vitalism which said that all living systems of the reaction.
possessed a 'vital force' which was absent in non-living systems.
Compounds derived from living natural sources (organic) were 2. HYBRIDIZATION
thought to be fundamentally different from inorganic compounds.
Ill
Hybridisation is a process in which two or more atomic orbitals of
comparable energy of the valence-shell of an atom ( central atom
of the molecule or ion) either in its ground state or in its excited
state mix together and give rise to the formation ofnew degenerate
Living Systems Non-living Systems
orbitals which are called hybrid orbitals.
The vital force could be philosophically thought as the mysterious
force God instilled in the living systems. Hybridization % s-character
In 1823, Friedrich Wohler joined Berzelius as his student. In 1828, sp3 25.0
Wohler made a discovery which changed the definition of organic sp2 333
chemistry. Wohler conducted the following experiment.
sp 50.0
NH4
El) e
OCN(aq)
evaporation
- - - • O=C(NH 2)i(s)
Ammonium Cyanate Urea Crystab 2.1 Applications of Ilybridization
(Inorganic) (Organic)
• Size of Hybrid Orbitals
Wohler successfully synthesized an organic compound starting As % s-character increases, size of hybrid orbital decreases.
from an inorganic compound. Following this, many others Therefore
synthesized organic compounds starting from inorganic
compounds. Thus, the theory of vitalism and the definition of Size of Hybrid Orbital : sp3 > sp2 > sp
organic chemistry lost its meaning. • Electronegativity of Hybrid Orbitals
But what was common in all the above compounds synthesized As % s-character increases, electronegativity of hybrid orbital
was the presence of carbon. Carbon shows a special property increases. Therefore
catenation. Carbon can connect with other carbon atoms to form EN of Hybrid Orbital: sp > sp2 > sp3
long chains and rings (self-catenation) and can connect with atoms 2.2 Dienes
of many other elements in the periodic table (cross-catenation).
Because of this reason, carbon can form a wide variety of Dienes are organic compounds containing two double bonds.
compounds. Therefore, the modern definition of organic There are three types of dienes :
chemistry is the study of carbon compounds. (a) Isolated (b) Conjugated (c)Cumulated
Probably, the vital force can be explained by the fact that most of (a) Isolated Diene:
the life-giving and life-sustaining functions are performed by In this case, double bonds are separated by atleast one sp3 carbon.
carbon compounds, for example, the human tissues and skin are
formed by proteins, respiration is possible due to haemoglobin, CH2=CH-CH 2-CH=CH2
the information in our genes is carried out in the form of DNA/
RNA etc.
i i i i i
.1 2 3 2 2
sp sp sp sp sp
General Organic Chemistry is the detailed study of the basic
concepts and facton that govern the progress and outcome of
reactions.
, Molecule CJ 1t LP Hybridization Geometry Shape
•ctt.i 4 0 0 sp3 Tetrahedral Tetrahedral
•CH2=CH2 3 l 0 sp2 Trigonal planar Trigonal planar
H•c = CH 2 2 0 sp Linear Linear
Hybridization ofCommon Molecules
(b) Conjugated Diene: (A) Characterstics oflnductive Effect
Double bonds are separated by only one single bond ( or 4 sp2 I / EN0 > ENc (H•logeos)
carbons in a row).
CH2=CH-CH=CH2
i i i i
2 2 2 2
-c-G-ENG"'- ENc(C,H)
sp sp sp sp I~
(c) Cumulated Diene: ENG< ENc (Metals)
Both sets of double bonds are at the same carbon. There are broadly three types of groups/atoms that may be
CH 3-CH=C=CH-CH 3 attached to carbon as illustrated. Although C is more
electronegative than H, the electronegativity difference is small
A substituted allene
and the bond is generally consider non-polar.
An allene is CH2=C=CH 2
Stability of Dienes: • Nature of Inductive Effect
The relative stabilities of dienes follows the order Inductive effect is a permanent effect and can be directly
Conjugated> Isolated> Cumulated correlated to its dipole moment.
Important: It is a weak effect as the shifting of electrons takes place only
through sigma bonds.
.. I
Stab1hty oc - - - - - - - - - - - -
Energy Content of the molecule • Effect ofbranched carbon chain
An illustration has been marked for operation of inductive effect
3. ELECTRONIC DISPLACEMENT EFFECT which is self-explanatory.
oo(J)
Electronic Displacement effect C C
I
... I~
oo(J) fo(J)
-C-C-r-C__...C~CI
r,6
Pennanent Effect Temporary Effect
+
Inductive Mesomeric
...
Hyperconjugation
i
Electromeric
C
I
C
~oo(J)
Effect Effect Effect effect More the number of o, lesser the effect
3.1 I nducti\'c effect • FJectron Donating and FJectronwithdrawing Groups
When two unlike atoms form covalent bond, the electron-pair Inductive effect may be due to single atom or a group of atoms.
forming the sigma bond is never shared equally between the two Relative inductive effects are measured with reference to hydrogen.
atoms but is shifted slightly towards the more electronegative Those which donate electrons to carbon chain are called electron-
species. donating groups (EDG) or electron-releasing groups (ERG) and
are said to exert +I effect. Those which withdraw electrons from
carbon chain are called electron-withdrawing groups (EWG) and
are said to exert-I effect.
, Important: Example
I. I.E. ofalkyl groups: 3°> 2° > 1° >-CH3
(a) Compare the acidic strength of:
2. In general, greater is the number of carbons in an alkyl group,
(I) CH3 CH 2CH2-COOH
greater is its +I effect.
3. For problem-solving, we take electronegativity of sp-hybridized (II) CH3CH2CH-COOH
3
carbon to be more than sp hybridized nitrogen. I
Cl
(8) Applications of Inductive Effect
(III) CH3 CH-CH2-COOH
• Effect on Acidic/Basic Strength
I
EWG increases acidic strength and decreases basic strength. ERG Cl
decreases acidic strength and increases basic strength. (JV) CH2CH2CH2-COOH
Example I
Cl
Compare the acidic strength : Solution:
01) CH2-C00H
I
Cl
CH 2-C00H
(III) I
F
Solution:
An alkyl group is donating only ifno other EWG is present on it.
Therefore, groups like -CH2Cl and -CH2F become electron
withdrawing groups.
Order ofAcidic Strength : III > II > I
Effect of Distance
If the ERG/EWG moves away, the inductive effect diminishes.
Order of acidic strength : II> III> IV> I
Series of +I and -I groups in order of their strength
,-1 Series (EWG)
0
e II
-NR3 >-N02 >-CN>-F>-C00H>-C->-Cl>-Br>-I>-0H>-0R>-C6 H5 >-O=C->-C=C->H
IH Series (ERG)
0 CH 3 CH3 H
e II
- 0 > -C-0 > CH3 -
e
1-
I > CH3 -
1-
I > CH 3-
1-
I > CH 3- > D- > H-
CH 3 H H
(3) (2') (1°)
& ISOMERISM
1. INTRODUCTION M•OI
The making and breaking of bonds usually occurs in several
In 1807, Berzelius proposed the term 'Organic Chemistry' for the discrete steps before transforming into products. The detailed
study ofcompounds derived from natural sources. This was based sequential description of all the steps is called the mechanism
on the theory of vitalism which said that all living systems of the reaction.
possessed a 'vital force' which was absent in non-living systems.
Compounds derived from living natural sources (organic) were 2. HYBRIDIZATION
thought to be fundamentally different from inorganic compounds.
Ill
Hybridisation is a process in which two or more atomic orbitals of
comparable energy of the valence-shell of an atom ( central atom
of the molecule or ion) either in its ground state or in its excited
state mix together and give rise to the formation ofnew degenerate
Living Systems Non-living Systems
orbitals which are called hybrid orbitals.
The vital force could be philosophically thought as the mysterious
force God instilled in the living systems. Hybridization % s-character
In 1823, Friedrich Wohler joined Berzelius as his student. In 1828, sp3 25.0
Wohler made a discovery which changed the definition of organic sp2 333
chemistry. Wohler conducted the following experiment.
sp 50.0
NH4
El) e
OCN(aq)
evaporation
- - - • O=C(NH 2)i(s)
Ammonium Cyanate Urea Crystab 2.1 Applications of Ilybridization
(Inorganic) (Organic)
• Size of Hybrid Orbitals
Wohler successfully synthesized an organic compound starting As % s-character increases, size of hybrid orbital decreases.
from an inorganic compound. Following this, many others Therefore
synthesized organic compounds starting from inorganic
compounds. Thus, the theory of vitalism and the definition of Size of Hybrid Orbital : sp3 > sp2 > sp
organic chemistry lost its meaning. • Electronegativity of Hybrid Orbitals
But what was common in all the above compounds synthesized As % s-character increases, electronegativity of hybrid orbital
was the presence of carbon. Carbon shows a special property increases. Therefore
catenation. Carbon can connect with other carbon atoms to form EN of Hybrid Orbital: sp > sp2 > sp3
long chains and rings (self-catenation) and can connect with atoms 2.2 Dienes
of many other elements in the periodic table (cross-catenation).
Because of this reason, carbon can form a wide variety of Dienes are organic compounds containing two double bonds.
compounds. Therefore, the modern definition of organic There are three types of dienes :
chemistry is the study of carbon compounds. (a) Isolated (b) Conjugated (c)Cumulated
Probably, the vital force can be explained by the fact that most of (a) Isolated Diene:
the life-giving and life-sustaining functions are performed by In this case, double bonds are separated by atleast one sp3 carbon.
carbon compounds, for example, the human tissues and skin are
formed by proteins, respiration is possible due to haemoglobin, CH2=CH-CH 2-CH=CH2
the information in our genes is carried out in the form of DNA/
RNA etc.
i i i i i
.1 2 3 2 2
sp sp sp sp sp
General Organic Chemistry is the detailed study of the basic
concepts and facton that govern the progress and outcome of
reactions.
, Molecule CJ 1t LP Hybridization Geometry Shape
•ctt.i 4 0 0 sp3 Tetrahedral Tetrahedral
•CH2=CH2 3 l 0 sp2 Trigonal planar Trigonal planar
H•c = CH 2 2 0 sp Linear Linear
Hybridization ofCommon Molecules
(b) Conjugated Diene: (A) Characterstics oflnductive Effect
Double bonds are separated by only one single bond ( or 4 sp2 I / EN0 > ENc (H•logeos)
carbons in a row).
CH2=CH-CH=CH2
i i i i
2 2 2 2
-c-G-ENG"'- ENc(C,H)
sp sp sp sp I~
(c) Cumulated Diene: ENG< ENc (Metals)
Both sets of double bonds are at the same carbon. There are broadly three types of groups/atoms that may be
CH 3-CH=C=CH-CH 3 attached to carbon as illustrated. Although C is more
electronegative than H, the electronegativity difference is small
A substituted allene
and the bond is generally consider non-polar.
An allene is CH2=C=CH 2
Stability of Dienes: • Nature of Inductive Effect
The relative stabilities of dienes follows the order Inductive effect is a permanent effect and can be directly
Conjugated> Isolated> Cumulated correlated to its dipole moment.
Important: It is a weak effect as the shifting of electrons takes place only
through sigma bonds.
.. I
Stab1hty oc - - - - - - - - - - - -
Energy Content of the molecule • Effect ofbranched carbon chain
An illustration has been marked for operation of inductive effect
3. ELECTRONIC DISPLACEMENT EFFECT which is self-explanatory.
oo(J)
Electronic Displacement effect C C
I
... I~
oo(J) fo(J)
-C-C-r-C__...C~CI
r,6
Pennanent Effect Temporary Effect
+
Inductive Mesomeric
...
Hyperconjugation
i
Electromeric
C
I
C
~oo(J)
Effect Effect Effect effect More the number of o, lesser the effect
3.1 I nducti\'c effect • FJectron Donating and FJectronwithdrawing Groups
When two unlike atoms form covalent bond, the electron-pair Inductive effect may be due to single atom or a group of atoms.
forming the sigma bond is never shared equally between the two Relative inductive effects are measured with reference to hydrogen.
atoms but is shifted slightly towards the more electronegative Those which donate electrons to carbon chain are called electron-
species. donating groups (EDG) or electron-releasing groups (ERG) and
are said to exert +I effect. Those which withdraw electrons from
carbon chain are called electron-withdrawing groups (EWG) and
are said to exert-I effect.
, Important: Example
I. I.E. ofalkyl groups: 3°> 2° > 1° >-CH3
(a) Compare the acidic strength of:
2. In general, greater is the number of carbons in an alkyl group,
(I) CH3 CH 2CH2-COOH
greater is its +I effect.
3. For problem-solving, we take electronegativity of sp-hybridized (II) CH3CH2CH-COOH
3
carbon to be more than sp hybridized nitrogen. I
Cl
(8) Applications of Inductive Effect
(III) CH3 CH-CH2-COOH
• Effect on Acidic/Basic Strength
I
EWG increases acidic strength and decreases basic strength. ERG Cl
decreases acidic strength and increases basic strength. (JV) CH2CH2CH2-COOH
Example I
Cl
Compare the acidic strength : Solution:
01) CH2-C00H
I
Cl
CH 2-C00H
(III) I
F
Solution:
An alkyl group is donating only ifno other EWG is present on it.
Therefore, groups like -CH2Cl and -CH2F become electron
withdrawing groups.
Order ofAcidic Strength : III > II > I
Effect of Distance
If the ERG/EWG moves away, the inductive effect diminishes.
Order of acidic strength : II> III> IV> I
Series of +I and -I groups in order of their strength
,-1 Series (EWG)
0
e II
-NR3 >-N02 >-CN>-F>-C00H>-C->-Cl>-Br>-I>-0H>-0R>-C6 H5 >-O=C->-C=C->H
IH Series (ERG)
0 CH 3 CH3 H
e II
- 0 > -C-0 > CH3 -
e
1-
I > CH3 -
1-
I > CH 3-
1-
I > CH 3- > D- > H-
CH 3 H H
(3) (2') (1°)
