ORGANIC CHEMISTRY
                     INTRODUCTION TO
GENERAL ORGANIC 
CHEMISTRY
ANALYTICAL MINDS
-A UNIT OF BHUBAN 
ENTERPRISES
INTRODUCTION
 Organic chemistry is the chemistry discipline that is concerned with 
the study of compounds containing carbon that is chemically 
bonded to hydrogen. Organic chemistry encompasses the synthesis, 
identification, modeling, and chemical reactions of such compounds.
 The range of chemical compounds studied in organic chemistry 
include hydrocarbons (compounds containing 
only carbon and hydrogen), carbons  containing other 
elements, especially oxygen, nitrogen, sulphur, phosphorus and 
the certainly halogens.
 The following is an example of an organic molecule Methane(CH4).    
                   (The line-angle structural formula shows four                    
                                   carbon-hydrogen single bonds (σ, in black), 
and the typical                                        3D shape of tetrahedral 
molecules, with ~109° interior bond angles.)                                        
      
CLASSIFICATION OF ORGANIC MOLECULE
ORGANIC COMPOUNDS are of two types:
1. ALIPHATIC COMPOUNDS:  open chain 
compounds.
2. CLOSED CHAIN COMPOUNDS:  closed 
chain compounds. These are again 
classified into two types:
A. HETEROCYCLIC COMPOUNDS:  ring 
skeleton of compounds containing carbon 
atoms along with atoms of other elements.
B. HOMOCYCLIC COMPOUNDS:  ring skeleton 
of compounds containing only carbon atoms. 
These are of two types: 
i. Alicyclic compounds:  these compounds 
have resemblance in properties with 
aliphatic compounds.
ii. Aromatic compounds:  compound 
containing at least one benzene ring and 
having alternating double bonds within the 
ring. They have agreeable odor. These are 
further divided into two parts:
• Benezoid :  carbocyclic aromatic.
• Non-Benezoid: heterocyclic aromatic.     
STRUCTURAL REPRESENTATION OF ORGANIC 
 ORGANIC  MOLECULES can be reprMeseOnteLdE inC thUe LfoEllowing ways:
 Complete structural formula:  A structural formula in which two electron covalent bond is 
depicted by a dash is called complete structural formula.
 Condensed structural formula: The structural formula obtained after deleting some or all 
of the covalent bonds and by indicating the number of identical groups attached to an 
atom by a subscript. The structural formula so obtained is called condensed structural 
formula. 
 Bond line structural formula: The structural formula obtained by representing carbon-
carbon bond by zigzag lines and not highlighting the carbon and hydrogen atom is known 
as bond line structural formula.
FUNCTIONAL GROUP:
A Functional group may be 
defined as an atom or group 
of atoms which largely 
determines the properties of 
an organic compound.
The family 
of carboxylic acids contains 
a carboxyl (COOH) 
functional group. Acetic 
acid, shown above , is an 
example.
HOMOLOGOUS SERIES:
A homologous series may be 
defined as a series of similarly 
constituted compounds in 
which the members possess 
the same functional group and 
The above diagram is the homologous series 
have similar chemical of alkenes while the diagram below portrays 
characteristics and the two the homologous series of the alkanes.
consecutive members differ in 
their molecular formula by- 
       
CLEAVAGE OF COVALENT BONDS
 Organic reactions involve breaking of bonds in the reacting molecules and 
formation of new bonds to give rise to product molecules. The breaking of bonds 
can take place in two ways-
a. HOMOLYTIC CLEAVAGE:  When the bonding electrons are equally divided into 
the atoms of a bond resulting in the formation of free radicals are known as 
homolytic cleavage.
b. HETEROLYTIC CLEAVAGE: When the bonding electron pair goes to the more 
electronegative atom of a covalent bond resulting into the formation of positively 
and negatively charged species are known as heterolytic cleavage.
REACTION INTERMEDIATES
 REACTION  INTERMEDIATES are generally charged or neutral but electron deficient 
unstable species which are formed from the cleavage of bonds during chemical reactions. 
They are as the following:
 Free Radical:        
i. Have one odd electron as it is formed due to homolytic cleavage.
ii. Para-magnetic in nature due to the presence of unpaired electrons.          
iii. Have both sp2 and sp3 hybridization.
iv. Mostly undergoes hyperconjugation.
v. Stability of free radicals is as the following:
 Carbocation:
i. Positively charged carbocation having 6 valance electrons due to the                                  
                   lacking of octet .
ii. It is sp2 hybridized and has a triangular planner structure with bond angle 120°.
       
iii. It has vacant p orbital which is perpendicular to the plane ,so it acts as a lewis 
      acid.
iv. Stability of the carbocation is as the following:
 Carbanion:
i. These are sp3 hybridized , negatively charged trivalent carbon .
ii. Has one pair of non-bonded electrons. 
iii. It has a tetrahedral shape with bond angle 109 ° 28` , so it has pyramidal shape . 
iv. Stability of carbanion is as the following:
ATTACKING SPECIES 
 NUCLEOPHILE: Nucleophiles are electron donating species. They are of two types:
 Neutral nucleophile: They have non-bonded donatable electrons. 
 Charged nucleophile: These have less no of electrons due to vacant                                                 
                                                                    orbitals.
 ELECTROPHILE:  Electrophiles are positively charged or electron deficient neutral species which 
can accept a pair of electrons in its vacant site. These are electron loving species.        
                                                                            
ELECTRONIC EFFECTS
Effects in organic chemistry : 
Displacement of electrons :
 Temporary effect - Hyperconjugation 
 Permanent effect - Inductive effect & Resonance
INDUCTIVE EFFECT :  
 Only seen in sigma bonds. 
 It depends upon distance.
 Seen in ground state of a molecule. It is of two types :
 +I effect 
 -I effect
RESONANCE : 
 It occurs in conjugate system i.e. sigma & pi system.
 Here electron release occurs via the pi bond. 
 Here we see double electron transfer. It is of two types : 
 -R effect :  Eg: resonance of nitrobenzene
 +R effect : Eg: resonance of aniline
HYPERCONJUGATION : 
 It occurs in sigma-sigma-pi system . 
 It is known as no bond resonance.
 Stability depends on the availability of the no of alpha hydrogen (more alpha hydrogen, 
more stability)
HYBRIDIZATION OF ORGANIC COMPOUNDS
The phenomenon of intermixing of orbitals of the same atom having slightly different energies to 
form new orbitals which have identical shapes and equivalent energies is known as hybridization.
Hybridization is classified into six types : 
 sp :  Two equivalent orbitals formed due to intermixing of one                                                      
                                 s & one p orbital are called sp hybrid orbitals and the                                
                                                            phenomenon is known as sp-hybridization. Eg: Ethyne
 sp2:  Three equivalent orbitals formed due to intermixing of one s & two p orbital are called 
sp2 hybrid orbitals and the phenomenon is known as sp2-hybridization. Eg: Ethene
 sp3: Four equivalent orbitals formed due to intermixing of one                                                       
                                s & three p orbital are called sp3 hybrid orbitals and the                               
                                                             phenomenon is known as sp3-hybridization. Eg: Ethane
 Sp3d: Five equivalent orbitals formed due to intermixing of one                                                      
                                 s ,three p orbital and one d orbital are called sp3d hybrid                          
                                                         orbitals and the phenomenon is known as sp3d-
hybridization.                                                                                        Eg: PCl5
 Sp3d2: Six equivalent orbitals formed due to intermixing of one                                                     
                                  s ,three p orbital and two d orbital are called sp3d2 hybrid orbitals and 
the                                                                                            phenomenon is known as sp3d2-
hybridization. Eg: SF6
 Sp3d3:Seven equivalent orbitals formed due to intermixing of one                                                 
                                      s ,three p orbital and three d orbitals are called sp3d3 hybrid orbitals 
and the                                                                                            phenomenon is known as 
sp3d3-hybridization. Eg: IF7
ISOMERISM IN ORAGANIC MOLECULES
ISOMERISM in organic chemistry is of two types:
 Stereoisomerism- phenomenon where organic 
compounds have  same molecular formula but 
have difference in spatial arrangement of atoms. 
They are of two types again:
• Geometrical isomerism: isomerism arising due 
to restricted rotation of molecules.
• Optical isomerism: Optical isomers are two 
compounds which contain the same number 
and kinds of atoms, and bonds (i.e., the 
connectivity between atoms is the same), and 
different spatial arrangements of the atoms, 
but which have non-superimposable mirror 
images. Each non-superimposable mirror 
image structure is called an enantiomer.
 STRUCTURAL ISOMERISM:  The isomers having different molecular structures due to the 
different arrangement of atoms in their molecules. These are of six types:
 Chain isomerism: In this type of isomerism, the isomers have  different                                        
                         skeletons of carbon atoms. Eg: butane and 2-methylbutane.
 Position isomerism: In this type of isomerism, the isomers have                                                     
                      different position of functional group or multiple bond.                                             
                                                    Eg: propane and  2-methylpropane.
 Functional isomerism: In this type of isomerism, the isomers have  different                                 
                               functional group and thus belong to different families. Eg: ethanol and           
                                          methoxymethane.
 Metamerism: In this type of isomerism, the isomers differs in structure due to difference in 
distribution of carbon atoms about the functional group.                                                                
                                                                    Eg: diethyl ketone and methyl propyl ketone. 
 Tautomerism:  This is a special type of functional isomerism where isomers 
exists simultaneously  in dynamic equilibrium with each other. It arises due to 1,3 
migration of hydrogen atom from one polyvalent atom to other within the same 
molecule.
 Ring-chain isomerism: In this type of isomerism ,one isomer possess an open 
chain structure while the other has a cyclic structure.
 ORGANIC REACTIONS in general can be classified into the following types:
 SUBSTITUTION REACTION:  When an atom or group of molecules is replaced by another 
atom or group of molecules without changing the structure of the resting part of the 
molecule is known as substitution reaction. It is of three types: 
 Free radical substitution reaction: here the attacking species is a free radical. For example let us 
consider the reaction involving halogenation of alkane in presence of uv rays.
 CH   +  Cl CH Cl  +  HCl 
                         4 2 3
The organic product is chloromethane. 
 The mechanism: The mechanism involves a chain reaction. The over-all process is known as 
free radical substitution, or as a free radical chain reaction. It consists of three steps.
• Initiation: The chain is initiated (started) by UV light breaking a chlorine molecule into free 
radicals. Cl2 2Cl  
 
 CH4  +  Cl CH3   +  HCl 
• Propagation :These are the reactions which keep the ch ai nCH 3g  o+  iCnl2g- CH3Cl  +  Cl  
 
• Termination: These are reactions which remove free radicals from the system without 
replacing them by new ones.
 2Cl Cl2 
 CH3   +  Cl CH3Cl 
 CH3   +  CH3 CH3CH3 
 
 Electrophilic substitution reaction:  This reaction involves the attack of an electrophile. It generally 
happens in reactions of compounds containing benzene rings.                                                                 
                                             
       Suppose the electrophile is a positive ion X+.
       The general mechanism:   
   First stage-
Two of the electrons in the delocalized system are attracted towards the X+ and form a bond with it. This has 
the effect of breaking the delocalization, although not completely
The ion formed in this step isn't the final product. It immediately goes on to react with                                      
                    something else. It is just an intermediate.
There is still delocalisation in the intermediate formed, but it only covers part of the ion. 
    Second stage-
   A lone pair of electrons on Y- forms a bond with the hydrogen atom at the top of the ring.                               
                   That means that the pair of electrons joining the hydrogen onto the ring aren't needed any            
                                    more. These then move down to plug the gap in the delocalized electrons, so restoring 
the                                                    delocalized ring of electrons which originally gave the benzene its special 
stability.
Other types of electrophilic substitution reaction:
 HALOGENATION
 NITRATION
 SULPHONATION
 FRIEDEL CRAFT ALKYLATION AND ACYLATION.
 Nucleophilic substitution reaction:  The replacement of one nucleophile by other 
nucleophile is known as nucleophilic substitution reaction. It is of two types:
 Nucleophilic substitution unimolecular reaction (SN1) - it has two steps
a) Formation of carbocation-
b) Formation of product-
Important facts about  SN1 reaction:
1. The rate of reaction increases for more substituted substrate.
2. Substitution of a nucleophile attached to a chiral center leads to the formation of 
a racemic mixture.
3. Ionization through SN1 path is accelerated in the presence of polar solvents.
4. Reactivity of a nucleophile has no effect on the SN1 reaction .
5. The solvent is the nucleophile in many SN1 reactions . This is also called solvolysis 
reaction.
 Nucleophilic substitution bimolecular reaction (SN2):  it is a one step process.
o The  SN2  reaction is a one step process with single transition state but without any 
intermediate.
o The rate of the reaction depends upon the concentration of the substrate and the concerned 
nucleophile.
o The nucleophiles attacks from the back side of the leaving group.
                                                                                                                                  Mechanism: 
o Important facts about  SN2 reaction:
1. When the carbon bearing the nucleophile becomes more substituted ,the rate of reaction      
                                  decreases.
2. Generally non-polar or less polar solvents are suitable for SN2 reaction.
3. The rate of reaction increases with the increase in nucleophilicity of the                                   
                           attacking nucleophile.
 ADDITION REACTION:  In this reaction ,the reagent and the substrate combine with each 
other to form a single product without loosing any part of the reagent and the substrate. It 
is of three types:
 Electrophilic addition reaction:  An electrophilic addition reaction is an addition reaction 
where a molecule is attacked by an electrophile. The molecule has a region of high electron 
density which is attacked by something carrying some degree of positive charge.
 Mechanism:
 Nucleophilic addition reaction: This reaction happens in two distinct stages. The first 
involves an addition reaction where the initial attack is by a nucleophile, which is followed 
by an elimination reaction .So the mechanism is also known as nucleophilic addition 
reaction.
a) Stage 1:                                                                                      b)    Stage 2: 
Finally the chloride ion plucks the hydrogen off the original nucleophile. It removes it as a 
hydrogen ion, leaving the pair of electrons behind on the oxygen or nitrogen atom in that 
nucleophile. That cancels the positive charge.
 Free radical addition reaction:  
o The most common example is the HBr addition to unsymmetrical alkene in presence of 
organic peroxide. The free radical addition to alkene consists  of the following steps-
Propagation can occur in two steps:
Termination:
 REARRANGEMENT REACTION:   The term rearrangement refers to the migration of a group 
from one atom to another within the same molecule.
Eg : The rearrangement of ammonium cyanate NH4NCO to urea (NH2)2CO in aqueous 
solution at 50 oC
 ELIMINATION REACTION:  Reaction in which two groups or atoms are removed from a 
molecule to form an unsaturated linkage or center are known as elimination reaction.
 E1 mechanism: E1 stands for unimolecular elimination and has the following specificities.
 It is a two-step process of elimination: ionization and deprotonation.
 Ionization: the carbon-halogen bond breaks to give a carbocation intermediate.
 Deprotonation of the carbocation.
 E1 typically takes place with tertiary alkyl halides, but is possible with some secondary alkyl 
halides.
 The reaction rate is influenced only by the concentration of the alkyl halide because carbocation 
formation is the slowest step, ie. the rate-determining step. Therefore, first-order kinetics apply 
(unimolecular).
 The reaction usually occurs in the complete absence of a base or the presence of only a weak 
base (acidic conditions and high temperature).
 E1 reactions are in competition with SN1 reactions because they share a common carbocation 
intermediate.
 An example reaction of tert-butylbromide with potassium ethoxide in ethanol
 E2 mechanism:  E2 stands for bimolecular elimination. The reaction involves a one-step 
mechanism in which carbon-hydrogen and carbon-halogen bonds break to form a double bond 
(C=C Pi bond).
The specifics of the reaction are as follows:
 E2 is a single step elimination, with a single transition state.
 It is typically undergone by tertiary substituted alkyl halides, but is possible with some secondary 
alkyl halides and other compounds.
 The reaction rate is second order, because it's influenced by both the alkyl halide and the base 
(bimolecular).
 Because the E2 mechanism results in the formation of a pi bond, the two leaving groups (often a 
hydrogen and a halogen) need to be antiperiplanar. An antiperiplanar transition 
state has staggered conformation with lower energy than a synperiplanar transition state which is 
in eclipsed conformation with higher energy. The reaction mechanism involving staggered 
conformation is more favorable for E2 reactions (unlike E1 reactions).
 E2 typically uses a strong base. It must be strong enough to remove a weakly acidic hydrogen.
 In order for the pi bond to be created, the hybridization of carbons needs to be lowered 
from sp3 to sp2.
 The C-H bond is weakened in the rate determining step               
An example is the reaction of isobutyl bromide                                                                                          
    with potassium with potassium ethoxide  in  ethanol.                                                                             
                                                               The reaction products are isobutylene, ethanol and                    
                                                                             potassium potassium bromide.                                      
                                                                          
THANK YOU
PRESENTATION CREDITS
DR. TATHAGATA DEB
MR. SHIVAM SAHA
ANALYTICAL MINDS
-A UNIT OF BHUBAN ENTERPRISES