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In Chemistry, inductive effect refer to the permanent formation in a molecule due to the unequal sharing of σ electrons in a molecule.
Inductive effect operate to σ-bond
Partial charge development
Can be neglected after 3rd Carbon atom
Effect depend on distance
Inductive effect is the partial shifting or Displacement of σ electrons towards the more
electronegative atom . As a result partial charges are developed in a molecule.
Inductive Effect in Chloroethane:
Here Carbon is less electronegative than Chlorine so Cl will pull the shared electron pair more towards itself. As a result polarity or partial charges are developed on chlorine (partial negative )and carbon (partial positive).
Chlorine will pull the electron pair more than the carbon due to more electronegativity .Due to this the carbon becomes electron deficient bearing partial positive charge .This carbon then pull the electrons from the adjacent carbon so this effect travel and decreases with distance.
Classification of Inductive Effect:
Inductive effect is classified into following 2 types:
Positive inductive effect (+I effect)
Negative inductive effect (-I effect)
Difference between +I & -I Effect:
Positive inductive effect (+I effect):
When an electron donating or electron releasing group(such as alkyl group) is introduced to a carbon chain the charged is transferred through the chain. This results in a permanent dipole in a molecule where the electron donating group is called +I group and this effect is known as +I effect.
For example :
Here methyl group(CH3) is an electron donating or releasing group which increases the stability of carbocation (which is electron deficient) by donating electron. Here Methyl group is +I Group and this effect is known as +I effect.
Negative inductive effect (-I effect):
When an electronegative atom (e.g. halogen) is introduced to a chain of atoms(generally carbon atom), resulting in unequal sharing of electrons generates a positive charge which is transmitted through the chain. This results in a permanent dipole in a molecule where the electronegative atom(electron withdrawing group)holds a negative charge is called a –I group and this effect is known as –I effect(Positive inductive effect).
Here Chlorine(Cl) is an electron withdrawing group which pulls the electron pair from adjacent carbon & this carbon in turn pulls electron from the neighboring carbon ,this effect will travel and decrease (up to 3 carbon if present) . Here Chlorine is -I Group and this effect is known as -I effect (negative inductive effect).
Every atom /molecule or ion want to become stable .
To attain stability atom /molecule or ion must have a complete outer most shell (octet).
Carbocation carbon having 6 valence shell electron indicates the incomplete octet (8 electrons).Therefore, carbocation is highly reactive , unstable and seeks electrons to complete valence electrons .Therefore ,carbocation is an electrophile.
Is carbocation Lewis acid or Lewis base?
Carbocation is a Lewis acid because of incomplete valence electron ,it can accept electron pair to be stable.
Hyperconjugation is the stabilizing interaction of the σ electrons(usually C-H or C-C)with an adjacent p-orbital(empty or partially filled or a” π” – orbital) .
Hyperconjugation is known as No bond Resonance or σ-bond” π” orbital resonance.
Hyperconjugation plays an important role in the stability of the following:
Hyperconjugation Effect in Carbocation:
Rules for Hyperconjugation in Carbocations:
Positively charged carbon with empty p – orbital
C-H sigma bond electrons
The C-H sigma electrons are dispersed or shifted towards the empty p- orbital. As a result of the dispersion(delocalization ) of electrons ,the positive charge on carbon get dispersed and a carbocation get stabilized.
Ethyl Carbocation- Example of Hyperconjugation:
In ethyl carbocation, the positively charged carbon has empty p-orbital (due to the electron deficiency ,carbocation is an electrophile).The sigma electrons are delocalizes between C-H and empty p-orbital .As a result of this interaction, the positive charge on carbon get dispersed and stabilized.
More Hyperconjugation = More stability of Carbocation
How you can calculate the stability of carbocation with hyperconjugation :
Calculating the total number of alpha hydrogen to find the stability of carbocation plays a vital role.
More no. of alpha hydrogen = More hyperconjugation = More stable carbocation
Carbon adjacent to the positively charged carbon is α carbon and all the hydrogen attached with this carbon are α hydrogens.
Stability order of carbocation:
More alkyl groups attached to the positively charged carbon = More Hyperconjugation = More stability
Carbocation is defined as the positively charged carbon atom having three bonds .
Carbocation is highly unstable and reactive due to incomplete carbon octet. Therefore, it is a reaction intermediate in a chemical reaction.
Classification of Carbocation:
Carbocations are classified on the basis of no of carbon groups (alkyl groups)attached with the positively charged carbon atom.
If no carbon is attachedto the carbon with positive chargeis termed as methyl carbocation.
If 1 carbon is attached to the carbon with positive charge is termed as primary carbocation.
Primary carbocation is also known as 10 carbocation.
If 2 carbon is attachedto the carbon with positive chargeis termed as secondary carbocation.
Secondary carbocation is also known as 20 carbocation.
If 3 carbon is attachedto the carbon with positive chargeis termed as tertiary carbocation.
Tertiary carbocation is also known as 30 carbocation.
Identify which one is primary ,secondary or tertiary carbocation!!!
Here 1 carbon is attached to the carbon with positive charge ,so it is primary carbocation.
CH3- CH2-CH+-CH2- CH2–CH3
Here 2 carbon is attached to the carbon with positive charge ,so it is secondary carbocation.
Stability order of Carbocation:
More the alkyl groups attached to the positively charged carbon, more the stability of carbocation.
Tertiary carbocation is the most stable carbocation because three carbon groups (methyl groups) are attached to the positively charged carbon ,increasing the stability by donating electrons to the electron deficient carbon of carbocation.
Whereas ,methyl carbocation is the least stable carbocation as no alkyl group is attached to the positively charged carbon.
Increasing order of carbocation stability is as follow:
As a result of homolytic cleavage of methane molecule ,the shared electron pair is evenly distributed between the carbon and hydrogen of methane results in the formation of methyl free radical and hydrogen free radical .
Methyl radical( .CH3) is an organic compound derived from methane(CH4 ) is the reaction intermediate that is highly reactive, short lived and unstable.
Methyl Radical Formula:
Methyl free radical is represented by .CH3
Methyl radical Formation:
Homolytic cleavage between C-H bond in methane molecule results in the formation of methyl free radical and hydrogen free radical.
Methyl radical Lewis Structure:
Methyl radical have central carbon atom( 4 electrons in valence shell) is surrounded by 3 hydrogen atoms (each hydrogen having 1 valence electron).As a result of covalent bond between carbon and hydrogen ,methyl radical having 7 electrons (odd no. of electrons) in total as you can see in diagram:
Central carbon atom in methyl free radical having 3 bond pair and one unpaired electrons so the total 7 electrons around the carbon atoms represent the incomplete valence electrons(incomplete octet) .That’s why methyl radical is highly reactive and unstable.
Methyl radical Shape or Geometry:
According to the valence shell electron pair repulsion theory, when three bond pair electrons are present around the central atom, it will result in the formation of trigonal planar shape or geometry of methyl radical.
Methyl Radical Bond Angle:
According to the valence shell electron pair repulsion theory, if a molecule having trigonal planar shape or geometry so it will have an angle of 1200 .Therefore methyl radical having a bond angle of 1200 with trigonal planar geometry .
Methyl Radical Hybridization:
The easiest trick to find the hybridization type is to count the total number of sigma bonds (single covalent bond) and lone pair electrons around the central atom so that you can determine the type of hybridization easily.
Formula to find Hybridization:
Type of hybridization= Total no. of sigma bond + Total no. of lone pair electrons
sp3 hybridization= Total no. of sigma bond + Total no. of lone pair electrons = 4 hybrid orbitals
sp2 hybridization= Total no. of sigma bond + Total no. of lone pair electrons = 3 hybrid orbitals
sp hybridization= Total no. of sigma bond + Total no. of lone pair electrons = 2 hybrid orbitals
In methyl radical, we have 3 sigma bonds and 1 un paired (not involved in hybridization) so the total of 3 hybrid orbitals results in sp2 hybridization.
Atom or group of atoms (molecules) having unpaired valence electrons is called free radical.
Methyl Free radical Shape:
As the carbon in methyl radical having 3 bond pair and one unpaired electron results in trigonal planar shape and bond angle of 1200 .
Methyl Free radicalHybridization:
Remember that any chemical specie (molecule or ion) having trigonal shape and 1200 bond angle results in sp2 hybridization so methyl free radical is sp2 hybridized specie having 3 bond pairs around the central carbon atom.
Methyl Free radicalformation from methane:
In the presence of light ,homolytic cleavage of a stable methane molecule results in the even distribution of electrons among the products (methyl free radical and hydrogen free radical).
Cl2 is a stable Chlorine molecule .When the homolytic cleavage of the chlorine molecule takes place in the presence of light ,it will results in the even distribution of electrons between the products as chlorine free radicals .
As you can see in the diagram that the chlorine free radicals having 7 valence electrons (unpaired / odd electron numbers) indicates chlorine free radical formation.
Why free radicals are highly reactive?
free radicals are highly reactive due to the unpaired valence electron.
The force of attraction in which hydrogen atom ,which is covalently bonded to a highly electronegative atom in a molecule is attracted by the lone pair electron of another electronegative atom in a nearby molecule is called hydrogen bonding.