Basic concepts like Inductive effect, hyperconjugation, steric effect and tautomerism are explained in organic chemistry.

1. BS CHEMISTRY + BS ZOOLOGY
Lecture#4
M.Phil. Organic Chemistry
Basic Concepts of Chemical Bonding

2. INDUCTIVE EFFECT
• Definition:
I.E is defined as the increase in the electron density at a near by
atom due to the difference in electronegativity.
OR
Polarization of σ bonds within a molecule induced by an adjacent polar bond
through movement of sigma electrons.
• In chloroethane Cl is more electronegative inducing dipole on carbon no. 2(β)
through carbon no. 1(α ).
β α

3. NEGATIVE INDUCTIVE EFFECT
• Inductive effect can be classified into two types.
1. Electron withdrawing effect, Negative I.E. (-I)
e.g., NH3, CN, COOH, F, Cl, Br, I, RO, OAr, COOR, SH, OH, Ar.
1. Electron donating effect, Positive I.E. (+I).
e.g., O-, COO-, R3C, R2CH, CH3
• Chloroacetic acid is 100 times stronger acid than acetic acid. why?

4. NEGATIVE INDUCTIVE EFFECT
• Flouroacetic Acid is more stronger than chloroacetic acid.
• As fluorine is more electronegative than chlorine so it withdraws electron
more strongly than chlorine.
• 3-chloropropanoic acid is weaker than acetic acid
• Inductive effect diminishes as no. carbons increases.

5. POSITIVE INDUCTIVE EFFECT
• Electron donating group destabilize the anion and decreases it acidity.
• Acetic acid is 10 times less acidic than Formic acid.
CH3COOH < HCOOH
• Basicity: Depends on the unshared pair (lp) of electrons.
• Electron donating(repelling) effect of alkyl groups makes alkyl amines more
basic than simple ammonia.
• T- amine is less Basic due to stability of conjugate acid and solvation by water
as solvent.
• Field Effect (depend upon geometry of the molecule).

6. STERIC EFFECT
• Destabilization caused by Van Der Waal repulsions that are present in close
proximity of each other is referred as Steric effect.
• Atoms in molecules occupy certain amounts of space. If they are brought too
close to each other, their electron clouds may repel each other causing a steric
strain that may affect the reactivity of the molecule.

7. APPLICATIONS
1. Stability of two geometrical isomers:
2. Hydrolysis of Haloalkanes:
• 1o haloalkane undergo SN2
• Neopentyl bromide is 1o but t-butyl
group cause steric hindrance.
• So, reaction follow sN1 by
1,2 methyl shift.
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8. APPLICATIONS
3. Effect on Nucleophilicity.
• tert-butoxide ion is100 times stronger base than methoxide ion, because it is less
sterically hindered.
4. Acidity of Alcohols:
• Acidity decreases with increase in no. of carbons.
• CH3OH > C2H5OH > 2-Propanol > tert-butanol.
5. Basicity of Amines:
• (CH3)2NH > CH3NH2 < (CH3)3N
• The steric hindrance in t-amines makes
them less basic.
• In some cases, steric effect increases basicity
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9. HYPERCONJUGATION
• Delocalization sigma σ electrons is called Hyperconjugation.
• It involves σ-П overlap, analogous to П-П overlap.
• When the σ electrons are in conjugation with the pi electrons or with orbital is
called Hyperconjugation. i.e.
• H do not leave the molecule because 2 does not exist, it is a canonical form.
• Reasons for form 2 is C-H bond here is weaker than normal C-H bond.
• And the bond between C2 and C3 has some double bond character.
• C-C bond in above str. Is shorter (1.47nm) than normal C-C bond (1.54nm).

10. HYPERCONJUGATION
• The more hyperconjugation structures the more stable is compound.
• The stability order of carbonium ion is as follows.
• Following are the 10 structures of tert-butyl carbocation.

11. TAUTOMERISM
• Definition:
• Two structural isomers that exist in dynamic equilibrium and are readily
interconvertible called Tautomer and phenomenon is call tautomerism.
• Tautomerism that involves proton transfer from one part of molecule to the
other is known as proton Tautomerism.

12. TAUTOMERISM
• The most common example of proton transfer is Keto- enol tautomerism
• 99% (1.5 x 10-4)
• Proton from carbon 1 is sifted to O of the carbonyl group forming enol form and
this is called Enolization
• Since keto-enol forms are interconvertible so their stability can be determined
by their %age in equilibrium mixture.
• The one which is form in higher percentage is more stable and vice versa.
• Monocarbonyl compound is more stable than its enol form. as
1 2
Enol form
Keto from

13. TAUTOMERISM
• Compounds having two carbonyl groups shows enol form is more stable than
keto form.
• The greater stability is due to H-bonding
Hydrogen bonding