The document discusses key concepts in organic chemistry, focusing on chemical bonding, inductive effects, acidity, and basicity of various compounds. It explains the classification of inductive effects as electron withdrawing and donating, providing examples and their influence on acidity and basicity. Additionally, it covers steric effects, hyperconjugation, and tautomerism, highlighting their significance in molecular stability and reactivity.

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