1. NEW CHAPTER
BASIC CONCEPTS
BINDING AND RESONANCE

2. Bonding Patterns
Localized Electrons: When electrons are restricted on single atom (as lone pair) or between two bonded atoms only.
Delocalized Electrons: When electrons spread over an area,
such as in benzene,  electrons spread over whole ring.
Resonance structures
Mechanisms

3. A valid organic mechanism uses: (a) curved arrows (b) Lewis structures
A mechanism is step by step description of how reactants become products (Or Pathway to product)
A valid organic mechanism uses:
(a) curved arrows
(b) Lewis structures
(c) and reactions
This is a mechanism

4. Curved Arrows Notice the tail of the arrow must start
at an electron pair.

5. Resonance Structures:
Resonance Structures are two Lewis structures having the
Same placement of atoms but a different arrangement of
electron.

6. Drawing Resonance Structures (continued)
Rule [3]: Resonance structures must be valid Lewis structures. Hydrogen must have two electrons and no second-row element can have more than eight.

7. Rules for Drawing Resonance Structures
Rule [1]: The placement of atoms and single bonds always stays the same.
Rule [2]: Two resonance structures must have the same number of unpaired electrons.
C is not a resonance str of A and B

8. Resonance
None of these structure represents benzene.
The real structure of benzene is a resonance hybrid of these contributing structures.
The contributing structures have no real structure existence but these only exist in our imagination.
All the molecules of benzene have one structure which can't be drawn, but which resembles the contributing structure to varying extent.
Example: Mule

9. What is resonance?
Resonance is defined as the representation of a real structure as a weighted average of two or more contributing structure is called resonance. The contributing structure is called canonical form and the real structure is called resonance hybrid.
The resonance hybrid is similar to each of the contributing structures but identical to non of them.
For example the various structure of benzene

10. Resonance
The energy of the actual molecule is less than the contributing structures .
The contributing structure has different energies. Some have high and some have low energies.
The contributing structure which has the lowest energy is more resemble to the actual molecule and is called major contributor.
The contributing structure which has the highest energy is less contributing to the hybrid one and is called the minor contributor.

11. Resonance Energy
The difference of energy between the actual molecule and the contributing structure of the lowest energy is called the resonance energy.
The double headed arrow represents resonance which means that molecule is better represented by several Lewis structure than by one.
The contribution of structure (1) and (2) to the actual structure has been calculated to be 39 % each where as (3), (4) and (5) is 7.3% each

12. Resonance Energy
Complete Hydrogenation of benzene to Cyclohexane delivers
208.4 kJ/mol.
While hydrogenation of 1 double bond required kj/mol.
Difference in energy is ─208.4 = kJ/mol.

13. Resonance Effect
The decrease in electronic density at one position and the corresponding increase else where is called the resonance ( or mesomeric effect). For example in ammonia resonance is absent, the unshared pair of electrons is located on the nitrogen atom.
However, if one of the hydrogen atoms of ammonia is replaced by a benzene ring. The pair of nitrogen is delocalized over the ring, resulting in the decrease of electron density o the nitrogen atom and the corresponding increase electron density on the ring as shown below.
NH2 group in aniline donates to the ring by the resonance effect.

14. Electron Withdrawing Group (-M):
Similarly, nitrobenzene the –NO2 group withdraws electron from the ring by a similar effect
Some of the common electron donating group (+M ) and electron withdrawing (-M) groups are listed below
Electron Withdrawing Group (-M):
Electron Donating Group (+M ) :

15. Inductive Effect
The permanent diapole induced by a bond on another bond is called as inductive effect. This effect also the effect the reactivity of a compound.
If a carbon atom is joined to an atom X of higher ectronegativity than carbon
The bonding electrons of the C  X bond will be displaced away from the carbon atom.
The bonding electrons of the C  X bond will be displaced towards atom X.
Carbon atom will exhibit a partial positive charge
Atom X will exhibit a partial negative charge.

16. Inductive Effect
If a carbon atom is joined to an atom Y of lower electronegativity than carbon
The bonding electrons of the C  Y bond will be displaced away from atom Y
The bonding electrons of the C  Y bond will be displaced towards the carbon atom
Carbon atom will exhibit a partial negative charge
Atom Y will exhibit a partial positive charge

17. Inductive Effect
When an electron-withdrawing group (X) is linked to carbon
 the group develops a partial negative charge
 exert a negative inductive effect (-I)

18. Inductive Effect
Represented by an arrow head in the middle of the covalent bond pointing in the direction of the displacement of electrons

19. Inductive Effect
When an electron-releasing group (Y) is linked to carbon
 the group develops a partial positive charge
 exert a positive inductive effect (+I)

20. Alkyl groups like CH3, C2H5, C3H7
Inductive Effect
1. Groups which exhibit negative inductive effect (i.e. electron-withdrawing groups)
NO2 > F > COOH > Cl > Br > I
2. Groups which exhibit positive inductive effect (i.e. electron-releasing groups)
Alkyl groups like CH3, C2H5, C3H7

21. Inductive Effect
The stabilities of the carbocations in decreasing order:

22. Why is tert-Butyl Carbocation the Most Stable among the Four Carbocations?
Three electron-releasing methyl groups surrounding the central carbon atom
Help reduce the positive charge on the central carbon atom by exerting positive inductive effects

23. Inductive Effect
The greater the number of alkyl groups attached to the central carbon atom
 the more dispersion the charge
 the more stable the carbocation

24. Formic acid is 10 times stronger acid than acetic acid.
It is due to the inductive effect of (CH3) methyl group attached to carbon in acetic acid. As CH3 group is an electron donating group.
This it donates electron though inductive effect to the carbon and as result the carbon shift electrons to (OH) group and becomes electron rich and thus cant be replaced from acid and hence the strength of the acid is decreased. Because we know that an acid will be strong if donate (-H+) more easily.

25. On the other hand hydrogen attached to carbon in formaic acid not an electron donating group and thus the Oxygen of OH group attracts electron from the O-H bond and hydrogen becomes electron deficient and so easily b replaced
This is the reason that formic acid is stronger acid that acetic acid and this is due to the permanent dipole
Other example. Chloro acetic acid is 100 times acidic than acetic acid.

26. Electron withdrawing inductive effect (-I) or
electron donating inductive effect (+I)
The functional groups responsible for producing inductive effect can be classified with an electron withdrawing inductive effect (-I) or with an electron donating inductive effect (+I) relative to Hydrogen depending on whether they are more electronegative or less electronegative than H. some of the common –I and +I groups are listed below approximately in the order of decreasing inductive effect.
Electron with drawing groups (-I)
-NR3, -NH3, -NO2, -CN, -CO2H, -F, -Cl, -Br, -I, -OAr -CO2R, -OR, -COR, -OH, etc
Electron donating groups (+I)
-O-, -CO-, -CR3, -CHR2, -CH2R, -CH3, -D

27. Hyperconjugation Sigma bond in conjugation with p orbital
The system in which the sigma electrons are in conjugation
Sigma bond in conjugation with p orbital is also called hyperconjugation
Explanation
The molecule of propylene in which C-H is in conjugation with an unsaturated system. The sigma electron of the C-H bond are delocalized and a canonical form such as (b).

28. In this canonical form there is no bond between the carbon and hydrogen atom.
This type of resonance is called no bond resonance and this system of conjugation where the sigma electron of a C-H bond are in conjugation with Pi electron of unsaturated system or with a p orbital is known as hyperconjugation.
This no bond resonance between C-H is partially delocalized through conjugation.

29. Hydrogen Bonding
Hydrogen bonding is an attractive force which occurs in any compound whose molecules contain O-H or N-H bonds (as in water, alcohols, acids, amines and amides. The O-H bond, for example, is a highly polar bond. Oxygen is more electronegative than H and pulls the bonding electrons closer to it. As a result of this displacement, the oxygen atom acquires a small
negative charge and H small d- d+

30. Hydrogen bonds in Ethane
Alcohols have abnormally high boiling points relative to their molecular weights due to their ability to hydrogen bond
Hydrogen bonds in Ethane
Hydrogen bonds

31. R-O-H has a structure similar to that of water
Hydroxyl group is very polar
Hydrogen bonds can form readily

32. GOOD LUCK