General Organic Chemistry - General Organic Chemistry, Organic Chemistry - IIT JAM PDF Download

Organic Reagents: Organic reagents can be classified into two categories such as electron rich reagents like Base/Nucleophile and Electron deficient reagents like Acid/Electrophile

1. Nucleophile [nucleus loving]: 8 e^– having lone pair or –ve charge. If they attack at electron deficient center where e^– densit y is low-this is called nucleophile.
(1) Anions:

(2)  With complete octet and lone pair.

(3)  Alkenes/alkynes, RH = CHR, Benzene.

(4)  CH₂ = CH – EDG → —OH, –OR, —NH₂, –NR₂.

(5) Organometallic compounds [OMC]: The alkyl or aryl groups of OMC are nucleophile such as,  
(Gilman reagent)

(6)  Ambident nucleophiles – having two donor sites.

All enolate are ambident ligands.

•  Note: The regioselect ivit y of ambident Nu^– depend upon: React ion condit ion, solvent, P, T incoming reagent (electrophile), hardness and softness of incoming reagent.

2. Electron deficient reagents like Acid/Electrophile: Inco mplete octet or vacant p orbital p or d orbital/s

(1) Incomplete octet having vacant p orbitals BeCl₂, BF₃, BCl₃, BBr₃ BI₃ (2p – 5p), Carbocations, Carbene, Nitrene, benzyne

Note: All cat ions are charged electrophiles except cations of IA, IIA group elements, 

group elements, Al³⁺ and 

But  are not electrophiles.

Note: Na⁺ is neit her Arrhenius acid or Lewis acid nor electrophile

(2) Vacant d orbitals: PCl₃, PCl₅, SiF₄, SnCl₄, ZnC_l2, FeCl₃, (Used in Beckmann rearrangement), SO₃
Zn ⁺⁺ , Cu ^{+ +} , Ag ⁺ , Pt ^{+ +} , Fe^{+ +} , Cr ^{++ +} , Ni ^{+ +} 

(3)  Atom in elemental state

(4)  Alkene having EWG.

(5)  Ketenes    

(6) Carbon center of carbonyl group [C = O] acid derivatives, CO₂

3. Ambiphiles: Those reagents which can act both electrophile and nucleophile. e.g.,

Note: Br₂, I₂ and ICl are also ambiphiles.

Now the questions arise in mind about electron rich species [reagent]?

Q1. H₂O (8 e^– having lone pair) or NaOH is electron rich species, where H₂O work as base and where H₂O

work as nucleophile [Ligand, reducing agent or HOMO]?

Here I am showing different role of H₂O:

• H₂O as base: When electron rich species attack on H⁺, called base

 H₂O + HCl → H₃O⁺ + Cl^-

•  H₂O as nucleophile: When electron rich species attack on carbocation or carbon, called nucleophile

•  H₂O as a ligand: When electron rich species donate atleast one electron pair to metal or metal cation [Generally transition metal], called ligand
  = transition metal. 
• H₂O as reducing agent (reductant):

Q2. About any electron rich species or electron deficient species following type of question arises in mind that:

• Which is strong base or weak base / more basic or less basic
  Which is most stable anion or less stable anion (if base is anionic)
  Which one is most reactive base or less reactive base
  Which base will form major product and which base will form minor product

Now how will we give the answer: Electronic Effect

• The answer of all question in organic chemistry arises in the mind can be achieved by the study o f electronic factors/ effects or parameters:
• For the comparison between any electrons rich species or electron deficient species for example basicity or nucleophilicity etc. there is a need of some electronic factors, which will decide.

1. Primary Effects

(a) Electro negativity of atom (Pauling scale)

(b) % S of character

(c) Size of atom

2.  Secondary Effects

•  When primary factors become equal then we consider secondary factors.

Inductive Effect: In a covalent single bond between unlike atoms, the electron pair forming the s bond is never shared absolutely equally between the two atoms; it tends to be attracted a little more towards the more electronegative atom of the two.

Non-polar covalent bond (no inductive effect)
Polar covalent bond (-I effect by Cl)
Polar covalent bond  (+I effect by O^–)

Thus in an alkyl chloride, the electron density tends to be greater nearer chlorine than carbon, as the former is the more electronegative; this is generally represented.

If the carbon atom bonded to chlorine is itself attached of further carbon atoms, the effect can be transmitted further.

Polarization of one bond caused by the polarization of an adjacent bond is known as an inductive effect.

Functional groups can be classified as electron withdrawing (–I) or electron donating (+I) groups relative to hydrogen. This means, for example, that NO₂, a –I group, will draw electrons to itself more than a hydrogen atom would if it occupied the same position in the molecule.

Thus, in α-nitrotoluene, the electrons in the N–C bond are farther away from the carbon atom than the electrons in the H–C bond of toluene.  Similarly, the electrons of the C–Ph bond are farther away from the ring in a-nitrotoluene than they are in toluene. Field effects are always co mparison effects. For example, compare the –I or +I effect of one group with another (usually hydrogen). Therefore, it may be said that, compared wit h hydrogen, the NO₂ group is electron withdrawing and the O^– group is electron donating or electron releasing.  However, there is no actual donating or withdrawing of electrons, but rather electron distortion or electron redistribution. While withdrawing and releasing terms are convenient to use, the terms merely represent a difference in the posit ion of electrons due to the difference in electronegativity between H and NO₂ or between H and O^–.

1. Permanent & partial shift ing of s electrons.
2. Magnitude of induct ive effect decreases with increase in distance.
3. It is followed with DNP (distance number, power)

4. 

+I group

-CH₂ - CH₃ > - CT₃ > - CD₃ > - CH₃ > - T > - D > - H

[Note: Heavier isotopes have more +I power]

- I group

 –I Power

Since θ₁ > θ​₂ that is why quaternary nitrogen (A) is more electronegative than ammonium nitrogen (B).
Therefore quaternary nitrogen (A) shows more –I effect than ammonium ion (B).
Here primary factor (electronegativity of the nitrogen atom) playing more dominating role than +I effect of alkyl group (R)

(Considering steric factor because the size of nitrogen is small) Electron withdrawing substituents (more deactivating) decreases the reactivity of the benzene ring toward electrophilic aromatic substitution reaction.