General Organic Chemistry - General Organic Chemistry, Organic Chemistry Notes - IIT JAM

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 General Organic Chemistry - General Organic Chemistry, Organic Chemistry Notes - IIT JAM
General Organic Chemistry - General Organic Chemistry, Organic Chemistry Notes - IIT JAM
General Organic Chemistry - General Organic Chemistry, Organic Chemistry Notes - IIT JAM

 

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

 General Organic Chemistry - General Organic Chemistry, Organic Chemistry Notes - IIT JAM
General Organic Chemistry - General Organic Chemistry, Organic Chemistry Notes - IIT JAM

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: General Organic Chemistry - General Organic Chemistry, Organic Chemistry Notes - IIT JAM

(2)  With complete octet and lone pair.

 General Organic Chemistry - General Organic Chemistry, Organic Chemistry Notes - IIT JAM

(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,  
General Organic Chemistry - General Organic Chemistry, Organic Chemistry Notes - IIT JAM(Gilman reagent)

(6)  Ambident nucleophiles – having two donor sites.

 General Organic Chemistry - General Organic Chemistry, Organic Chemistry Notes - IIT JAM
General Organic Chemistry - General Organic Chemistry, Organic Chemistry Notes - IIT JAM
 

All enolate are ambident ligands.

 General Organic Chemistry - General Organic Chemistry, Organic Chemistry Notes - IIT JAM

  •  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

 General Organic Chemistry - General Organic Chemistry, Organic Chemistry Notes - IIT JAM

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

 

group elements, Al3+ and General Organic Chemistry - General Organic Chemistry, Organic Chemistry Notes - IIT JAM

But General Organic Chemistry - General Organic Chemistry, Organic Chemistry Notes - IIT JAM are not electrophiles.

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

(2) Vacant d orbitals: PCl3, PCl5, SiF4, SnCl4, ZnCl2, FeCl3, (Used in Beckmann rearrangement), SO3
Zn ++ , Cu + + , Ag + , Pt + + , Fe+ + , Cr ++ + , Ni + + 

 

(3)  Atom in elemental state

 General Organic Chemistry - General Organic Chemistry, Organic Chemistry Notes - IIT JAM

(4)  Alkene having EWG.

 General Organic Chemistry - General Organic Chemistry, Organic Chemistry Notes - IIT JAM

(5)  Ketenes   General Organic Chemistry - General Organic Chemistry, Organic Chemistry Notes - IIT JAM 

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

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

 General Organic Chemistry - General Organic Chemistry, Organic Chemistry Notes - IIT JAM     General Organic Chemistry - General Organic Chemistry, Organic Chemistry Notes - IIT JAM

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

 General Organic Chemistry - General Organic Chemistry, Organic Chemistry Notes - IIT JAM

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

 General Organic Chemistry - General Organic Chemistry, Organic Chemistry Notes - IIT JAM

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

 General Organic Chemistry - General Organic Chemistry, Organic Chemistry Notes - IIT JAM

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.

                     General Organic Chemistry - General Organic Chemistry, Organic Chemistry Notes - IIT JAM
               General Organic Chemistry - General Organic Chemistry, Organic Chemistry Notes - IIT JAM
             General Organic Chemistry - General Organic Chemistry, Organic Chemistry Notes - IIT JAM

1. Primary Effects

(a) Electro negativity of atom (Pauling scale)

Bond          Electro negativity        Difference b/w electro negativity          Difference b/w pKa         pKa
C—H                  2.5                                            0.5                                                   —                             55
N—H                  3.0                                            0.5                                                    20                            35 
O—H                  3.5                                            0.5                                                    20                           15
F—H                   4.0                                            0.5                                                    20                            3

Higher the pKa value, lower the acidity and vice-versa.

 

(b) % S of character

% S of character Compound

CH3—CH

General Organic Chemistry - General Organic Chemistry, Organic Chemistry Notes - IIT JAM

Hybridization       % S character            % P Character
 

  sp3                             25                                75

  sp2                                  28                                 72

  sp2                                  33                                 67

  sp                              50                                 50 

Higher the pKa value, lower the acidity and vice-versa.

Electro negativity of carbon atom

General Organic Chemistry - General Organic Chemistry, Organic Chemistry Notes - IIT JAM

Increases

pKa value

55
 

42
 

38
 

25

(c) Size of atom

Size of atom   

General Organic Chemistry - General Organic Chemistry, Organic Chemistry Notes - IIT JAM

Size increases 

  Bond             pKa             Bond              pKa               Bond               pKa

  F—H             3                HO—H              16                H3O+                   –2

Cl—H             –7                HS—H              7                H3S+                     +2*

Br—H            –9                 HSe—H            2                  —                          —

I—H               –10               HTe—H           –3                 —                         —

*T he acidity order for the positive charge and H3O+ > H3S+ (Jerry March)

 

2.  Secondary Effects

General Organic Chemistry - General Organic Chemistry, Organic Chemistry Notes - IIT JAM
General Organic Chemistry - General Organic Chemistry, Organic Chemistry Notes - IIT JAM

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

 

Molecule                     pKa                 Primary factors        Secondary factors

H2O                               16                      Equal                           No effect

EtOH                             17                      Equal                          +I effect of Et

General Organic Chemistry - General Organic Chemistry, Organic Chemistry Notes - IIT JAM               10                      Equal                          –R effect of benzene

General Organic Chemistry - General Organic Chemistry, Organic Chemistry Notes - IIT JAM            5                         Equal                              –M effect

General Organic Chemistry - General Organic Chemistry, Organic Chemistry Notes - IIT JAM0 Equal –2 × –M


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 General Organic Chemistry - General Organic Chemistry, Organic Chemistry Notes - IIT JAM (no inductive effect)
Polar covalent bond General Organic Chemistry - General Organic Chemistry, Organic Chemistry Notes - IIT JAM(-I effect by Cl)
Polar covalent bond General Organic Chemistry - General Organic Chemistry, Organic Chemistry Notes - IIT JAM (+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.

 General Organic Chemistry - General Organic Chemistry, Organic Chemistry Notes - IIT JAM

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

 General Organic Chemistry - General Organic Chemistry, Organic Chemistry Notes - IIT JAM

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.

 General Organic Chemistry - General Organic Chemistry, Organic Chemistry Notes - IIT JAM

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 Ogroup 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. General Organic Chemistry - General Organic Chemistry, Organic Chemistry Notes - IIT JAM

 

+I group

General Organic Chemistry - General Organic Chemistry, Organic Chemistry Notes - IIT JAM
-CH2 - CH3 > - CT3 > - CD3 > - CH3 > - T > - D > - H

[Note: Heavier isotopes have more +I power]


- I group

General Organic Chemistry - General Organic Chemistry, Organic Chemistry Notes - IIT JAM


 –I Power

 General Organic Chemistry - General Organic Chemistry, Organic Chemistry Notes - IIT JAM General Organic Chemistry - General Organic Chemistry, Organic Chemistry Notes - IIT JAM

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)

General Organic Chemistry - General Organic Chemistry, Organic Chemistry Notes - IIT JAM

(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. 

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