Page 3 - Microsoft Word - LN on Organic Chemistry

Isomers differ by the arrangement of atoms or groups around the C=C double bond.
Cis: The isomer having similar groups on the same side of the double bonded carbon.
Trans: The isomer having similar groups on opposite side of double bonded carbon.
Electron displacement in Organic compounds:
It is the shifting of covalent bonds in presence of an atom or group. It is of 4 types.
1. Inductive effect: It is the permanent shifting of electron pair towards more
electronegative atom or group in a carbon chain. It is of 2 types.
- I effect: If an atom or group which is more electronegative than carbon is
attached, it will attract electron pair towards itself. This is called -I effect.
The decreasing order of -I effecting groups are:

-NR3 > -NO2 > -CN > -COOH > -CHO > C=O > F > Cl > Br > I > -OC6H5 > -OR > -OH > -C6H5

+ I effect: If an atom or group which is less electronegative than carbon is
attached, carbon will attract electron pair towards itself. It is called +I effect.
The +I effecting groups are: (CH3)3C- > (CH3)2CH- > CH3CH2- > CH3- > D > H
2. Electromeric effect: It is the complete transfer of shared pair of electrons
towards one of atoms joined by multiple bonds in presence of attacking reagent.
+ E effect: Transfer of electrons takes place towards the attacking reagent.
- E effect: Transfer of electrons takes place away from the attacking reagent.
3. Resonance effect:
It is the shifting of pi bonds from one part to another in a conjugated pi system.
+R effect: Transfer of electrons is away from the atom or group. It takes place
when electron donating group is attached to the conjugated pi system.
The +R effecting groups are: -OH, -OR, -SH, -SR, -NH2, -NHR, -NR2, -Cl, -Br, -I
-R effect: Transfer of electrons is towards the atom or group. It takes place when
electron withdrawing group is attached to the conjugated pi system.
The -R effecting groups are: -NO2, -CN, -COOH, -COOR, -SO3H, -CHO, C=O, -COCl.

4.Hyperconjugation: It is the shifting of α C-H bond involving delocalization of sigma
and pi bond orbitals.

Reaction Intermediates: These are short lived and highly reactive fragments
obtained by homolytic or heterolytic bond cleavage. It is of 3 types.

(i)Free radicals: It is an atom or group of atoms having an unpaired electron. It is
obtained by homolytic bond cleavage.

. . . .
Relative stabilities of free radicals: (CH3)3C > (CH3)2CH > CH3CH2 > CH3
(ii)Carbocations: It is an organic ion carrying a positive charge on carbon atom. It is
obtained by heterolytic bond cleavage.

+ + + +
Relative stabilities of carbocations: (CH3)3C > (CH3)2CH > CH3CH2 > CH3
(iii)Carbanions: It is an organic ion carrying a negative charge and one lone pair of
electrons on carbon atom. It is obtained by heterolytic bond cleavage.
- - - -
Relative stabilities of carbanions: (CH3)3C > (CH3)2CH > CH3CH2 > CH3