EASY
11th Tamil Nadu Board
IMPORTANT
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Which of the following species does not acts as a nucleophile?

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Important Points to Remember in Chapter -1 - Basic Concepts of Organic Reactions from Tamil Nadu Board Chemistry Standard 11 Vol II Solutions

1. Cleavage of covalent bond

All organic molecules contain covalent bonds which are formed by the mutual sharing of electrons between atoms. These covalent bonds break in two different ways, namely homolytic cleavage (symmetrical splitting) and heterolytic cleavage (unsymmetrical splitting).

2. Inductive effect:

(i) –I Effects of certain groups follow the order :

—NO2>—CN>—COOH>—F>—Cl>—Br>—I>—OH>—C6H5>—H

(ii) + I Effects of certain alkyl groups follow the order :

CH33C—>CH32CH—>CH3CH2—>CH3—>—H

3. Electromeric Effect:

(i) Electromeric Effect is a temporary effect which operates in unsaturated compounds in the presence of an attacking reagent.

(ii) Inductive effect is a permanent effect while electromeric effect is temporary in nature.

4. Resonance:

Certain organic compounds can be represented by more than one structure and they differ only in the position of bonding and lone pair of electrons. Such structures are called resonance structures (canonical structures) and this phenomenon is called resonance. This phenomenon is also called mesomerism or mesomeric effect.

5. Hyperconjugation

Hyperconjugation is noticed in those species which have atleast one α-hydrogen atom.

6. Reaction intermediates:

(i) Carbocation is planar (sp2 hybridised). The relative order of the stabilities of carbocations is: C6H53C⊕>C6H52C⊕H>C6H5C⊕H2>CH33C⊕>CH32C⊕H>CH3C⊕H2>C⊕H3

(ii) Carbanion is pyramidal (sp3 hybridised). The relative order of the stabilities of carbanions is : C6H53C⊕<C6H52C⊕H<C6H5C⊕H2    <C⊕H3<CH3C⊕H2<CH32C⊕H<CH33C⊕

(iii) Free radical is nearly planar (sp2 hybridised). The relative order of stabilities of free radicals is : C6H53C•>C6H5C•H2>CH33C•>CH32C•H>CH3C•H2>C•H3

(iv) Electrophiles are positively charged or electron deficient species.

(v) Nucleophiles are negatively charged or electron rich species.

7. Types of organic reactions:

Different types of organic reactions are substitution reactions, addition reactions, elimination reactions, oxidation and reduction reactions and rearrangement reactions.