INDUCTIVE EFFECT:- ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯ Definition:- ¯¯¯¯¯¯¯¯¯¯ The polarization of a σ bond due to electron withdrawing or electron donating effect of adjacent groups or atoms is called inductive effect. ...See More Photo: INDUCTIVE EFFECT:- ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯ Definition:- ¯¯¯¯¯¯¯¯¯¯ The polarization of a σ bond due to electron withdrawing or electron donating effect of adjacent groups or atoms is called inductive effect. The features of inductive effect :- ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯ 1. It arises due to electronegativity difference between two atoms forming a sigma bond and is transmitted through the sigma bonds. 2. The magnitude of the inductive effect decreases while moving away from the groups causing it. 3. It is a permanent effect and influences the chemical and physical properties of compounds. Examples:- ¯¯¯¯¯¯¯¯¯¯ The C-Cl bond in the butyl chloride, CH3-CH2-CH2-CH2-Cl is polarized due to electronegativity difference. The electrons are withdrawn by the chlorine atom. Thus the first carbon atom gets partial positive charge. Then, this carbon atom drags electron density partially from the next carbon, which also gets partial positive charge. Thus the inductive effect is transmitted through the carbon chain. However the inductive effect is weakened through the way its going on. Usually beyond 3rd C, the effect is not significant. The way how the inductive effect is transmitted:- ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯ CH3→CH2→CH2→CH2→Cl Types of Inductive effect:- ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯ This classification is done depending on their strength of electron withdrawing or electron releasing nature with respect to hydrogen and there is two types. 1. Negative Inductive Effect or -I effect 2. Positive Inductive Effect or +I effect. 1) Negative inductive effect (-I):- ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯ The electron withdrawing nature of groups or atoms is called as negative inductive effect. The groups in the decreasing order of their -I effect: NH3+ > NO2 > CN > SO3H > CHO > CO > COOH > COCl > CONH2 > F > Cl > Br > I > OH > OR > NH2 > C6H5 > H 2) Positive inductive effect (+I):- ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯ The electron releasing nature of the groups or atoms is called positive Inductive effect. The groups in the decreasing order of their +I effect. C(CH3)3 > CH(CH3)2 > CH2CH3 > CH3 > H Why alkyl groups are showing positive inductive effect? `````H `````↓ ``H→C→ `````↑ `````H C-H bond is partial + charge is on H and - charge on C. Therefore each H act as electron donating groups. Hence the alkyl group is electron donating. Applications and consequences of Inductive effect:- ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯ 1. Stability of carbonium ions:- The stability of carbonium ions increases with increase in number of alkyl groups due to their +I effect. The alkyl groups release electrons to carbon, bearing positive charge and thus stabilizes the ion. The order of increasing stability is: 3° > 2° > 1° > methyl 2. Stability of free radicals:- Like C+, the stability of free radicals increases with increase in the number of alkyl groups. Thus the stability of different free radicals is as that of C+:- 3° > 2° > 1° > methyl 3. Stability of carbanions:- The electron donating alkyl groups destabilize the carbanions by increasing the electron density hence the stability of carbanions decreases with increase in the number of alkyl groups. Thus the order of stability of carbanions is that of reverse of C+:- 3° < 2° < 1° < methyl 4. Another useful approach is acidic strength of Carboxilic acids and phenols and basic strength of amines. I. Acidic strength of carboxylic acids and phenols:- The electron withdrawing groups (-I) decrease the negative charge on the carboxylate ion and thus by stabilizing it. Hence the acidic strength increases when -I groups are present. But the +I groups decrease the acidic strength. II.Basic strength of amines:- The electron donating groups increase the basic strength of amines whereas the electron withdrawing groups decrease the basic nature. The order of basic strength of alkyl and aryl amines with respect to ammonia is :- CH3NH2 > NH3 > C6H5NH2 5. Reactivity of carbonyl compounds:- The +I groups increase the electron density at carbonyl carbon. Hence their reactivity towards nucleophiles decreases. Therefore formaldehyde is more reactive than acetaldehyde and acetone towards nucleophilic addition reactions. ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯
Posted on: Sat, 27 Jul 2013 11:38:33 +0000
Trending Topics
Recently Viewed Topics
© 2015