The effect which appears due to electronic distribution is called electronic effect.
Classification
The normal C–C bond has no polarity as two atoms of same electronegativity (EN) value are connected to each
other. Hence the bond is nonpolar
I Effect The group which withdraws electron cloud is known as – I group and its effect is called – I
effect. Various groups are listed in their decreasing – I strength as follows
Resonance is the phenomenon in which two or more structures involving in identical position of atom, can be
written for a particular species, all those possible structures are known as resonating structures or canonical
structures
Types of Conjugation
The P.E. difference between the most stable resonating structure and resonance hybride is called resonace
energy.
All the canonical forms (resonating structure) must have proper lewis structure. For instance none of them
may have a carbon atom with five bonds
Nonpolar (uncharged) structure are most stable. Charge separation decreases stability. Separating opposite
charges requires energy. Therefore, structures in which opposite charges are separated have greater energy
(lower stability) than those that have no charge separation
Mesomeric effect is defined as permanent effect of p electron shifting from multiple
bond to atom or from multiple bond to single bond or from lone pair to single bond
Positive Mesomeric effect
Negative Mesomeric effect
It is delocalisation of sigma electron with p-orbital.
Stability of Alkenes : More is the number of hyperconjugative structures more stable is the alkene.
"More alkylated alkenes are more stable
It is a temporary effect. The organic compound having a multiple bond ( double or triple
bond) show this effect in the presence of an attacking reagent only.
The following rules are useful in predicting whether a particular compound is aromatic or non–aromatic.
Comparision between electronic effects
Applications of electronic effects
Reactive, shortlived, high energy, unstable species, those are formed in the course of organic reactions are
called reaction intermediates
Definition : A carbon intermediate which contain three bond pair & a positive charge on it is called carbocation
Definition A carbon intermediate which contain three bond pair and a negative charge on it, is called carbanion
Homolysis of covalent bond results into free radical intermediates possess the unpaired electrons.
Definition : There is a group of intermediates in which carbon forms only two bonds. These neutral divalent carbon
species are called carbenes. Most carbenes are highly unstable that are capable of only fleeting existence.
Soon after carbenes are formed, they usually react with another molecules
Nitrenes
The benzene ring has one extra C – C p bond in benzyne
