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This effect is seen when groups like alkyl groups are attached to a molecule. These groups are less electron-withdrawing and tend to give electrons to the rest of the molecule. Figure 1: Inductive Effect of Different Groups. The inductive effect has a direct effect on the stability of molecules, especially organic molecules. If a carbon atom has a partial positive charge, an electron releasing group such as an alkyl group can reduce or remove this partial positive charge by providing electrons.
Then the stability of that molecule is increased. Resonance effect describes the effect on the stability of a molecule due to the interaction between pi bond electrons. Lone electron pairs can also contribute to the resonance of a molecule if there are any lone pairs present on atoms of the molecule.
The resonance effect causes the delocalization of electrons between atoms. Molecules having double bonds are involved in resonance. In order to determine the real structure of a molecule, we can use resonance structures. The real structure of a molecule is an intermediate structure obtained through resonance stabilization.
Resonance structures are not isomers of the original molecule. Figure 2: Resonance Effect in Nitrobenzene. If a particular molecule has no other resonance structures but only one structure, then it is the most stable structure in which the molecule can exist.
Resonance structures are drawn as Lewis structures. By writing all possible structures for a molecule, we can determine the most stable intermediate structure for that molecule. Inductive Effect: Inductive effect is the effect that is caused by the transmission of an electrical charge throughout a chain of atoms. Resonance Effect: Resonance effect describes the effect on the stability of a molecule due to the interaction between pi bond electrons.
Inductive Effect: The inductive effect occurs due to the polarization of bonds. Resonance Effect: Resonance effect occurs due to the presence of single bonds and double bonds together. Inductive Effect: The electronegativity values of atoms affect the degree of inductive effect. Resonance Effect: The number of double bonds and their arrangement affects the resonance effect.
Inductive effect and resonance effect are related to the distribution of electrons between atoms of molecules. A sigma bond between two atoms, which differ in their electronegativity, is polarized due to displacement of bond pair towards the more electronegative atom.
In this process, the electronegative atom gets partial negative charge while the other atom gets partial positive charge. Thus induced polarity is transmitted through the sigma bonds in the molecule by creating a permanent dipole. This phenomenon is referred to as inductive effect. It is represented by an arrow pointing towards the more electronegative atom carrying partial negative charge. The electrons are withdrawn by the chlorine atom.
Thus the first carbon atom gets partial positive charge. In turn, this carbon atom drags electron density partially from the next carbon, which also gets partial positive charge. This will continue further and is how the inductive effect is transmitted through the carbon chain. One must note that the inductive effect weakens away along the chain and is not that much significant beyond the 3rd carbon atom. Also note that inductive effect is a permanent effect and is inherent to the molecule, while the electromeric effect is a temporary effect is only created in the presence of attacking electrophilic or nucleophilic reagents.
The strength of inductive effect is measured by comparing with that of hydrogen. The electron withdrawing nature of groups or atoms is called as negative inductive effect. It is indicated by -I. Following are the examples of groups in the decreasing order of their -I effect:.
Why alkyl groups are showing positive inductive effect? Though the C-H bond is practically considered as non-polar, there is partial positive charge on hydrogen atom and partial negative charge on carbon atom. Therefore each hydrogen atom acts as electron donating group. This cumulative donation turns the alkyl moiety into an electron donating group. This results in greater stability of carbocation. Whereas, the -I groups destabilize the carbocations as they increase the positive charge by withdrawing electron density.
Note that any factor that increases the charge either negative or positive on an ion results in destabilization while any factor that reduces the charge results in stabilization of that ion. For example, the order of stability of a few carbocations containing alkyl groups is as follows:.
The tertiary carbocation containing three alkyl groups is more stable than the secondary carbocation with two alkyl groups and which in turn is more stable than the primary carbocation. Methyl carbocation is the least stable among the given. In the same way the stability of free radicals increases with increase in the number of alkyl groups.
Now the order is reversed. The tertiary carbanion is least stable while the methyl carbanion is most stable among the given. A protonic acid is always in equilibrium with its conjugate base that is formed by loss of a proton. Any factor that stabilizes the negatively charged conjugate base favors greater ionization of acid. The electron withdrawing groups showing negative inductive effect -I reduce the negative charge on the conjugate base like carboxylate ion by pulling the electron density and thus by stabilizing it.
Hence the acidic strength increases when -I groups are present. On the same lines, the acidic strength of phenols increases when -I groups are present on the ring.
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