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Concept
Inductive effect
Summary
In chemistry, the inductive effect in a molecule is a local change in the electron density due to electron-withdrawing or electron-donating groups elsewhere in the molecule, resulting in a permanent dipole in a bond.
It is present in a σ (sigma) bond, unlike the electromeric effect which is present in a π (pi) bond.
The halogen atoms in an alkyl halide are electron withdrawing while the alkyl groups have electron donating tendencies. If the electronegative atom (missing an electron, thus having a positive charge) is then joined to a chain of atoms, usually carbon, the positive charge is relayed to the other atoms in the chain. This is the electron-withdrawing inductive effect, also known as the -I effect. In short, alkyl groups tend to donate electrons, leading to the +I effect. Its experimental basis is the ionization constant. It is distinct from and often opposite to the mesomeric effect.
Covalent bonds can be polarized depending on the relative electronegativity of the two atoms forming the bond. The electron cloud in a σ-bond between two unlike atoms is not uniform and is slightly displaced towards the more electronegative of the two atoms. This causes a permanent state of bond polarization, where the more electronegative atoms has a fractional negative charge (δ–) and the less electronegative atom has a fractional positive charge (δ+).
For example, the water molecule has an electronegative oxygen atom that attracts a negative charge. This is indicated by δ- in the water molecule in the vicinity of the O atom, as well as by a δ+ next to each of the two H atoms. The vector addition of the individual bond dipole moments results in a net dipole moment for the molecule. A polar bond is a covalent bond in which there is a separation of charge between one end and the other - in other words in which one end is slightly positive and the other slightly negative. Examples include most covalent bonds. The hydrogen-chlorine bond in HCl or the hydrogen-oxygen bonds in water are typical.
Official source
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