While nucleophiles donate two electrons in exchange for forming two-electron covalent bonds with the electrophiles, the negative charge due to the two electrons is not obvious in many instances. Neutral molecules like Benzene, water, and ammonia can act as nucleophiles.
A broad way to categorize nucleophiles is as charged or neutral (uncharged).
Dipole-dipole interactions occur in polar molecules where the difference in electronegativity between the combining atoms creates positive and negative dipoles. These opposite poles align and result in electrostatic attraction throughout the polar medium. So, naturally, the strength of the interaction would depend on the magnitude of the charges and their distance, explained by the Coulombic law. So, the higher the magnitude of the charges and the lesser the distance between them, the stronger the dipole-dipole attractive interaction.
An important thing about an atom is that it is made of three main components- protons, neutrons, and electrons.
Polar molecules show Keesom forces. Polar molecules have heteroatoms that differ in electronegativity values such that the electronegativity difference between the two atoms in a polar covalent bond is greater than 0.5 but less than 1.7. For example, HF, HCl, R-OH, etc.
The +I effect is an electron-donating (or an electron-pushing) inductive effect by an atom or group of atoms relative to Hydrogen. It means that a +I group like methyl (-CH3) will push electrons away from itself more than the hydrogen atom would if it occupied the exact position in the molecule.
The push of electrons is represented with an arrow over the bond, (>) indicating the direction of the electron flow.
If a two-electron covalent bond breaks symmetrically, each of the two atoms receive one electron; it is a homolytic bond cleavage.
A homolytic cleavage is shown using a fish-hook arrow, which implies one-electron movement.
The atoms or group of atoms are classified based on the Inductive effect as electron-withdrawing (-I) or electron-donating (+I) relative to Hydrogen.
The common functional groups showing +I and -I effect are:
+I group | -I group |
|---|---|
O- |
Pre-Requisite Reading: Nucleophiles, Electrophiles
Debye interactions require polar molecules to show polar-nonpolar type of intermolecular attractive interactions. Therefore, the polar atoms participating in Debye interactions must have comparatively high electronegativity to show stronger interactions. If the electronegativity difference (0.5-1.7) is greater in a polar molecule, the polarity it induces on the neighboring non-polar atom will also be more significant, leading to stronger Debye interactions.
Debye intermolecular forces of attraction occur between polar and nonpolar atoms or molecules.
When a polar molecule is in the vicinity of a nonpolar molecule, the electronegative end of that polar molecule attracts the electron cloud of the adjacent nonpolar molecule, thereby distorting it and inducing a pole separation. So, the polar molecule is said to have induced polarity in the neighboring nonpolar molecule.