Hydrogen bonding involves electron cloud transfer from hydrogen atom to the neighbouring electronegative atom and occurs in any system containing a proton donor group (X-H; OH, COOH, CONH2 ) and a proton acceptor provided the s-orbital of the proton can effectively overlap the p or pi orbital of the acceptor group. The strength of the hydrogen bond is at a maximum when the proton donor group and axis of lone pair orbital are collinear and is inversely proportional to the distance between X and Y.
When hydrogen is bonded to one of the highly electronegative atoms such as florine, oxygen, or nitrogen the shared pair of electrons of the covalent bond moves towards the more electronegative atom and the bond becomes considerable polar with the hydrogen atom carrying a partial positive charge and more electronegative atom carrying a partial negative charge.
When such molecule come closure , dipole-dipole attraction weakly binds the molecules together through hydrogen and is known as <b>hydrogen bonding</b>
<b>Classification of Hydrogen Bonding:-</b>
<b>1. Intermolecular Hydrogen Bonding :- </b> Intermolecular hydrogen bonding resulting in association of two or more molecule of the same or different compounds is known as intermolecular hydrogen bonding. Example of this is , the hydrogen bonding in water, alcohols and carboxylic acid is intermolecular .
<b>2. Intramolecular Hydrogen Bonding :-</b> Intramolecular hydrogen bond is formed between two atoms of the same molecule. Result of a five or six membered ring known as chelate ring, is formed.
Intramolecular hydrogen bonding occurs in o-Hydroxycorbonyl compounds, salicylic. And also in o-dihydroxybenzene and o-nitrophenol etc.
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