Hydrogen Bonding PDF

 DEFINITIO N: The hydrogen bond is a special type of dipole-dipole interaction between the hydrogen atom in polar bond such as N-H,O-H,F-H and electronegative atom O,N, or F atom. This interaction is written as A-H…..B or A-H…..A, where A and B represents...

 DEFINITIO N: The hydrogen bond is a special type of dipole-dipole interaction between the hydrogen atom in polar bond such as N-H,O-H,F-H and electronegative atom O,N, or F atom. This interaction is written as A-H…..B or A-H…..A, where A and B represents O,N or F atom. A-H is one molecule or part of a molecule and B is a part of another molecule while dotted line represents the hydrogen bond. These three atoms lie along a straight line, but angle AHB or AHA can deviate as much as 3 0̊̊ from linearity e.g hydrogen bonding in NH3, H2O and HF. STRENGTH OF HYDROGEN BOND The strength of hydrogen bond vary between 8 and 42KJ/mol, where the normal bond energy is in the order of 200 to 400 KJ/mol. The strength of hydrogen bond is weaker than covalent bond and its strength depends upon electronegative atom. Larger the electronegativity value, greater is the strength of hydrogen bond. BOND BOND STRENGTH KJ/mol 4 2 3 0 1 2. Effect on water solubility: A hydrogen bonded substance is generally soluble in another hydrogen bonded substance For example: alcohol are soluble in water but alkanes are not. This is because nonpolar alkane molecule cannot break into the hydrogen bonded sequence of water. It cannot replace the hydrogen bonds that would have to be broken to let it in. An alcohol molecule is capable of hydrogen bonding. It can slip in the hydrogen bonded sequence in water. It can replace the hydrogen bonds that must be broken to let it in. Alcohols of lower molecular weight are soluble but as the hydrophobic carbon change length increases solubility decreases sharply. Polar alcohol slips into hydrogen bonded sequence in water THE END