Question

Is dipole dipole force and hydrogen bond same?if yes how

Answer 1

They have some similarities, and you will find some instructors arguing H-bonding can just be regarded as quite strong dipolar attractions, of the partial negative charge on the oxygen for the partial positive charge on a hydrogen bonded to an electronegative atom.

This is not strictly speaking correct, however. The H-bond is a true chemical bond, with the proton binding two electronegative atoms together in the same way an electron binds two positive nuclei together in a covalent bond. The lightness of the proton is crucial, as it gives a strong quantum mechanical aspect to the H-bond. You can see the quantum mechanical nature by the fact that H-bonding is saturable, like a normal bond, and quite unlike classical dipole-dipole forces. Furthermore, it can be shown, through detailed calculations, that the proton is delocalized between the two oxygen atoms.

That is, if you have a water molecule with two lone pairs on the oxygen, it can form two and ONLY two H-bonds, just as a carbon atom can form four and ONLY four covalent bonds. This is what I mean by "saturation" -- when you reach the limit, you can't add any more bonds. The situation is quite different for classical interactions, like dipole-dipole interactions. These never saturate. If you have a dipolar water molecule attracted to another dipolar molecule, e.g. ammonia, then there is no limit to the number of molecules that can interact, aside from finding enough space for them all to crowd together. You can have 1 H2O and 1 NH3, or 1 and 2, or 1 and 5, or 1 and 12. There's no point at which the attraction saturates and gets cut off.

This is how it really is, but you'll have to also be guided by your instructor, who may want you to classify H-bonding as a dipole interaction.