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London Dispersion, dipole-dipole and hydrogen bonds are all types of intermolecular attractions:
London dispersion: weak attractive forces caused by instantaneous dipole-induced dipole attraction. The molecule may be polar but sometimes the charge can shift to one side and cause London dispersion forces thus creating an attraction.
Dipole-dipole: Attractions between molecules that have poles.
Hydrogen bond: an extra strong dipole-dipole attraction between a hydrogen bound covalently to nitrogen, oxygen, or fluorine and another nitrogen, oxygen, or fluorine atom.
The structure of a molecule and a group of molecules is defined by these forces, and it is also defined by temperature. Water forms a ring structure when frozen.
Several species from the alcohol family are chosen to test for the effect of dipole-dipole force. They are all relatively small molecules chosen to minimize the effect of London Dispersion forces.
Propane and paraffin from the alkane family are chosen to study the effects of London Dispersion forces, due to their non-polar nature.