What is the effect of molecular structure on molecular properties?
The molecular structure affects the molecular properties because the shape of of a molecule has a lot to do with the polarity of the compound.
Polar compounds tend to dissolve in polar compounds, have higher boiling and higher melting points and form solids or liquids.
Non polar compounds tend to dissolve in non polar compounds, have lower boiling and lower melting points and form liquids and gases.
Of course, these are generalizations and have exceptions.