How does molecular geometry affect the melting point of an organic compound?
The molecular geometry determines how stable the compound is in its solid form.
This is directly related to physical properties (density, molecular weight, etc) of the substance, the compound's structure (polar, nonpolar compounds), and the resulting intermolecular forces in between the compounds
In the solid phase, intermolecular forces of the compound are strong enough to maintain a crystalline shape. There are several different geometries for crystal structures, and depending on the substance's properties, it will form a different type of crystal
Some forms may be more or less stable than others. More stable crystal structures will require higher temperatures to melt in order to overcome the thermodynamic stability in its structure (ie: more heat needed to break apart the intermolecular forces).