[Treebeard]

I am a bit curious as to the difference between different solvents. I feel I understand the basic concept of a polar and a non-polar solvent, but what exactly is a dipolar solvent. I know that in some instances non polar solvents can be substituted (lingroin for petroleum ether etc.)
Can you substitute one dipolar for another?

For that matter, other than trial and error is there a property (molecular weight, boiling point) that can be checked to see if two solvents are likely to be interchangeable. I know about the lingroin/ petrol ether example because they are both distillates of crude oil.

[Phlogiston]

I am a bit curious as to the difference between different solvents. I feel I understand the basic concept of a polar and a non-polar solvent, but what exactly is a dipolar solvent. I know that in some instances non polar solvents can be substituted (lingroin for petroleum ether etc.)
Can you substitute one dipolar for another?

For that matter, other than trial and error is there a property (molecular weight, boiling point) that can be checked to see if two solvents are likely to be interchangeable. I know about the lingroin/ petrol ether example because they are both distillates of crude oil.

Interchangeability depends on the application.  As for dipolar solvents, they are a sub-set of all polar solvents, those that have a dipole.  An example would be water, which has a dipole.  An example of a polar, yet non-dipolar solvent, would be carbon dioxide- although it has a quadrupole moment, it has no dipole moment and is thus not dipolar.

In more general terms, I would venture to say that "polar solvent" and "dipolar solvent" are used somewhat interchangeably within chemistry.