Which is best solvent for rotovaps

@broken_glassware Which data are you using? If the units are in kilojoules per mole . . . . convert to kilojoules per kilorgram (or per liter) and you’ll see that methanol has higher heat of evaporation per unit mass/volume.

@Rowan I think it’s due to intermolecular forces being stronger with methanol. Here is an explanation that I like. Maybe someone can correct if this seems off:

“The dominant intermolecular force in both cases is the hydrogen bonding through the OH group, this is taken to be of similar strength for both ethanol and methanol as it is localised to the hydroxyl. Methanol, being the smaller molecule, therefore has a larger proportion of its mass (over 50%) in the hydroxyl group and is more polar. Therefore it experiences stronger overall intermolecular electrostatic forces as a function of its mass.”
-https://www.quora.com/What-has-a-higher-IMF-methanol-or-ethanol

However a carbon-carbon bond seems relatively strong to me. I’m calling for a real chemist!

4 Likes

Methanol is more polar and thus more h-bonding that jacks up the heat of vaporization. Less than ethanol but pretty close

1 Like

Ah the good old mol to volume conversion

1 Like

I’m a real chemist! I wasted 11 years of my life studying that crap. Hence not looking at volume, instead just mol values hahaha.

The extra carbon allows for more london dispersion forces (these hold molecules against other molecules), which make heavier carbon chains boil at higher temps. But the strength of hydrogen bonding is less diluted on methanol hence the effect

3 Likes