How does molecular shape affect boiling point in organic compounds?

[staka]

In organic chemistry,

What causes a compound to be more soluble than others?
What causes a compound to have a higher boiling point than others?

I think the more molecular mass a compound has, the higher boiling point.
However, methoxymethane and ethanol both have the same molecular mass but in different shape. What causes it to have a higher boiling point?

 

[HeartSoul132]

Whichever can be broken apart easier will have a lower boiling point, I believe. Look for differences in bond strength in the molecules, e.g double-bond vs a single, etc.

 

[staka]

Methoxymethane and ethanol are both single bonded compounds.
Ethanol has OH on its own.. does it have higher or lower boiling point than methoxymethane?

 

[HeartSoul132]

Since the bonds are all single, in this case, you'll mainly want to look at Intermolecular Forces (IMF). Look for things such as differences in hydrogen bonding (H to a O,N,F - requires a lot of energy to break). (The -OH group as well)

 

[staka]

oh alright, thanks. so higher boiling point in ethanol.

 

[HeartSoul132]

I believe so, no problem.

 

[Borek]

Whichever can be broken apart easier will have a lower boiling point, I believe. Look for differences in bond strength in the molecules, e.g double-bond vs a single, etc.

Bonds and their strength have nothing to do with the boiling point! Boiling point and melting point depend on the intermolecular forces, not on the internal structure of the molecule.

Molecules are not broken apart during boiling, they are separated but intact.

 

[staka]

So which will have a higher boiling point?

 

[Borek]

Think in terms of intermolecular bonds.

What types do you know? Which are the strongest?

Why water has a very high boiling point?

 

[staka]

Oh hydrogen bonding significantly affects it.. much higher boiling point in ethanol than of methoxymethane.

 

[Borek]

Wasn't that hard.

 

[HeartSoul132]

Bonds and their strength have nothing to do with the boiling point! Boiling point and melting point depend on the intermolecular forces, not on the internal structure of the molecule.

Molecules are not broken apart during boiling, they are separated but intact.

I mentioned IMF in mypost. And according to my chemistry professor, bond strength makes a difference in boiling point as well.

 

[Borek]

according to my chemistry professor, bond strength makes a difference in boiling point as well.

Ask for examples.

 

[HeartSoul132]

Maybe prof. meant bond-strength as in dipole-dipole, hydrogen, etc.?

 

[ace123]

Dipole-Dipole moments and hydrogen bonding is a form of intermolecular force. Bond strength is between 2 atoms in a chemical bond. There is no way they can be used as synonyms.

 

[HeartSoul132]

I hear people say hydrogen bonds alone are weak, so it seems it is used that way in conversation.

 

[queenofbabes]

Well, perhaps so, but for now it's probably easier for you to distinguish between formal bonds (covalent/ionic) and intermolecular forces, lest you get confused!

 

[vishal007win]

while checking out for the factors that affect the parameter, we go for the one that has maximum effect, not towards which having least.
solubility is mainly determined by the dipole dipole interactions, hydrogen bonding.
while boiling point is more or less dependent on same parameters too.
in solubility the interactions with the solvent-solute molecules is imp.
while in boiling point its between same molecules.

 

[ace123]

Individual hydrogen bonds may be relatively weak but a larger number of such bonds is anything but weak. Have you ever seen two pieces of glass be stuck together because of water between the pieces. It is virtually impossible to lift one glass from the other without shattering the glass.