OCHEM higher boiling point question

[joonkimdds]

choose the compound with the highest boiling point.
a) CH3CH2OCH2CH3
b) CH3CH2CH2Ch2CH3
c) CH3Ch2Ch2Ch2NH2
d) C(CH3)4
e) Ch3Ch2CH(CH3)2


when I compare alkanes; B,D,E, I think B has the higher boiling point
because B has the least branch.

Tell me if I am wrong but I think
A is dipole-dipole bond
B is covalent bond
C is H bond(dipole-dipole)

and I think the order of higher boiling point is
cation-anion > covalent bond> ion-dipole > dipole dipole
so I think answer is B, but I am not sure.

can someone please check this for me and see if I understood it correctly?

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[TheRighteous]

I think C has the highest boiling point since hydrogen bonding is a much stronger intermolecular force than that found in long carbon chains, which is Van Der Waals force.

Covalent bond is not an intermolecular force, but an intramolecular one. So, it doesn't even apply here.

 

[joonkimdds]

I think C has the highest boiling point since hydrogen bonding is a much stronger intermolecular force than covalent-covalent bonding.

actually the answer key says C is the answer too but isn't H bond also dipole dipole bond?
if then both dipole dipole and H bond should have the lowest boiling point according to

cation-anion > covalent bond> ion-dipole > dipole dipole

by the way, if it's true that H bond has higher boiling point than covalent bond, does it also have higher BP than cation-anion bonding?

 

[TheRighteous]

Sorry, I editted my answer to make it less confusing.

Covalent bonding occurs intramolecularly, not intermolecularly. The boiling point is basically the threshold when intermolecular forces are broken and the molecules go into a gaseous state.

"cation-anion > covalent bond> ion-dipole > dipole dipole "

I believe this is for intramolecular bonds, not intermolecular bonds.

 

[delsol7]

C is correct.
The strongest intermolecular bond is Hydrogen bond (H with F, O, N). Also, it doesn't have branch so it will stack up nicely to have Dispersion force too.

B is incorrect because it only has Dispersion force. Covalent bond is only within the molecule not intermolecule bonding force.

 

[joonkimdds]

C is correct.
The strongest intermolecular bond is Hydrogen bond (H with F, O, N). Also, it doesn't have branch so it will stack up nicely to have Dispersion force too.

B is incorrect because it only has Dispersion force. Covalent bond is only within the molecule not intermolecule bonding force.

why does it matter whether it's intra or inter molecular bond?
even though C-C-C-C-C-C is covalent bond within the molecule, it still has higher boiling point than ion-dipole or dipole-dipole bond that are intermolecular bond so I don't know why intra vs. inter really matters.😕

 

[TheRighteous]

why does it matter whether it's intra or inter molecular bond?
even though C-C-C-C-C-C is covalent bond within the molecule, it still has higher boiling point than ion-dipole or dipole-dipole bond that are intermolecular bond so I don't know why intra vs. inter really matters.😕

This is more related to general chemistry than organic chemistry.

Boiling is a phase change, it has nothing to do with the intramolecular bonds in the molecule. What happens in boiling is that the molecules break free from each other and go into a gaseous state. It's not like boiling pentane will yield methane, ethane, propane, or whatever. So, it is all about intermolecular bonds. Covalent bonding occurs intramolecularly, so your original post with the order of boiling point based on bonds is not quite right.

Yes, pentane has covalent bonding between carbons to carbons and carbons to hydrogens. However, in between molecules of pentane, there are only Van der Waals Forces. On the other hand, n-butylamine, which has both Van der Waals Froces and hydrogen bonding in between each molecule, has much stronger intermolecular forces.