Why do alkanols have higher boiling points than their corresponding alkanes? (1 Viewer)

[xnerd96x]

Hi guys!

This is my first post ! yay

anyway, what i am really here to ask is why do alkanols in general have higher boiling points than their corresponding alkanes?

I know that alkanols have weak dispersion forces due to the ethyl group, and they have extensive hydrogen bonding, but would someone be able to explain the reason succinctly?

Nerdout

 

[deswa1]

Alkanes only undergo dispersion forces which are weak. Alkanols have the OH functional group which means it can also undergo much stronger hydrogen bonding.

The stronger the intermolecular bonds, the more energy is required to break them -> higher MP/BP

 

[Galapagos]

Alkanes only undergo dispersion forces which are weak. Alkanols have the OH functional group which means it can also undergo much stronger hydrogen bonding.

The stronger the intermolecular bonds, the more energy is required to break them -> higher MP/BP

+1 this is a good summary

 

[xnerd96x]

Thanks guys for the quick response, but just wondering, even as ethanol can form strong hydrogen bonding, so more energy is required to break its bonds, if we were to take one molecule of ethanol and an alkane by itself

(so it hasn't formed bonds or attracitve forces with another molecule), then how do we explain it?

 

[2xL]

Thanks guys for the quick response, but just wondering, even as ethanol can form strong hydrogen bonding, so more energy is required to break its bonds, if we were to take one molecule of ethanol and an alkane by itself

(so it hasn't formed bonds or attracitve forces with another molecule), then how do we explain it?

Lol how would you boil one molecule of that substance is the question..totally out of context imo and won't be assessed.

 

[jkerr138]

This is my response, hopefully it answers your question.
1) Why do alkane and alcohols have different boiling points for the same numbers of carbons.
Alkanes have a different boiling points compared to alcohols due to the alkanes not being associated with Hydrogen bonding. The alkanes are made up of singular covalent bonds which don’t have hydrogen bonds, which results in a low boiling point whereas alcohols have a hydroxide ion which forms into a hydroxyl group leading to a higher electronegativity between oxygen and hydrogen compared to carbon and hydrogen.

Carbon and hydrogen have very similar electro negativities resulting in them being nonpolar. This will result in the hydroxide ion bonding with other hydrogen’s leading to stronger forces to break those bonds, which results in different boiling points between alkanes and alcohols.

Another factor is that alkanes do not have a polar group, which means that the alkane’s only intermolecular force is dispersion forces, where as alcohol groups have a hydroxide group which means that the forces are hydrogen bonding.

Since Alkanes don’t have hydrogen bonding, and only dispersion forces, there isn’t as much energy required to break those bonds, compared to alcohols as alcohols have hydrogen bonding, which is stronger than dispersion forces in the specification of breaking those bonds. The amount of electrons within the alkane compound determines how much energy is required to break these bonds. This is also another reason as to the differences in the boiling point between alkanes and alcohol.


Josh Kerr

 

[QZP]

This is my response, hopefully it answers your question.
1) Why do alkane and alcohols have different boiling points for the same numbers of carbons.
Alkanes have a different boiling points compared to alcohols due to the alkanes not being associated with Hydrogen bonding. Poor leading sentence. Start with what determines MP/BP. The alkanes are made up of singular covalent bonds which don’t have hydrogen bonds, which results in a low boiling pointwhy? whereas alcohols have a hydroxide ion which forms into a hydroxyl group leading to a higher electronegativity between oxygen and hydrogen compared to carbon and hydrogen.a hydroxyl group does not "lead" to the a "higher" electronegativity (which is also incorrect - greater difference in electronegativity*)

Carbon and hydrogen have very similar electro negativities resulting in them being nonpolar. This will result in the hydroxide ion bonding with other hydrogen’s leading to stronger forces to break those bonds, which results in different boiling points between alkanes and alcohols. Overall this was confusing. Are you saying the hydroxyl group detaches to form a hydroxide ion which then reacts with hydrogen? To form what - H2O? Also, BP/MP does not relate to the energy required to break covalent bonds but rather intermolecular bonds

Another factor sounds like the same thing to me is that alkanes do not have a polar group, which means that the alkane’s only intermolecular force is dispersion forces, where as alcohol groups have a hydroxide group which means that the forces are hydrogen bonding.

Since Alkanes don’t have hydrogen bonding, and only dispersion forces, there isn’t as much energy required to break those bonds, compared to alcohols as alcohols have hydrogen bonding, which is stronger than dispersion forces in the specification of breaking those bonds. The amount of electrons within the alkane compound determines how much energy is required to break these bonds.careful here. other factors are involved in the strength of dispersion forces including shape of molecule. Also I believe its incorrect to refer to them as bonds This is also another reason as to the differences in the boiling point between alkanes and alcohol.unecessary repetition


Josh Kerr

you revived an ancient thread btw

 

[iloveschool1996]

that is such a decent response

 

[someth1ng]

Wow, that was a bad response - so much wrong...