What has a higher melting/boiling point Aldehyde or Ketone?

Watch
adam32900
Badges: 0
Rep:
?
#1
Report Thread starter 3 years ago
#1
If two molecules (one an aldehyde one a ketone) of similar Mr are compared which would have a higher boiling point and why?
0
reply
TSR Jessica
Badges: 19
Rep:
?
#2
Report 3 years ago
#2
Sorry you've not had any responses about this. Are you sure you've posted in the right place? Here's a link to our subject forum which should help get you more responses if you post there.


Just quoting in Danny Dorito so she can move the thread if needed :wizard:
Spoiler:
Show
(Original post by Danny Dorito)
x
0
reply
R T
Badges: 13
Rep:
?
#3
Report 3 years ago
#3
(Original post by adam32900)
If two molecules (one an aldehyde one a ketone) of similar Mr are compared which would have a higher boiling point and why?
I doubt there is any consistent trend in BP when you compare the two.

Perhaps ketone's may have a slightly higher BP for low-Mr compounds. This is because the intermolecular forces are mostly made up of the polar interactions between C=O groups of different molecules. Ketone's have alkyl donating groups on both sides of the C=O bond (aldehydes only have one) and so its dipole will be greater, making the polar interaction stronger, the intermolecular force stronger, and the boiling point higher.

However obviously larger compounds will run into complications from london dispersion forces and steric effects preventing polar interactions in certain setups (ketones suffering more than aldehydes for sure). So long term I doubt there will be any simple trend that can easily be explained without a lot of detail.
0
reply
charco
Badges: 17
Rep:
?
#4
Report 3 years ago
#4
(Original post by Oli.Cich)
Ketones have a higher boiling points than aldehydes (with a similar Mr). This is because, with ketones, there are two alkyl groups around the C=O bond which donate electrons, making ketones more polar than aldehydes.
This has to be incorrect.

We know that aldehydes are more reactive than ketones as there is only one alkyl group inducing electrons towards the partially positive carbonyl carbon. This makes the aldehyde MORE polarised than the ketone (stabilised by two alkyl groups).

The variation in bp of ketones and aldehydes with similar Mr is not a general phenomenon. The lower members has ketones with higher bp and the higher members have aldehydes with higher bp.

pentanal and pentanone both have the same bp (102ºC)
0
reply
X

Quick Reply

Attached files
Write a reply...
Reply
new posts
Back
to top
Latest
My Feed

See more of what you like on
The Student Room

You can personalise what you see on TSR. Tell us a little about yourself to get started.

Personalise

With no certainty that exams next year will take place, how does this make you feel?

More motivated (86)
31.62%
Less motivated (186)
68.38%

Watched Threads

View All