Boiling point of Cyclohexene and 2-methylbut-1-ene

Click For Summary

Discussion Overview

The discussion revolves around the boiling points of cyclohexene and 2-methylbut-1-ene, specifically in the context of comparing their boiling points to that of water. Participants explore various factors influencing boiling points, including molecular weight, hydrogen bonding, and molecular structure.

Discussion Character

  • Debate/contested
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • One participant asserts that water has the highest boiling point due to hydrogen bonding, followed by cyclohexene and then 2-methylbut-1-ene.
  • Another participant claims that boiling point is directly proportional to molecular weight, citing the molecular weights of cyclohexene (82) and 2-methylbut-1-ene (70) to support that cyclohexene has a higher boiling point.
  • A different participant agrees with the molecular weight argument but cautions that this approach may not be reliable for comparing different types of molecules, referencing isopropyl and butene as an example.
  • Another participant discusses the impact of molecular structure, noting that branching decreases surface area and thus affects boiling points, using isopropane and butane as an example.
  • One participant suggests that while molecular weight is a straightforward method for comparison, it may not always be the most accurate due to other influencing factors.

Areas of Agreement / Disagreement

Participants express differing views on the best method for comparing boiling points, with some advocating for molecular weight while others highlight the importance of considering additional factors such as hydrogen bonding and molecular structure. No consensus is reached on a singular approach.

Contextual Notes

Participants note that the effectiveness of using molecular weight as a comparison method may depend on the specific compounds being analyzed, and that other factors like hydrogen bonding and surface area can also play significant roles.

disneychannel
Messages
48
Reaction score
0
So i just took a final and the question was

Arrange the following solvents in order of boiling point.
water 2-methylbut-1-ene cyclohexane

So the answer was Water>cyclohexene> 2-methylbut-1-ene.

I understand by the hydrogen bonding that water is definitely #1. But I can't seem to understand why cyclohexene is greater in BP. Unless I specifically know the property, I don't see how I could figure it out?
 
Chemistry news on Phys.org
Boiling point is directly proportional to the molecular weight.
So,higher the molecular weight,higher the boiling point.
Mol wt of cyclohexene=82
Mol wt of 2-methylbut-1-ene=70
Hence boiling point of cyclohexene is greater than that of 2-methylbut-1-ene.
 
Vineeth T said:
Boiling point is directly proportional to the molecular weight.
So,higher the molecular weight,higher the boiling point.

In general you are right, but there are also other effects and I would never use this approach to compare quite different molecules. Despite having identical molar mass isopropyl and butene don't have identical boiling points.
 
Hi!Borek.

In the case of iso-propane and butane, butane has higher boiling point than iso-propane.
This is because branching decreases surface area.
More the surface area more the Vander Waals' force of attraction(hence more the boiling point).

We have different approaches in comparing the boiling points of two compounds.
We can also compare boiling points with their relative tendency to form hydrogen bonds.
So for a given set of compounds we can compare using any of the above methods,but we should see which method suits the best.

In the case of cyclohexane and 2-methylbut-1-ene we cannot compare their boiling points using their relative H-bonding or by the surface area method.So the best method to compare is using their molecular weights.
 
Vineeth T said:
So the best method to compare is using their molecular weights.

It is the simplest method that can be applied, but for the reasons you have listed it is not guaranteed to work, so calling it "the best" is an exaggeration.
 

Similar threads

  • · Replies 6 ·
Replies
6
Views
4K
  • · Replies 2 ·
Replies
2
Views
3K
  • · Replies 10 ·
Replies
10
Views
24K
Replies
15
Views
3K
  • · Replies 2 ·
Replies
2
Views
44K
  • · Replies 2 ·
Replies
2
Views
3K
  • · Replies 9 ·
Replies
9
Views
2K
Replies
23
Views
3K
Replies
3
Views
2K
  • · Replies 2 ·
Replies
2
Views
7K