Melting and boiling points

[Neodymium]

Hello, beautiful people,

I am presently comparing the melting points and the boiling points of a series of cycloalkanes and their isomers. Attached (below) are the figures representing two graphs:

1) Comparison of melting points between a series of cycloalkanes and their isomers;

2) Comparison of boiling points between a series of cycloalkanes and their isomers.

The x-axis represents the number of carbon atoms on the molecule whereas the y-axis represents the temperature (m.p. or b.p.) in degrees Celsius. I have observed from the graphs that the temperature (m.p. and b.p.) of the isomer series tend to be lower than the series of cycloalkanes. Also, the temperature (m.p. or b.p.) tend to increase with the number of atoms in the molecule.

The molecules of interest are, for the series of cycloalkanes, cyclopropane (3 carb atoms), cyclobutane (4), cyclopentane (5), cyclohexane (6), cycloheptane (7), cyclooctane (8), cyclononane (9) and cyclodecane (10). As for the isomer series, they are propene (3), 1-butene (4), 1-pentene (5), 1-hexene (6), 1-heptene (7), 1-octene (8), 1-nonene (9) and 1-decene (10). 

I also observe that the difference, for the melting points, between the two series is far greater than for the boiling points (The y and x-axis have the same graduations). I cannot explain this phenomenon. Can anyone help me advance hypothesis of enlighten me with theories that might explain this? 

Thank you very much.

Neo60

OP/N: I apologize in advance for any English mistakes in the post, as it is my third language, as well as for the graphs, that are in French. Also, I have just finished 12th grade, so if you would use advanced theory to support a hypothesis for the phenomenon I have observed above, please, explain it as you would to a student who haven't had his or her first Organic Chem's class, yet.

 

 

 

 

Edited August 16, 2017 by Neodymium
The order of the graph, as firstly submitted, was wrong and the list of molecules of interest were later added.

[studiot]

Look at the bonding in the solid phase.

Can cycloalkanes form covalent or ionic crystals?

[Neodymium]

3 hours ago, studiot said:

Look at the bonding in the solid phase.

Can cycloalkanes form covalent or ionic crystals?

Thank you for your reply. I believe the bonding is covalent, since the atoms of the molecules (C and H) have a small difference of  electronegativity.

The two series also have a difference in van der Waals interactions forces (stronger in the cycloalkanes series than in the isomer series), explaining, I believe, why the temperatures (m.p. and b.p.) of the cycloalkanes (blue trendline) are higher than that of the isomer series (orange trendline). Please correct me if I am wrong.

Still, I don't understand how the bonding in the solid phase can explain the difference in gap between the two trendlines.  

[studiot]

I assume this is homework/coursework.

Did you look up bonding in solid (cyclo) alkanes?

How do you think covalent bonding would work?

There's plenty about.

http://www.chemguide.co.uk/organicprops/alkanes/background.html

The solid to liquid transition is breaking the bonds of a regular array of some sort.

The liquid to gas transition is simply freeing nearly non polarised molecules from short term random liasons.

Edited August 16, 2017 by studiot