[maakii]

Hi everyone,

I just did a lab experiment where I had to separate a mixture of o-vanillin (http://en.wikipedia.org/wiki/Ortho-Vanillin) and vanillin (http://en.wikipedia.org/wiki/Vanillin) in water using steam distillation. o-vanillin distilled out with water first, and so it should be more volatile and less polar. Also, it has a lower boiling point of 265oC compared to vanillin which has a boiling point of 285oC.

However, we also did a TLC of vanillin vs o-vanillin in 3:1 hexanes:EA. And on the TLC plates, we saw that vanillin moved up higher on the TLC plate as compared to o-vanillin (it basically smeared up the plate more than o-vanillin). This seems to prove that vanillin is less polar than o-vanillin. Therefore we seem to have a contradiction.

Can anyone help explain why this might be so? Thank you in advance!

[sjb]

Hi everyone,

I just did a lab experiment where I had to separate a mixture of o-vanillin (http://en.wikipedia.org/wiki/Ortho-Vanillin) and vanillin (http://en.wikipedia.org/wiki/Vanillin) in water using steam distillation. o-vanillin distilled out with water first, and so it should be more volatile and less polar. Also, it has a lower boiling point of 265oC compared to vanillin which has a boiling point of 285oC.

However, we also did a TLC of vanillin vs o-vanillin in 3:1 hexanes:EA. And on the TLC plates, we saw that vanillin moved up higher on the TLC plate as compared to o-vanillin (it basically smeared up the plate more than o-vanillin). This seems to prove that vanillin is less polar than o-vanillin. Therefore we seem to have a contradiction.

Can anyone help explain why this might be so? Thank you in advance!

Why do you think boiling point and polarity are positively correlated? Do you feel, for instance that candle wax is more polar than water?

[maakii]

Hmm, I think I get what you mean. Water has significant hydrogen bonding which candle wax does not. o-vanillin has more intra-molecular hydrogen bonding which leads to lower boiling points, am I right?

Does the intra-molecular hydrogen bonding argument apply to TLC retention as well? Since if the o-vanillin has intra-molecular hydrogen bonding, would it not be retained less by the silica since it interacts less with it? Thanks!

[rickydun]

Hi everyone,

I just did a lab experiment where I had to separate a mixture of o-vanillin (http://en.wikipedia.org/wiki/Ortho-Vanillin) and vanillin (http://en.wikipedia.org/wiki/Vanillin) in water using steam distillation. o-vanillin distilled out with water first, and so it should be more volatile and less polar. Also, it has a lower boiling point of 265oC compared to vanillin which has a boiling point of 285oC.

However, we also did a TLC of vanillin vs o-vanillin in 3:1 hexanes:EA. And on the TLC plates, we saw that vanillin moved up higher on the TLC plate as compared to o-vanillin (it basically smeared up the plate more than o-vanillin). This seems to prove that vanillin is less polar than o-vanillin. Therefore we seem to have a contradiction.

Can anyone help explain why this might be so? Thank you in advance!

are you imperial student??

[Grundalizer]

Higher boiling points mean MORE intermolecular forces, because the molecules are "holding on to each other" more, making it harder for them to enter the gas phase.

In this case, if you say o-vanilin boils at a lower temperature, then it is less polar than vanilin.

TLC plates don't directly translate into boiling point info.  Was it a silica gel or alum plate?  I'm guessing silca gel.

Your solvent was hexane and ethyl acetate?  In that case, the solvent was more non-polar than it was polar.  Smearing can be due to impurities, too high of a concentration in your beginning dots, or a stronger affinity to the solid face (silica gel) than to the solvent.  People usually mess with concentrations of the solvent a lot before they find one that works well, so remember that on the TLC Plate you dont only have intermolecular forces at play, you have affinity to solid phase, liquid phase, and affinity to itself--so a lot more going on

How many times did you run the plate?  Should always run at least 2 or 3 plates to rule out abnormalities.

[Muyonaise]

I'm guessing you are an imperial student.
I ran that TLC 3 times and got messed up results each time. I've been told that the solvent we used for the TLC was wrong which is why we got such contradictory answers.

[Muyonaise]

are you Kai Ma Btw?

[Grundalizer]

No I'm not Kai Ma, and I'm a student in the USA.  Try a different solvent..like 7:1 toluene/ ethanol