O-H..N Bonds: Can Mevlar Outperform Kevlar?

[bomba923]

(According to Wikipedia, the strongest hydrogen bonds are O—H...N bonds, occurring between a hydroxyl's hydrogen and a nearby nitrogen atom. That's when I thought of Kevlar...)[/size]

Can Mevlar* be stronger than Kevlar? (see the attached images)

(*My slight modification of the Kevlar monomer )

 

[geo_alchemist]

only experiment can tell you that. there are many factors effecting on this, not only hydrogen bond strength. but also in kevlar, hydrogen bonds are formed between oxygen and hydrogen of benzene ring. this will not happened in your Mevlar* because of steric factor.

 

[bomba923]

only experiment can tell you that. there are many factors effecting on this, not only hydrogen bond strength. but also in kevlar, hydrogen bonds are formed between oxygen and hydrogen of benzene ring. this will not happened in your Mevlar* because of steric factor.

? Mevlar* does not introduce any steric hindrance to H-bonding.

If you're referring to this image, simply replace each $$\text{O} \cdots \text{H} - \text{N}$$ with $$\text{O} - \text{H} \cdots \text{N}$$, and move the double bonds from C=O to C=N (to get Mevlar*). No H-bonds involving benzene hydrogens are affected.

Since $$\text{O} - \text{H} \cdots \text{N}$$ type H-bonds are stronger than $$\text{O} \cdots \text{H} - \text{N}$$ type H-bonds, I reason than Melvar* might be a material stronger than Kevlar.

Although only experimentation can determine that (as you said), I don't have any money and a google search of "kevlar isomers" didn't provide anything useful :( [/size]

 

[geo_alchemist]

? Mevlar* does not introduce any steric hindrance to H-bonding.

If you're referring to this image, simply replace each $$\text{O} \cdots \text{H} - \text{N}$$ with $$\text{O} - \text{H} \cdots \text{N}$$, and move the double bonds from C=O to C=N (to get Mevlar*). No H-bonds involving benzene hydrogens are affected.

Since $$\text{O} - \text{H} \cdots \text{N}$$ type H-bonds are stronger than $$\text{O} \cdots \text{H} - \text{N}$$ type H-bonds, I reason than Melvar* might be a material stronger than Kevlar.

Although only experimentation can determine that (as you said), I don't have any money and a google search of "kevlar isomers" didn't provide anything useful :( [/size]

Ok, but there is a significant difference between Kevlar and Mevlar* 3D models. In Kevlar benzene rings ar almost in the same "flat surface" (sorry about bad English) but not in Mevlar*.
so this is not simple enough to say something without experiment

 

[bomba923]

Ok, but there is a significant difference between Kevlar and Mevlar* 3D models. In Kevlar benzene rings ar almost in the same "flat surface" (sorry about bad English) but not in Mevlar*.

Actually, neither Kevlar nor Melvar* is quite as planar as your models show (see my attached 3D images; in fact, Mevlar* appears slightly more planar than Kevlar )

Secondly, the (--NH-C(O)--) in Kevlar and the (--N=C(OH)--) in Mevlar are free to rotate between the benzenes (which can rotate as well). The rotation (energy) barrier to a planar conformation would be overcome via the formation of H-bonds (in either molecule, but especially in Mevlar*)

 

[Gokul43201]

I don't see what's preventing either of the phenyl groups from rotating (ie., no reason for planarity) in both structures.

 

[geo_alchemist]

this 3D models are created by computer, not me, which calculated that kevlar is more planar ("CambridgeSoft", "chem 3D ultra"). but as I already told, experiment is the best way. ;-)

 

[3trQN]

Is spaggetti stronger than noodles?