CCL: hydrogen bond

Dear Partha,


are you familiar with the IUPAC definition of a hydrogen bond? E.g. here:">


Based on that, it’s clear that there is indeed a POSSIBILITY of a H-bond, as you have a potential H-bond donor (N-H) and two possible acceptors (the N atoms, and the pi-electron system). However, it also seems likely that the interaction will be quite weak, to the point of the existence of a H-bond being a borderline case, likely depending on the conditions (see the footnotes in the linked pdf). 


Some quick-and-dirty calculations on my laptop (using Spartan ’20, wB97xD and a 6-31+G(d) basis set set - and yes I know there are better basis sets available but this should be good enough for the present purpose) confirm this: for the H-bond to the N atom, the distance is pretty large (H…N is almost 2.4 Å), the NHN angle is far from linear (about 129 degrees), the N-H bond length increase and vibrational redshift (compared to isolated methyl amine) are on the order of 0.002 Å and a few wavenumbers, respectively, and interaction energy is only about 20 kJ/mol (of which a lot, possibly even most, is probably just basis set superposition error due to my small basis set). 


For the H-bond to the pi-system, the distance (to the center of the ring) is even longer (almost 2.6 Å), the interaction energy is even lower (about 10 kJ/mol), the N-H bond length is identical (to 0.001 Å) to isolated methyl amine, and the frequencies are actually blueshifted by a few cm-1 (the latter may just be an artefact though). So this is likely not a H-bond at all, as per the IUPAC definition


Whether or not you want to call the first interaction (from the methyl amine NH to the pyrazine N) a H-bond really really depends on what you want to do with this information.


Best regards,

Theo Kurtén

(University of Helsinki, Finland)



From:\ <\> on behalf of Partha Sengupta <owner-chemistry/a\>
Date: Friday, 5. May 2023 at 17.15
To: Kurten, Theo C <theo.kurten/a\>
Subject: CCL: hydrogen bond

I am not interested in ChatGpt. I ask the question to be answered from a chemical point of view. I repeat the question again" Is there any possibility between the hydrogen bond formation between pyrazine and methyl amine". If there is any chance please give me the references.





Dr. Partha Sarathi Sengupta
Associate Professor
Vivekananda Mahavidyalaya, Burdwan