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C−H ··· O Interactions as Isofunctional Replacements for N−H···O Interactions − Dimer Formation of Methyl 5‐Amidopyrrole‐2‐carboxylates in the Solid State
Author(s) -
Schmuck Carsten,
Lex Johann
Publication year - 2001
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/1099-0690(200104)2001:8<1519::aid-ejoc1519>3.0.co;2-2
Subject(s) - hydrogen bond , chemistry , dimer , supramolecular chemistry , crystallography , pyridinium , carboxylate , pyrrole , chloride , stereochemistry , crystal structure , molecule , medicinal chemistry , organic chemistry
In the solid state, the chloride salt of methyl 5‐amidopyridinium‐pyrrole‐2‐carboxylate ( 2 ) forms discrete dimers held together by two rather long N−H ··· O hydrogen bonds in combination with two short C−H ··· O interactions between the pyridinium C3−H and the ester CO. Structural and thermodynamic evidence is presented which demonstrates that the observed C−H ··· O hydrogen bonds are indeed important for bonding in these dimers. A comparison with the solid‐state structure of the chloride salt of 5‐(guanidiniocarbonyl)pyrrole‐2‐carboxylic acid ( 3 ), which forms similar dimers to 2 , reveals that the binding geometries for the two C−H ··· O contacts in 2·2 are identical to those of two N + −H ··· O hydrogen bonds in 3·3 . According to theoretical calculations the energy associated with these two C−H ··· O interactions is also similar to that of the two N + −H ··· O hydrogen bonds as both dimers 2·2 and 3·3 have nearly the same calculated interaction energies. Dimer 3·3 is predicted to be only slightly more stable than 2·2 . These data demonstrate that C−H ··· O interactions can serve as full isofunctional replacements for more conventional N−H ··· O hydrogen bonds in supramolecular arrangements.