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The Structure of 1 H ‐Perimidin‐2(3 H )‐one and Its Derivatives in the solid state (x‐ray crystallography and CP/MAS 13 C‐NMR), in solution ( 13 C‐NMR), and in the gas phase (mass spectrometry)
Author(s) -
Claramunt Rosa M.,
Dotor Julio,
Sanz Dionisia,
FocesFoces Concepción,
LlamasSaniz Antonio L.,
Elguero José,
Flammang Robert,
Morizur Jean Pierre,
Chapon Erik,
Tortajada Jeanine
Publication year - 1994
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.19940770115
Subject(s) - chemistry , tautomer , crystallography , molecule , crystal structure , planarity testing , solid state , stereochemistry , organic chemistry
The X‐ray crystal and molecular structures of 1‐methyl‐ 1 H ‐perimidin‐2(3 H )‐one ( 5b ) and 1,3‐dimethyl‐1 H ‐perimidin‐2(3 H )‐one ( 6 ) were determined. The crystals are built of piles of dimers faced head‐to‐head in 5b and of alternating independent head‐to‐tail molecules in 6 , both along the b axis. Semiempirical calculations at the AM 1 level revealed that the eclipsed conformation of the Me groups with respect to the CO group, found in the crystals, is the most stable. The lack of planarity of the whole molecules is a consequence of the packing forces since it is not found in the calculations. A comparative NMR study was carried out in solution ( 1 H and 13 C) and in the solid state (CP/MAS 13 C) for 1 H ‐perimidin‐2(3 H )‐one ( 2 ) and 1 H ‐benzimidazol‐2(3 H )‐one ( 3 ) with the conclusion that in both heterocycles the oxo tautomer is the most abundant. The structure in the gas phase was approached by mass spectrometry. In the case of 3 , the oxo tautomer loses CO after ionization, while the oxo form of 2 tautomerizes to the hydroxy form which loses, H 2 O after a [1,3]‐H shift. AM 1 calculations were carried out on the ground and ionized states of 2 .