The Structure of 1H‐Perimidin‐2(3H)‐one and Its Derivatives in the solid state (x‐ray crystallography and CP/MAS ¹³C‐NMR), in solution (¹³C‐NMR), and in the gas phase (mass spectrometry)

Abstract

The X-ray crystal and molecular structures of 1 -methyl-1H-perimidin-2(3H)-one (5b) and 1,3-dimethyl-IHperimidin-2(3H)-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 6 axis. Semiempirical calculations at the AM1 level revealed that the eclipsed conformation of the Me groups with respect to the C=O 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 ('H and I3C) and in the solid state (CP/MAS I3C) for lH-perimidin-2(3H)-one (2) and 1H-benzimidazol-2(3H)-one (3) with the conclusion that in both heterocycles the 0x0 tautomer is the most abundant. The structure in the gas phase was approached by mass spectrometry. In the case of 3, the 0x0 tautomer loses CO after ionization, while the 0x0 form of 2 tautomerizes to the hydroxy form which loses H,O after a [1,3]-H shift. AM1 calculations were carried out on the ground and ionized states of 2.

Electron ionization-induced fragmentation of N-alkyl- o-nitroanilines: observation of new types of ortho-effects

“…Another work was published by Ramana and Vairamani 4 who investigated the fragmentation of N-benzyl-o-nitroaniline (9). Ramana and Sudha 5 have also published a detailed study of the fragmentation of N-(2-propynyl)-o-nitroaniline (10).…”

“…However, semi-empirical calculations for compounds with a similar structure show that, after ionization, the energy gap between two tautomers decreases substantially. 10 The 6-membered ring-closure product a6 can rearrange further by proton transfer from carbon to nitrogen yielding ion a7 (Scheme 3). This process has also to be considered as a reasonable alternative to the a2-a5 sequence.…”

Solution and solid state (CPMAS) NMR studies of the tautomerism of six‐membered heterocyclic compounds related to 2‐pyridones

“…A recent survey of the physical methods to study tautomerism [1] reveals that there are no examples of the use of solid state NMR ( 13 C and 15 N) to establish the tautomer present in the solid state in the case of six-membered heterocyclic rings (azines). On the contrary, examples of application to five-membered rings (azoles) abound [2][3][4][5][6][7][8]. To demonstrate the possibilities of CPMAS NMR for the study of the tautomerism of azines, four "classical" compounds were selected: 2-pyridone (1), 4(3H)-pyrimidone (2), uracil (3) and cytosine (4).…”

Structural and Mechanistic Insights of Substituted Perimidine - Experimental and Computational Studies

“…However, they did not report a structure [14]. The structures of 1-methyl-1H-perimidin-2(3H)-one and 1,3-dimethyl-IH-perimidin-2(3H)-one were reported by Claramunt et al [15] Another example of 2-methylsulfanyl-1H-perimidin-3-ium iodide was reported by Ghorbani [16]. However, mechanistic details are not available for the formation of perimidines or their derivatives.…”