Abstract
: γ‐Butyrolactone and γ‐butyrolactam were reacted in the superacidic systems XF/MF5 (X=H, D; M=As, Sb). Salts of the monoprotonated species of γ‐butyrolactone were obtained in terms of [(CH2)3OCOH]+[AsF6]−, [(CH2)3OCOH]+[SbF6]− and [(CH2)3OCOD]+[AsF6]− and the analogous lactam salts in terms of [(CH2)3NHCOH]+[AsF6]−, [(CH2)3NHCOH]+[SbF6]− and [(CH2)3NDCOD]+[AsF6]−. The salts were characterized by low temperature Raman and infrared spectroscopy and for both protonated hexafluoridoarsenates, [(CH2)3OCOH]+[AsF6]− and [(CH2)3NHCOH]+[AsF6]−, single‐crystal X‐ray structure analyses were conducted. In addition to the experimental results, quantum chemical calculations were performed on the B3LYP/aug‐cc‐pVTZ level of theory. As in both crystal structures C⋅⋅⋅F contacts were observed, the nature of these contacts is discussed with Mapped Electrostatic Potential as a rate of strength.
Highlights
Preparation rearrangement of an oxime into an amide under ring expansion.[2,7]. Another synthesis strategy for both cyclic com- The synthesis of salts of monoprotonated γ-butyrolactone and pounds is the catalyzed cyclodehydration of the corresponding γ-butyrolactam was performed according to Equations. (2) and hydroxyl acid,[8] respectively amino acid.[9]
In the case of protonated γ-butyrolactone and γbutyrolactam, we found C···F contacts
Natural Population Analysis charges (NPA) for the neutral compounds as well as for the protonated species of γbutyrolactone (Figure S1) and γ-butyrolactam (Figure S2) are displayed in the Supporting Information. Both Mapped Electrostatic Potentials (MEP) show that the electron deficient moiety
Summary
In the case of protonated γ-butyrolactone and γbutyrolactam, we found C···F contacts Such contacts, which differ from hydrogen bonds, have only rarely been observed.[24,25,26] To investigate the nature of these contacts, Mapped Electrostatic Potentials (MEP) of the free cations [(CH2)3OCOH]+ and [(CH2)3NHCOH]+ were calculated. Natural Population Analysis charges (NPA) for the neutral compounds as well as for the protonated species of γbutyrolactone (Figure S1) and γ-butyrolactam (Figure S2) are displayed in the Supporting Information Both MEPs show that the electron deficient moiety (region displacement ellipsoids). The more positive MEP value of [(CH2)3OCOH]+ represents the ability to form two contacts, which are slightly weaker than that in (4) Summarizing these results, it can be stated that in protonated γbutyrolactone, the localization of the positive charge on the sp2-hybridized carbon atom is even stronger than in protonated γ-butyrolactam.
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