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A computational study has been performed for protonated oxygen- or nitrogencontaining heterocyclic derivatives of cyclopropane and cyclopropanone. We have searched for the most stable conformations of the protonated species using density functional theory with the B3LYP functional and the 6-31G(2df,p) basis set. More accurate enthalpy values were obtained from G4 calculations. Proton affinities and gas-phase basicities were accordingly derived. Keywords: protonated cyclopropane and cyclopropanone derivatives, enthalpy, Gibbs energy, proton affinity, gas-phase basicity, QTAIM analysis. Nous avons realise une etude de modelisation sur des derives heterocycliques protones du cyclopropane ou de la cyclopropanone contenant un atome d'oxygene ou d'azote. Nous avons recherche les conformations les plus stables au moyen de la theorie de la fonctionnelle de la densite, en utilisant la fonctionnelle B3LYP et la base 6-31G(2df,p). La meilleure exactitude des valeurs d'enthalpie a ete obtenue grace aux calculs selon le modele G4. De ces resultats ont ete derivees les affinites protoniques et les basicites en phase gazeuse. [Traduit par la Redaction] Mots-cles: derives protones du cyclopropane et de la cyclopropanone, enthalpie, energie de Gibbs, affinite protonique, basicite en phase gazeuse, theorie quantique des atomes dans les molecules., Introduction The structure and energetics of species with three-membered rings and the amide linkage have been actively studied by both the experimental and theoretical chemical communities. It is now acknowledged [...] more...

Species with three-membered rings and the amide linkage are well studied. A quick perusal of the literature with SciFinder finds some 50 000 references to cyclopropanes and almost 300 000 references to amides. In the current paper, we discuss the structure and energetics of two understudied three-membered ring amides, 1,2-oxaziridine-3-one (5) (simultaneously describable as the simplest cyclic carbamate and simplest hydroxamate) and aziridine-2,3-dione (7) (simultaneously describable as the simplest imide and simplest α-ketoamide), with but 5 and nearly 10 references, respectively, for these two classes of compounds. Neither 1,2-oxaziridine-3-one (5) nor aziridine-2,3-dione (7), nor any derivative thereof, has been isolated. Calculational theory ameliorates the paucity of experimental information. The current study reports our computational findings for these and related species (e.g., enols and imidols) where we have used the G3(MP2) //B3LYP method. Key words: amides, cyclopropane and cyclopropanone derivatives, enthalpy of formation, molecular structure and energetics, strained organic molecules. Les especes cycliques a trois atomes et le lien amide sont largement etudies. Un survol de la litterature dans SciFinder permet de trouver quelque 50 000 references sur les cyclopropanes et pres de 300 000 sur les amides. Dans le present article, nous abordons la structure et l'energetique de deux amides cycliques a trois atomes ayant fait l'objet de tres peu d'etudes, la 1,2-oxaziridin-3-one (5) (qui peut etre decrite simultanement comme le carbamate cyclique le plus simple et l'hydroxamate le plus simple) et l'aziridin-2,3-dione (7) (qui peut etre decrite comme l'imide le plus simple et l'a-cetoamide le plus simple), dont les deux classes de composes renvoient respectivement seulement 5 et pres de 10 references. Ni la 1,2-oxaziridin-3-one (5), ni l'aziridine-2,3-dione (7), ni tout autre de leurs derives n'ont ete isoles. Les calculs theoriques ameliorent la situation creee par la rarete des donnees experimentales. La presente etude expose nos resultats computationnels sur ces especes et leurs derives (p. ex., les enols et les imidols) pour lesquels nous avons utilise la methode G3(MP2) //B3LYP. [Traduit par la Redaction] Mots-cles : amides, derives du cyclopropane et de la cyclopropanone, enthalpie de formation, structure moleculaire et energetique, molecules organiques contraintes., Introduction Species with three-membered rings and the amide linkage are well studied. A quick perusal of the literature with SciFinder1 finds some 50 000 references to cyclopropanes, almost 1000 references [...] more...

Small ring nitrogen heterocycles, azabicyclobutanes and azirines, were investigated by computational methods in order to address the discrepancy between their regioisomers 1‐ and 2‐azabicyclobutane and 1H‐ and 2H‐azirines. Both 1‐azabicyclobutane and 2H‐azirine are well known synthetic starting points to larger nitrogen heterocycles whereas 2‐azabicyclobutane and 1H‐azirine and their derivatives have yet to be reported as isolable compounds. Calculated parameters such as structure, base strength (proton affinities), NICS values and enthalpies of formation from which strain energies are derived are reported. The destabilization of the less stable regioisomers is attributed to homoantiaromaticity in 2‐azabicyclobutane and antiaromaticity in 1H‐azirine. Two stereoisomers exist for 2‐azabicyclobutane with the endo‐ stereoisomer being more stable. This phenomenon is indicative of the hydrogen bond acceptor properties of the neighboring cyclpropane and the π‐bond character of the central bond in 2‐azabicyclobutane. [ABSTRACT FROM AUTHOR] more...

We ask whether the energy of a π-orbital, εi, can equal e or π, or some rational multiple of either number? From the molecular and mathematical framework of Hückel molecular orbital theory (HMO), this question is answered in the negative. [ABSTRACT FROM AUTHOR] more...