A total of 202 organic solvents and the gas phase were placed on a solvent basicity scale for hydrogen bond acceptor based on parameter SB. The value of such a parameter can readily be determined from the UV/Vis spectrum for an appropriate acid probe (5‐nitroindoline) (NI) and its non‐acid homomorph (1‐methyl‐5‐nitroindoline) (MNI). The proposed scale can advantageously substitute the more widely used solvent scales such as Gutmann's donor number (DN), the Koppel‐Palm B(MeOD) scale, and the Taft‐Kamlet β scale. While data for the proposed scale are derived only from electronic transitions, they are accurately descriptive of solvent basicity in both spectroscopy (UV/Vis, IR and NMR) and miscellaneous chemical areas (thermodynamic, kinetics, and electrochemistry).
Uber die Anwendung des AMl-und PM3-Verfahrens fur energiereiche VerbindungenDas neue semiempirische Verfahren MNDO-PM3 (PM3), eingefiihrt von Stewart, wird verglichen mit dem bekannten AM I-Verfahren (Austin I Modell), eingefuhrt von Dewar, zur Berechnung nitro-substituierter Verbindungen und einiger energiereicher Materialien. Das PM3-Verfahren leistet mehr als das AM1-Verfahren. Die AbstoBung zwischen einsamen Elektronenpaaren wird besser beschrieben mit dem PM3-Leve1, und die bei der AMI-Methode iibliche systematische Korrektur mit ca. -9 kcal/mol fur jede C-NO,-Gruppe betragt dann +3,5 kcal/mol beim PM3-Level. Die Ergebnisse mit PM3 fur N-N0,haltige Verbindungen sind direkt vergleichbar mit den experimentell im Gaszustand erhaltenen Werten.
SummaryStewart's new semi-empirical method MNDO-PM3 (PM3) is compared with the well known Dewar's AM1 method in the study of nitro substituted compounds, and some energetic materials. PM3 method shows better performances than the AM1 one. Adjacent lone pairfione pair repulsion are better described at PM3 level and the known systematic correction of about -9 kcal/mol for each C-NO, group of the AM1 method becomes +3.5 kcal/mol at PM3 level. PM3 results for N-NO, containing compounds are directly comparable with experimental gasphase data.
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De I'utilisation des methodes AM1 et PM3 sur des composes energetiquesLa nouvelle rnethode semi-empirique MNDO-PM3 (PM3) introduite par Steward est comparee B la cCl2bre nikthode AM1 de Dewar pour le calcul de composts nitrosubstituks et de quelques matCriaux CnergCtiques. La mCthode PM3 est plus performante que la mtthode AM1. La rCpulsion entre des paires dClectrons isolCes est mieux dCcrite avec la mCthode PM3: la correction systCmatique usuelle d'env. -9 kcal/mol pour chaque groupe C-NO, de la mtthode AM1 devient +3,5 kcal/mol si l'on utilise PM3. Les rksultats obtenus avec PM3 pour des composCs contenant le groupe N-NO, sont directement comparables aux valeurs obtenues experimentalement i M a t gazeux.
Energy and dipole moment calculations show 3‐nitro‐5‐ amino‐1,2,4‐triazole is the most stable tautomer of ANTA either in the gas phase and polar solvents, in agreement with X‐ray findings. Our calculations predict that the 5‐nitro‐3‐amino‐1,2,4‐triazole tautomer is more sensitive to shock or impact. Some discrepancies between semiempirical (AMI and PM3) calculations and ab initio (up to 6‐31G*//6‐31G) are studied.
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