Conformational and Bonding Properties of 3,3-Dimethyl- and 6,6-Dimethyl-1,5-diazabicyclo[3.1.0]hexane: A Case Study Employing the Monte Carlo Method in Gas Electron Diffraction

Abstract

Gas-phase structures of two isomers of dimethyl-substituted 1,5-diazabicyclo[3.1.0]hexanes, namely, 3,3-dimethyl- and 6,6-dimethyl-1,5-diazabicyclo[3.1.0]hexane molecules, have been determined by gas electron diffraction method. A new approach based on the Monte Carlo method has been developed and used for the analysis of precision and accuracy of the refined structures. It was found that at 57 °C 3,3-dimethyl derivative exists as a mixture of chair and boat conformers with abundances 68(8)% and 32(8)%, respectively. 6,6-Dimethyl-1,5-diazabicyclo[3.1.0]hexane at 50 °C has only one stable conformation with planar 5-ring within error limits. Theoretical calculations predict that the 6,6-dimethyl isomer is more stable in comparison to the 3,3-dimethyl isomer with energy difference 3-5 kcal mol(-1). In order to explain the relative stability and bonding properties of different structures the natural bond orbitals (NBO), atoms in molecules (AIM), and interacting quantum atoms (IQA) analyses were performed.

Solid‐State and Gas‐Phase Structures and Energetic Properties of the Dangerous Methyl and Fluoromethyl Nitrates

“…[a] Values correspond to equilibrium structure. In parentheses are total standard deviations obtained from Monte Carlo simulations as described earlier . [b] Contribution of GED data to refined value, estimated according to the W2 method .…”

“…Identification and characterization is possible by NMR spectroscopy.I nc ontrast to the 1 HNMR resonance of the methyl group in MN (4.10 ppm), the methylene group of FMN gives rise to adoublet at 5.98 ppm ( 2 J F, H = 52.0 Hz);the downfield shift is due to the strong electron-withdrawing effect of fluorine.F MN shows at riplet at À155.9 ppm in its 19 FNMR spectrum, and ad oublet of triplets at 99.1 ppm ( 1 J F, C = 228.8, 1 J C,H = 182.4 Hz) in its 13 CNMR spectrum.…”

“…In parentheses are total standard deviations obtained from Monte Carlo simulationsas described earlier. [19] [b] Contribution of GED data to refined value, estimated accordingtothe W2 method. [20] [c] Weighted root-meansquare deviation of model rotational constantsf rom experimental.…”

Interacting Quantum Atoms—A Review

“…In this investigation it was proposed that the origin of gauche stability is electrostatic polarisation interactions occurring between fluorine atoms [ 126 ]. Indeed, IQA has been applied to diverse conformational puzzles—Cukrowski et al studied the stability of the 2-butene conformers and determined that the origin of the relative energies lies in the interactions between various fragments and cannot be attributed to any specific contact [ 127 ], Matczak and coworkers investigated the energetic components governing the conformational behaviour of diheteroaryl ketones and thioketones [ 128 ], Vishnevskiy et al used IQA to explain the relative stability dimethylsubstituted 1,5-diazabicyclo[3.1.0]hexanes [ 129 ], Uhlemann and coworkers the explored the interaction in the potential energy surface of the sulfanilamide-water complex, and the sulfanilamide dimer [ 130 ] and Maxwell and Popelier determined the cause of the torsional preferences of a series of dipeptides [ 131 ].…”

Festkörper‐ und Gasphasenstrukturen sowie energetische Eigenschaften des gefährlichen Methyl‐ und Fluormethylnitrats

“…[a] Werte entsprechen der Gleichgewichtsstruktur. In Klammern sind die mit der Monte‐Carlo‐Methode berechneten Gesamtstandardabweichungen angegeben. [b] Beitrag der GED‐Daten zu den verfeinerten Werten, geschätzt nach der Methode W2 .…”