Molecular structure of 6-cyclopropyl-1,5-diazabicyclo[3.1.0]hexane: gas phase electron diffraction and theoretical study

The molecular structure and conformational composition of 6-cyclopropyl-1,5-diazabicyclo[3.1.0]hexane were determined by gas phase electron diffraction and quantum chemical calculations. The gas phase electron diffraction data were well reproduced for the mixture of two conformers with anti-boat and gauche-boat mutual ring orientation having 15 and 85% relative abundance, respectively. The standard enthalpy of formation of substance under study was calculated using atomization reactions, yielding value of 307.9 ± 3.3 kJ mol^-1 in gas phase.     

6,6′-Bis(1,5-diazabicyclo[3.1.0]hexane)

The interaction of 1,3-diaminopropane with glyoxal and NaOCl in water at pH 9.5–10.5 afforded the previously unknown 6,6′-bis(1,5-diazabicyclo[3.1.0]hexane). According to X-ray diffraction data, both bicyclic fragments of the title compound adopt a boat conformation. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 623–625, March, 1999.     

First synthesis of 1,5-diazabicyclo[3.1.0]hexane complexes with cadmium salts

Complexes of bicyclic diaziridines 6,6′-bi(1,5-diazabicyclo[3.1.0]hexane) (L ¹ ) and 6-(4-methoxyphenyl)-1,5-diazabicyclo[3.1.0]hexane (L ² ) with the salts Cd(NO₃)₂ · 4H₂O and Cd(ClO₄)₂ · 6H₂O have been synthesized. The fact of complexation has been established by cyclic voltammetry. The crystal structure of complex L ¹ with Cd(NO₃)₂ (the coordination number of cadmium is 8) has been studied by X-ray diffraction.     

Molecular structure of caffeine as determined by gas electron diffraction aided by theoretical calculations

The molecular structure of caffeine (3,7-dihydro-1,3,7-trimethyl-1H-purine-2,6-dione) was determined by means of gas electron diffraction. The nozzle temperature was 185 °C. The results of MP2 and B3LYP calculations with the 6-31G⁷ basis set were used as supporting information. These calculations predicted that caffeine has only one conformer and some of the methyl groups perform low frequency internal rotation. The electron diffraction data were analyzed on this basis. The determined structural parameters (r_g and ∠_α) of caffeine are as follows: <r(NC)_ring> = 1.382(3) Å; r(CC) = 1.382(←) Å; r(CC) = 1.446(18) Å; r(CN) = 1.297(11) Å; <r(NC_methyl)> = 1.459(13) Å; <r(CO)> = 1.206(5) Å; <r(CH)> = 1.085(11) Å; ∠N₁C₂N₃ = 116.5(11)°; ∠N₃C₄C₅ = 121. 5(13)°; ∠C₄C₅C₆ = 122.9(10)°; ∠C₄C₅N₇ = 104.7(14)°; ∠N₉–C₄=C₅ = 111.6(10)°; <∠NCH_methyl> = 108.5(28)°. Angle brackets denote average values; parenthesized values are the estimated limits of error (3σ) referring to the last significant digit; left arrow in parentheses means that this parameter is bound to the preceding one.     

1,5-Diazabicyclo[3.1.0]hexanes and 1,6-diazabicyclo[4.1.0]heptanes: a new method for the synthesis,quantum-chemical calculations,and X-ray diffraction study

A new method was developed for the synthesis of 6-substituted 1,5-diazabicyclo[3.1.0]hexanes and 7-substituted 1,6-diazabicyclo[4.1.0]heptanes by condensation of N-monohalotrimethylene- and N-monohalotetramethylenediamines with carbonyl compounds in the presence of bases. X-ray diffraction studies and quantum-chemical B3LYP/6-31G* calculations demonstrated that the conformations of the resulting bicyclic systems are stabilized by stereoelectronic interactions. As a result, a boat conformation prevails in 1,5-diazabicyclo[3.1.0]hexanes, whereas the energies of chair, half-chair, and boat conformations of 1,6-diazabicyclo[4.1.0]heptanes are equalized.     

Electron Diffraction Study of the Molecular Structure of 6,6'-Bis(1,5-diazabicyclo[3.1.0]hexane)

Gas-phase electron diffraction using quantum-chemical calculations was employed to study the molecular structure for 6,6'-bis(1,5-diazabicyclo[3.1.0]hexane). The conformation of the bicyclic fragment is boat or anti relative to the exocyclic bond.     

Conformational analysis of 2-phenyl-1,3-diazabicyclo[3.1.0]hexane

The 2-phenyl-1,3-diazabicyclo[3.1.0]hexane molecule was subjected to conformational analysis within the framework of the Westheimer method. The optimum conformations of two of its possible stereoisomers (endo and exo) were found, and the equilibrium concentrations of the latter were calculated and found to be 62 and 38%, respectively. The results of the calculations are in good agreement with the PMR spectroscopic data.     

Molecular structure and force field of boron tribromide as determined from combined analysis of gas electron diffraction and spectroscopic data and supported by quantum-chemical density-functional calculations

The thermal-average parameters of BBr₃ at 21(1) °C were obtained from a conventional analysis of gas electron diffraction (GED) data (r_g(B---Br) = 190.0(4) pm). The equilibrium structure and the force constants were refined from a joint analysis of the GED intensities and vibrational frequencies using different approximations. The simplest approximation (quadratic potential function in rectilinear coordinates) is suitable for the refinements of the equilibrium bond length (r^h_e(B---Br) = 189.6(4) pm) and the force constants of BBr₃. The molecule is planar within the error limits. Quantum-chemical density-functional calculations supported planarity of the molecule.     

Molecular structure and conformation of chloronitromethane as determined by gas-phase electron diffraction and theoretical calculations

The molecular structure of chloronitromethane was studied in the gas phase at a nozzle-tip temperature of 373 K. The experimental data were interpreted using a dynamic model where the molecules are undergoing torsional motion governed by a potential function: V = V2/2x(1 - cos 2tau) + V4/2x(1 - cos 4tau) with V2 = 0.81(30) and V4 = 0.12(40) kcal/mol (tau is the dihedral angle between the C-Cl and N-O bond). The conformer with a zero degree dihedral angle is the most stable conformer. Comparison with results from HF/MP2/B3LYP 6-311G(d,p) calculations were made. The important geometrical parameter values (for the eclipsed form) obtained from least-squares refinements are the following: r(C-H) = 1.061(18)A, r(C-N) = 1.509 (5)A, r(N-O) = 1.223(1)A, r(C-Cl) = 1.742(2)A, angleClCN = 115.2(7) degrees, angleO4NC = 118.9(10) degrees, angleO5NC = 114.9(16) degrees, and angleClCH 115(4) degrees.     

Molecular structure of carphedon as studied by gas electron diffraction and quantum chemical calculations

The gas-phase structure and conformational properties of carphedon (C₁₂H₁₄N₂O₂, phenylpiracetam, 2-oxo-4-phenyl-1-pyrrolidineacetamide) have been determined by gas electron diffraction (GED) and quantum chemical calculations (B3LYP and MP2 with 6-31G and cc-pVDZ basis sets). Since quantum chemical calculations demonstrate that the orientation of the acetamide group is fixed by a strong intramolecular N–H(amide)···O(pyrrolidone) hydrogen bond, the number of possible conformers is reduced considerably. Depending on the conformation of the pyrrolidine ring, envelope with out-of-plane C4 atom and acetamide group on the same side of the plane (“+”) or envelope with C4 and acetamide group on opposite sides (“?”), and on the orientation of the phenyl ring, axial (Ax), or equatorial (Eq), four relevant conformations, Ax?, Ax+, Eq?, and Eq+, exist. According to both quantum chemical methods (B3LYP and MP2 with cc-pVDZ basis sets) these four conformers differ by less than 2 kcal/mol in free energies. However, the two methods predict different relative free energies. The GED data were analyzed with different models. With a single-conformer model the best fit of the experimental GED intensities (agreement factor R _f = 4 %) is obtained with the Ax+ conformer. Using a two-conformer model the fit improves considerable for a 50(11):50(11) mixture of Ax? and Eq+ conformers (R _f = 2.7 %). No further improvement is obtained with a three-conformer model and large uncertainties for relative contributions occur. The geometric parameters of gaseous carphedon are compared with those in the crystal phase, where two molecules are connected by two intermolecular N–H···O hydrogen bonds, and with gas-phase values of piracetam.     

Molecular structure of 5-fluorouracil from gas-phase electron diffraction data and quantum-chemical calculations

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Molecular structure of (cyanomethoxy)(dimethylamino)methane as studied by gas-phase electron diffraction and quantum-chemical calculations

The molecular structure of (cyanomethoxy)(dimethylamino)methane in the gas phase is investigated by means of gas-phase electron diffraction and quantum-chemical studies for the first time. It is shown that in the gaseous state, (cyanomethoxy)(dimethylamino)methane is a mixture of gauche-anti (65%) and anti-gauche (35%) conformers. The slight influence of the anomeric effect on the compound’s structural parameters was noted.     

Kinetics and mechanism of the anodic dissolution of gold in solutions of 1,5-diazabicyclo[3.1.0]hexane and its precursors

Studies of the electrochemical behavior of hexahydropyrimidine, 1,5-diazabicyclo[3.1.0]hexane, and 1,3-diaminopropane on a gold electrode via cyclic voltammetry allow us to conclude that gold anodes are subject to corrosion in presence these compounds, yielding complexes that migrate into the solutions and discharge on the counter electrode, producing gold metal deposit. 1,5-Diazabicyclo[3.1.0]hexane is found to form complexes with gold that are much more stable that those formed by hexahydropyrimidine and 1,3-diaminopropane.     

Molecular structure and conformation of diethylmethylamine determined by gas electron diffraction and vibrational spectroscopy combined with theoretical calculations

We have investigated the molecular structure and conformation of diethylmethylamine, C(4)H₃C(2)H₂N(1)[CH₃]C(3)H₂C(5)H₃, by gas electron diffraction and vibrational spectroscopy with the aid of theoretical calculations. Diffraction data are consistent with a conformational mixture of 35(14)% tt + 27(14)% g⁺t + 20(17)% g⁻t + 18(23)% g⁺g⁺ where the numbers in parentheses denote three times the standard errors (3σ). Normal-coordinate analysis based on B3LYP/6-311+G^** calculations supports the existence of the four conformers. The dihedral angle ₁(C4C2N1C3) (= −₂(C5C3N1C2)) of the tt conformer was 170(4)° whereas the ₁ and ₂ values of the other conformers were fixed at the B3LYP/6-311++G(2df,p) values: 72.4° and −163.3° for the g⁺t, −66.0° and −158.2° for the g⁻t, and 60.3° and 63.5° for the g⁺g⁺. Average values of the structural parameters (r_g/Å and _α/°) with 3σ are: r(N–C) = 1.462(2), r(C–C) = 1.523(3), r(C–H) = 1.113(2), CNC = 111.6(5), NCC = 114.5(5), NCH/CCH_Me = 110.6(5).     

Molecular structure of 1,1-difluoroethylene as determined by gas phase electron diffraction and microwave data

The structure of 1,1-difluoroethylene was determined, from gas phase electron diffraction data obtained independently in Leiden and Tokyo and the rotational constants of F₂CCH₂, F₂CCHD and F₂CCD₂ derived from the microwave study by Chauffoureaux. The two electron diffraction data agreed without significant discrepancy. From a joint least squares analysis of the diffraction and microwave data, the following r_g bond distances and r_z bond angles were derived: CC = 1.340 ± 0.006 Å, C-F = 1.315 ± 0.003 Å, C-H = 1.091 ± 0.010 Å, ∠C-C-F = 124.7 ± 0.3°, ∠C-C-H = 119.0 ± 0.4°, where the uncertainties represent estimated limits of error.     

Molecular structure and conformation of gaseous vinyldimethylchlorosilane as determined by electron diffraction

The molecular structure of vinyldimethylchlorosilane has been determined by gas phase electron diffraction at room temperature. The least squares values of the bond lengths (r_g) and bond angles (∠_α) are : r(CH) = 1.086(6) Å, r(CC) = 1.347(5) Å, r(SiC=) = 1.838(6) Å, r(SiC) = 1.876(3) Å, r(SiCl) = 2.078(2) Å, ∠CCSi = 127.8° (1.2) and ∠=CSiCl = 107° (1). Models with pure syn form and a mixture of syn and gauche gave equally good agreement with the diffraction data.     

Molecular structure of N-chlorosuccinimide studied by gas-phase electron diffraction and quantum-chemical methods

The molecular structure of N-chlorosuccinimide has been studied by GED method at the nozzle temperature of 116 °C. Vibrational corrections to the r _a parameters, Δ(r _a − r _e), have been calculated using the scaled quadratic and cubic force constants from B3LYP/6-31G(df,p) calculations. The force field scaling has been carried out using the IR and Raman spectra of the solid N-chlorosuccinimide. The molecular skeleton and the bond conformation around nitrogen were found to be planar within large experimental errors. The equilibrium geometrical parameters derived from the experimental data assuming C _2v molecular symmetry and those from MP2(fc)/6-311G(3df,2pd) calculations are in a good agreement.     

The molecular structure and conformations of oxepane as determined by gas electron diffraction

The electron-diffraction data for gaseous oxepane, collected at 310 K, can be explained in terms of a 53:47% mixture of two twist-chair conformations. Using the nomenclature of Crerner and Pople [1], the conformations are characterised by q₂ = 0.579 å, q₃ = 0.685 Å, φ₂ = 13.3°, φ₃, = 63.0° and q₂ = 0.511 Å. q₃ = 0.588 Å, ø₂ = 116.1°, ø₃ = 217.6°. The other structural parameters (r_a-structure) are r_CO = 1.419 Å, r_cc = 1.531 Å, r_CH = 1.105 Å, ∠H-C-H = 106.0°, with a mean ring valency angle of 112-0° for the former conformation, and of 116.2° for the latter. There is a good agreement between the experimental geometries and the results from molecular mechanics calculations.