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6‐Iodo‐3‐(triflamidomethyl)‐4‐triflyl‐1,4,2,7‐oxazadisilepane 1 and the product of its cyclization, 2,2,4,4‐tetramethyl‐6,8‐bis (triflyl)‐3‐oxa‐6,8‐diaza‐2,4‐disilabicyclo[3.2.2]nonane 2, have been studied by gas‐phase electron diffraction and DFT calculations. The conformational equilibrium in the gas phase was shown to include three and two conformers for 1 and 2, respectively, in contrast to only one conformer determined by single crystal X‐ray diffraction. The structural analysis of the conformers was performed and the pathways of the conformational transitions were analyzed. [ABSTRACT FROM AUTHOR]

[Display omitted] Based on gas electron diffraction experiments supported by quantum chemical simulations, the molecular structure of 6-phenyl-1,5-diazabicyclo[3.1.0]hexane (PhDBH) in the gas phase was determined, which is characterized by the puckering motion of the five-membered ring typical of bicyclo[3.1.0]- hexanes. It was found that the previously determined crystal packing is accompanied by a certain torsional twisting of the molecule, requiring activation energy. Based on the simulations of PhDBH clusters, it was shown that the energy is compensated by intermolecular interactions. [ABSTRACT FROM AUTHOR]

Oleg M. Nefedov (1931−2023) Soviet/Russian academician was a physical organic chemist whose research interest focused on the generation and structure of small unstable species. He had a brilliant career in the scientific hierarchy. [ABSTRACT FROM AUTHOR]

Synchronous electron diffraction/mass spectrometry was used to study the composition and structure of molecular forms existing in a saturated vapor of cobalt(II) oxopivalate at T = 410 K. It was found that monomeric complexes Co4O(piv)6 dominate in the vapor. The complex geometry possesses the C3 symmetry with bond lengths Co–Oc = 1.975(5) Å and Co–O = 1.963(5) Å, as well as bond angles Oc–Co–O = 111.8(3)°, Co–Oc–Co = 110.4(6)°, O–Co–O = 107.1(3)° in the central OcCo4 fragment and four OcCoO3 fragments. The presence of an open 3d shell for each Co atom leads to the possibility of the existence of electronic states of the Co4O(piv)6 complex with Multiplicities 1, 3, 5, 7, 9, 11, and 13. For them, the CASSCF and XMCQDPT2 calculations predict similar energies, identical shapes of active orbitals, and geometric parameters, the difference between which is comparable with the error of determination by the electron diffraction experiment. QTAIM and NBO analysis show that the Co–Oc and Co–O bonds can be attributed to ionic (or coordination) bonds with a significant contribution of the covalent component. The high volatility and simple vapor composition make it possible to recommend cobalt (II) oxopivalate as precursors in the preparation of oxide films or coatings in the CVD technologies. The features of the electronic and geometric structure of the Co4O(piv)6 complex allows for the conclude that only a very small change in energy is required for the transition from antiferromagnetically to ferromagnetically coupled Co atoms. [ABSTRACT FROM AUTHOR]

The molecular structure and conformational and rotational composition of 3,7,9-tris(trifluoromethylsulfonyl)-3,7,9-triazabicyclo[3.3.1]nonane 1 have been investigated by synchronous gas-phase electron diffraction/mass spectrometry GED/MS and theoretical calculations (B3LYP and M06-2X with cc-pVTZ and aug-cc-pVTZ basis sets) and compared to the X-ray structure. All 16 possible conformers and rotamers were calculated, differing by the conformations of the two piperazine rings, orientation of the CF3 groups relative to these rings, and non-equivalence of the two wings of the butterfly structure. The optimized geometry of the most stable 1-c-out-2-c-out conformer coincides with that in the crystal. In contrast to only one conformer determined by X-ray, the GED analysis revealed the presence of five conformers, 1-c-out-2-c-out (I), 1-c-in-2-c-out (II), 1-c-out-2-c-in (III), 1-b-out-2-c-out (IV), 1-c-out-2-b-out (V) in the ratio of I:(II + III):IV:V = 36(10):42(6):22(10):0(10). The experimental results are better reproduced by calculations performed for 428 K (the temperature of the GED experiment) than for 298 K (standard), and most satisfactorily at the M06-2X/aug-cc-pVTZ level of theory. [ABSTRACT FROM AUTHOR]

Based on the data of the gas electron diffraction/mass spectrometry (GED/MS) experiment, the composition of the vapor over rhenium tetrafluoride at T = 471 K was established, and it was found that species of the Re2F8 is present in the gas phase. The geometric structure of the Re2F8 molecule corresponding to D4h symmetry was found, and the following geometric parameters of the rh1 configuration were determined: rh1(Re-Re) = 2.264(5) Å, rh1(Re-F) = 1.846(4) Å, α(Re-Re-F) = 99.7(0.2)°, φ(F-Re-Re-F) = 2.4 (3.6)°. Calculations by the self-consistent field in full active space approximation showed that for Re2F8, the wave function of the 1A1g ground electronic state can be described by the single closed-shell determinant. For that reason, the DFT method was used for a structural study of Re2X8 molecules. The description of the nature of the Re-Re bond was performed in the framework of Atom in Molecules and Natural Bond Orbital analysis. The difference in the experimental values of r(Re-Re) in the free Re2F8 molecule and the [Re2F8]2− dianion in the crystal corresponds to the concept of a triple σ2π4 (ReIV-ReIV) bond and a quadruple σ2π4δ2 (ReIII-ReIII) bond, respectively, which are formed between rhenium atoms due to the interaction of d-atomic orbitals. The enthalpy of dissociation of the Re2F8 molecular form in two monomers ReF4 (ΔdissH°(298) = 109.9 kcal/mol) and the bond energies E(Re-Re) and E(Re-X) in the series Re2F8→Re2Cl8→Re2Br8 molecules were estimated. It is shown that the Re-Re bond energy weakly depends on the nature of the halogen, while the symmetry of the Re2Br8 (D4d) geometric configuration differs from the symmetry of the Re2F8 and Re2Cl8 (D4h) molecules. [ABSTRACT FROM AUTHOR]

A comprehensive study of saturated vapors of 4-n-propyloxybenzoic acid (POBA) by gas electron diffraction (GED) and mass spectrometric (MS) methods supplemented by quantum chemical (QC) calculations was carried out for the first time. An attempt was made to detect dimeric forms of the acid in the gaseous state. It has been established that at the temperature of GED experiment, vapor over a solid sample contains up to 20 mol.% of cyclic dimers with two O-H...O hydrogen bonds. The main geometrical parameters of gaseous monomers and dimers of POBA are obtained. The distance r(O...O) = 2.574(12) Å in the cyclic fragment of the gaseous dimer is close to that in the crystal structure (2.611 Å). In the mass spectrum of the POBA recorded the ions of low intensity with a mass exceeding the molecular mass of the monomer were detected. The presence of ions, whose elemental composition corresponds to the dissociative ionization of the dimer, confirms the results of the GED experiment on the presence of POBA dimers in the gas state. The results of GED studies of acetic acid, benzoic acid, and POBA were compared. It is shown that the COOH fragment saves its geometric structure in monomers, as well as the COOH...HOOC fragment with two hydrogen bonds in dimers of different acids. The intermolecular interaction energy in considered acid dimers was estimated using QC calculations (B97D/6-311++G **). The significant value of last (>84 kJ/mol) is the reason for the noticeable presence of dimers in the gas phase. [ABSTRACT FROM AUTHOR]

Fluoromethyl triflate (superfluoromethyl, SFM, FH 2 COSO 2 CF 3 ) and fluoromethyl fluorosulfonate (magic fluoromethyl, MFM, FH 2 COSO 2 F) are two easily synthesized, highly effective and non-ozone depleting fluoromethylation reagents. They are analogous to the well-known and widely used methylation reagents H 3 COSO 2 CF 3 and H 3 COSO 2 F. Both SFM and MFM have been fully characterized by multinuclear NMR spectroscopy ( 1 H, 13 C, 17 O, 19 F, 33 S). Their structures have been determined in the solid state on in situ grown crystals by X-ray diffraction and in the gas phase by electron diffraction. The fluoromethylation efficiency of SFM and MFM was shown by reactions with chalcogen nucleophiles of differing nucleophilicity. All fluoromethylated products were isolated as pure compounds and characterized by NMR and vibrational spectroscopy, as well as in some cases by single crystal X-ray diffraction., (© 2024 The Author(s). Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

By DFT method with B3LYP, PBE, CAM-B3LYP, and B97D functionals, it was found that the molecule 4-(4-tritylphenoxy)phthalonitrile (TPPN) has four conformers. The geometric structure, vibrational frequencies, electronic characteristics, and thermodynamic functions of conformers, as well as the structure and energy of transition states, were determined. IR spectrum of TPPN film contains vibrational bands belonging to different conformers. The assignment of bands was performed basing the distribution of normal vibration energy on internal coordinates. A synchronous electron diffraction/mass spectrometric experiment was performed to determine the structure of conformers in a saturated TPPN vapor. The elemental composition of the ions recorded in the mass spectrum indicates the thermal stability of TPPN at least up to T = 200 °C. The difference in the structure of tetrasubstituted metal phthalocyanines, which can be synthesized from different TPPN conformers, has been shown. [ABSTRACT FROM AUTHOR]

Abstract Difluorothiophosphoryl isocyanate, F2P(S)NCO was characterized with UV/vis, NMR, IR (gas and Ar‐matrix), and Raman (liquid) spectroscopy. Its molecular structure was also established by means of gas electron diffraction (GED) and single crystal X‐ray diffraction (XRD) in the gas phase and solid state, respectively. The analysis of the spectroscopic data and molecular structures is complemented by extensive quantum‐chemical calculations. Theoretically, the Cs symmetric syn‐conformer is predicted to be the most stable conformation. Rotation about the P−N bond requires about 9 kJ mol−1 and the predicted existence of an anti‐conformer is dependent on the quantum‐chemical method used. This syn‐orientation of the isocyanate group is the only one found in the gas phase and contained likewise in the crystal. The overall molecular structure is very similar in gas and solid, despite in the solid state the molecules arrange through intramolecular O⋅⋅⋅F contacts into layers, which are further interconnected by S⋅⋅⋅N, S⋅⋅⋅C and C⋅⋅⋅F contacts. Additionally, the photodecomposition of F2P(S)NCO to form CO, F2P(S)N, and F2PNCO is observed in the solid Ar‐matrix.

Kozo Kuchitsu (1927‒2021) was a Professor of Chemistry at Tokyo University and, upon his retirement, at several other schools. He was also one of the leading electron diffraction researchers of the determination of molecular structure. He greatly contributed to the enhancement of the accuracy of structure determination. His activities had a significant impact in the international community of structural chemistry. [ABSTRACT FROM AUTHOR]

The equilibrium structure of the 3,3,6-trimethyl-1,5-diazabicyclo[3.1.0]hexane (TMDABH) molecule was studied for the first time by means of gas-phase electron diffraction (GED) supplemented with quantum chemical calculations. TMDABH exists as a mixture of two conformers of Cs point group symmetry, namely, a chair and a boat. The fractions of these two forms are 74 and 26% respectively, if the reference approximation was obtained at the MP2/aug-cc-PVTZ level, and 81 and 19%, if the reference approximation was generated at the DFT-B3LYP/cc-pVTZ level. The agreement between the theoretical and experimental molecular intensities is characterized by Rf disagreement factors of 5.06 and 6.93%, respectively. Based on the more accurate MP2/aug-cc-PVTZ quantum chemical approximation, the energy difference between the global minimum, which corresponds to the chair conformer of TMDABH, and the local minimum of the boat on the potential energy surface (PES) was found to be 1.39 kcal/mol. Moreover, NMR, IR, and Raman spectroscopic studies were carried out. According to the joint analysis of the data obtained, the most important equilibrium parameters of the chair and boat TMDABH conformers were determined to be as follows (bond lengths in Å, angles in degrees, for boat form in square brackets, Cs symmetry): N1N5 = 1.554(2) [1.520(2)], C2C3 = 1.525(2) [1.539(2)], N1C2C3 = 105.7(14) [108.8(14)], θ = C2-C3-C4/C2-N1-N5-C4 = 37.4(6) [−16.6(6)], φ = N1-C6-N5/C2-N1-N5-C4 = 72.9(3) [73.9(3)]. Comparison of especially NN bond lengths reveals a strong dependence on the bicyclic system conformation. [ABSTRACT FROM AUTHOR]

The gaseous structures, thermochemical properties and dehydrogenation reaction energy profiles of the borane complexes of pyrrolidine and piperidine have been investigated using gas electron diffraction (GED) and state-of-the-art computational methods. These complexes are of interest because of their potential as hydrogen storage materials for future onboard transport applications. A comparative structural and thermochemical analysis revealed structures with a slight difference in the essential B–N bond length, with the piperidine borane having a longer bond even though it has a stronger B–N bond according to predicted bond dissociation energies, a trend common with amine boranes. To identify the most favourable dehydrogenation pathway, BH3-catalysed and BH3-uncatalysed dehydrogenation channels have been explored, where the former has been shown to be the favourable process for both complexes. The energy requirements for the hydrogen release reactions are expected to be minimal as evidenced from the calculated dehydrogenation reaction energies, implying their suitability for onboard chemical hydrogen storage. [ABSTRACT FROM AUTHOR]

Several ethylenedioxy‐bridged bisarenes with a variety of type and number of aryl groups were synthesized to study non‐covalent dispersion‐driven inter‐ and intramolecular aryl–aryl interactions in the solid state and gas phase. Intramolecular interactions are preferably found in the gas phase. DFT calculations with and without dispersion correction show larger interacting aromatic groups increase the stabilization energy of folded conformers and decrease the intermolecular centroid–centroid distance. Single‐molecule structures generally adopt folded conformations with short intramolecular aryl–aryl contacts. Gas electron diffraction experiments were performed exemplarily for 1‐(pentafluorophenoxy)‐2‐(phenoxy)ethane. A new procedure for structure refinement was developed to deal with the conformational complexity of such molecules. The results are an experimental confirmation of the existence of folded conformations of this molecule with short intramolecular aryl–aryl distances in the gas phase. Solid‐state structures are dominated by stretched structures without intramolecular aryl–aryl interactions but interactions with neighboring molecules. [ABSTRACT FROM AUTHOR]

Difluorothiophosphoryl isocyanate, F2P(S)NCO was characterized with UV/vis, NMR, IR (gas and Ar‐matrix), and Raman (liquid) spectroscopy. Its molecular structure was also established by means of gas electron diffraction (GED) and single crystal X‐ray diffraction (XRD) in the gas phase and solid state, respectively. The analysis of the spectroscopic data and molecular structures is complemented by extensive quantum‐chemical calculations. Theoretically, the Cs symmetric syn‐conformer is predicted to be the most stable conformation. Rotation about the P−N bond requires about 9 kJ mol−1 and the predicted existence of an anti‐conformer is dependent on the quantum‐chemical method used. This syn‐orientation of the isocyanate group is the only one found in the gas phase and contained likewise in the crystal. The overall molecular structure is very similar in gas and solid, despite in the solid state the molecules arrange through intramolecular O⋅⋅⋅F contacts into layers, which are further interconnected by S⋅⋅⋅N, S⋅⋅⋅C and C⋅⋅⋅F contacts. Additionally, the photodecomposition of F2P(S)NCO to form CO, F2P(S)N, and F2PNCO is observed in the solid Ar‐matrix. [ABSTRACT FROM AUTHOR]

Equilibrium and vibrationally averaged structures of CO2 have been determined using combination of available experimental rotational constants and high level quantum-chemical calculations. Gas electron diffraction patterns of CO2 and CCl4 have been measured and analyzed. A method for fine control of electron diffraction background smoothness is proposed. The patterns of CO2 were used for calibration of electron wavelength. From the patterns of CCl4, molecular structure has been refined. The determined, in this work, parameters can be recommended as reference values in calibration of gas electron diffraction experiments. For CO2, these values are ra(C=O) = 1.1641 (1), ra(O...O) = 2.3241 (1), l(C=O) = 0.0358 (2), l(O...O) = 0.0473 (4) Å, c3(C=O) = 3.12 × 10− 6, c3(O...O) = 2.88 × 10− 6 Å3. The values for CCl4 are ra(C-Cl) = 1.7665 (7), ra(Cl...Cl) = 2.8828 (12), l(C-Cl) = 0.0502 (4), l(Cl...Cl) = 0.0721 (3) Å, and c3(C-Cl) = 0.0, c3(Cl...Cl) = 0.0 Å3. [ABSTRACT FROM AUTHOR]

[Display omitted] • The GED structure of 2,5,9,12- tetraethylbenzo[f]quinolino[3,4-b][1,7]naphthyridine-6,8(5H,9H)-dione in comparison to XRD one. • Intramolecular interactions according to AIM and NCI approaches. The semi-experimental molecular structure of 2,5,9,12-tetraethylbenzo[ f ]quinolino[3,4- b ][1,7]naphthyridine-6,8(5 H ,9 H)-dione has been determined using the gas electron diffraction method in combination with the quantum chemical calculations. It was compared to X-ray diffraction data known from literature. Close to planar configuration of the frame is found to be undistorted. Conformational analysis revealed a set of isoenergetic conformers of the compound, the intramolecular interactions were characterized with the use of AIM and NCI approaches. Mean vibrational amplitudes (u ij ,h1) and anharmonic vibrational corrections (r ij ,e - r ij ,a) were calculated for the experimental temperature of 606 K using the quadratic and cubic force constant fields. [ABSTRACT FROM AUTHOR]

An improved synthesis of the simplest nitric acid ester, methyl nitrate, and a new synthesis of fluoromethyl nitrate use the metathesis of the corresponding iodomethanes with silver nitrate. Both compounds were identified by spectroscopy and the structures determined for in situ grown crystals by X‐ray diffraction as well as in the gas phase by electron diffraction. Fluorination leads to structures with shorter C−O and N−O bonds, has an energetically destabilizing effect and increases friction sensitivity, but decreases detonation performance. [ABSTRACT FROM AUTHOR]

A solution is sought for problems in experimental gas electron diffractometry. An experiment is performed that meets the requirements of the International Organization for Standardization for measuring processes and equipment. The scattering process is expressed through the densities of volumetric charge density fluxes transferred through the irradiated volume. The advantages of a molecular beam as a target for fast electrons of the probe are demonstrated. It is proposed that the ratio of attained results to used resources be used for quantitative estimates of the efficiency of a measuring system. The efficiencies of an electron source of an electron diffractometer, a target, and an instrument background manufactured at the laboratory of Moscow State University are estimated as = 6.36 × 10−18, = 2.24 × 10−11, and = 1.06 × 10−20, respectively. It is established that the detection of a useful signal at S = 28 Å−1 requires the transfer of a probe charge of 2.2 × 105 C through the irradiated volume at a target charge of 6.25 × 10−2 C and a signal/noise ratio of 870 at S = 28 Å−1. [ABSTRACT FROM AUTHOR]

The molecular structure of thiosalicylamide (2-hydroxythiobenzamide) was investigated in the gas phase at 401 K by means of gas electron diffraction (GED) combined with quantum chemical (QC) calculations. Special attention was paid to the internal rotation of the thioamide group. Structural refinement was performed taking into account rovibrational corrections to the thermal-average internuclear distances calculated with harmonic and anharmonic (cubic) MP2/cc-pVTZ force constants in terms of static and dynamic models. It was shown that both models fitted the GED data equally well. The results of the GED refinement revealed that in the equilibrium structure, the thioamide group is twisted by about 30° with respect to the phenol ring plane. This is the result of an interatomic repulsion of hydrogen atom in the amide group from the closest hydrogen atom of the benzene ring, which overcomes the energy gain from the π−π conjugation of the thioamide group and the aromatic system of thiosalicylamide. Natural bond orbital (NBO) analysis and comparison of the thiosalicylamide molecular structure with those of related compounds revealed hydrogen-bonded fragment between the hydroxyl and thiocarbonyl groups. The structure of thiosalicylamide in the gas phase was found to be markedly different from that in the solid phase due to the effect of intermolecular hydrogen bonding in the crystal. [ABSTRACT FROM AUTHOR]

Two new silicon/phosphorus‐based frustrated Lewis pairs (FLP), F3SiCH2PtBu2 (1) and Cl3SiCH2PtBu2 (2) were prepared from lithiated di‐tert‐butylmethylphosphane, LiCH2PtBu2, and the corresponding silicon tetrahalides. They were characterised by NMR spectroscopy and by single‐crystal X‐ray diffraction. A gas phase electron diffraction study of 1 identified two conformers of similar energy in the vapor. The reactivity of both, 1 and 2, towards a series of small molecules was investigated. Phenyl isocyanate was found to undergo addition reactions of its C‐N unit to afford five‐membered SiCPC(O)N‐ring structures. Cl3SiCH2PtBu2 (2) was converted with perfluorophenyllithium and 3,5‐bis(trifluoromethyl)phenyllithium. The reaction with LiC6F5 resulted in the ortho‐fluoride substitution product (C6F5)2SiCH2(C6F4)PtBu2 (5), while the aryl reagent without ortho‐fluoride groups, leads to the intramolecular Lewis pair (C8H3F6)3SiCH2PtBu2 (6). The FLP reactivity of 6 was tested. [ABSTRACT FROM AUTHOR]

This commentary is addressing gas electron diffraction in Norway from the late 1930s up to 2017. The account is about the people involved, the methods developed, and the chemical questions addressed. The development was based on three strong characteristics: Academic excellence, a holistic strategy, and a comprehensive international cooperation and publication. Two strong personalities—Odd Hassel and Otto Bastiansen—established the fundament; their contributions were pivotal. Their ability to obtain funding, to recruit highly qualified co-workers, and their international network were central to the development. The investments in structure chemistry and electron diffraction were exceptionally visionary and daring. The story is rather unique. It is about how a small university at Europe's periphery in the late 1930s was able to establish a world-leading research group. [ABSTRACT FROM AUTHOR]

Abstract The structures of free hemiporphyrazine and dicarbahemiporphyrazine molecules were determined by gas-phase electron diffraction and DFT calculations. Distance corrections (r e – r a) were calculated using two different approaches: commonly applied Sipachev's algorithm and a recently developed technique based on molecular dynamics simulations. Both approaches examined against each other for the first time in the refinement of a relatively large (52 atoms) structure were found to result in almost the same final structural parameters. Gas-phase structures of hemiporphyrazine and dicarbahemiporphyrazine are saddle distorted, in contrast to the planar structure previously found for the solid-state hemiporphyrazine. Doubly charged anionic form of hemiporphyrazine was calculated to be significantly saddle distorted, while the anion of dicarbahemiporphyrazine was determined to possess a planar equilibrium structure. Structural features of the molecules and their doubly charged anionic forms are discussed in terms of AIM and NBO analyses. Graphical abstract Image 1 Highlights • Free hemiporphyrazine and dicarbahemiporphyrazine molecules are saddle distorted. • Vibrational corrections (r e – r a) were obtained from MD simulations. • Doubly charged anion of hemiporphyrazine is significantly saddle distorted. • Doubly charged anion of dicarbahemiporphyrazine is planar. • Calculated configurations of the anions are interpreted based on AIM and NBO analysis. [ABSTRACT FROM AUTHOR]

Abstract 1-(N,N-dimethylamino)-1-silacyclohexane 1 was synthesized. Contributions of the conformers of 1, Eq- trans : Eq- gauche : Ax- trans , were found to be 55(15):15(15):30(15) mol.% in gas phase at 288 K from gas electron diffraction. The enthalpy Δ H = 0.29(15) kcal/mol for Ax-to-Eq transition was measured by temperature dependent Raman spectroscopy of liquid 1 and its solutions. Geometry, conformational properties and intramolecular conversion were explored by theoretical calculations. The nitrogen bond configurations for 1 was found to be close to planar, with a sum of the bond angles of ca. 350-355° that is quite different from those analogs in which the N atom is connected to a carbon atom rather than to a silicon atom. Graphical abstract Image 1 Highlights • Axial and equatorial conformers contribute to1-NMe 2 -1-silacyclohexane. • Equatorial conformers dominate in gas and liquid phases. • The substituent may occupy trans –and gauch -orientations. • Nitrogen bond configuration is of low pyramidality. [ABSTRACT FROM AUTHOR]

The conformational properties and the molecular structure of dichlorophosphoryl isocyanate, Cl2P(O)NCO, were studied by combining vibrational spectroscopy (IR and Raman), gas‐phase electron diffraction (GED), X‐ray crystallography (XRD), and quantum‐chemical calculations. Computationally, two conformers of Cs symmetry with the P=O bond being in syn or anti configuration relative to the NCO group are predicted to be close in energy (ca. 2 kJ mol–1). Experimentally, both gas‐phase and matrix‐isolation IR spectra of Cl2P(O)NCO suggest the presence of a single conformer, which was determined to be the energetically more favorable syn‐conformer. This was also found to exist in the solid state by low‐temperature XRD. However, the molecule in the solid state is significantly distorted from ideal Cs symmetry with an O–P–N–C dihedral angle of 38.1(1)° due to intermolecular C···O contacts [2.881(4) Å]. In the gas phase, the GED analysis suggests that the molecule exists predominantly as syn‐conformer but with dynamic behavior about the two minimum structures (syn and anti). [ABSTRACT FROM AUTHOR]

Abstract: The equilibrium structure of the 4-cyanopyridine molecule was determined from experimental data for the first time. The computations performed at the CCSD(T) level agree well with the results of the combined electron diffraction and microwave data analysis. The effect of the para-cyano substituent on the geometry of the pyridine ring is observed in comparison with the literature data for the pyridine molecule. [ABSTRACT FROM AUTHOR]

The equilibrium ( r e ) molecular structure of thiobenzamide along with r h1 structure has been determined in gas phase using gas electron-diffraction (GED) at about 127 °C and quantum-chemical calculations (QC). Rovibrational distance corrections to the thermal averaged GED structure have been computed with anharmonic force constants obtained at the MP2/cc-pVTZ level of theory. According to the results of GED and QC thiobenzamide exists as mixture of two non-planar enantiomers of C 1 symmetry. The selected equilibrium geometrical parameters of thiobenzamide ( r e , Å and ∠ e , deg) are the following: (C S) = 1.641(4), (C N) = 1.352(2), (C C) = 1.478(9), (C C) av  = 1.395(2), CCN = 114.7(5), CCS = 123.4(5), C2C1C7S = 31(4), C6C1C7N = 29(4). The structure of thiobenzamide in the gas phase is markedly different to that in the literature for the single crystal. The differences between the gas and the solid structures are ascribed to the presence of intermolecular hydrogen bonding in the solid phase. [ABSTRACT FROM AUTHOR]

The structure and internal rotation of the bromonitromethane molecule are studied using electron diffraction analysis and quantum chemical calculations. The electron diffraction data are analyzed within the models of a general intramolecular anharmonic force field and quantum chemical pseudoconformers to account for the adiabatic separation of a large amplitude motion associated with the internal rotation of the NO2 group. The following experimental bond lengths and valence angles are obtained for the equilibrium orthogonal configuration of the molecule with Cs symmetry: re(N=O) = 1.217(5) Å, re(C-N) = 1.48(2) Å, re(C-Br) = 1.919(5) Å, ∠еBr-C-N = 109.6(9)°, ∠еO=N=O = 125.9(9)°. The equilibrium geometry parameters are in good agreement with CCSD(T)/cc-pVTZ calculations. Thermally averaged parameters are calculated using the equilibrium geometry and quadratic and cubic quantum chemical force constants. The barrier to internal rotation cannot be determined reliably based on the electron diffraction data used in this work. There is a 82% probability that the equilibrium configuration with orthogonal C-Br and N=O bonds is most preferable, and internal rotation barrier does not exceed 280 cm-1, which agrees with CCSD(T)/cc-pVTZ calculations. [ABSTRACT FROM AUTHOR]

[Display omitted] • For the first time the molecule structure of 3,4-dicyanofuroxan has been investigated experimentally by means of GED method. • The joint GED and QC computational investigations have yielded an equilibrium molecular structure of 3,4-dicyanofuroxan. • The best agreement with experimental data has shown CCSD(T)/cc-pVTZ level of theory. • Possible resonance, electronic and steric effects in 3,4-dicyanofuroxan have been discussed. Equilibrium molecular structure of 3,4-dicyanofuroxan has been determined for the first time by means of gas electron diffraction (GED) and quantum chemical (QC) calculations. The GED values have been compared to those obtained from QC computations at different levels of theory. It has been discovered that the value of the O1−N2 bond is very sensitive to the QC method applied. The best fit to the experimental data has performed CCSD(T)/cc-pVTZ, whereas DFT methods applied in this work have been found to be less accurate. Peculiar features of 3,4-dicyanofuroxan molecular structure have been revealed by applying NBO, AIM and NCI analyses. [ABSTRACT FROM AUTHOR]

The synthesis and results of gas electron diffraction (GED), temperature-dependent Raman spectroscopy, along with detailed quantum chemical (QC) study of 1-methoxy-1-silacyclohexane 1 are reported. Within the series of the QC results, DFT(B3LYP, PBE0, M06, M062X), and MP2, the conformational preference predictions are rather contradictive. From the both GED and Raman experimental methods applied, the vapour and liquid phases of 1 were found to exist as a mixture of two conformers, gauche- axial and gauche -equatorial, with almost equal contributions, while the trans -forms are much less stable. In addition, theoretical calculations on the cyclohexane analog, methoxycyclohexane 2 , are performed in order to compare with the conformational properties of 1 . The latter is predicted not to diminish the axial/equatorial ratio, as contrasted to the expectations at switching the point of the substituent attachment from Si to C. [ABSTRACT FROM AUTHOR]

The molecular structure of tryptamine was studied by gas-phase electron diffraction (GED) and quantum chemical calculations (DFT/B3LYP and MP2 methods with cc-pVTZ basis set). The best fit of the experimental scattering intensities (R-factor = 3.8%) was obtained for the four-conformer model. The experimental structural parameters are found to be in good agreement with the results of theoretical calculations. The geometric parameters of gaseous tryptamine are compared with those in the crystal phase. The standard enthalpy of formation of tryptamine in the gas phase was calculated using Gaussian-4 theory, yielding value of 133.6 ± 3.3 kJ/mol. [ABSTRACT FROM AUTHOR]

Three compounds with phenyl and pentafluorophenyl rings bridged by (CH2)3 and (CH2)2SiMe2 units were synthesized by hydrosilylation and C−C coupling reactions. Their solid-state structures are dominated by intermolecular π stacking interactions, primarily leading to dimeric or chain-type aggregates. Analysis of free molecules in the gas phase by electron diffraction revealed the most abundant conformer to be significantly stabilized by intramolecular π-π interactions. For the silicon compounds, structures characterized by σ-π interactions between methyl and pentafluorophenyl groups are second lowest in energy and cannot be excluded completely by the gas electron diffraction experiments. C6H5(CH2)3C6F5, in contrast, is present as a single conformer. The gas-phase structures served as a reference for the evaluation of a series of (dispersion-corrected) quantum-chemical calculations. [ABSTRACT FROM AUTHOR]

Tris(pentafluorosulfanyl)amine, N(SF 5 ) 3 , and the bis(pentafluorosulfanyl)aminyl radical, N(SF 5 ) 2, have been synthesized and characterized by gas electron diffraction, single crystal XRD, NMR, EPR, FT-IR, Raman, and UV–vis spectroscopy, and by their thermal decompositions. The amine possesses a planar molecular structure of D 3 symmetry with an unusually long N S bond of 1.829(6) Å. The long N S bonds are in accordance with the small Arrhenius activation barrier for the decay into N(SF 5 ) 2 and SF 5 radicals of 6.9 kcal mol −1 , and its half-life at room temperature is only 50 min. The aminyl radical possesses C 2 symmetry with N S = 1.692(4) Å and S N S = 135.1(5)°, and its structure is similar to that of FN(SF 5 ) 2 . This radical is much more stable than the amine (half-life at room temperature is 130 min). Dimerization and formation of the corresponding hydrazine, (SF 5 ) 2 NN(SF 5 ) 2 , was not observed, nor was the nitrene:NSF 5 or its isomer FN SF 4 . [ABSTRACT FROM AUTHOR]

The conformational preference of the cyano group of the 1-cyano-1-silacyclohexane was studied experimentally by means of gas electron diffraction (GED) and dynamic nuclear magnetic resonance (DNMR) as well as by quantum chemical (QC) calculations applying high-level coupled cluster methods as well as DFT methods. According to the GED experiment, the compound exists in the gas-phase as a mixture of two conformers possessing the chair conformation of the six-membered ring and C s symmetry while differing in the axial or equatorial position of the substituent (axial = 84(12) mol %/equatorial = 16(12) mol %) at T = 279(3) K, corresponding to an A value ( G ax – G eq ) of −1.0(4) kcal mol −1 . Gas-phase CCSD(T) calculations predict an A value of −0.72 kcal mol −1 at 279 K. In contrast, the low-temperature 13 C NMR experiments resulted in an axial/equatorial ratio of 35/65 mol % at 120 K corresponding to an A value of 0.14 kcal mol −1 . An average value for Δ G # e→a = 5.6 ± 0.1 kcal mol −1 was obtained for the temperature range 110–145 K. The dramatically different conformational behaviour in the gas-phase (GED) compared to the liquid phase (DNMR) suggests a strong solvation effect. According to natural bond orbital analysis the axial conformer of the title compound is an example of stabilization of a form, which is not favored by electrostatic effects and is favored predominantly by steric and conjugation effects. [ABSTRACT FROM AUTHOR]

This paper reviews advances of modern gas electron diffraction (GED) method combined with high-resolution spectroscopy and quantum chemical calculations in studies of the impact of intramolecular dynamics in free molecules of pentahalides. Some recently developed approaches to the electron diffraction data interpretation, based on direct incorporation of the adiabatic potential energy surface parameters to the diffraction intensity are described. In this way, complementary data of different experimental and computational methods can be directly combined for solving problems of the molecular structure and its dynamics. The possibility to evaluate some important parameters of the adiabatic potential energy surface – barriers to pseudorotation and saddle point of intermediate configuration from diffraction intensities in solving the inverse GED problem is demonstrated on several examples. With increasing accuracy of the electron diffraction intensities and the development of the theoretical background of electron scattering and data interpretation, it has become possible to investigate complex nuclear dynamics in fluxional systems by the GED method. Results of other research groups are also included in the discussion. [ABSTRACT FROM AUTHOR]

The tautomeric and structural properties of 5-hydroxy-2,2,6,6-tetramethyl-3-heptanone, (dipivaloylmethane, C(CH 3 ) 3 C(O)CH 2 C(O)C(CH 3 ) 3 ) have been studied by means of gas-phase electron diffraction (GED) and quantum chemical calculations (B3LYP and MP2 approximation with different basis sets up to aug-cc-pVTZ). Both, quantum chemistry and GED analyses resulted in the presence of 100(5)% enol tautomer at 296(3)K. Quantum chemical calculations predict the existence of two enol conformers in about equal amounts. In both conformers the enol ring possesses C s symmetry and they possess different torsional orientations of the two tert-butyl groups. The experimental data refinement results in an enol tautomer, in which the tert-butyl group adjacent to the carbonyl group possesses an intermediate orientation between those in “enol1” and “enol 2” forms (torsional angle is about 30°), and the tert-butyl group adjacent to the hydroxyl group slightly deviates from orientation in the theoretical conformers (by about 10°). The enol ring possesses C S symmetry with a strongly asymmetric hydrogen bond. The experimental geometric parameters are reproduced very closely by the B3LYP/aug-cc-pVTZ method. [ABSTRACT FROM AUTHOR]

Dichlorofluoromethyl thiocyanate, CCl 2 FSCN, was structurally studied in the solid and in the gas phase by means of single-crystal X-ray (XRD) and gas electron diffraction (GED), respectively. In the gas phase the title molecule adopts two stable conformers, described by the FC–SC dihedral angle. The gauche -conformer (FC bond with respect to the SC bond) is more stable than the anti- conformer. In this work we present the first experimental evidence for the existence of the anti -CF 2 ClSCN form. In the solid state only the most stable gauche -conformer was found. Intermolecular interactions were detected in the crystal structure and analyzed. A structural comparison of the results with those of related species as CCl 2 FSCN, CCl 3 SCN and CH 2 ClSCN is presented. [ABSTRACT FROM AUTHOR]

Molecular structure and conformational behavior of N -phenylpiperidine ( NPhP ) were investigated by synchronous gas-phase electron diffraction/mass spectrometry (GED/MS) and quantum chemistry. Due to influence of steric repulsion and hyperconjugation, NPhP may exist in two conformers, equatorial and axial chair forms. Both experiment and theoretical calculations suggest a C 1 symmetry of the conformers, with the plane perpendicular to the phenyl group turned by ca. 30–40° (equatorial) and 0–20° (axial) about the plane perpendicular to the piperidine ring symmetry plane. According to the QC calculations, NPhP may exist as two conformers, equatorial and axial, with a ratio of Eq:Ax = 92:8 (B3LYP), 87:13 (B3LYP-GD3), 84:16 (M06-2X), 83:17 (MP2/6-311G**) and 76:24% (MP2/cc-pVTZ). Except for the latter, these values are in good agreement with the experimental GED data of 90(10):10(10)%. A comparative analysis of similar compounds, phenylcyclohexane and 1-phenylheterocyclohexanes, was performed. Conformational properties depend on the C Ph X bond distance and hyperconjugation between the phenyl ring and the lone pair on the heteroatom. The contribution of the axial form of 1-phenylcyclohexane derivatives increases in the series of the heteroatom X in the cyclohexane ring: C → N → Si → P. [ABSTRACT FROM AUTHOR]

A semi-experimental equilibrium structure of free molecules of pyrazinamide has been determined for the first time using gas electron diffraction method. The refinement was carried using regularization of geometry by calculated quantum chemical parameters. It is discussed to which extent is the final structure experimental. A numerical approach for estimation of the amount of experimental information in the refined parameters is suggested. The following values of selected internuclear distances were determined (values are in Å with 1 σ in the parentheses): r e (C pyrazine —C pyrazine ) av = 1.397(2), r e (N pyrazine —C pyrazine ) av = 1.332(3), r e (C pyrazine —C amide ) = 1.493(1), r e (N amide —C amide ) = 1.335(2), r e (O amide —C amide ) = 1.219(1). The given standard deviations represent pure experimental uncertainties without the influence of regularization. [ABSTRACT FROM AUTHOR]