Computational study on the crystal structure, thermodynamic properties, detonation performance and pyrolysis mechanism of a novel high density cage compound 10-(5-nitrimino-1,2,3,4-tetrazol-1-yl)methyl-2,4,6,8,12-pentanitrohexaazaisowurtzitane

A novel polynitro cage compound 10-(5-nitrimino-1,2,3,4-tetrazol-1-yl)methyl-2,4,6,8,12-pentanitro-hexaazaisowurtzitane, composed of CL-20 and tetrazole framework, has been designed. DFT-B3LYP/6-31G(d) and molecular mechanics methods are employed to calculate its IR spectrum, heat of formation, thermodynamic properties, and crystal structure. Besides, the stability of this compound is evaluated using the bond dissociation energy. The result shows that the initial step of thermal decomposition is the rupture of N–NO₂ bond in the side chain. This compound is most likely to crystallize in the P-1 space group, and corresponding cell parameters are Z = 2, a = 7.65 Å, b = 14.30 Å, c = 10.36 Å, α = 91.53°, β = 50.83°, γ = 89.44°, and ρ = 2.025 g cm^?3. Detonation velocity and detonation pressure of this compound are estimated to be 9.090 km s^?1 and 38.078 GPa using the Kamlet–Jacobs equation, similar to those of CL-20. Considering detonation performance and thermal stability, this compound meets the requirements of exploitable high energy density materials.     

Theoretical investigation of a high density cage compound 1,3,5,7,9,11-hexanitrotetradecahydro-1H-1,3,4,5,7,7b,9,11,12a,12b1,12b2,13-dodecaaza-4,8,12-(epimethanetriyl)cyclohepta[l]cyclopenta[def] phenanthrene

The B3LYP/6-31G** method was used to investigate IR and Raman spectra, heat of formation, and thermodynamic properties of a new designed polynitro cage compound 1,3,5,7,9,11-hexanitrotetradecahydro-1H-1,3,4,5,7,7b,9,11,12a,12b¹,12b²,13-dodecaaza-4,8,12-(epimethanetriyl)cyclohepta[l]cyclopenta[def]phenanthrene. The detonation and pressure were evaluated using the Kamlet–Jacobs equations based on the theoretical density and HOFs. The bond dissociation energies and bond orders for the weakest bonds were analyzed to investigate the thermal stability of the title compound. The results show that N₈–NO₂ bond is predicted to be the trigger bond during pyrolysis. There exists an essentially linear relationship between the WBIs of N–NO₂ bonds and the charges – $ Q_{{{\text{NO}}_{ 2} }} $ on the nitro groups. The crystal structure obtained by molecular mechanics belongs to the P2₁ space group, with lattice parameters Z = 2, a = 11.4658 Å, b = 15.2442 Å, c = 10.2451 Å, ρ = 2.07 g cm^?3. The designed compound has high thermal stability and good detonation properties and is a promising high-energy density compound.     

2-Propylamino-5-[4-(2-hydroxy-3,5-dichlorobenzylideneamino) phenyl]-1,3,4-thiadiazole: X-ray and DFT-calculated structures

2-Propylamino-5-[4-(2-hydroxy-3,5-dichlorobenzylideneamino) phenyl]-1,3,4-thiadiazole, formulated as C₁₈H₁₆Cl₂N₄OS (I), was synthesized. The crystal and molecular structure of (I) have been determined by ¹H-NMR, IR, and X-ray single crystal diffraction. The compound (I) crystallizes in the monoclinic, space group P2(1)/c with unit cell parameters a = 9.0576(2) Å, b = 24.3382(8) Å, c = 9.0585(2) Å, M _r = 407.31, V = 1851.13(9) Å³, Z = 4, R ₁ = 0.036, and wR ₂ = 0.096. Molecular geometry from X-ray experiment of (I) in the ground state has been compared using the density functional method (B3LYP) with 6-31G(d) basis set. To determine conformational flexibility, molecular energy profile of (I) was obtained by semi-empirical (PM3) calculations with respect to selected degree of torsional freedom, which was varied from ?180° to +180° in steps of 10°. The results are indicative that the Schiff base, which contains a thiadiazole ring, prefers to be in E-configuration. In addition, molecular electrostatic potential, frontier molecular orbitals, and natural bond orbitals analysis were performed by the B3LYP/6-31G(d) method.     

The molecular structure, bonding, and energetics of oxovanadium phthalocyanine: an experimental and computational study

A mass spectrometric study of saturated vapor over oxovanadium phthalocyanine showed the thermal stability and monomeric vapor composition of this compound. The molecular structure of oxovanadium phthalocyanine (VOPc) was determined using a combination of gas-phase electron diffraction (GED), mass spectrometry, and quantum chemical calculations. According to GED, the VOPc molecule has C_4v symmetry. Experimental structural parameters are in good agreement with the parameters obtained by UB3LYP/cc-pVTZ calculations. The vanadium atom has a five-coordinated square-pyramidal geometry, being shifted above the plane of the four isoindole nitrogen atoms by 0.576(14) Å. The parameters of the square pyramid VN₄ are r _h1(V–N) = 2.048(7) Å, r _h1(N···N) = 2.780(12) Å. The vanadium–oxygen bond length is r _h1(V–O) = 1.584(11) Å. NBO analysis shows polar character of coordination bonds with significant covalent contribution and pronounced direct donation. X-ray crystallography and GED give different coordination bond lengths according to the different physical meaning of the parameters obtained by these methods. The enthalpy of sublimation [?H _s ^o (593–678 K)] is 53.3 ± 0.8 kcal/mol.     

Computational characterization of 2, 4, 6, 8, 10, 12, 13-heptaazatetracyclo [5.5.1.03,11.05,9]tridecanes as potential energetic compounds

The characters of high density and high heat of formation of cage molecules have attracted a lot of investigations as potential energetic materials. Several such compounds have been synthesized, e.g., octanitrocubane, hexanitrohexaazaisowurzitane (CL-20), and 4-trinitroethyl-2, 6, 8, 10, 12-pentanitrohexaazaisowurtzitane(TNE-CL-20). In the present study, a new cage compound, namely 2, 4, 6, 8, 10, 12, 13-heptaazatetracyclo [5.5.1.0^3,11.0^5,9] tridecane (HATT), was proposed. Density functional theory has been employed to study the geometric and electronic structures for a series of nitro derivatives of HATT at the B3LYP/6-31G(d,p) level. Thermodynamic properties derived on the basis of statistical thermodynamic principles are linearly correlated with the numbers of nitro group as well as the temperature. Detonation performance was evaluated based on the calculated densities and heats of formation. It is found that some title compounds have high densities of ca. 1.9 g cm^?3, detonation velocities over 9.0 km s^?1, and detonation pressures of about 40.0 GPa and may be novel potential candidates of high energy density compounds (HEDCs). Thermal stability and pyrolysis mechanism of the nitro HATTs were investigated by calculating the bond dissociation energies (BDE). In conjunction with the detonation performance and thermal stability, HATTs with no less than five nitro groups are recommended as the preferred candidates of HEDCs. These results provide basic information for the further studies of cage compounds.     

Structure,bioactivity and theoretical study of 1-cyano-<Emphasis Type="Italic">N</Emphasis>-p-tolylcyclo-propanecarboxamide

A novel cyclopropane derivative, 1-cyano-N-p-tolylcyclopropanecarboxamide (C₁₂H₁₂N₂O, Mr = 200.24) was synthesized and its structure was studied by X-ray diffraction, FTIR, ¹H and ¹³C NMR spectrum and MS. The crystals are monoclinic, space group P2_1/c with a = 7.109 (4), b = 13.758 (7), c = 11.505 (6) Å, α = 90.00, β = 102.731 (8), γ = 90.00 °, V = 1097.6 (9) ų, Z = 4, F(000) = 312, D _c  = 1.212 g/cm³, μ = 0.0800 mm^?1, the final R = 0.0490 and wR = 0.1480 for 1,375 observed reflections with I > 2σ(I). A total of 6,109 reflections were collected, of which 2,290 were independent (R _int = 0.0290). Theoretical calculation of the title compound was carried out with HF/6-31G (d,p), B3LYP/6-31G (d,p), MP2/6-31G (d,p). The full geometry optimization was carried out using 6-31G(d,p) basis set, and the frontier orbital energy. Atomic net charges were discussed, and the structure-activity relationship was also studied. The preliminary biological test showed that the synthesized compound is bioactive against the KARI of Escherichia coli.     

Spectroscopic characterization,X-ray structure and DFT studies on 4-[3-(2,5-dimethylphenyl)-3-methylcyclobutyl]-N-methylthiazol-2-amine

The titled molecule 4-[3-(2,5-dimethylphenyl)-3-methylcyclobutyl]-N-methylthiazol-2-amine (C₁₇H₂₂N₂S) is synthesized and characterized by ¹H NMR, ¹³C NMR, IR, and X-ray single crystal determination. The compound crystallizes in the monoclinic space group P2_1/c with a = 6.3972(4) Å, b = 9.4988(6) Å, c = 26.016(2) Å and β = 93.496(7)°. In addition to the molecular geometry from the X-ray determination, vibrational frequencies and gauge, including the atomic orbital (GIAO), ¹H and ¹³C NMR chemical shift values of the titled compound in the ground state are calculated using the density functional (B3LYP) method with 6-31G(d), 6-31++G(d,p) and 6-311+G(2d,p) basis sets. The calculated results show that the optimized geometries can well reproduce the crystal structure. Moreover, the theoretical vibrational frequencies and chemical shift values show good agreement with the experimental values. The predicted nonlinear optical properties of the titled compound are greater than those of urea. DFT calculations of the molecular electrostatic potentials and frontier molecular orbitals of the titled compound are carried out at the B3LYP/6-31G(d) level of theory.     

Structure of gallium(III) monofluoride phthalocyaninate: A quantum chemical study

The B3LYP/6-31G quantum chemical method is used to calculate the structural parameters of [F(PcGaF)₇]^-, [(PcGaF)₆PcGa]⁺ heptamers and the (PcGaF)_∞, polymer of gallium(III) monofluoride phthalocyaninate. The eclipsed (ecl.) configuration (D _4h point symmetry group) corresponds to the energy minimum of the [FGa(Pc)FGa(Pc)F]^- dimer. The calculated equilibrium bond lengths in the central unit of all-ecl. heptamer (GaN 1.988 Å; GaF 1.933 Å) are similar to the bond lengths in the all-ecl. polymer (GaN 1.988 Å and GaF 1.940 Å) and to the respective single crystal X-ray diffraction parameters.     

Synthesis of Some Octahedral Nickel(II) Complexes of One Isomer of Isomeric Me8[14]anes: X-ray Structure of Diisothiocyanato(3,10-C-meso-3,5,7,7,10,12,14,14-octamethyl-1,4,8,11-tetraazacyclotetradecane, LC)nickel(II), [NiLC(NCS)2]

One isomer, L_C of the isomeric Me₈[14]anes, L_A, L_B and L_C; on reaction with Ni(NCS)₂ produces a six coordinate octahedral diisothiocyanato complex, [NiL_C(NCS)₂]. This complex undergoes axial substitution reactions with the small ligands to yield corresponding monosubstituted derivatives having general formula [NiL_C(NCS)X] whereas X = Cl, Br, I, NO₂ or NO₃. The complexes have been characterized on the basis of analytical, spectroscopic, magnetic and conductance data. The structure of [NiL_C(NCS)₂] (triclinic, space group P?1, α = 8.0421(17) Å, β = 8.9085(18) Å, χ = 9.687(2) Å, α = 67.561(3) Å, β = 82,896(4) Å, ζ = 598.7(2) Å³, Z = 2, Dc = 1.352 mg/m³, μ(Mo Kα) = 1.003 mm^?1) was confirmed by X-ray crystallography.     

Crystallographic and conformational analysis of (<Emphasis Type="Italic">E</Emphasis>)-2-isopropyl-4-(<Emphasis Type="Italic">p</Emphasis>-tolyldiazenyl)phenol

The molecular and crystal structures of the title compound, C₁₆H₁₈N₂O, were characterized and determined by single crystal X-ray diffraction method in addition to spectroscopic means such as IR, UV–VIS and ¹H NMR. The compound crystallizes in orthorhombic space group P bca, with a = 9.3350(5) Å, b = 23.4878(13) Å, c = 26.5871(12) Å, Z = 16, D _calc. = 1.1591(1) g/cm³, μ (MoK_α) = 0.073 mm^?1. Monomers of the compound in the crystal structure are linked into C(7) and C(8) chains generated by translation along the [1 0 0] direction with the aid of O–H···N type H-bonds which serve to the stabilization of periodic organization of the molecules beside major and minor component in the disordered azo fragment. In order to describe conformational flexibility and the crystal packing effects on the molecular conformation, potential barriers regarding the rotation along both Ar–N bonds were calculated by varying the related torsional degrees of freedom in every 10° ranging from ?180° to +180° via quantum chemical calculations at DFT/B3LYP level.     

Synthesis,spectroscopic characterization,crystal structures,and theoretical studies of (<Emphasis Type="Italic">E</Emphasis>)-2-(2,4-dimethoxybenzylidene)thiosemicarbazone and (<Emphasis Type="Italic">E</Emphasis>)-2-(2,5-dimethoxybenzylidene)thiosemicarbazone

Two thiosemicarbazones, (E)-2-(2,4-dimethoxybenzylidene)thiosemicarbazone (24-MBTSC (1)) and (E)-2-(2,5-dimethoxybenzylidene)thiosemicarbazone (25-MBTSC (2)), derived from 2,4-dimethoxybenzaldehyde and 2,5-dimethoxybenzaldehyde, respectively, with thiosemicarbazide have been synthesized and their structures were characterized by elemental analyses, FT-IR, ¹H NMR spectroscopy, and X-ray single-crystal diffraction analysis. Molecular orbital calculations have been carried out for 1 and 2 by using an ab initio method (HF) and also density functional method (B3LYP) at 6-31G basis set. Compound 1 crystallizes in the monoclinic system, space group P2₁/c, with a = 8.1342(5) Å, b = 18.1406(10) Å, c = 8.2847(6) Å, β = 109.7258(17)°, V = 1150.75(12) Å³, and Z = 4, whereas compound 2 crystallizes in the orthorhombic system, space group Pbca, with a = 11.0868(6) Å, b = 13.1332(6) Å, c = 15.9006(8) Å, V = 2315.2(2) Å³, and Z = 8. The compounds 1 and 2 displays a trans-configuration about the C=N double bond.     

Structural characterization of <Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">N</Emphasis>′-bis(2-methoxyethyl) -4,5-bis(2,4,6-trimethylphenyl)imidazolinium hexafluorophosphate

The crystal and molecular structure of the N,N′-bis(2-methoxyethyl)-4,5-bis(2,4,6-trimethylphenyl)- imidazolinium hexafluorophosphate, which is the first example of 1,3- and 4,5-disubstituted imidazolinium salts, have been determined and characterized by X-ray single crystal diffraction technique,¹H, ¹³C, ³¹P and ¹⁹F NMR spectroscopy. The compound, C₂₇H₃₉N₂O₂ ⁺·PF₆ ^?, crystallizes in the orthorhombic space group Pba2 with a = 15.8139(4) Å, b = 22.9346(7) Å, c = 8.069(3) Å. Two charge-assisted C–H\(\cdots\)F type crystal packing interactions between the imidazolinium C–H bonds and the F atoms of hexafluorophosphate counteranions build up zigzag chains along a-axis of the unit cell and indicate that the C–H bonds of the imidazolinium ring are also polarized. In addition, the title salt was modeled by DFT calculations in order to verify charge transfer mechanism observed in its imidazolinium ring.     

Synthesis and crystal structure of diferrocenylmethoxyethylamine

The reaction of diethanolamine with diferrocenylmethyl carbonium (2) that was generated by diferrocenylmethanol (1) treated with BF₃ in CH₂Cl₂ provided the synthesis of title compound diferrocenylmethoxyethylamine (3). The structure of 3 was determined by the X-ray diffraction (XRD) with crystal data: monoclinic P2₁/n space group and a=5.8419(14) Å, b=13.572(3) Å, c=23.839(6) Å, α=90°, β=91.827(5)°, γ=90°, V=1889.2(8) Å³, Z=4, D _c =1.558 mg·m^?3, μ=1.548 mm^?1, F(000)=920. The intra- and inter-molecular H bonding modes in 3 were demonstrated both in molecular crystal structure and IR spectral characterization.     

Synthesis of diferrocenylmethoxyethanol via reaction of diferrocenylmethyl cabonium with glycol and its crystal structure

The new compound diferrocenylmethoxyethanol has been synthesized from the reaction of glycol in the presence of triethylamine with diferrocenylmethyl carbonium which was generated by diferrocenylmethanol treated with BF₃ in CH₂Cl₂ without separation from the reaction mixture. Diferrocenylmethoxyethanol was characterized by elemental analysis, ¹H NMR and IR. The structure was also confirmed by a X-ray single crystal study. It was found that diferrocenylmethoxylethanol crystallized in a monoclinic P2₁ space group and a=5.8250(8) Å, b=7.4034(10) Å, c=21.773(3) Å, α=90°, β=95.020(3)°, γ=90°, V=935.4(2) Å³, Z=2, D _c=1.577 mg·m^?3, μ=1.566 mm^?1, F(0 0 0)=460.     

Structures and stability of SCBO+/− and SBCO+/−: prediction of very short yet classical triple bonding of sulfur

Compounds containing the sulfur triple bonding have continued to attract chemists’ attention. In this article, with an attempt to predict intrinsically stable species with sulfur-related triple bonding, we report a thorough computational study of two charged systems [B,C,O,S]⁺ and [B,C,O,S]^? at the CCSD(T)/aug-cc-pVTZ//B3LYP/6-311+G(3df,2p)+ZPVE level for singlet and triplet potential energy surfaces, aug-cc-pVTZ-B3LYP, M06-2X, and CCSD(T) levels for critical structures, as well as the CCSD(T)/aug-cc-pVQZ and G4 levels for adiabatic bond dissociation energy (ABDE). A total of 26 isomers and 25 transition states were located. The cationic and anionic [B,C,O,S] have the singlet and triplet ground states, respectively. For both systems, the former low-lying isomers are the linear SCBO^+/? 01 and SBCO^+/? 02, both of which contain the S≡X (X = C, B) bonding and are kinetically very stable against interconversion and fragmentation. With the increased valence electron number in the order of SCBO/SBCO⁺ < SCBO/SBCO < SCBO/SBCO^?, the SX bond distance elongates as 1.5653 < 1.6126 < 1.6924 Å for X = B and 1.4715 < 1.5319 < 1.6100 Å for X = C at the M06-2X/aug-cc-pVTZ level. Notably, SBCO⁺ bears the shortest S≡B bond known to date, while SCBO⁺ bears the shortest S≡C bond among the known classical and non-protonated compounds (the well-known F₃SCCF₃ and F₃SCSF₅ have been termed as “nonclassical” because of their unusually low ABDE of SC bond). Future mass spectroscopic studies are greatly appealed for the characterization of the cationic and anionic SCBO^+/? 01 as well as SBCO^+/? 02.     

Melting of orthorhombic betulin

Orthorhombic (s.g. P 2₁ 2₁ 2, a = 28.6145 Å, b = 27.4115 Å, c = 6.9536 Å, V = 5454.1 Å³) betulin (C₃₀H₅₀O₂) was found in this study to melt at 245 °C with the enthalpy of fusion 40.3 J mol^?1. The shape of the peak of melting gives rise to the belief that there are several polymorphs of betulin.     

A theoretical prediction of the molecular and electronic structures,thermodynamic properties,and stability of 1,3-diazido-2-methyl-2-nitropropane (DAMNP)

1,3-Diazido-2-methyl-2-nitropropane (DAMNP) is a newly synthesized azido compound and may be a potential candidate of the plasticizer of propellants. For better understanding its properties, the molecular conformations, electronic structure, IR spectrum, thermodynamic properties, pyrolysis mechanism, and specific impulse (I _S) were studied using the B3LYP/6-31++G** method of density functional theory (DFT). The electronic structure of DAMNP was analyzed by the natural atomic charges, bond orders, donor–acceptor interactions, and molecular electrostatic potential (MEP). Results show that the main contributions to the highest occupied molecular orbital and the lowest unoccupied molecular orbital are from –N₃ and –NO₂, respectively. The most negative area on the MEP locates at the O atoms of –NO₂, which agrees with the atomic charges distributions. The pyrolysis mechanism was investigated by considering three possible bond dissociations (C–N₃, C–NO₂, and N–N₂). Results show that the pyrolysis of DAMNP starts from the rupture of N–N₂ finished cooperatively via the H-transfer process to eliminate N₂. The lowest energy needed for pyrolysis is 165.13 kJ mol^?1. To verify the reliability of the method, the organic azido compound CH₃N₃ was also considered. DAMNP has a slightly higher thermal stability than CH₃N₃. However, using DAMNP to replace the plasticizer nitroglycerin of the nitramine modified double-base propellant leads to a decrease in I _S. Therefore, whether DAMNP can be really used as a plasticizer or not is worth further considerations.     

Growth,structural, crystallisation,thermal decomposition and dielectric behaviour of melaminium bis(hydrogen oxalate) single crystal

Single crystals of melaminium bis (hydrogen oxalate) (MOX) single crystals have been grown from aqueous solution by slow solvent evaporation method at room temperature. X-ray powder diffraction analysis confirms that MOX crystallises in monoclinic system with space group C2/c. The calculated lattice parameters are a = 20.075 ± 0.123 Å b = 8.477 ± 0.045 Å, c = 6.983 ± 0.015 Å, α = 90°, β = 102.6 ± 0.33°, γ = 90° and V = 1,159.73 (Å)³. Thermogravimetric analysis at three different heating rates 10, 15 and 20 °C min^?1 has been done to study the thermal decomposition behaviour of the crystal. Non-isothermal studies on MOX reveal that the decomposition occurs in two stages. Kinetic parameters [effective activation energy (E _a), pre-exponential factor (ln A)] of each stage were calculated by model-free method: Kissinger, Kim–Park and Flynn–Wall method and the results are discussed. A significant variation in effective activation energy (E _a) with conversion progress (α) indicates that the process is kinetically complex. The linear relationship between the ln A and E _a was established (compensation effect). DTA analyses were conducted at different heating rates and the activation energy was determined graphically from Kissinger and Ozawa equation. The average effective activation energy is calculated as 276 kJ mol^?1 for the crystallization peak. The Avrami exponent for the crystallization peak temperature determined by Augis and Bennett method is found to be 1.95. This result indicates that the surface crystallization dominates overall crystallization. Dielectric study has also been done, and it is found that both dielectric constant and dielectric loss decreases with increase in frequency and is almost a constant at high frequency region.     

Comparative theoretical studies of substituted bridged bipyridines and their N-oxides

In this work, the experimental synthesized bipyridines azo-bis(2-pyridine),4,4′-dimethyl-3,3′-dinitro-2,2′-azobipyridine, and N,N′-bis(3-nitro-2-pyridinyl)-methane-diamine and a set of designed bipyridines that have similar frameworks but different linkages and substituents were studied theoretically at the B3LYP/6-31G* level of density functional theory. The gas-phase heats of formation were predicted based on the isodesmic reactions, and the condensed-phase heats of formation and heats of sublimation were estimated in the framework of the Politzer approach. The crystal densities have been computed from molecular packing and results show that incorporation of –N=N–, –N=N(O)–, –CH=N–, and –NH–NH– into bipyridines is more favorable than –CH=CH– and –NH–CH₂–NH– for increasing the density. The predicted detonation velocities (D) and detonation pressures (P) indicate that –NH₂, –NO₂, and –NF₂ can enhance the detonation performance, and –NO₂ and –NF₂ are more favorable. Introducing –N=N–, –N=N(O)–, and –NH–NH– bridge groups into bipyridines is also favorable for improving their detonation performance. The oxidation of pyridine N always but that of –N=N– bridge does not always improve the detonation properties. E4–O, the derivative with –N=N– bridge and two –NF₂ substituent groups, has the largest D (9.90 km/s) and P (47.47 GPa). An analysis of the bond dissociation energies shows that all derivatives have good thermal stability.     

Molecular structure and conformation of nitrobenzene reinvestigated by combined analysis of gas-phase electron diffraction,rotational constants,and theoretical calculations

The molecular structure and conformation of nitrobenzene has been reinvestigated by gas-phase electron diffraction (GED), combined analysis of GED and microwave (MW) spectroscopic data, and quantum chemical calculations. The equilibrium r _e structure of nitrobenzene was determined by a joint analysis of the GED data and rotational constants taken from the literature. The necessary anharmonic vibrational corrections to the internuclear distances (r _e ? r _a) and to rotational constants (B _e ⁽ⁱ⁾  ? B ₀ ⁽ⁱ⁾ ) were calculated from the B3LYP/cc-pVTZ quadratic and cubic force fields. A combined analysis of GED and MW data led to following structural parameters (r _e) of planar nitrobenzene (the total estimated uncertainties are in parentheses): r(C–C)_av = 1.391(3) Å, r(C–N) = 1.468(4) Å, r(N–O) = 1.223(2) Å, r(C–H)_av = 1.071(3) Å, \({\angle}\)C2–C1–C6 = 123.5(6)°, \({\angle}\)C1–C2–C3 = 117.8(3)°, \({\angle}\)C2–C3–C4 = 120.3(3)°, \({\angle}\)C3–C4–C5 = 120.5(6)°, \({\angle}\)C–C–N = 118.2(3)°, \({\angle}\)C–N–O = 117.9(2)°, \({\angle}\)O–N–O = 124.2(4)°, \({\angle}\)(C–C–H)_av = 120.6(20)°. These structural parameters reproduce the experimental B ₀ ⁽ⁱ⁾ values within 0.05 MHz. The experimental results are in good agreement with the theoretical calculations. The barrier height to internal rotation of nitro group, 4.1±1.0 kcal/mol, was estimated from the GED analysis using a dynamic model. The equilibrium structure was also calculated using the experimental rotational constants for nitrobenzene isotopomers and theoretical rotation–vibration interaction constants.