Computational DFT studies on a series of toluene derivatives as potential high energy density compounds

Based on the full optimized molecular geometric structures at B3LYP/6-31G**, B3LYP/6-31+G**, B3P86/6-31G**, and B3P86/6-31+G** levels, the densities (ρ), detonation velocities (D), and pressures (P) for a series of toluene derivatives, as well as their thermal stabilities, were investigated to look for high energy density compounds (HEDCs). The heats of formation (HOFs) are also calculated via designed isodesmic reactions. The calculations on the bond dissociation energies (BDEs) indicate that the BDEs of the initial scission step are between 48 and 59 kcal/mol, and pentanitrotoluene is the most reactive compound, while 2,4,6-trinitrotoluene is the least reactive compound for toluene derivatives studied. A good linear relationship between BDE/E and impact sensitivity is also obtained. The condensed phase HOFs are calculated for the title compounds. These results would provide basic information for the further studies of HEDCs. The detonation data of pentanitrotoluene show that it meets the requirement for HEDCs.     

Phosphoramides: Synthesis,Spectroscopy, and X‐ray Crystallography

A series of new phosphoramides with general formula RP(O)X₂, where R = amino/p‐methylphenoxy and X = amine, were synthesized and characterized by ¹H, ¹³C, ³¹P nuclear magnetic resonance (NMR), and infrared (IR) spectroscopy and elemental analysis. The ³¹P{¹H} NMR spectra show that among compounds 7–9 containing 2‐, 3‐, and 4‐aminopyridinyl moieties, respectively, the shielding order of the P atom decreases as 7 > 9 > 8 . Also, the structure of compound 7 was determined by X‐ray crystallography. In this structure, repeated noncentrosymmetric dimers are formed by two strong intermolecular N(1)‐H(1N)…N(2) and N(3)‐H(3N)…O(1) hydrogen bonds. Taking into account weak intermolecular C(17)‐H(17C)…N(4), C(17)‐H(17E)…N(4), C(2)‐H(2A)…O(2), and also weak aromatic C—H…C interactions, a three‐dimensional polymeric chain is created in the crystalline network. The density functional theory calculations at B3LYP, B3PW91, and M06 levels using the 6–31+G** basis set were in good agreement with the X‐ray crystallography data.     

Experimental and calculated H, C and P NMR spectra of pyridine-2-phosphono-4-carboxylic acid

Pyridine-2-phosphono-4-carboxylic acid (MC1) is a compound that possesses potential neuroactivity. In this work the ¹H, ¹³C and ³¹P NMR spectra of MC1 dissolved in D₂O in solution, in the 1.5-9.0 pD range, are presented. Theoretical calculations of the NMR spectra, as well as structural parameters of expected compounds, were performed at the B3PW91/6-311G** and B3PW91/6-31G** level, respectively, for all five possible forms of MC1 (cation, zwitteranion and three anions). Consecutive deprotonation of MC1 and its influence on the structure of the ligand are discussed in detail.     

Spectroscopic characterization and <Emphasis Type="Italic">Ab initio</Emphasis> calculations of new diazaphosphole and diazaphosphorinane

Phosphoryl chloride is used as a starting material to synthesize new diazaphosphole, (1) and diazaphosphorinane, (2). The products are characterized by ¹H, ¹³C, ³¹P NMR, and IR spectroscopy. A high value ² J(PNH) = 17.0 Hz, 17.2 Hz is measured for two non-equivalent NH protons of endocyclic nitrogen atoms in compound 1, while it greatly decreases to 4.5 Hz in 2. Also, great amounts are obtained for two ² J(P,C) as well as two ³ J(P,C) in the ¹³C NMR spectrum of 1, but they are zero in 2. Here, the effect of ring strain and ring size on the structural and spectroscopic parameters is observed. The ³¹P NMR spectra reveal that δ(³¹P) of compound 1 is far much more downfield (12.63 ppm) relative to that of compound 2 (−10.39 ppm). Furthermore, ab initio quantum chemical calculations are performed to optimize the structures of these molecules by density functional theory (B3LYP) and Hartree-Fock (HF) methods, using the standard 6−31+G** basis set. The stabilization energies are calculated by the equation ΔE _{stabilization} = E _molecule − ΣE _i , where i = atom. To obtain the atomic hybridizations, NBO computations are made at the B3LYP/6−31+G** level. Also, by NMR calculations the ¹H, ¹³C, ³¹P chemical shifts are obtained and compared with the experimental ones.     

Synthesis,spectroscopy, computational study and prospective biological activity of two novel 1,3,2-diazaphospholidine-2,4,5-triones

The preparation of two new 1,3,2-diazaphospholidine-2,4,5-triones is reported. Thus, 2-chloro-1,3,2-diazaphospholidine-2,4,5-trione [ClP(O)(NHC(O)C(O)NH) (I)] and 2-benzylamino-1,3,2-diazaphospholidine-2,4,5-trione [C₆H₅CH₂NHP(O)(NHC(O)C(O)NH) (II)] have been synthesized by the reaction of POCl₃ with the corresponding carboxylic diamide salts. The characterization of the compound I was performed by multinuclear (¹H, ¹³C, ³¹P) NMR and FTIR spectroscopies, elemental analysis and also mass spectrometry. Both compounds show two signals at room temperature in the low field region of the ¹H NMR spectrum, which collapsed to a single peak when the temperature is increased. Dynamic NMR (¹H DNMR) and quantum chemical studies were performed to gain insight from this conversion process. The free activation energies, calculated at the coalescence temperatures are 18.51 and 17.45 kcal/mol for compounds (I) and (II), respectively, which are associated with a tautomeric interconversion process, most likely between the lactam and lactim forms. The relative energy, molecular geometry and vibrational properties of several plausible tautomers were analyzed by using quantum chemical calculations at the HF/6-311G** and B3LYP/6-311++G** levels of the theory. The nuclear magnetic shielding tensors have been calculated for both tautomeric forms using the gauge independent atomic orbital (GIAO) method at the B3LYP/6-311++G(3df,2p) level of approximation. A biological activity prediction using the PASS software shows that compound (I) can be characterized by a superb anti-HIV activity whereas compound (II) is a very good antineoplastic.     

Synthesis,characterization, and quantum chemical calculational studies on 3-<Emphasis Type="Italic">p</Emphasis>-methylphenyl-4-amino- 1, 2, 4-triazole-5-thione

The title compound of 3-p-methylphenyl-4-amino-1, 2, 4-triazole-5-thione was synthesized and characterized by elemental analysis, IR, electronic spectra, and X-ray single crystal diffraction. Quantum chemical calculations of the structure, natural bond orbital, and thermodynamic functions of the title compound were performed by using B3LYP/6-311G** and HF-6-311G** methods. Both the methods can well simulate the molecular structure. Vibrational frequencies were predicted, assigned and compared with the experimental values, and B3LYP/6-311G** method is superior to HF/6-311G** method to predict the vibrational frequencies. Electronic absorption spectra calculated by B3LYP/6-311G** method have some red shifts compared with the experimental ones and natural bond orbitals analyses indicate that the two absorption bands are mainly derived from the contribution of n → π^* and π → π^* transitions. On the basis of vibrational analyses, the thermodynamic properties of the title compound at different temperatures have been calculated, revealing the correlations between C ⁰ _p,m , S ⁰ _m , H ⁰ _m , and temperatures.     

Quadrupole coupling constants of deuterons in molecular clusters Ca<Superscript>2+</Superscript>(D<Subscript>2</Subscript>O)<Subscript><Emphasis Type="Italic">n</Emphasis></Subscript> (<Emphasis Type="Italic">n</Emphasis> = 6, 8, 10, 18)

Characteristic features of the structure of Ca²⁺ hydration shells were considered. The results of quantum chemical calculations were compared with experimental data obtained from the study of nuclear magnetic relaxation of deuterons in aqueous solutions of calcium salts. The influence of the basis set and computational procedure on the calculated ²D quadrupole couling constants (QCC) in isolated water molecule was investigated. The ²D QCC in molecular clusters (D₂O)₅ and Ca²⁺(D₂O) _n (n =6, 8, 10, 18) were calculated using the B3LYP/6-31++G** density functional method.     

Toward the comprehensive calculations on the relationship between 1H, 13C, 31P chemical shifts, 2JPH,and the bonding structure of different phosphoryl benzamides

A comprehensive investigation was performed on ¹H, ¹³C, and ³¹P nuclear magnetic resonance (NMR) chemical shifts (CSs) of phosphoryl benzamide derivatives (C₆H₅C(O)NHP(O)R₁R₂), (R₁, R₂ = aziridine [L₁], azetidine [L₂], pyrrolidine [L₃], piperidine [L₄], azepane [L₅], 4-methylpiperidine [L₆], propane-2-amine [L₇], and 2-methylpropane-2-amine [L₈]) by the gauge-independent atomic orbital method (GIAO) to find the most accordant level of theory with the experimental values. To achieve this goal, all the structures were optimized using the B3LYP, BP86, PBE1PBE, M06-2X, MPWB1K, and MP2 methods with 6–31+G* basis set. Computed structural parameters demonstrate that BP86 has the best agreement to the experimental values between the other methods. The def2-TZVP and aug-cc-pVDZ basis sets were also employed to inspect the effect of different types of basis sets with higher polarization and diffuse functions. The correlation between the empirical and computational values attests that 6–31+G* basis set is the optimum case regarding minimization of the costs and results. The comparison between calculated and experimental CSs at all mentioned combinations illustrated that in accordance with structural results, the best level of theory in CSs is also BP86/6–31+G*. Besides, ²J_PH values were computed with an acceptable agreement to experimental data at the optimum level of theory. The dependency between ²J_PH and the bonding structure of studied ligands was also scrutinized by the Natural Bond Orbital (NBO) analysis that interprets the relationship between the electronic properties and ²J_PH values.     

Is tetrahedral H42+ a minimum? Anomalous behavior of popular basis sets with the standard p exponents on hydrogen

The nature of the tetrahedral H₄²⁺ stationary point (minimum or triply degenerate saddle) depends remarkably upon the theoretical level employed. Harmonic vibrational analyses with, e.g., the 6-31G** (and 6-31 + +G**) and Dunning's [4s2p1d;2s1p] [D95(d,p)] basis sets using the standard p exponent suggest (erroneously) that the T_d geometry is a minimum at both the HF and MP2 levels. This is not the case at definitive higher levels. The C₃H₄²⁺ structure with an apical H is another example of the failure of the calculations with the 6-31G**, 6-311G**, and D95(d,p) basis sets. Even at MP2/6-31G** and MP2/ cc-pVDZ levels, the C_3v structure has no negative eigenvalues of the Hessian. Actually, this form is a second-order saddle point as shown by the MP2/6-31G** calculation with the optimized exponent. The D_4h methane dication structure is also an example of the misleading performance of the 6-31G** basis set. In all these cases, energy-optimized hydrogen p exponents give the correct results, i.e., those found with more extended treatments. Optimized values of the hydrogen polarization function exponents eliminate these defects in 6-31G** calculations. Species with higher coordinate hydrogens may also be calculated reliably by using more than one set of p functions on hydrogen [e.g., the 6-31G(d,2p) basis set]. Not all cases are critical. A survey of examples, also including some boron compounds, provides calibration. © 1993 John Wiley & Sons, Inc.     

Ab initio, density functional theory and structural studies of 4-amino-2-methylquinoline

The Fourier transform infrared (FTIR) and FT-Raman spectra of 4-amino-2-methylquinoline (AMQ) have been recorded in the range 4000–400 and 4000–100 cm⁻¹, respectively. The experimental vibrational frequency was compared with the wavenumbers obtained theoretically by ab initio HF and DFT–B3LYP gradient calculations employing the standard 6-31G** and high level 6-311++G** basis sets for optimised geometry of the compound. The complete vibrational assignment and analysis of the fundamental modes of the compounds were carried out using the experimental FTIR and FT-Raman data, and quantum mechanical studies. The geometry and normal modes of vibration obtained from the HF and DFT methods are in good agreement with the experimental data. The potential energy distribution of the fundamental modes was calculated with ab initio force fields utilising Wilson's FG matrix method. The NH-π interactions and the influence of amino and methyl groups on the skeletal modes are investigated.     

Study of methanetriol decomposition mechanisms

Using ab initio HF/6–31G** and MP2/6–31G** calculations alternative reactions HC(OH)₃ → HCO₂H + H₂O and HC(OH)₃ + H₂O → HCO₂H + 2H₂O are investigated and the results are compared with relevant PM3, HF/3–21G, and HF/6–31G data. Reactant and product complexes as well as transition states are located on corresponding potential energy surfaces. © 1996 John Wiley & Sons, Inc.     

Methanediol decomposition mechanisms: A study considering various ab initio approaches

The alternative decomposition reactions CH₂(OH)₂ → CH₂O + H₂O and CH₂(OH)₂ + H₂O → CH₂O + 2H₂O are investigated using the semiempirical PM 3 as well as the ab initio HF /3-21G , HF /6-31G , HF /6-31G **, and MP 2/6-31G ** calculations. Reactants, products, and appropriate transition states are located on corresponding potential energy surfaces and compared with those reported in earlier studies. © 1996 John Wiley & Sons, Inc.     

Synthesis of some cyclopentenones and crystal structure of 4-hydroxy-3,4-bis(4-methoxyphenyl)-5,5-dimethyl-2-cyclopenten-1-one

Abstract  

Sodium-hydroxide-catalyzed condensation of di-p-methyl- and di-p-methoxybenzil with acetone derivatives was investigated in methanol. Di- and trisubstituted products were obtained as cyclopentenones, while tetraaryl-substituted systems were isolated as cyclopentadienones. The structures of the products were identified by elemental analysis, infrared (IR), nuclear magnetic resonance (¹H NMR), and mass spectroscopy. The solid-state structure of 4-hydroxy-3,4-bis(4-methoxyphenyl)-5,5-dimethyl-2-cyclopenten-1-one was further studied by single-crystal X-ray diffraction analysis. The title compound crystallizes in an orthorhombic space group and intermolecular O–H···O and C–H···O hydrogen bonds stabilize the crystal lattice.     

Structural,Electronic, Reactivity,and Conformational Features of 2,5,5-Trimethyl-1,3,2-diheterophosphinane-2-sulfide,and Its Derivatives: DFT,MEP, and NBO Calculations

In this study, we used density functional theory (DFT) and natural bond orbital (NBO) analysis to determine the structural, electronic, reactivity, and conformational features of 2,5,5-trimethyl-1,3,2-di-heteroatom (X) phosphinane-2-sulfide derivatives (X = O (compound 1), S (compound 2), and Se (compound 3)). We discovered that the features improve dramatically at 6-31G** and B3LYP/6-311+G** levels. The level of theory for the molecular structure was optimized first, followed by the frontier molecular orbital theory development to assess molecular stability and reactivity. Molecular orbital calculations, such as the HOMO–LUMO energy gap and the mapping of molecular electrostatic potential surfaces (MEP), were performed similarly to DFT calculations. In addition, the electrostatic potential of the molecule was used to map the electron density on a surface. In addition to revealing molecules’ size and shape distribution, this study also shows the sites on the surface where molecules are most chemically reactive.     

NMR parameters of SiC-doped (6,0) zigzag single-walled boron phosphide nanotubes: a density functional study

Abstract  

Nuclear magnetic resonance (NMR) parameters including isotropic and anisotropic chemical shielding parameters and electronic structures were calculated using density functional theory (DFT) for silicon–carbide-doped boron phosphide nanotubes. Geometry optimizations were carried out at the B3LYP/6-31G* level of theory using the Gaussian 03 program suite. The isotropic and anisotropic chemical shielding parameters were calculated for the sites of various ¹³C, ²⁹Si, ¹¹B, and also ³¹P atoms in pristine and SiC-doped (6,0) zigzag boron phosphide nanotube models. The calculations indicated that doping of ¹¹B and ³¹P atoms by C and Si atoms had a more significant influence on the calculated shielding tensors than did doping of the B and P atoms by Si and C atoms. In comparison with the pristine model, Si- and C-doping of P and B sites of the zigzag nanotubes reduces the energy gaps of the nanotubes and increases their electrical conductance.     

Ab initio study of possible intermediates in the no(4Π) catalyzed geometric isomerizations of olefins

The geometries of acyclic and three-membered ring (nitroxide) H₄C₂NO radicals in their ground ²Π electronic states have been optimized completely at ab initio UHF and ROHF theoretical levels with the STO-3G and the 6-31G** basis sets. The optimizations favour the cyclic nitroxide structure energetically. However ΔE(acyclic - cyclic) at the UHF and ROHF/6-31G** levels are only 3.2 and 1.9 kcal mol^-1, respectively. Incomplete MP2/6-311G** optimizations support these results. The zero-point energy computed at the ROHF/6-31G** level for the nitroxide radical is 2.5 kcal mol^-1 higher than that for the acyclic structure, thus reversing the relative energies by 0.6 kcal mol^-1. The energies of the two radical structures, relative to the sum of those for ethylene and NO, are very close to literature values of the activation energies for the thermal, NO catalyzed geometrical isomerizations of olefins. Thus cyclic nitroxide intermediates may play a role not only in the Hg 6(³P₁) photosensitized, but also in the thermal, NO-catalyzed geometric isomerizations of olefins. Paper dedicated to Professor Otto P. Strausz; presented in part at the 75th Canadian Chemical Congress and Exhibition, Edmonton, May 31 – June 4, 1992.     

Potential Functions of Internal Rotation around the Csp2-X Bonds and Intermolecular Interactions in the Compounds CH2 = CHXCH3 (X = O,S, Se)

The potential functions of internal rotation around the Csp ²-X bonds in the CH₂ = CHXCH₃ molecules (X = O, S, Se) were determined by MP2/6-31G* and MP2/6-31G** calculations. The stationary points were identified by solution of vibrational problems. The rotation barriers were evaluated taking into account the zero-point vibration energy. The intramolecular interactions were considered in terms of the method of natural bond orbitals. The degrees of hybridization, energies, and populations of the orbitals of the lone electron pairs of the O, S, and Se atoms, the energies of their donor-acceptor interaction with the antibonding * and * orbitals of the double bond, and the natural atomic charges in various conformations were determined.     

An Ab Initio Molecular Orbital Theory and Density Functional Theory (DFT) Study of Conformers and Rotamers of 4-Substituted (Methyl, Hydroxymethyl, Methanoyl, Ethanoyl, Cyano, Fluoro, Chloro, Bromo, Acetoxy) Tetrahydro-2H-thiopyran-1,1-dioxides

The structures and energies of axial and equatorial conformers and rotamers of 4-substituted tetrahydro-2H-thiopyran-1,1-dioxides (tetrahydrothiopyran-1,1-dioxides, thiacyclohexane-1,1-dioxides, thiane-1,1-dioxides, and 1,1-dioxothianes; CH₃, CH₂OH, CHO, COCH₃, CN, F, Cl, Br, and OCOCH₃) were calculated using the hybrid density functionals B3LYP, B3P86, and B3PW91, as well as MP2 and the 6-31G(d), 6-31G(2d), 6-31G(3d), 6-31G(d,p), and 6-31+G(d) basis sets. MP2/6-31+G(d)/ /HF/6-31+G(d) [–G° = 1.73 kcal/mol], B3P86/6-31G(d) [–G° = 1.75 kcal/mol], and B3PW91/6-31G(d) [–G° = 1.85 kcal/mol] gave conformational free energy (G°) values at 180 K for 4-methyltetrahydro-2H-thiopyran-1,1-dioxide which were similar to the reported experimental values for methylcyclohexane (–G° = 1.80 kcal/mol), 4-methyltetrahydro-2H-thiopyran (–G° = 1.80 kcal/mol), and other 4-methyl-substituted heterocycles. All levels of theory showed that the conformational preferences of the 4-methanoyl (4-formyl), 4-ethanoyl (4-acetyl), and 4-cyano substituents were small. The HF calculations gave conformational free energy (G°) values for 4-chlorotetrahydro-2H-thiopyran-1,1dioxide which were closer to the experimental value than the MP2 and density functional methods. The best agreement with available experimental data for 4-bromotetrahydro-2H-thiopyran-1,1-dioxide was obtained from the HF/6-31G(2d), HF/6-31G(3d), and B3LYP/6-31G(2d) calculations, and, for 4-acetoxytetrahydro-2H-thiopyran-1,1-dioxide, from the HF/6–31G(3d) calculations. The conformational free energies (G°) and relative energies (E) of the conformers and rotamers have been compared with the correspondingly substituted cyclohexanes and tetrahydro-2H-thiopyrans and are discussed in terms of dipole–dipole (electrostatic) interactions and repulsive nonbonded interactions (steric) in the most stable axial and equatorial conformers. The axial S=O bond lengths are shorter than the equatorial S=O bond lengths and the C2–C3 bond lengths in the substituents with carbon-bonded to the ring are shorter than the C3–C4 and C4–C-5 bond lengths. In contrast, the C2–C3 bond lengths in the 4-halogen and 4-acetoxy substituents are longer than the C3–C4 and C4–C-5 bond lengths.     

Ab initio study of dehalohydrogenation reaction of 2-halo-2,3-dihydrophosphinine

Decomposition of 2-fluoro-2,3-dihydrophosphinine (1), 2-chloro-2,3-dihydrophosphinine (3), 2-bromo-2,3-dihydrophosphinine (5) to phosphinine was investigated using Molecular orbital and density functional theory. Study on the B3LYP/6-311+G** level of theory revealed that the required energy for the decomposition of compounds 1, 3, and 5 to phosphinine is 30.56 kcal·mol^?1, 28.23 kcal·mol^?1, and 24.03 kcal·mol^?1, respectively. HF/6-311+G**//B3LYP/6-311+G** calculated barrier height for the decomposition of compound 1, 3, and 5 to phosphinine is 57.56 kcal·mol^?1, 37.26 kcal·mol^?1, and 30.77 kcal·mol^?1, respectively. Also, MP2/6-311+G**//B3LYP/6-311+G** results indicated that the barrier height for the decomposition of compound 1, 3, and 5 to phosphinine is 46.59 kcal·mol^?1, 47.28 kcal·mol^?1, and 42.57 kcal·mol^?1, respectively. Natural bond orbital (NBO) population analysis and nuclear independent chemical shift (NICS) results showed that, reactants are non-aromatic but products of elimination reaction are aromatic, C-H and C-X bonds are broken and H-X bond is appear.     

Quantum-Chemical Study of Alkyl Carbenium Ions in 100% Sulfuric Acid

A quantum-chemical study of neutral and protonated monoalkyl sulfates RHSO₄and [RH₂SO₄]⁺(where R = CH₃, C₂H₅, iso-C₃H₇, and tert-C₄H₉) is carried out. Calculations are performed using the Hartree–Fock method in the 6-31G** and 6-31++G** basis sets taking into account electron correlation according to the Müller–Plesset perturbation theory MP2/6-31+G*//6-31+G*. Protonated tert-butyl sulfate was also calculated by the DFT B3LYP/6-31++G** method. It was found that monoalkyl sulfates are covalent compounds, and the complete abstraction of alkyl carbenium ions from them has substantial energy cost: 196.4, 161.7, 150.8 and 136.0 kcal/mol, respectively. Protonated methyl and ethyl sulfates are also covalent compounds according to the calculation. They have lower but still high energies of heterolytic dissociation (65.0 and 33.5 kcal/mol, respectively). The energy of R⁺abstraction from protonated isopropyl sulfate is much lower: 23.6 kcal/mol. The main covalent state and the ion–molecular pair, which is a carbenium ion [C(CH₃)₂H]⁺solvated by the H₂SO₄molecule, have about the same energy. The ground state of protonated tert-butyl sulfate corresponds to the ion–molecular complex [C(CH₃)⁺ ₃H₂SO₄] with still lower energy of carbenium ion [C(CH₃)₃]⁺abstraction, which is equal to 10.0 kcal/mol. Calculation according to the DFT B3LYP/6-31++G** method shows the absence of a minimum for the protonated tert-butyl sulfate with a covalent structure on the potential energy surface.