A comparative spectroscopic,electronic structure and chemical shift investigations of o-Chloronitrobenzene,p-Chloronitrobenzene and m-Chloronitrobenzene

The structural characteristics and substituent effects of o-Chloronitrobenzene, m-Chloronitrobenzene and p-Chloronitrobenzene have been analysed by experimental FTIR, FT-Raman and FT-NMR spectroscopic studies. A detailed quantum chemical calculations have been performed using DFT/B3LYP method with 6-311++G^**, 6-31G^** and cc-pVTZ basis sets. Complete vibrational analyses of the compounds were performed. The temperature dependence of thermodynamic properties has been analysed. The atomic charges and charge delocalisation of the molecule have been performed by natural bond orbital (NBO) analysis. Molecular electrostatic surface potential (MESP), total electron density distribution and frontier molecular orbitals (FMOs) are constructed at B3LYP/6-311++G^** level to understand the electronic properties. The charge density distribution and site of chemical reactivity of the molecules has been obtained by mapping electron density isosurface with electrostatic potential surfaces (ESPs). The electronic properties, HOMO and LUMO energies were measured by time-dependent TD-DFT approach. ¹H and ¹³C NMR spectra were recorded and ¹H and ¹³C nuclear magnetic resonance chemical shifts of the molecule were calculated. The ¹H and ¹³C nuclear magnetic resonance (NMR) chemical shifts of the molecules in chloroform solvent were calculated by using the Gauge-Independent Atomic Orbital (GIAO) method and are found to be in good agreement with experimental values.     

Interpretation of vibrational and NMR spectra of allyl acrylate: An evidence for several conformers

The mid-IR, far-IR, and Raman spectra of allyl acrylate were measured and interpreted with support of the B3LYP/aug-cc-pVDZ calculated anharmonic vibrational spectra followed by the potential energy distribution analysis. The experimental ¹H and ¹³C NMR spectra of allyl acrylate dissolved in CDCl₃ or C₆D₆ were interpreted by means of the B3LYP/aug-cc-pVDZ-su2 calculated NMR chemical shifts and J(¹H,¹H) and J(¹H,¹³C) coupling constants. Exactly ten stable allyl acrylate conformers (five s-cis and five s-trans) were found after careful B3LYP/aug-cc-pVDZ and MP2/aug-cc-pVDZ scan of the conformational space. The experimental IR and Raman spectra are in good agreement with the theoretical spectra of the most stable conformers 1 with a presence of the second stable conformer 2, both exhibiting cis arrangement of the acrylic moiety. There are however two bands in the IR spectra, at ca. 1270 and 1260 cm⁻¹, that definitely indicate the conformers with trans arrangement of the acrylic moiety to be present in liquid allyl acrylate. The bands at ca. 2990 and 1650 cm⁻¹ are suggested to be due to Fermi resonances engaging CH and CC stretching vibrations, respectively. The careful inspection of the room temperature ¹H and ¹³C NMR spectra of allyl acrylate suggest that a dominating form of the allyl acrylate molecule in an inert solvent exhibits the cis conformation of the acrylic moiety and an extended allyl group.     

The determination of sulfoxide configuration in six-membered rings using NMR spectroscopy and DFT calculations

Cyclic six-membered ring sulfoxides and sulfones were prepared by a stepwise in situ oxidation of the corresponding sulfides with meta-chloroperbenzoic acid in an NMR tube. The oxidation was followed by NMR spectra and the ¹H and ¹³C NMR data were collected. The geometries of all of the compounds were optimized using the DFT B3LYP/6-31G^∗∗ method and the ¹³C and ¹H NMR chemical shifts were calculated for geometry-optimized structures with the DFT B3LYP/6-31++G^∗∗ method. The calculated ¹³C NMR chemical shifts induced by oxidation (Δδ values) are in very good agreement with the experimental data and can be used to determine the oxidation state of the sulfur atom (-S-, -SO-, -SO₂-). The characteristic differences of the induced oxidation chemical shifts of carbon atoms at the α- and β-position to sulfur were successfully used for distinguishing between the diastereoisomeric sulfoxides.     

Experimental (FT-IR, FT-Raman, H, C NMR) and theoretical study of alkali metal 2-aminonicotinates

The influence of lithium, sodium, potassium, rubidium and cesium on the electronic system of 2-aminonicotinic acid (2-ANA) was studied by the methods of molecular spectroscopy. The vibrational (FT-IR, FT-Raman) and NMR (¹H and ¹³C) spectra of 2-aminonicotinic acid and its alkali metal salts were recorded. Characteristic shifts and changes in intensities of bands along the metal series were observed. The changes of chemical shifts of protons (¹H NMR) and carbons (¹³C NMR) in the series of studied alkali metal 2-aminonicotinates (2-AN) were observed too.Optimized geometrical structures of the studied compounds were calculated by the B3LYP method using the 6-311++G** basis set. Aromaticity indices, atomic charges, dipole moments and energies were also calculated. The theoretical chemical shifts in ¹H and ¹³C NMR spectra and theoretical wavenumbers and intensities of IR and Raman spectra were determined. The calculated parameters were compared to the experimental characteristics of the studied compounds.     

Tacticity of poly(butyl-α-cyanoacrylate) chains in nanoparticles: NMR spectroscopy and DFT calculations

NMR spectroscopy and quantum chemical calculations were applied for structural characterization and determination of the preferred stereochemical sequence distribution of the monomer units in the homopolymer chains of poly(butyl-α-cyanoacrylate) nanoparticles. The stereochemical sequence distribution of the monomer units was defined by analysis of their high-resolution 1D ¹H and ¹³C NMR and 2D J-resolved, ¹H/¹³C HSQC and ¹H/¹³C HMBC NMR spectra. The results were verified by employment of B3LYP/6-31G(d) calculations and are consistent with the preferred tendency of polymer chains of PBCN to adopt syndiotactic placements. The proton and carbon chemical shielding were calculated at BPW91/6-31+G(2d,p) level using the GIAO approach and B3LYP/6-31G(d) optimized geometry.     

Crystal and molecular structure of 3-(2-amino-pyridinium)-propionate monohydrate

A novel betaine derivative, 3-(2-amino-pyridinium)-propionate monohydrate, has been synthesized and its structure studied by X-ray diffraction, FTIR, Raman, ¹H and ¹³C NMR spectroscopies and by DFT calculations. The crystals are monoclinic, space group P2₁/c with a=8.0800(16), b=15.242(3), c=7.1698(14) Å, β=104.30(3)° and Z=4. Each oxygen atom of the carboxylate group is engaged in two intermolecular hydrogen bonds, one with water molecule and the other with amine group. The water molecules link the molecules of 3-(2-amino-pyridinium)-propionate into planar zigzag chains along the b axis. The screening constants for ¹H and ¹³C atoms have been calculated by GIAO/B3LYP/6-31 G(d,p) and analyzed. Linear correlations between the experimental ¹H and ¹³C chemical shifts and the computed screening constants have been obtained. Raman and FTIR spectra of the title betaine have been investigated.     

Synthesis,spectroscopic and configurational study,and ab initio calculations of new diazaphospholanes

New 2-substituted diazaphospholane-2-oxides (I-III, V-VIII) and diazaphosphorinane-2-oxide (IV) were synthesised and characterised by ¹H, ¹³C, and ³¹P NMR, IR spectroscopy, and elemental analysis. The presence of chiral diamino groups in compounds II and V–VIII gives rise to various diastereomers so that the ³¹P{¹H} NMR spectra demonstrated three and two peaks with different ratios, respectively. Also, the ¹H and ¹³C{¹H} NMR spectra of compounds II and V–VIII revealed three and two sets of signals for the related conformers (diastereomers). Interestingly, the ³¹P NMR spectrum of V in D₂O indicated a great upfield shift (Δδ = 19.0) for ³¹P relative to the value obtained in DMSO-d₆ (solvent effect). The two signals in V split further to three signals in the presence of β-cyclodextrin. Moreover, conformational analysis of diazaphospholane V was studied by ab initio calculations at the HF and B3LYP levels of theory using the Gaussian 98 program. Results indicated that among four suggested diastereomers (C1–C4) of V, C1 and C3 containing methyl group in the equatorial position are the most stable forms.     

Structure and tautomerism of 4-substituted 3(5)-aminopyrazoles in solution and in the solid state: NMR study and Ab initio calculations

Annular tautomerism of 3(5)-aminopyrazoles containing a cyano, thiocyanato, or aryl substituent in the 4-position has been studied by ¹H and ¹³C NMR in solution, cross-polarization and magic-angle spinning ¹³C NMR in the solid state, and ab initio quantum chemical calculations (B3LYP/6-31G**). The title compounds in the solid state exist as 3-amino tautomers. A rare case of slow (on the NMR time scale) annular prototropic tautomerism has been observed in DMSO-d ₆: signals of particular tautomers (3- and 5-aminopyrazoles) have been detected in the NMR spectra. 4-Cyano and 4-thiocyanato derivatives exist preferentially as 5-amino tautomers, whereas 4-methoxy analog is represented mainly by the 3-amino tautomers. Ab initio calculations (B3LYP/6-31G**) for the gas phase and DMSO solution (in terms of the polarizable continuum model) have shown increase of the relative stability of more polar 5-amino tautomer in going to DMSO.     

Quantum‐chemical,IR, NMR,and X‐ray diffraction studies on 2‐(4‐chlorophenyl)‐1‐methyl‐ 1H‐benzo[d]imidazole

The title molecule, 2‐(4‐chlorophenyl)‐1‐methyl‐1H‐benzo[d]imidazole (C₁₄H₁₁ClN₂), was prepared and characterized by ¹H NMR, ¹³C NMR, IR, and single‐crystal X‐ray diffraction. The molecular geometry, vibrational frequencies, and gauge including atomic orbital (GIAO) ¹H and ¹³C NMR chemical shift values of the title compound in the ground state have been calculated by using the Hartree‐Fock (HF) and density functional theory (DFT/B3LYP) method with 6‐31G(d) basis sets, and compared with the experimental data. The calculated results show that the optimized geometries can well reproduce the crystal structural parameters, and the theoretical vibrational frequencies and GIAO ¹H and ¹³C NMR chemical shifts show good agreement with experimental values. The energetic behavior of the title compound in solvent media has been examined using B3LYP method with the 6‐31G(d) basis set by applying the Onsager and the polarizable continuum model (PCM). Besides, molecular electrostatic potential (MEP), frontier molecular orbitals (FMO) analysis, and nonlinear optical (NLO) properties of the title compound were investigated by theoretical calculations. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

Synthesis,molecular conformation,vibrational, electronic transition,and chemical shift assignments of 4-(thiophene-3-ylmethoxy)phthalonitrile: a combined experimental and theoretical analysis

This work presents the synthesis and characterization of a novel compound, 4-(thiophene-3-ylmethoxy)phthalonitrile (TMP). The spectroscopic properties of the compound were examined by FT-IR, FT-Raman, NMR, and UV techniques. FT-IR and FT-Raman spectra in solid state were observed in the region 4000–400 cm⁻¹ and 3500–50 cm⁻¹, respectively. The ¹H and ¹³C NMR spectra were recorded in CDCl₃ solution. The UV absorption spectrum of the compound that dissolved in THF was recorded in the range of 200–800 nm. The structural and spectroscopic data of the molecule in the ground state were calculated using density functional theory (DFT) employing B3LYP exchange correlation and the 6-311++G(d,p) basis set. The vibrational wavenumbers were calculated and scaled values were compared with experimental FT-IR and FT-Raman spectra. The complete assignments were performed on the basis of the experimental results and total energy distribution (TED) of the vibrational modes, calculated with scaled quantum mechanics (SQM) method. Isotropic chemical shifts (¹³C NMR and ¹H NMR) were calculated using the gauge-invariant atomic orbital (GIAO) method. A study on the electronic properties, such as HOMO and LUMO energies, were performed by time-dependent DFT (TD-DFT) approach. The HOMO and LUMO analyses have been used to elucidate information regarding charge transfer within the molecule. Comparison of the calculated frequencies, NMR chemical shifts, absorption wavelengths with the experimental values revealed that DFT method produces good results.     

Nicotinamide solvation state in aqueous dimethyl sulfoxide

The solvation state of biologically active compound vitamin B₃, viz., 3-pyridinecarboxamide, in an aqueous-dimethyl sulfoxide solvent of a variable composition was studied by ¹H and ¹³C NMR and IR spectroscopy. Below X _DMSO ?0.65 molar fraction, the solvation of the N heteroatom due to hydrogen bonds with water molecules weakens. At X _DMSO > 0.65 molar fraction, almost no changes are observed in the solvate state of the N heteroatom. The ¹H NMR spectra indicate that the degree of conjugation of the carbamide group with the heterocycle increases with an increase in the DMSO concentration. The structures of the dimethyl sulfoxide and mixed aqueous-dimethyl sulfoxide solvates of nicotinamide were optimized by the B3LYP/6311++(DP) method, and their ¹³C chemical shifts (GIAO) and IR spectra were obtained. According to the IR spectroscopic data, the number of hydrogen bonds involving the carbamide group decreases on going from H₂O to DMSO.     

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.     

The determination of sulfoxide configuration in five-membered rings using NMR spectroscopy and DFT calculations

Cyclic five-membered ring sulfoxides and sulfones were prepared by a stepwise in situ oxidation of the corresponding sulfides with meta-chloroperbenzoic acid in an NMR tube. The oxidation was followed by NMR and both ¹H and ¹³C NMR data were collected. The geometries of all of the compounds were optimized using the DFT B3LYP/6-31G⁷ method and the ¹³C and ¹H chemical shifts were calculated for geometry-optimized structures with the DFT B3LYP/6-31++G⁷ method. The calculated ¹³C chemical shifts induced by oxidation (Δδ values) were in very good agreement with the experimental data and could be used to determine the oxidation state of the sulfur atom (–S–, –SO–, –SO₂–). The characteristic differences of the induced oxidation chemical shifts of the carbon atoms in the α-position and β-position to sulfur were successfully used to distinguish between the diastereoisomeric sulfoxides and allowed configuration determination.     

Comprehensive 1H and 13C NMR assignment of 13 protobassic acid saponins

This study aimed to carry out complete ¹H and ¹³C NMR assignment of 13 protobassic acid saponins, including arganins A–C ( 1 – 3 ) and F ( 4 ), butyrosides B–D ( 5 – 7 ), tieghemelin ( 8 ), 3′-O-glucosyl-arganin C ( 9 ), Mi-saponins A–C ( 10 – 12 ), and mimusopsin ( 13 ), recorded in methanol-d₄. This was accomplished by the analysis of high-resolution one-dimensional (1D) NMR (¹H and ¹³C), two-dimensional (2D) NMR (¹H–¹H COSY, HSQC, and HMBC), and selectively excited 1D TOCSY spectra. Before this study, ¹H and ¹³C NMR data of arganins A–C ( 1 – 3 ) and F ( 4 ) were partially assigned. Our effort leads to their complete assignment, especially the glycon residue, and revises some reported data. Some revisions of the ¹H and ¹³C NMR data in the glycon part of butyroside C ( 6 ), tieghemelin ( 8 ), Mi-saponin A ( 10 ), and mimusopsin ( 13 ) were made. Those data of butyrosides B and D ( 5 & 7 ) and Mi-saponin B ( 11 ), which had not been recorded in methanol-d₄, are provided. In addition, the ¹H and ¹³C NMR data of Mi-saponin C ( 12 ) are reported for the first time. These data, being recorded in methanol-d₄, should be more friendly for use as a reference for identifying the related triterpenoid saponins.     

H and C NMR spectroscopy of 9-acridinones

The ¹H and ¹³C NMR spectra of 9-acridinone and its five derivatives dissolved in CDCl₃, CD₃CN and DMSO-d₆ were measured in order to reveal the influence of the constitution of the compounds and features of the solvents on chemical shifts and ¹H-¹H coupling constants. Experimental data were compared with theoretically predicted chemical shifts, on the GIAO/DFT level of theory, for DFT (B3LYP)/6-31G^∗∗ optimized geometries of molecules—also for four other 9-acridinones. This comparison helped to ascribe resonance signals in the spectra to relevant atoms and enabled revelation of relations between chemical shifts and physicochemical features of the compounds. It was found that experimentally or theoretically determined ¹H and ¹³C chemical shifts of selected atoms correlate with theoretically predicted values of dipole moments of the molecules, as well as bond lengths, atomic partial charges and energies of HOMO.     

MP2, DFT and ab initio calculations on thioxanthone

Density functional theory (DFT), HF and MP2 calculations have been carried out to investigate thioxanthone molecule using the standard 6-31+G(d,p) basis set. The results of MP2 calculations show a butterfly structure for thioxanthone. The calculated results show that the predicted geometry can well reproduce the structural parameters. The predicted vibrational frequencies were assigned and compared with experimental IR spectra. A good harmony between theory and experiment is found. The theoretical electronic absorption spectra have been calculated using CIS method. ¹³C and ¹H NMR of the title compound have been calculated by means of B3LYP density functional method with 6-31+G(d,p) basis set. The comparison of the experimental and the theoretical results indicate that density functional B3LYP method is able to provide satisfactory results for predicting NMR properties.     

Synthesis of new cyano-substituted analogues of Tröger's bases from bromo-derivatives. A stereochemical dependence of long-range (nJHH,n = 4, 5, and 6) proton–proton and proton–carbon (nJCH,n = 1, 2, 3, 4, and 5) coupling constants of these compounds

A free-catalyst microwave-assisted cyanation of brominated Tröger's base derivatives ( 2a - f ) is reported. The procedure is simple, efficient, and clean affording the nitrile compounds ( 3a - e, I ) in very good yields. Complete assignment of ¹H and ¹³C chemical shifts of 2a - f, I and 3a - d, I was achieved using gradient selected 1D nuclear magnetic resonance (NMR) techniques (1D zTOCSY, PSYCHE, DPFGSE NOE, and DEPT), homonuclear 2D NMR techniques (gCOSY and zTOCSY), and heteronuclear 2D NMR techniques (gHSQCAD/or pure-shift gHSQCAD, gHMBCAD, bsHSQCNOESY, and gHSQCAD-TOCSY) with adiabatic pulses. Determination of the long-range proton–proton coupling constants ⁿJ_HH (n = 4, 5, 6) was accomplished by simultaneous irradiation of two protons at appropriate power levels. In turn, determined coupling constants were tested by an iterative simulation program by calculating the ¹H NMR spectrum and comparing it to the experimental spectrum. The excitation-sculptured indirect-detection experiment (EXSIDE) and ¹H-¹⁵N CIGARAD-HMBC (constant time inverse-detection gradient accordion rescaled heteronuclear multiple bond correlation) were applied for determination of long-range carbon–proton coupling constants ⁿJ_CH (n = 2, 3, and 4) and for assignment of ¹⁵N chemical shift at natural abundance, respectively. DFT/B3LYP optimization studies were performed in order to determine the geometry of 2c using 6-31G(d,p), 6-311G(d,p), and 6–311 + G(d,p) basis sets. For calculation of ¹H and ¹³C chemical shifts, ⁿJ_HH (n = 2, 3, 4, 5, and 6), and ⁿJ_CH (n = 1, 2, 3, and 4) coupling constants, the GIAO method was employed at the B3LYP/6-31G(d,p), B3LYP/6-31+G(d,p), B3LYP/6-311+G(d,p), B3LYP/6-311++G(2d,2p), B3LYP/cc-pVTZ), and B3LYP/aug-cc-pVTZ) levels of theory. For the first time, a stereochemical dependence magnitude of the long-range ⁿJ_HH (n = 4, 5, and 6) and ⁿJ_CH (n = 1, 2, 3, 4, and 5) have been found in bromo-substituted analogues of Tröger's bases.     

Synthesis,experimental, and DFT studies on FT-IR, 1H,and 13C NMR spectra of azo-linked dihydropyridines

An efficient one-pot synthesis of dihydropyridines by solid state three-component condensation reactions of aldehydes, dimedone, and ammonium acetate in the presence of HY-Zeolite has been achieved. The conversion took short time to form the products in excellent yields. HY-Zeolite can be recovered and reused. Density Functional Theory (DFT) calculations at the B3LYP level is used to optimize the geometry and calculate FT-IR, ¹H, and ¹³C NMR spectra of the compounds. We found that the calculated values are in accordance with the experimental data.     

An Experimental and Theoretical Study on Influence of H‐bonding on the Synthesized Azo Derivatives Structures

We have reported a simple and efficient reaction for the synthesis of some new functionalized azo structures which were prepared by electron deficient acetylenic compounds in the presence of triphenylphosphine. The characterization of the synthesized azo compounds has been determined by FTIR, UV‐Vis, ¹H NMR, ¹³C NMR and Mass spectroscopic techniques. The influence of H‐bonding on the products has been shown by different experimental analysis. Also, the regioselectivity of the reaction, tautomerization equilibrium and the stability of products was investigated using DFT calculations at the B3LYP/6‐31G level of theory.