14N Quadrupole Coupling Tensor Research Articles

Hydrogen Bonds in Cocrystals and Salts of 2-Amino-4,6-dimethylpyrimidine and Carboxylic Acids Studied by Nuclear Quadrupole Resonance

(14)N and (17)O nuclear quadrupole resonance frequencies have been measured in 1:1 cocrystals and salts of 2-amino-4,6-dimethylpyrimidine and several carboxylic acids. A systematic decrease of the (17)O quadrupole coupling constant on increasing strength of the hydrogen bond is observed in cocrystals bound by O-H···N hydrogen bonds. The O-H distances deduced from the line widths of the (17)O NQR lines show that the hydrogen atom is in a hydrogen bond formed by a carboxylic groups for about 0.01 nm displaced from the oxygen atom toward the center of the hydrogen bond. In the O-H···N hydrogen bond formed by the hydroxyl group, which is only slightly longer than the hydrogen bonds formed by the carboxyl group, the hydrogen atom is much less displaced. A linear relation between the (14)N quadrupole coupling constant and the sum of the inverse third powers of the H···A (A = O or N) distances is deduced for the amino group. A linear correlation of the principal values of the (14)N quadrupole coupling tensor in -NH2, as observed in the solid phase and in the gas phase, is analyzed in a simple model assuming a displacement of the electron charge in the N-H σ bond and simultaneous deformation of the nitrogen lone pair electron orbital. At the ring nitrogen position, hydrogen bonding and proton transfer produce a large decrease of the (14)N quadrupole coupling constant. A linear correlation of the principal values of the (14)N quadrupole coupling tensor is observed in cocrystals and salts of 2-amino-4,6-dimethylpyrimidine. This correlation differs from the correlation observed in substituted pyrimidine, where the hydrogen atoms are replaced by other atoms or functional groups. The difference is analyzed in a model, which assumes that the hydrogen bonding and substituents affect the nitrogen lone pair and π electron orbitals. The analysis shows that the two effects are nearly independent.

Theoretical study of N–H· · ·O hydrogen bonding properties and cooperativity effects in linear acetamide clusters

We investigated geometry, energy, \({\nu_{{\text{N--H}}}}\) harmonic frequencies, 14N nuclear quadrupole coupling tensors, and \({n_{\rm O}\to \sigma _{{\text{N--H}}}^\ast}\) charge transfer properties of (acetamide) n clusters, with n = 1 − 7, by means of second-order Moller-Plesset perturbation theory (MP2) and DFT method. Dependency of dimer stabilization energies and equilibrium geometries on various levels of theory was examined. B3LYP/6-311++G** calculations revealed that for acetamide clusters, the average hydrogen-bonding energy per monomer increases from −26.85 kJ mol−1 in dimer to −35.12 kJ mol−1 in heptamer; i.e., 31% cooperativity enhancement. The n-dependent trend of \({\nu_{{\text{N--H}}}\,{and}\,^{14}}\) N nuclear quadrupole coupling values were reasonably correlated with cooperative effects in \({r_{{\text{N--H}}}}\) bond distance. It was also found that intermolecular \({n_{\rm O}\to \sigma_{{\text{N--H}}}^\ast}\) charge transfer plays a key role in cooperative changes of geometry, binding energy, \({\nu_{{\text{N--H}}}}\) harmonic frequencies, and 14N electric field gradient tensors of acetamide clusters. There is a good linear correlation between 14N quadrupole coupling constants, C Q (14N), and the strength of Fock matrix elements (F ij ). Regarding the \({n_{\rm O}\to \sigma_{{\text{N--H}}}^\ast}\) interaction, the capability of the acetamide clusters for electron localization, at the N–H· · ·O bond critical point, depends on the cluster size and thereby leads to cooperative changes in the N–H· · ·O length and strength, N–H stretching frequencies, and 14N quadrupole coupling tensors.

14N and 17O electric field gradient tensors in benzamide clusters: Theoretical evidence for cooperative and electronic delocalization effects in N–H⋯O hydrogen bonding

Nuclear quadrupole coupling tensors of 14N and 17O nuclei in benzamide clusters (up to n = 6) were calculated via density functional theory. Results revealed that N–H⋯O hydrogen bonds around the benzamide molecule in crystalline lattice have significant influence on 14N and 17O nuclear quadrupole coupling tensors. n-dependent trend in 14N quadrupole coupling tensors significantly correlates with cooperative effects of R(N–H⋯O) hydrogen bond distance. Natural bonding orbital analysis, NBO, was used to rationalize the quadrupole coupling results in terms of substantial n O → σ N – H ∗ charge transfer in (benzamide) n=1−6 clusters. It was found that intermolecular n O → σ N – H ∗ interactions play a key role in cooperative change of 14N and 17O quadrupole coupling tensors. There is an acceptable linear correlation between 14N or 17O quadrupole coupling tensors with strength of Fock matrix elements (Fij). This suggests that both 14N and 17O quadrupole coupling measurements can provide a useful probe for electron delocalization effects in both gaseous and condensed media.

Density functional theory study of N–H⋯O, O–H⋯O and C–H⋯O hydrogen-bonding effects on the 14N and 2H nuclear quadrupole coupling tensors of N-acetyl-valine

Hydrogen-bonding effects in the crystalline structure of N-acetyl-valine, NAV, were studied using the 14N and 2H quadrupole coupling tensors via density functional theory. The calculations were carried out at the B3LYP level with the 6-311++G(d,p) and 6-311+G(d) basis sets. The theoretical quadrupole coupling components and their relative orientation in the molecular frame axes at the nitrogen site are compared to experimental values. This nucleus is involved in a rather strong intermolecular O CNH⋯O CNH hydrogen bond, r N–H⋯O(1) = 2.04 Å and ∠N–H⋯O(1) = 171.53°. A reasonably good agreement between the experimentally obtained 2H quadrupole coupling tensors and the B3LYP/6–311++G(d,p) calculations is achievable only in molecular model where a complete hydrogen-bonding network is considered.

A theoretical study of 17O, 14N and 2H nuclear quadrupole coupling tensors in the real crystalline structure of acetaminophen

A systematic computational investigation was carried out to characterize the 17O, 14N and 2H electric field gradient, EFG, tensors in the acetaminophen real crystalline structure. To include the hydrogen bonding effects in the calculations, the most probable interacting molecules with the target molecule in the crystalline phase were considered through the various molecular clusters. The calculations were performed with the B3LYP method and 6-311++G ∗∗ and 6-311+G ∗ standard basis sets using the Gaussian 98 suite of programs. Calculated EFG tensors were used to evaluate the 17O, 14N, and 2H nuclear quadrupole resonance, NQR, parameters in acetaminophen crystalline structure, which are in good agreement with the available experimental data. The difference between the calculated NQR parameters of the monomer and molecular clusters shows how much hydrogen bonding interactions affect the EFG tensors of each nucleus. These results indicate that both O–H⋯O and N–H⋯O hydrogen bonding have major influence on the NQR parameters. Moreover, the quantum chemical calculation indicated that the intermolecular hydrogen bonding interactions play an essential role in determining the relative orientation of quadrupole coupling principal components in the molecular frame axes.

14N nuclear quadrupole resonance of some sulfa drugs

The 14N nuclear quadrupole double resonance spectra of different polymorphs of sulfanilamide, sulfadiazine, sulfamerazine and sulfamethazine have been measured and the 14N quadrupole coupling tensors have been determined. The obtained 14N spectra are compared with those of other sulfa drugs like sulfathiazole. It is shown that different polymorphs can be easily discriminated. The application of this technique for non-destructive analysis, polymorph determination and quality control in the production of pharmaceuticals is stressed.

Microwave Measurements of 14N and D Quadrupole Coupling for (Z)-2-Hydroxypyridine and 2-Pyridone Tautomers

Rotational spectra for the two tautomers (Z)-2-hydroxypyridine and 2-pyridone and their deuterated isotopomers were measured in the microwave range between 4 and 14 GHz using a pulsed beam Fourier transform microwave spectrometer. Nitrogen and deuterium quadrupole hyperfine structure was completely resolved for many of the observed transitions, and the measured 14N quadrupole coupling tensors are quite different for these two tautomers. The eQqcc(N) values have opposite signs. The 14N quadrupole coupling strengths for (Z)-2-hydroxypyridine in the principal inertial axis system are as follows: eQqaa(N) = −0.076(11), eQqbb(N) = −2.283(6), and eQqcc(N) = 2.359(6) MHz. The 14N and D nuclear quadrupole coupling strengths for (Z)-2-deuteriohydroxypyridine in the principal inertial axis are eQqaa(N) = −0.1465(4), eQqbb(N) = −2.2045(4), and eQqcc(N) = 2.3510(4) MHz and eQqaa(D) = −0.0250(9), eQqbb(D) = 0.1699(4), and eQqcc(D) = −0.1449(4) MHz. The 14N quadrupole coupling strengths for 2-pyridone in the principal inertial axis system are eQqaa(N) = 1.496(4), eQqbb(N) = 1.269(4), and eQqcc(N) = −2.765(4) MHz. The 14N and D nuclear quadrupole coupling strengths for 1-deuterio-2-pyridone in the principal inertial axis system are as follows: eQqaa(N) = 1.511(2), eQqbb(N) = 1.249(5), and eQqcc(N) = −2.759(5) MHz and eQqaa(D) = −0.110(7), eQqbb(D) = 0.354(6), and eQqcc(D) = −0.244(6) MHz. New, improved, experimental rotational constants were obtained for the H and D isotopomers of both tautomers. Kraitchman analysis indicates the “tautomeric” hydrogen atom is at a distance of 2.653(2) Å in 2-hydroxypyridine and a distance of 2.124(1) Å in 2-pyridone from the centers of mass of the two tautomers, respectively. The DFT calculated eQq(N) values for both the tautomers and the deuterated tautomers are in good agreement with the present experimental values. The Townes−Dailey model has been used to analyze the new quadrupole coupling data of the tautomers and the results are presented in terms of nitrogen atom p-orbital occupation numbers.

A molecular beam Fourier transform microwave study of 2-methylpyridine and its complex with argon: structure, methyl internal rotation and 14N nuclear quadrupole coupling

The rotational spectrum of 2-methylpyridine (α-picoline, CH3C5H4N) in the two lowest levels of methyl internal rotation (m=0, ±1) has been recorded in the frequency range from 2 to 15 GHz using a molecular beam Fourier transform microwave spectrometer. The high resolution and sensitivity of this spectroscopic technique allowed resolution of hyperfine structures due to l4N nuclear quadrupole coupling with high accuracy and detection of the spectra of the 15N- and all 13C-isotopomers. These investigations considerably extend the results from an earlier study on the normal species (Dreizler, H., Rudolph, H. D., and Mader, H., 1970, Z. Naturforsch., 25a, 25); improved rotational and centrifugal distortion constants as well as all components of the 14N quadrupole coupling tensor have been obtained. Analysis of the spectra of the isotopomers yielded the I4N quadrupole coupling constants χ cc and χ aa – χ bb (for the 13C species), the potential parameter V 3 for the barrier hindering the internal rotation of the methyl group, and, in particular, ro, rs r m (1) and r m (2) structural parameters for the molecule. In addition to the microwave studies on the monomer, we have also investigated the rotational spectrum of the weakly bound dimer of normal 2-methylpyridine with Ar. The results obtained for the quadrupole coupling constants and the hindering potential for the internal methyl rotation show that the corresponding parameters are not significantly, or only slightly, changed in the complex.

Influence of hydrogen bond geometry on quadrupole coupling parameters: A theoretical study of imidazole–water and imidazole–semiquinone complexes

Density functional theory (DFT) was used to calculate electric field gradients that give rise to quadrupole couplings for nuclei with a nuclear spin I > 1/2. A systematic theoretical investigation of the influence of hydrogen bond geometry on 14N quadrupole coupling tensors of (methyl-)imidazole is presented for the hydrogen-bonded systems imidazole–water and methylimidazole–benzosemiquinone. It reveals a strong dependence of the corresponding interaction parameters on the intermolecular arrangement, especially for the asymmetry parameter η. For both systems the largest influence on the electric field gradients was found for a variation of the hydrogen bond length r(O–N), the effects of an in- or out-of-plane distortion of the bond geometry were found to be less pronounced. Furthermore, a comparison of the 14N quadrupole parameters of the hydrogen-bonded models with those of free (methyl-)imidazole allowed a characterization of specific hydrogen bonding interactions to the amino group of imidazole or histidine. Finally, the implications of the presented studies for the interpretation of experimental quadrupole coupling data of biologically relevant semiquinone–histidine systems, as e.g. found in bacterial reaction centres or photosystem II, are discussed.

Structural and electronic information on two solid iminophosphoranes, obtained from NMR

Phosphorus-31 and carbon-13 CPMAS NMR spectra have been obtained for imino(triphenyl)phosphorane and amino(triphenyl)phosphonium bromide. Detailed analysis yields information about the 31P shielding tensor and the 14N quadrupole coupling tensor. The static 31P spectrum of the bromide was also analysed in terms of the relevant tensors. Ab initio calculations at the hf/6-31g* level reproduce the observed data well, except for the isotropic shifts, which require a larger basis set and/or higher level of theory. The orientations of the tensors in the molecular frame are derived for the bromide from the calculations.

EPR and ENDOR Studies of 1H and 14N Hyperfine and Quadrupolar Couplings in Crystals of l-O-Serine Phosphate after X-Irradiation at 295 K

Single crystals of l-O-serine phosphate, (HOOC)CH(NH3+)CH2OPO3-H, were X-irradiated at 295 K and studied using EPR, ENDOR, and FSE techniques. At this temperature, three carbon-centered radicals were identified. Radical I, the deamination product (HOOC)ĊHCH2OPO3-H, is shown to have undergone a major molecular reorientation upon formation. Radical II is identified to be the product (HOOC)CH(NH3+)ĊHOPO3-H. This species exhibits a nonplanar site for the lone electron density. This deviation from planarity is ascribed to electrostatic interaction between the lone electron orbital and lone pairs centered on the neighboring oxygen atom. Hyperfine interaction with the β-nitrogen of the amino group is observed. Both the 14N hyperfine and quadrupole coupling tensors are determined and the signs of the hyperfine coupling tensor principal values are deduced from interpretation of the quadrupole tensor employing the Townes−Dailey approach. The β14N isotropic interaction is well described by a Heller and McConnell type cos2 θ rule. The results found in the present work, together with other recent observations, yield estimated values of the constants B0 = 1.0 MHz and B2 = 34.5 MHz. Radical III exhibits the structure (HOOC)CH(NH3+)ĊH2, formed by scission of the phosphate−ester bond at the carbon side. No β14N coupling is observed for this radical due to a dihedral angle close to 90°. Possible mechanistic routes for the formation of these radicals are discussed in comparison with previously published data on serine and other alkyl phosphate derivatives.

Determinationof the 14N quadrupole coupling tensor of an ℓ-alanine single crystal by overtone NMR

The overtone NMR approach was examined for determination of the quadrupole coupling tensor of the 14N nucleus in a single crystal and demonstrated for ℓ-alanine.

Rotational spectrum of 3-butynenitrile in the microwave and radiofrequency range using one- and two-dimensional Fourier transform techniques

Microwave and radiofrequency Fourier transform spectra have been measured for 3-butynenitrile (propargyl cyanide), HCCCH 2CN, as its normal isotopomer in the ground vibrational state. Single- and double-resonance pulse-type experiments have been performed to yield spectra in one- and two-frequency dimensions. The 14N quadrupole hyperfine structure has been resolved and the quadrupole coupling constants χ + = 2.256 MHz and χ − = −1.835 MHz have been obtained. Ab initio calculations (GAUSSIAN 86) have been undertaken to confirm the assumption of a nearly cylindrically symmetric 14N quadrupole coupling tensor. The additional information has been exploited to show that the CN group is bent away from the HCC group through an angle in the CH 2CN chain of 0.9°.

A Reanalysis of 14N Nuclear Quadrupole Coupling and Methyl Internal Rotation in the Rotational Spectra of Monomethyl Oxazoles and Isoxazoles

Abstract Previously published rotational frequencies of 2-, 4-, and 5-methyl oxazole and of 3- and 5-methyl isoxazole are reanalysed to obtain correct rotational constants (A constants in the first place) on the basis of hypothetically unsplit rotational centre frequencies. With these, r0-structural parameters of the respective methyl group could be determined, thus allowing us to consider the influence of methyl substitution on the 14N-quadrupole coupling tensor and the structural relevance of the internal rotor angle given by torsional analysis. 14N nuclear quadrupole hfs and IAM methyl torsional analyses were redone with the correct rotational constants.

ChemInform Abstract: The Vibrational State Dependence of the 14N Quadrupole Coupling Tensor in Aniline. A Microwave Fourier‐Transform Study Combined with Semirigid Bender Calculations.

ChemInformVolume 19, Issue 39 Physical Organic Chemistry ChemInform Abstract: The Vibrational State Dependence of the 14N Quadrupole Coupling Tensor in Aniline. A Microwave Fourier-Transform Study Combined with Semirigid Bender Calculations. B. + KLEIBOEMER, B. + KLEIBOEMER Abt. Chem. Phys., Inst. Phys. Chem., Christian-Albrechts-Univ. Kiel, D-2300 KielSearch for more papers by this authorD. H. SUTTER, D. H. SUTTER Abt. Chem. Phys., Inst. Phys. Chem., Christian-Albrechts-Univ. Kiel, D-2300 KielSearch for more papers by this author B. + KLEIBOEMER, B. + KLEIBOEMER Abt. Chem. Phys., Inst. Phys. Chem., Christian-Albrechts-Univ. Kiel, D-2300 KielSearch for more papers by this authorD. H. SUTTER, D. H. SUTTER Abt. Chem. Phys., Inst. Phys. Chem., Christian-Albrechts-Univ. Kiel, D-2300 KielSearch for more papers by this author First published: September 27, 1988 https://doi.org/10.1002/chin.198839046AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume19, Issue39September 27, 1988 RelatedInformation

The Intramolecular Electric Field Gradient at the 14N-Nucleus in Monofluoroacetonitrile and an Improved Partial r0-Structure of the Molecule

Abstract The 14N quadrupole coupling tensor in CH2FCN and CD2FCN was determined from the hyperfine splittings of low J rotational transitions to give indirect structural information on the geometry of the CCN chain. The CCN chain turns out to be slightly bent (2° away from F), in excellent agreement with the result of an earlier ab initio calculation.

The Vibrational State Dependence of the 14N Quadrupole Coupling Tensor in Aniline . A Microwave Fourier-Transform Study Combined with Semirigid Bender Calculations

Abstract Experimental values for the diagonal elements of the 14N quadrupole coupling tensor derived from analysis of the hyperfine structure of low-J rotational transitions are reported for the two lowest states of the amino wagging mode. They show the expected difference due to averaging over the large amplitude amino wag. A semirigid bender analysis of previously published infrared data provides the inversion angle expectation values for use in a quantum-chemical calculation of the corresponding effective Cou­lomb field gradients at the nitrogen nucleus. The results are compared to those obtained earlier for the related molecules vinylamine, cyanamide and ammonia.

Orientation-selective 14N electron spin echo envelope modulation (ESEEM): The determination of 14N quadrupole coupling tensor principal axis orientations in orientationally disordered solids

We present an orientation-selective ESEEM (electron spin echo envelope modulation) technique. From a measurement of the variation of the amplitudes of modulation components at 14N pure quadrupole frequencies as a function of irradiation position within an EPR (electron paramagnetic resonance) powder pattern, we determine the orientation of the principal axes of the quadrupole coupling tensor relative to the principal axes of the tensor which governs the dispersion of the EPR spectrum in an orientationally disordered sample. The pure quadrupole frequencies appear when the EPR frequency is selected such that the nuclear Zeeman and the hyperfine interaction are approximately equal in magnitude. We have applied the method to a mercaptoethanol complex of myoglobin in which the pure quadrupole frequencies originate from 14N in the proximal imidazole ring. Our results enable us to validate the assignment of the quadrupole modulations to the metal-coordinated nitrogen of the imidazole ring, to correlate the principal axes with the principal values of the quadrupole coupling tensor, and to determine the orientation of the imidazole ring relative to the principal axes of the (low-spin) Fe(III) g matrix. These findings are discussed and compared with results of previous studies.

A simple approach for relating molecular and structural information to the dipolar coupling 13C 14N in CPMAS NMR

High-resolution solid-state 13C NMR spectra of 13C adjacent to 14N show a characteristic deformation observed mostly as asymmetric doublets, due to the dipolar coupling between 14N and 13C not suppressed by magic-angle spinning. A simple theoretical approach allows one to derive an analytical equation which relates the observed splittings with (a) the 14N quadrupole coupling tensor, (b) the intenuclear distance, (c) the applied magnetic field, and (d) the orientation of the internuclear vector in the principal axis system of the electric field gradient. The analytical treatment is completely general and the results obtained are in good agreement with solid-state 13C NMR data taken from the literature.

Determination of the 14N quadrupole coupling tensors in a single crystal of l-histidine hydrochloride monohydrate by NMR spectroscopy

The 14N quadrupole coupling tensors of the NH 3 +, N2, and N3 nitrogen nuclei in a single crystal of l-histidine hydrochloride monohydrate were determined using proton enhanced 14N NMR with high-power proton decoupling. The signs of the 14N quadrupole coupling constant, e 2Qg h , for the three chemically distinct nitrogen nuclei could be determined by analyzing the lineshapes of the 13C CP-MAS NMR signals of the C2, C4, and C6 carbon nuclei which are directly bonding to one of those nitrogen nuclei. The 14N quadrupole coupling constants including their signs and the asymmetry parameters, η, were evaluated to be e 2Qg h = 1.147 MHz and η = 0.189 for the NH 3 + nitrogen nucleus, e 2Qg h = 1.465 MHz and η = 0.268 for the N2 nitrogen nucleus, and e 2Qg h = −1.287 MHz and η = 0.946 for the N3 nitrogen nucleus. The direction of the largest principal axis of the 14N quadrupole coupling tensor for the NH 3 + nitrogen nucleus is almost parallel to the NlC2 bond direction, while that for the N2 nitrogen nucleus makes an angle of 33° with the N2C4 bond direction in the C4N2C5 plane, and for the N3 nitrogen nucleus it is perpendicular to the C5N3C6 plane. Application of the Townes and Dailey model shows the orbital populations of the p μ and the NH orbitals are larger than those of the NC orbital of the N2 and N3 nitrogen nuclei. The difference between the 14N quadrupole coupling tensors of N2 and N3, can be attributed to the difference in the hydrogen bonding at those two sites.