Molecular Electric Field Gradients Research Articles

HF–DFT calculations of 14N and 35Cl quadrupole coupling constants on optimized molecular structures of pyridine and the monochloropyridines

14N and 35Cl nuclear quadrupole coupling constants in the monochloropyridines and 14N in pyridine have been determined in the principal axes of both the inertia and coupling constant tensors by HF–DFT calculations of the molecular electric field gradients on B3P86/6-31G(3d,3p) optimized molecular structures.In the case of 4-chloropyridine, the calculated 14N coupling constants are probably more accurate than the experimental values.Investigation of the substitution effect shows that the differences in nitrogen nqccs between 2-chloropyridine and pyridine are largely due to the presence of the chlorine substituent (as opposed to distortion of the ring). The small differences found in 3-chloropyridine can be understood as due to near cancellation of effects due to the substituent and ring distortion. In 4-chloropyridine, on the other hand, these effects are additive, accounting for the differences for this molecule.

The nuclear quadrupole moment of 14N. A theoretical prediction from full valence shell and full configuration interaction atomic wave functions

Full configuration interaction ab initio studies of the 2p 3p 1P1 state of N+ are carried out in order to obtain the molecular electric field gradient at the nitrogen nucleus. A careful calibration of the basis set leads to a q value (−0.94 a.u.) obtained using a 〈13s9p5d2f/10s7p5d2f〉 basis set with an estimated accuracy of ±0.01 a.u. Combined with the experimental nuclear quadrupole coupling constant for this system, we predict the nuclear quadrupole moment of 14N to be Q(14N)=(20.7±0.4) mb.

The effects of H-bonding, change of state and molecular distortion on 2H and 17O nuclear quadrupole coupling constants: general theoretical considerations and specific application to formic acid

The major emphasis here is in analysing the effect of H-bonding on the nuclear quadrupole coupling behaviour of 2H and 17O nuclei. Using ab initio quantum mechanical methods on the test molecule formic acid, the coupling amplitudes (nuclear quadrupole coupling constants e 2 qQ/h) and, also, coupling anisotropies (asymmetry parameter η) and orientations of the electric field gradient principal axis system with respect to molecular axes have been calculated. As formic acid contains 2H and 17O nuclei in a variety of functional groups — alkyl ( 2H), hydroxyl ( 2H and 17O) and carboxyl ( 17O) — it is a particularly efficient molecule for theoretical study. In addition the structures of its H-bonded complexes vary as a function of phase from the cyclic H-bonded gaseous dimer through a probably chain-like association in the liquid to a regular chain H-bonded solid phase. Thus in this work the consequences of differing H-bond geometries on nuclear quadrupole coupling of the given nuclei are investigated, and also the relative contributions to the coupling changes of geometric and electronic disortions resulting from H-bonding and lattice field effects in the solid, are evaluated. The theoretical results are compared with the most up-to-date experimental data available. General problems in calculating molecular electric field gradients are outlined and, in particular, errors resulting from uncertainties in experimental input geometries are critically assessed. Differences in computational emphasis for 2H as compared with 17O and other “heavy” nuclei are pointed out.

Quadrupole resonance of 14N and 2D in glycine, a model compound

Using double nuclear resonance techniques (DRLC) the quadrupole resonances spectrum of 14N is obtained in both protonated and deuterated glycine crystallized in each of three crystalline forms. In the deuterated samples the quadrupole resonance spectrum is obtained for each of the three amino deuterons again in each of the three crystalline forms. It is suggested that this system is ideal for a comparison between theoretical calculation and experiment measurement of molecular electric field gradients.

ChemInform Abstract: MOLECULAR STRUCTURE, QUADRUPOLE SPLITTING, AND MAGNETIC SUSCEPTIBILITY OF IRON IN DEOXYGENATED MYOGLOBIN AND HEMOGLOBIN

Chemischer InformationsdienstVolume 6, Issue 21 Organoelement Compounds ChemInform Abstract: MOLECULAR STRUCTURE, QUADRUPOLE SPLITTING, AND MAGNETIC SUSCEPTIBILITY OF IRON IN DEOXYGENATED MYOGLOBIN AND HEMOGLOBIN ALFRED TRAUTWEIN, ALFRED TRAUTWEINSearch for more papers by this authorREINHART ZIMMERMANN, REINHART ZIMMERMANNSearch for more papers by this authorFRANK E. HARRIS, FRANK E. HARRISSearch for more papers by this author ALFRED TRAUTWEIN, ALFRED TRAUTWEINSearch for more papers by this authorREINHART ZIMMERMANN, REINHART ZIMMERMANNSearch for more papers by this authorFRANK E. HARRIS, FRANK E. HARRISSearch for more papers by this author First published: May 27, 1975 https://doi.org/10.1002/chin.197521405AboutPDF 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. Volume6, Issue21May 27, 1975 RelatedInformation

Molecular structure, quadrupole splitting, and magnetic susceptibility of iron in deoxygenated myoglobin and hemoglobin

For three stereo-structural models of deoxymyoglobin (Mb) and deoxyhemoglobin (Hb) we derive electronic configurations and their mutual spin-orbit coupling. From the temperature dependent molecular electric field gradient (EFG) tensor we calculate temperature dependent quadrupole splittings, ΔE q(T), asymmetry parameters, η(T), and orientations of the EFG component V zz(T) with respect to the heme group. Comparing theoretical and experimental data we find a molecular electronic structure, which then is used to compute temperature dependent magnetic susceptibilities, χ(T). Theoretical and experimental χ(T) data are in reasonable agreement. From the consistency of our model calculations with experimental results we conclude that iron in Mb and Hb probably is pentacoordinated and considerably out of the heme plane by 0.4–0.8 A.

Hyperfine Structure of 7Li79,81Br by Molecular-Beam Electric Resonance

The molecular-beam electric-resonance technique has been used to measure the hyperfine interaction constants of the J=1, v=0 state of 7Li79,81Br in the limit of weak external fields. The results for the bromine and lithium nuclear electric quadrupole interaction constants, eqQBr and eqQLi, the spin-rotation constants, cBr and cLi, the ``tensor'' nuclear spin-spin interaction, c3, and the ``scalar'' nuclear spin-spin interaction are (in kilohertz) Li797BrLi817BreqQBr38368.104(36)32050.860(46)eqQLi211.04(10)211.03(13)cBr7.8816(58)8.4740(74)cLi0.859(15)0.815(19)c31.0710(61)1.1789(78)c40.0604(70)0.0711(89)A theory which permits the calculation of the optimum power required to drive the hyperfine transitions is presented and experimentally verified. A possible pseudoquadrupole effect is discussed, and recent calculations of molecular electric field gradients are used to determine the nuclear quadrupole moments.

Zur Abhängigkeit des molekularen elektrischen Feldgradienten qzz von der mittleren Molekülpolarisierbarkeit ᾱ.

Empirically a linear correlation is established between the average polarisability of the nonspherical molecules CH3Cl, CH2Cl2, CHCl3 and the molecular electric fieldgradient qzz at the chlorine nuclei as determined by “pure quadrupole spectroscopy”. As a consequence of this, a linear relationship between the raman-active vcC-Cl(π)A1 frequency and the “pure quadrupole resonance frequency” of these molecules is also found. In the case of ideal sphere-like molecules, for theoretical reasons, a linear relationship between the molecular electric field gradient and the inverse of the polarisability is proposed. The validity of this correlation is checked in the series of the compounds CCl4, SiCl4, GeCl4 and SnCl4. From the results obtained it is concluded that the correlations put forward are strongly dependent upon the molecular shape.

Empirical Correlation between the Molecular Electric Field Gradients and the Average Molecular Polarizabilities of some Halogen Compounds

A NUCLEAR quadrupole resonance signal1 is split into two components by electrostatic fields2 with up to maximum field strengths of 50 kV/cm. The separation between the two components is a linear function2 of the polarizability of the molecular species under investigation. The aim of this communication is to demonstrate the general validity of this particular relationship2 which is in fact independent of any restricting experimental conditions, for example application of an electrostatic field (Stark effect2). Although there are relatively few compounds for which both the nuclear quadrupole resonance and molecular polarizability data are available, the general validity of the correlation between the molecular polarizability and nuclear quadrupole resonance parameters, such as the molecular electric field gradients qzz, can be demonstrated conclusively in the series of the homologous compounds CH3C1, CH2Cl2 and CHCl3. The relevant experimental data3–7 are shown in Table 1 and illustrated in Fig. 1.

Molecular Beam Measurement of the Hyperfine Structure of 85Rb19F

Radio-frequency transitions between the hfs levels of the J=1 rotational state in 85Rb19F have been observed using a molecular beam electric resonance spectrometer. From these spectra we have obtained values for the constant eq1Q1, which characterizes the interaction between the electric quadrupole moment of the Rb nucleus with the molecular electric-field gradient; for the constants c1 and c2 which characterize the magnetic interaction between the Rb and F nuclei, respectively, and the rotational angular momentum J of the molecule; and for the constants c3 and c4 which describe the magnetic coupling of the two nuclear spins. Measurements have been made on the first-five vibrational states. The results for v=0 are eq1Q1=(−70.342±0.001) MHz,c1=(+0.52±0.02) kHz,c2=(+10.615±0.06) kHz,c3=(+0.80±0.06) kHz,c4=(+0.15±0.05) kHz.Values of these constants for v=1, 2, 3, and 4 are given with somewhat less precision.

Über die chemische Bindung in Gold(I)-jodid

The molecular electric field gradient (e qzz)610 at the nucleus of the gold isotope 197 is 42,7 · 1015 esu cm-3 according to our calculations. This value was used in calculating the quadrupole coupling constant in AuI and agreement is found with the experimental quadrupole coupling constant (e2 Q qzz)/h=508.296 MHz, if 50% s2-hybridisation and 21% ionicity are attributed to the gold-iodine bond. The ionicity in AuI is perhaps greater than in AuCl, as is indicated by the lower quadrupole coupling constant of Au197 in Aul. ( (e2 Q qzz) /h=508,296 MHz in AuI, 514,150 MHz in AuCl 1.) This result is discussed with respect to the Townes-Dailey rule

The equation of state of multipolar gases

The equation of state in the approximation of the second virial coefficient B is discussed theoretically for gases consisting of unlike multipolar molecules. A molecule of species i is assumed to posses a permanent 2n-pole moment M(n)i, as well as a 2n-pole moment P(n)i induced in it by the electric field F(n)i of order n of a neighbouring molecule of species j having the permanent 2m-pole electric moment M(m)j. Tensor formalism is used for deriving general expressions for the potential energy of electrostatic and inductional interaction of two multipolar molecules of species i and j. These energies then serve for computing two contributions to B: the one, of inductional type, is obtained in the first approximation and contains, in addition to terms with dipolar polarizability, terms accounting for the quadrupolar polarizability induced in the molecule by the molecular electric field gradient; the other, which is purely electrostatic, is obtained in the second approximation of the theory. Moreover, cross contributions to B between the electrostatic and inductional energies as well as contributions from dipolar anisotropy of dispersional-type interactions are computed. In computing the mean values of the respective powers of rij (the distance between the two molecules), a general Lennard-Jones (s-t)-type potential is applied. The theoretically derived non-central contributions to B are valid in general for molecules of arbitrary symmetry and arbitrary electrical structure; the expressions are applied to cases of axially symmetric, tetrahedral and octahedral molecules. For methane, the theoretical formulas allowed to determine numerically the octopole moment from experimental data on B to be ΩCH4 = 5 × 10−34 e.s.u. cm3.

Proton N.S.R. Spectrscopy. III. Molecular Electric Field Gradients Annihilation of Nitrogen Quadrupole Broadening by Means of Strong molecular El;ectric Field Gradients

Proton N.S.R. Spectrscopy. III. Molecular Electric Field Gradients Annihilation of Nitrogen Quadrupole Broadening by Means of Strong molecular El;ectric Field Gradients