A study of the transfer of the electronic influence of substituents in o-carboranes by nuclear quadrupole resonance

The ³⁵Cl NQR spectra of 2-substituted 1-chloromethyl-o-carboranes and of 1-chloromethyl-9,12-dihalogeno-o-carboranes have been investigated. The anomalous influence of two halogen atoms present in positions 9 and 12 of the carborane nucleus on the electron density of the chlorine atom in the CH₂Cl group is explained by the combined action of their –I and +M effects, and also by the effect of p d conjugation. The comparatively high ³⁵Cl NQR frequency for o-ClCH₂CB₁₀H₁₀CH is due to the large –I effect of the carboranyl group. The induction constants of a number of groups attached to the carborane ring have been evaluated. In the molecules of the 2-substituted 1-chloromethyl-o-carboranes spatial interaction between X and Cl clearly appears. The substituents X in compounds of this series can be divided into three types according to their electronic influence: 1) electron-donating substituents, 2) substituents containing a mobile hydrogen atom (capable of forming a hydrogen bond), and 3) substituents possessing an unshared pair of electrons capable of passing into the vacant 3d orbital of a chlorine atom.     

A deuterium nuclear quadrupole double resonance study of the ferroelectric phase transition in potassium dihydrogen phosphate

A study has been made of the nuclear quadrupole double resonance (NQDR) spectrum of deuterium in a powdered sample of potassium dihydrogen phosphate, KH₂PO₄ or KDP for short, both as a function of temperature and of percentage deuteration. Double transitions have also been observed and these enable the orientation of the ferroelectric electric field gradient (EFG) tensor to be determined.     

Line broadening effects in nuclear quadrupole resonance

The major broadening mechanism in Nuclear Quadrupole Resonance is the spread in the electric field gradient produced by crystal defects. In multilevel spin systems, the frequencies of the various possible resonances are different functions of the components of the electric field gradient. This paper examines the role of both the principal component of the field gradient and the asymmetry component in the relationship between the linewidths of the two resonances of I = $\text{5}\text{2}$ nuclei. Comparison with experimental data shows various ways in which defects interact with quadrupolar nuclei.     

14N nuclear quadrupole resonance in carbazoles

Nitrogen-14 nuclear quadrupole resonance frequencies at 77 K are reported for a series of carbazole compounds including N-vinylcarbazole. Differences in charge distribution between pyrrole and carbazole are explained on the basis of delocalization of pi electrons. Effects of the aldehyde and vinyl groups on charge distribution are discussed. Sigma bond polarization between the pyrrole nitrogen and the nitroso nitrogen toward the pyrrole nitrogen exists in N-nitrosocarbazole.     

An 17O nuclear quadrupole double resonance study of several crystal hydrates

Using the technique of double resonance with coupled multiplets (DRCM), ¹⁷O double resonance signals were detected in natural abundance from the H₂O molecule in the hydrates BeSO₄ · 4H₂O, AlCl₃ · 6H₂O, CH₃COOLi · 2H₂O, LiClO₄ · 3H₂O, Sr(OH)₂ · H₂O, Ba(OH)₂ · 8H₂O, LiBr · 2H₂O and MgSO₄ · 7H₂O.Using the DRCM technique approximate values for the HOH bond angle and the OH bond length were determined from the dipolar structure present on the ¹⁷O double resonance signals. A Townes and Dailey analysis was used to examine the small differences in the ¹⁷O quadrupole coupling constants and asymmetry parameters between these samples.     

14N nuclear quadrupole coupling in solid cinnolin-4-ones. A study by nuclear quadrupole resonance,x-ray crystallography and ab initio calculations

The ¹⁴N nuclear quadrupole coupling constants (NQCCs) for 1H-cinnolin-4-one and its 1- and 2-methyl derivatives have been obtained by nuclear quadrupole double resonance. The X-ray crystal structures of the 1H and 1Me compounds have been solved, and show lengths and angles consistent with related heterocycles; attempts to obtain an X-ray structure for the 2Me compound have so far been unsuccessful owing to disorder. Computed equilibrium structures by ab initio SCF methods for the Me derivatives and also the experimental 1H structures yielded electric field gradients, which were converted into NQCCs in reasonable agreement with experiment. The 2Me compound has unusual NQCC, both experimentally and in the theoretical study.     

The nuclear quadrupole double resonance spectrum of decaborane

The boron nuclear quadrupole double resonance spectrum of decaborane, B₁₀H₁₄, was taken at 77 K. The assignment of its ¹¹B lines to the various boron atoms of the molecule is based on the spectrum of μ,1,2,3,4,5,7,8,10-B₁₀H₂D₁₂, the theoretically verified intensity relations, and the transition frequencies calculated from a SCF study.     

Volume effects on the nuclear quadrupole resonance transition frequency

A suitable modification of a general thermodynamic procedure to correct experimental data, usually gathered at constant (room) pressure, to that which would be obtained had the volume been kept constant, the normal condition under which the theory is worked out. This allows therefore meaningful comparison of data with theory. This modification is applied to the pressure derivative at constant temperature of the Nuclear Quadrupole Resonance transition frequency as a function of the temperature. It is shown in p-dichlorobenzene and in p-chlorophenol that, by using very reasonable values for the various parameters appearing in the procedure, excellent agreement is found between theory and experimental data.