NMR, FTIR and DFT study of the interaction of the benzoate anion with meso-octamethylcalix[4]pyrrole (original) (raw)
Related papers
Journal of the American Chemical Society, 1984
Figure 4. Plot of AJCiw- ,-arbony, in 0-protonated benzaldehydes vs. those in 0-protonated acetophenones. that there is a linear free energy relationship between AJ values of two similar system. A plot of AJci,-c,b,, values in substituted 0-protonated benzaldehydes against the corresponding values in 0-protonated acetophenones is also linear (Figure 4) (r = 1 .O). These linear plots of AJ values indicate that the substituent effect on Jcc values (SCC) in systems t h a t are closely related in their electron demand is very similar. Jcc values can, a s shown in the present study, be valuable in the study of carbocationic systems. W e are continuing our further study on 13C-13C coupling in such electron-deficient systems. Experimental Section All acetophenones and benzaldehydes used were commercially available samples with 299% purity. Regular 13C NMR and I3C satellite spectra were recorded at 50.3 MHz with use of a Varian XL-200 su-perconducting NMR spectrometer equipped with a variable-temperature broad-band probe. The spectra of neutral acetophenones and benzaldehydes were obtained at room temperature in CDCI, solvent (-30% solution). The 0-protonated carboxonium ions were prepared by slow addition of the corresponding acetophenone or benzaldehyde to FSO3H at ca.-40 ' C (-25% solution), and the spectra were recorded in FSO3H at-35 'C. The pulse sequence used for the I3C satellite spectra, based on Freeman et aI.,l7 is 90' (x)-+-180°Cy)-r900(x)-A-90'(~)-Acq.(+), where T N (2n + 1)/4Jcc, A is a very short delay (-10 f i s) needed to reset the radio-frequency phase during which time double quantum COherance evolves,and $J and + are the phase of the last 90' "read" pulse and the receiver reference phase, respectively. Optimum setting of T for direct coupling is when n = 0 and thus is set at 4.5 ms (corresponding to a Jcc value of-55 Hz). The repetition rate of this sequence is-10 s, and reasonable S/N was achieved in 6-8 h of acquisition. The coupling constants can be directly measured from the "satellite" spectra." The accuracy of the coupling constants in a neutral compound are 10.2 Hz while those in the protonated carboxonium ions are 1 0. 3 Hz. Some of the coupling constants could not be measured accurately due to overlap of peaks or due to broadening because of slow rotation around the Cipo-Ccsrbnyl bond (in the carboxonium ions).
Arkivoc, 2009
17 O NMR Substituent Chemical Shift (SCS) values on the carbonyl and methoxy oxygens in methyl 2,6-dimethyl-4-X-benzoates 2' have been measured in acetonitrile-d 3 and compared with those of the 2,6-unsubstituted methyl 4-X-benzoates 2, the former exhibiting very little sensitivity to the effect of 4-substituents and not appearing to be related to π-electron density changes in such sterically hindered systems. Conversely 13 C NMR SCS values of the methoxy carbon of the ester function in either 2 and 2', although modest in size, exhibit a very good dual substituent parameter (DSP) correlation with the polar and resonance effect of 4-substituents and are therefore effective indicators of local πelectron densities. Moreover, 13 C NMR SCS values of the methoxy carbon of 2' exhibit an excellent linear correlation with those of 2,6-unsubstituted benzoates 2. Once more this agrees with our previous conclusion that the resonance interaction between the aromatic ring and the ester group is essentially related to a π-polarization effect, not involving charge-transfer between the two moieties and therefore not sensitive to steric hindrance to their coplanarity.
Counterintuitive interaction of anions with benzene derivatives
Chemical Physics Letters, 2002
Ab initio calculations were carried out on complexes between 1,3,5-trinitrobenzene (TNB) and anions, where the anion is positioned over the ring along the C 3 axis. This study combines crystallographic and computational evidences to demonstrate an attractive interaction between the anion and the p-cloud of TNB. This interaction is rationalized based on the important role of the quadrupole moment of TNB and the anion-induced polarization. In addition, this study has been extended to 1,3,5-trifluorobenzene (TFB), which possesses a very small quadrupole moment. As a result, minimum energy complexes have been found between TFB and both anions and cations due to the stabilization obtained from the ion-induced polarization. Ó
2012
Binding interaction of Tl + , Cs + , Li + Br À , and Cs + Br À with meso-octamethylcalix[4]pyrrole (1) in nitrobenzene-d 5 was studied using 1 H, 13 C, 7 Li, and 133 Cs NMR spectroscopy and DFT quantum-chemical calculations. Although originally declared as typical anion and ion pair receptor, 1 is shown to bind fairly strongly Tl + cations (equilibrium constant K = 1600 ± 80 mol À1 L À1). The binding of Cs + is much weaker (K = 370 ± 18 mol À1 L À1). Neither of these cations invert the conformation of 1. Li + Br À binds to 1 (K = 1790 ± 160 mol À1 L À1) forming at least four energetically close complexes without much change in its conformation. Cs + Br À prepared in situ from Li + Br À and the cesium salt of dicarbollyl cobaltate in the presence of 1 binds strongly to 1 (K = 103514 ± 4000 mol À1 L À1 , log K = 5.015) in spite of the slight competition of Li + ions. The cooperative binding of Cs + and Br À ions is shown, in accord with a recent suggestion in literature, to invert the natural conformation of 1, the four NH groups binding to Br À by hydrogen bonds and the aromatic rings forming a cup binding the embedded Cs + by its interaction with the p electron orbitals.
2009
University Science Instrumentation Centre, University of Kashmir, Srinagar-190 006, Jammu & Kashmir, India E-mail : smaal@rediffmail.com <em>Manuscript received 2 September 2008. revised 28 January 2009, accepted 19 March 2009</em> Modified Benesi-Hildebrand and Hanna-Ashbaugh equations have been used for the evaluation of association constants of the charge-transfer complexes by electronic spectroscopy and NMR spectroscopy, respectively. Association constants of charge-transfer complexes of aniline with various dinitrobenzenes have been calculated by electronic spectroscopy using the existing methods and compared with those calculated by the new method. Results show that the new equation has the advantages of measuring K directly rather than evaluating it from the product <em>K</em><sub>E</sub> leading to increased accuracy and being obeyed in cases where Foster-Hammick-Wardley and Scott equations fail. Similarly, association constant of dinitrot...
Arkivoc, 2009
17O NMR Substituent Chemical Shift (SCS) values on the carbonyl and methoxy oxygens in methyl 2,6-dimethyl-4-X-benzoates 2’ have been measured in acetonitrile-d3 and compared with those of the 2,6-unsubstituted methyl 4-X-benzoates 2, the former exhibiting very little sensitivity to the effect of 4-substituents and not appearing to be related to π-electron density changes in such sterically hindered systems. Conversely 13C NMR SCS values of the methoxy carbon of the ester function in either 2 and 2’, although modest in size, exhibit a very good dual substituent parameter (DSP) correlation with the polar and resonance effect of 4-substituents and are therefore effective indicators of local π-electron densities. Moreover, 13C NMR SCS values of the methoxy carbon of 2’ exhibit an excellent linear correlation with those of 2,6-unsubstituted benzoates 2. Once more this agrees with our previous conclusion that the resonance interaction between the aromatic ring and the ester group is essentially related to a π-polarization effect, not involving charge-transfer between the two moieties and therefore not sensitive to steric hindrance to their coplanarity.
Magnetic Resonance in Chemistry, 2007
The 15 N as well as 13 C and 1 H chemical shifts of eight push-pull benzothiazolium iodides with various p-conjugated chains between dimethylamino group and benzothiazolium moiety have been determined by NMR spectroscopy at the natural-abundance level of all nuclei in DMSO-d 6 solution. In general, the quaternary benzothiazolium nitrogen is more shielded [d(15 N-3) vary between −241.3 and −201.9 ppm] with respect to parent 3-methylbenzothiazolium iodide [d(15 N-3) = −183.8 ppm], depending on the length and constitution of the p-conjugated bridge. A larger variation in 15 N chemical shifts is observed on dimethylamino nitrogen, which covers the range of −323.3 to −257.2 ppm. The effect of p-conjugation degree has a less pronounced influence on 13 C and 1 H chemical shifts. Experimental data are interpreted by means of density functional theory (DFT) calculations. Reasonable agreement between theoretical and experimental 15 N NMR chemical shifts was found, particularly when performing calculations with hybrid exchange-correlation functionals. A better accord with experiment is achieved by utilizing a polarizable continuum model (PCM) along with an explicit treatment of hydrogenbonding between the solute and the water present in dimethylsulfoxide (DMSO). Finally, 13 C and 1 H NMR spectra were computed and analysed in order to compare them with available experimental data.
Conformational analysis, tautomerization, IR, Raman, and NMR studies of benzyl acetoacetate
Journal of Molecular Structure, 2011
A complete conformational analysis of the keto and enol forms of benzyl acetoacetate (BAA), a b-dicarbonyl compound, was carried out by ab initio calculations, at the density functional theory (DFT) level. By inspection of all possible conformers and tautomers, 22 stable cis-enol, 28 stable trans-enol, and five keto conformers were obtained.
Nuclear magnetic resonance of benzobisheterocyclic compounds
Journal of Heterocyclic Chemistry, 1966
The nuclear magnetic resonance spectra of forty-nine benzobisheterocyclic compounds, containing various heterocycles, were determined. The observed spectral data made possible the elucidation of the structure and also clarified the influences of the heterocyclic substituents and of heterocyclic rings on chemical shift values of the aromatic protons.