Fluorinated Tetraphosphonate Cavitands

Two synthetic protocols for the introduction of fluorine atoms into resorcinarene-based cavitands, at the lower and upper rim, respectively, are reported. Cavitand 1, bearing four fluorocarbon tails, and cavitand 2, which presents a fluorine atom on the para position of a diester phosphonate phenyl substituent, were synthesized and their complexation abilities toward the model guest sarcosine methyl ester hydrochloride were evaluated via NMR titration experiments. The effect of complexation on the 19F NMR resonance of the probe is evident only in the case of cavitand 2, where the inset of the cation-dipole and H-bonding interactions between the P=O bridges and the guest is reflected in a sizable downfield shift of the fluorine probe.

Model molecules to classify CH⋯O hydrogen-bonds

A set of molecules locked in the CH⋯O H-bonding conformation has been used to correlate the magnitude of the downfield shift of the 1H NMR signal due to the bridging hydrogen with the hybridization state of the acceptor oxygen and the CH⋯O H-bond strength.

Synthesis and Spectroscopic Characterization of l-Aspartic Acid Complexes with Metals of the Lanthanides Family

The complexes between l-aspartic acid and metals of lanthanide series (La3+, Pr3+, Eu3+, Gd3+) have been prepared and characterized using a variety of techniques including, infrared spectroscopy, 1H NMR, 13C NMR, elemental analysis and metal contents. The sought metal effect on the electronic environment of the chiral carbon and its neighbouring atoms was observed in case of Europium and Praseodymium. The 13C downfield shift indicates a lower electron density at the carbon with consequent downfield shift observed on the α-H attached to it increasing its acidity.

103Rh- und 15N-NMR-Untersuchungen an bindungsisomeren Hexakis(thiocyanato(N)-thiocyanato(S))-rhodaten(III) / 103Rh and 15N NMR Investigations on Bond Isomeric Hexakis(thiocyanato(N)-thiocyanato(S))rhodates(III)

By 103Rh and 15N NMR spectroscopy eight bond isomers of the preparatively feasible system [Rh(NCS)n(SCN)6-n]3-, n = 0-4, including the three pairs of stereoisomers for n = 2,3,4 are identified and assigned unequivocally by their clearly resolved signals. A downfield shift of approximately 540 ppm per isomerization step from S bonding to N bonding is observed in the 103Rh spectra. The non-separable stereoisomers exhibit a high field shift of 4-30 ppm of the trans/mer as compared to the cis/fac isomers. The spectra of the 99% isotopically 15N enriched bond isomers reveal splittings of the 103Rh signals into the expected multiplets with 1J(RhN) couplings of about 23 Hz, which are confirmed and determined more precisely to 21,0 Hz for SRhN axes and 24,1 Hz for NRhN axes from the 15N spectra. The 15N resonances are observed in three characteristic regions depending on the bond type of the ambident ligands and their geometrical arrangement. For S bonding the signals appear at lowest field between — 134 and —141 ppm, for N bonding in asymmetric axes NRhS between —269 and —271 ppm, and in symmetric axes NRhN at highest field between —292 and —297 ppm. Some signals in the S bonding region are split by a very small 3J(RhN) coupling of about 0,7 Hz.

33S NMR spectra of some sulfonated naphthalenes, naphthols, and their anions

The 33S NMR spectra of 11 naphthalenesulfonates, 11 hydroxynaphthalenesulfonates, two dihydroxynaphthalenesulfonates, and their anions have been measured in aqueous solutions. The 33S NMR chemical shifts of these compounds exhibit upfield shifts when related to ammonium sulfate as the standard. Introduction of a further sulfonic group causes a small upfield shift (up to 3 ppm). Introduction of a hydroxyl group causes a downfield shift (up to 5 ppm) unless the ring is further substituted. Formation of the anion from hydroxyl group causes an additional downfield shift (up to 6 ppm). The half-width of 33S NMR signals of sulfonated naphthalenes, naphthols, and their anions vary from 10 to 400 Hz.

103Rh-NMR-Untersuchungen an Chloro-Bromo-Rhodaten(III) und Bestimmung der Stabilitätskonstanten im System [RhClnBr6-n]3-, n = 0-6 / 103Rh NMR Studies of Chloro-Bromo-Rhodates(III) and Determination of the Stability Constants in the System [RhCl„Br6-n]3-, n = 0-6

By 103Rh NMR spectroscopy the ten compounds of the system [RhCl„Br6_„]3-, n = 0-6 are identified by separate signals. A downfield shift of approximately 160 ppm is observed per substitution of Cl by Br, and the stereoisomers for n = 2, 3, 4 are separated by at least 4 ppm. From the relative intensities of the 103Rh signals in equilibrated solutions, whose total contents of Rh. Cl and Br are known, six individual stability constants are calculated. Their product gives the overall stability constant, indicating [RhBr6]3- to be 36,300 times more stable than [RhCl6]3-. On treatment of [RhBr6]3- with HCl cis/fac isomers are formed stereospecifically, whereas the reaction of [RhCl6]3- with HBr gives trans isomers, n = 2 and 4, containing 20—30% of the cis compounds; only mer-[RhCl3Br3] 3- is obtained pure. The high resolution spectra of [RhCl6]3- and [RhBr6]3- are exhibit five signals each, reflecting the intensity patterns of the most abundant isotopomers within [Rh35Cln37Cl6-n]3-, n = 2-6, and [Rh79Br„81Br6_„]3-, n = 1-5, respectively.

Correlation of 31P nuclear magnetic resonance chemical shifts in aryl phosphinates with Hammett substituent constants: Inductive versus resonance interactions and relevance to pπ–dπ bonding

Substituent-induced chemical shifts and coupling constants in the 31P, 13C, and 1H nuclear magnetic resonance spectra of meta- and para-substituted phenyl dimethylphosphinates (1), methylphenylphosphinates (2), and diphenylphosphinates (3) have been determined in CDCl3 solvent. For all three series, a correlation of δ 31P with Hammett–Taft σ0 (or σ) constants is preferred over σ− on the basis of the correlation coefficient and standard deviations of the slope and intercept values. Electron-withdrawing substituents induce downfield shifts in δ 31P, in contrast to the inverse trends observed for structurally related series of oxyphosphorus acids and their derivatives. It is proposed that electron-withdrawing substituents act to deplete the electron density on the aryl oxygen, thereby weakening a pπ–dπ bonding interaction between the aryl oxygen and phosphorus. The resultants loss of d-orbital density on phosphorus causes a downfield shift in δ 31P in each of the phosphinate series. Phenyl substituents attached directly to phosphorus in series 2 and 3 increase the phosphoryl pπ–dπ back-bonding interactions, either through inductive or resonance effects, which leads to shielding of the phosphorus atom, overriding the anticipated downfield shift through inductive electron withdrawal of the phenyl substituents in series 2 and 3, relative to the methyls in series 1. Trends in Hammett ρ values for the plots of δ 31P and δ 13C versus σ0 and differences in the shielding of 13C and 1H nuclei of the methyl attached to phosphorus in series 1 and 2 suggest that the phenyl groups may interact in π bonding with the phosphorus atom through a resonance interaction.

Zusammensetzung von Rohsulfan, Nachweis der Sulfane H2S9 bis H2S35 Composition of Crude Sulfane Oil, Identification of the Sulfanes H2S9 to H2S35

In benzene solution the position of the 1H NMR signals of sulfanes, H2Sn, strongly depends on the sulfur chain length and on the sulfane concentration. Under proper conditions all sulfanes in a mixture are characterized by well-resolved NMR signals showing a downfield shift with increasing length of the sulfur chain. The shift differences between the higher homologues ( n > 8 ) remain nearly constant, thus allowing the assignment of the signals up to H2S35 and the determination of the complete sulfane distribution in crude oils. In sulfane mixtures without solvent as well as in CS2 and CCl4 solutions, however, H2S8 shows the largest downfield shift. The signals of the higher sulfanes overlap in a narrow range at slightly higher field and cannot be characterized except for the CCl4 solution where an assignment up to H2S11 is possible. The chemical shifts are interpreted in terms of inter- and intramolecular hydrogen bondings. The upfield shift caused by benzene is attributed to the formation of H2Sn · benzene complexes.

Lewis acid complexes of 1,2-diketones and their derivatives. The synthesis of seven-membered rings

The structures and charge distributions of Lewis and complexes of butane-2,3-dione, 1, cyclohexane-1,2-dione, 2, and 2-methoxycyclohex-2-en-1-one, 5, have been investigated by 1H nmr spectroscopy. A 1:1 complex was formed between 1 and SnCl4 which appeared to have a bridged structure. In the case of 2 and 5 both oxygens were again involved in complex formation with TiCl4 or SnCl4. In each case the large downfield shift of the vinyl proton resonance, H3, indicated extensive charge delocalization within the complexes and that these systems can be regarded as complexed α,β-unsaturated enones. The reactions of Lewis acid complexes of 2, 5, and the silyl ethers 2-(trimethylsiloxy)cyclohex-2-en-1-one, and 3-(trimethylsiloxy)-but-3-en-2-one, 11, with butadiene have been investigated. The acyclic enol ether 11 reacted with butadiene in the presence of either TiCl4 or SnCl4 to give products corresponding to both 4C + 3C and 4C + 2C cycloaddition reactions; in all other cases 4C + 2C products only could be isolated.