The 7-Cycloheptatrienylmethyl/7-Norcaradienylmethyl Cation System

1975 ◽  
Vol 53 (12) ◽  
pp. 1818-1828 ◽  
Author(s):  
Ivan Pikulik ◽  
Ronald F. Childs
Keyword(s):  
Lewis Acid ◽  
Chemical Shifts ◽  
Product Distribution ◽  
Carbonyl Oxygen ◽  
Lower Field ◽  
Model Compounds ◽  
Contrast Reaction ◽  
Cation System ◽  
Proton Resonances ◽  
Methyl Phenylacetate

Reaction of 7-carbomethoxycycloheptatriene with either BCl3 or BBr3 gave a 1:1 complex in which the Lewis acid was complexed to the carbonyl oxygen. The low temperature p.m.r. and u.v. spectra of these zwitterions indicated that they existed almost entirely in the norcaradiene forms 10 and 14, respectively. In contrast, reaction of N,N-dimethyl-1,3,5-cycloheptatriene-7-carboxamide with BCl3 was found to result in the formation of a mixture of the cycloheptatriene 12 (65%) and norcaradiene 13 (35%). Comparison of the chemical shifts of the cyclopropyl proton resonances of 10 and 14 with model compounds showed that their positions were anomolous, the C7 protons resonating at much higher and the C1 and C6 protons resonating at much lower field than expected and to account for this it is suggested that these norcaradienes are aromatic systems. Both 10 and 14 were thermally unstable and underwent an irreversible rearrangement to form the complex of methyl phenylacetate, the phenylmethylacylium cation and the appropriate counterion, [Formula: see text] respectively. The rate of these rearrangements and the product distribution was found to be dependent upon both the ratio of Lewis acid to ester used and the nature of the Lewis acid.

A study of the observable axial- and equatorial-2,4-dimethyl-2-adamantyl cations. Further examples of equilibrating nonclassical structures in "ordinary" tertiary carbocations

1990 ◽  
Vol 68 (10) ◽  
pp. 1889-1893 ◽  
Author(s):  
D. J. Buffam ◽  
T. S. Sorensen ◽  
S. M. Whitworth
Keyword(s):  
Chemical Shifts ◽  
The Other ◽  
Temperature Dependent ◽  
Lower Field ◽  
Tertiary Alcohols ◽  
Cation System ◽  
Different Temperatures ◽  
The Face ◽  
Opposite Face ◽  
C Nmr

The title cations have been prepared insitu from the corresponding tertiary alcohols, using three different superacid systems. The 13C NMR spectra were measured at a number of different temperatures, using the structurally related 13C peaks of internal 2-methyl-2-adamantyl cation as a reference. Using this protocol, one finds that the 13C chemical shifts of the four β carbons are quite temperature dependent, two of them shifting to higher field and the other two on the opposite face shifting to lower field, or vice versa, as the temperature is increased or decreased. This behavior is uniquely ascribed to a rapid equilibration between two "structures" for each cation system. The two structures in question involve selective C–C hyperconjugative delocalization on one face or the other of the 2-adamantyl skeleton. In the case of the 4-equatorial-methyl isomer, a structure with C–C hyperconjugation on the methyl-substituted face is most stable, while for the 4-axial-methyl cation, the structure with delocalization from the face opposite the substituent is favored. The former preference is regarded as stereoelectronic in origin while the latter is ascribed to steric effects. Keywords: non-planar carbocations, temperature dependent NMR shifts, stereoelectronic effects.

Comparison of the charge distributions and barriers to ring inversion of protonated eucarvone and its boron trihalide adducts

1977 ◽  
Vol 55 (20) ◽  
pp. 3495-3500 ◽  
Author(s):  
Ronald F. Childs ◽  
Yee-Chee Hor
Keyword(s):  
Lewis Acid ◽  
Boron Trifluoride ◽  
Positive Charge ◽  
Chemical Shifts ◽  
Carbonyl Oxygen ◽  
Uv Spectra ◽  
Inversion Process ◽  
Ring Inversion ◽  
Charge Distributions ◽  
Lewis Acid Adducts

The protonation and formation of the boron trifluoride, trichloride, and tribromide adducts of eucarvone, 1, are described. Examination of the nmr and uv spectra of these systems showed that in each case the proton or Lewis acid was bonded to the carbonyl oxygen of 1. From the various 13C chemical shifts of the Lewis acid adducts of 1, it is concluded that there is significantly less positive charge induced on the dienylic part of these molecules than is found with protonated 1. All of these cationic systems undergo a ring inversion process, the barriers of which are about 1 kcal/mol greater than that reported for the comparable inversion of 1.

Effects of Lewis acid on catalyzing gasification of sewage sludge and model compounds in supercritical water

2021 ◽  
Vol 46 (13) ◽  
pp. 9008-9018
Author(s):  
Miao Gong ◽  
Zhen Li ◽  
Mengqi Wang ◽  
Aixin Feng ◽  
Linlu Wang ◽  
...  
Keyword(s):  
Sewage Sludge ◽  
Lewis Acid ◽  
Supercritical Water ◽  
Model Compounds

New insights about the host–guest chemistry of the tungsten oxo complex of calix[4]arene, and novel "one pot" difunctionalizations of calix[4]arene using tetrachlorometal(VI) oxide (M = Mo, W)

2004 ◽  
Vol 82 (10) ◽  
pp. 1452-1461 ◽  
Author(s):  
Pascal Mongrain ◽  
Jasmin Douville ◽  
Jonathan Gagnon ◽  
Marc Drouin ◽  
Andreas Decken ◽  
...  
Keyword(s):  
Water Molecule ◽  
Lewis Acid ◽  
Chemical Shifts ◽  
Strong Interactions ◽  
Ir Absorption ◽  
One Pot ◽  
X Ray ◽  
Strong Lewis Acid ◽  
Successful Removal ◽  
Coordinated Water

The strong Lewis acid tungsten oxo complex of calix[4]arene can be obtained in both hydrated and non-hydrated forms. This complex coordinates a water molecule inside the cavity via strong O···W interactions with relatively short distances of 2.284(4) and 2.329(2) Å for the tungsten oxo complex of calix[4]arene··H2O·aniline (1), and the tungsten oxo complex of calix[4]arene·H2O·toluene (2·toluene), respectively. The strong interactions are also deduced by the relatively high H2O elimination temperature observed by TGA and DSC (above 200 °C). The coordinated water molecule inside the calix[4]arene cavity is characterized by a strong IR absorption at 3616 cm–1, and a narrow resonance at ~1.2 ppm (the chemical shifts of the uncoordinated water are 1.55 and 1.60 ppm in C6D6 and CDCl3, respectively). This water molecule gives rise to H-bonds with aniline in 1. The tungsten oxo complex of 5,11,17,23-tetrabromocalix[4]arene (4), also binds H2O as the characteristic signatures are observed. The successful removal of H2O in 2, is performed under mild conditions using bis(tetrahydrofuran)-uranyl nitrate as a competitive Lewis acid. When this reaction is performed in acetonitrile, butyronitrile or tert-butylnitrile, the corresponding tungsten oxo complexes of calix[4]arene·acetonitrile (3), ·butyronitrile (5), and ·tert-butylnitrile (6) are obtained. The use of uranyl as a H2O abstractor is unprecedented. The X-ray structure of 3 consists of a tungsten oxo complex of calix[4]arene coordinated by an acetonitrile molecule (d(W···N = 2.412(2) Å). The tetra-5,11,17,23-choromethyl-25,26,27,28-tetrahydroxycalix[4]arene reacts with M(O)Cl4 (M = Mo, W) in a 1:1 stoichiometry, via a tetra Friedel–Crafts addition of benzene or toluene, followed by a lower-rim complexation of the metal oxide, to form "flower-shaped" calix[4]arenes. This "one pot" double functionalization is unprecedented.Key words: calix[4]arene, tungsten, molybdenum, X-ray, host–guest, Friedel–Crafts, Lewis acid, uranyl, DSC, TGA.

Determination of chemical shifts in 6-condensed syringylic lignin model compounds

Holzforschung ◽  
2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Lucas Lagerquist ◽  
Jani Rahkila ◽  
Patrik Eklund
Keyword(s):  
Chemical Shift ◽  
Methoxy Group ◽  
Chemical Shifts ◽  
Model Compounds ◽  
Correlation Peak ◽  
Lignin Model Compounds ◽  
Benzylic Alcohols ◽  
Lignin Model ◽  
C Nmr

Abstract A small library of 6-substituted syringyl model compounds with aliphatic, carboxylic, phenylic, benzylic alcohols and brominated substituents were prepared. The influence of the substituents on the chemical shifts of the compounds was analyzed. All of model compounds showed a characteristic increase in the 13C NMR chemical shift of the methoxy group vicinal to the substitution. This 13C NMR peak and its corresponding correlation peak in HSQC could potentially be used to identify 6-condensation in syringylic lignin samples.

Halogenation of Butyl Rubber—A Model Compound Approach

1984 ◽  
Vol 57 (2) ◽  
pp. 275-283 ◽  
Author(s):  
R. Vukov
Keyword(s):  
Model Compound ◽  
Product Distribution ◽  
Butyl Rubber ◽  
Methyl Groups ◽  
Reaction Site ◽  
Model Compounds ◽  
Reaction Conditions ◽  
Basic Study ◽  
Rubber Model ◽  
Trisubstituted Alkenes

Abstract The study of the halogenation behavior of butyl rubber model compounds has brought about a better understanding of the behavior of these systems. It has been established that the presence of methyl groups, in a position B to the reaction site in the butyl rubber model compound, profoundly influences the course of halogenation. Due to the steric hindrance imposed by these groups, both the products of chlorination and bromination deviate from patterns typical of other trisubstituted alkenes. In the case of chlorination, this deviation is demonstrated by the absence of addition products of chlorine across the double bond. In the case of bromination reactions, the change in product distribution is even more dramatic. Thus, substitution products normally not observed in bromination reactions of other trisubstituted alkenes become predominant products found in yields of between 70–90% depending on the precise reaction conditions. The behavior of the butyl model compound appears to be entirely consistent with the behavior of butyl rubber itself; the model compound approach is therefore a valuable tool for use in the basic study of this type of system.

The High Resolution NMR Spectra of Pesticides. III. The Carbamates

1970 ◽  
Vol 53 (1) ◽  
pp. 157-179 ◽  
Author(s):  
L H Keith ◽  
A L Alford
Keyword(s):  
Nuclear Magnetic Resonance ◽  
High Resolution ◽  
Nmr Spectra ◽  
Chemical Shifts ◽  
Coupling Constants ◽  
Hindered Rotation ◽  
Solvent Dependence ◽  
Nuclear Magnetic Resonance Spectra ◽  
High Resolution Nmr ◽  
Proton Resonances

Abstract The high resolution nuclear magnetic resonance spectra of 35 carbamate pesticides and a major metabolite of one pesticide are discussed. The chemical shifts and coupling constants are tabulated and reproductions of the more complex or unusual spectra are included. A concentration and solvent dependence of both the NH-proton and the NCH3-proton resonances of an N-monosubstituted carbamate is discussed. Hindered rotation is observed in the N,N-dimethylcarbamates, the thiolcarbamates and the dithiocarbamates, but not in the N-methylcarbamates.

Berechnung der 19F- und 195 Pt-NMR-Verschiebungen von FIuoro-Chloro-Bromo-Platinaten(IV) / Calculation of 19F and 195Pt NMR Shifts of Fluoro-Chloro-Brom o-Platinates(IV )

1997 ◽  
Vol 52 (4) ◽  
pp. 435-442 ◽  
Author(s):  
H.-H. Drews ◽  
W. Preetz
Keyword(s):  
Experimental Data ◽  
Chemical Shifts ◽  
Coupling Constant ◽  
Lower Field ◽  
Trans Influence ◽  
Nmr Signals ◽  
Increments Of Chemical Shifts ◽  
Good Agreement

By reaction of [PtBr4]2- with XeF2 in dichloromethane product mixtures containing nine fluoro-chloro-, four fluoro-bromo- and 15 fluoro-chloro-bromo-platinates(IV) are formed. All complexes are detectable by in situ l9F NMR measurements. Due to the increasing trans influence F < Cl < Br, the signals <5(19F) of symmetric F-Pt-F axes observed at highest field are shifted downfield on the average by 93 ppm as compared with δ(19F•) of F••Pt-Cl′ axes, and further to lower field by 40 ppm for <5(F••) of F••-Pt-Br″ axes. For the same reason the coupling constant 1J(F••Pt) ≈ 1099 Hz is by 13.3 % smaller than 1J(F•Pt) ≈ 1268 Hz, which is by 32.3 % smaller than δ(FPt) ≈ 1873 Hz. Based on the axis method, and taking into account characteristic increments of chemical shifts depending on cis influences, the calculation of the 195Pt NMR signals of 27 observed species of the system [PtFnCl6-n-mBrm]2- n, m = 0 - 6, has been successful. The 195Pt NMR shifts of further 29 so far not detected complexes are predicted. Using parameters depending on the geometry of the complex, the 19F NMR shifts of 28 F-containing platinates(IV) have been calculated in good agreement with the experimental data. 19F resonances are predicted for 19 so far missing complexes.

scholarly journals Stabilization of N-, N,N-, N,N′-methylated and unsubstituted simple amidine salts by multifurcated hydrogen bonds

2006 ◽  
Vol 20 (4) ◽  
pp. 169-176 ◽  
Author(s):  
Jarosław Spychała
Keyword(s):  
Chemical Shift ◽  
Hydrogen Bonds ◽  
Chemical Shifts ◽  
2D Nmr ◽  
Biological Properties ◽  
Carbonyl Oxygen ◽  
Relative Strength ◽  
Intramolecular Interactions ◽  
Covalent Bonds ◽  
Natural Isotopic Abundance

In the light of the usefulness of amidines in medicinal chemistry, this paper considers the effects on biological properties and chemical reactivities of organic molecules affected by intramolecular interactions. The study of chemical shifts has been an important source of information on the electronic structure of amidine salts and their ability to form non-covalent bonds with nucleic acids. The NMR and IR results demonstrate that hydrogen bonds are a force for promoting chemical reactions. The thymine O2 carbonyl oxygen in a close proximity to the amidinium cation does interact with the appropriately spaced amidinium NH donor moieties. The1H-15N 2D NMR (GHSQC and GHMBC) spectra with natural isotopic abundance of15N fully confirm the intramolecular character of the bonds. A rule able to estimate the relative strength of the new multifurcated hydrogen bonds is given. The appearance of the ΔδNHchemical shift differences near zero is due to the strong intramolecular interactions. The strength of the H-bond donation by acetamidines is reflected in the N–H dissociation/recombination process (positive charge shift has been invoked to explain other effects on benzamidines). The temperature dependence of chemical shift for the amidine NH protons in dimethyl sulfoxide solutions is herein discussed.

INFRARED SPECTRA OF 2,6-DIMETHYL-4-PYRONE COMPLEXES

1961 ◽  
Vol 39 (6) ◽  
pp. 1184-1189 ◽  
Author(s):  
Denys Cook
Keyword(s):  
Complex Formation ◽  
Oxygen Atom ◽  
Carbonyl Group ◽  
Lewis Acid ◽  
Frequency Band ◽  
Infrared Spectra ◽  
Donor Site ◽  
Carbonyl Oxygen ◽  
Acid Strength ◽  
Group A

The infrared spectra of 2,6-dimethyl-4-pyrone in solution, and in complexes with HgCl2, ZnCl2, BF3, SbCl5, and HBr have been recorded. A band at 1639 cm−1 in the free pyrone moves to progressively lower frequencies in the complexes as the Lewis acid strength increases, identifying this band as the carbonyl stretching frequency and the donor site as the carbonyl group. A higher-frequency band, at 1678 cm−1 in the free pyrone, moves to lower frequency on complex formation, but to a much smaller extent, and is to be identified with a stretching mode of the ring. The site of protonation in 2,6-dimethyl-4-pyrone salts has been unequivocally shown to be the carbonyl oxygen atom.

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