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.

REACTIONS OF AMIDES AND RELATED COMPOUNDS: I. N.M.R. (PROTON) INVESTIGATION OF N,N-DIMETHYLFORMAMIDE – LEWIS ACID ADDUCTS AND REMARKS ON THE RELATIVE STRENGTH OF LEWIS ACIDS

1965 ◽  
Vol 43 (2) ◽  
pp. 375-380 ◽  
Author(s):  
Stephen J. Kuhn ◽  
John S. McIntyre
Keyword(s):  
Chemical Shift ◽  
Lewis Acid ◽  
Lewis Acids ◽  
Methylene Chloride ◽  
Carbonyl Oxygen ◽  
Relative Strength ◽  
Proton Resonance ◽  
Lewis Acid Adducts ◽  
Related Compounds ◽  
Good Agreement

The proton resonance spectra of a number of Lewis acid – N,N-dimethylformamide adducts in 2-nitropropane and methylene chloride solutions have been investigated and an attempt has been made to correlate the relative strength of Lewis acids with the chemical shift of the methyl protons. The order obtained for the relative strength of Lewis acids shows good agreement with the results obtained by other methods. The complex formation has taken place on the carbonyl oxygen of the N,N-dimethylformamide in all cases. The DMF – Lewis acid mole ratios were 1:1 in ZnCl2, AlCl3, PF5, BiCl3, InCl3, AsF5, SbCl5, SbF5, BF3, BCl3, BBr3. The 2:1 DMF – Lewis acid complexes of ZnCl2, SnCl4, SnBr4, Snl4, TiCl4, ZrBr4 have also been investigated.

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.

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.

Wallach rearrangement of azoxypyridines and azoxypyridine N-oxides — Charge distributions and dramatic reactivity differences

2008 ◽  
Vol 86 (4) ◽  
pp. 298-304 ◽  
Author(s):  
Erwin Buncel ◽  
Sam-Rok Keum ◽  
Srinivasan Rajagopal ◽  
Eric Kiepek ◽  
Robin A Cox
Keyword(s):  
Sulfuric Acid ◽  
Positive Charge ◽  
Theoretical Calculations ◽  
Medium Effect ◽  
Mulliken Charge ◽  
Reaction Intermediates ◽  
Charge Distributions ◽  
First Time ◽  
Acid Region

Extension of our studies of the generic Wallach rearrangement (of azoxybenzene to 4-hydroxyazobenzene) to the heteroaromatic series (azoxypyridines and axoxypyridine N-oxides) has revealed some dramatic reactivity differences, particularly for the α and β compounds. We have studied the 3-isomers and the 4-isomers in each series, each with α and β forms, eight compounds in all, in the 100 wt% sulfuric acid region of acidity. In those cases in which a product could be observed, the α and β isomers both give the same one, the corresponding 4′-hydroxyazo compounds. All the compounds react much more slowly than does azoxybenzene itself, presumably because of the extra positive charge present in the substrates, but the β isomers have half-lives of seconds and the α isomers half-lives of hundreds of hours in the 100 wt% H2SO4 acidity region. The α compounds have measurable pKBH+ values, but the β compounds do not, exhibiting only a medium effect in the acidity region in which the α compounds protonate. This means that for the β compounds, the protonated intermediates must be much less stable and the postulated reaction intermediates must be much more stable than for the α compounds. To clarify this, we have obtained Mulliken charge distributions for the various species concerned, calculating the charge carried by each half of the molecule, larger charge separations being taken to indicate lesser stability. As far as we can establish, this is the first time that this technique has been used to indicate the stabilities of carbocationic species.Key words: azoxypyridines, azoxypyridine N-oxides, Wallach rearrangement, excess acidity, basicities, theoretical calculations, charge distributions, reactivities.

.lambda.5-Phosphonitriles and .lambda.3-Phosphinonitrenes: Evidence for Nitrene-Lewis Acid Adducts

1994 ◽  
Vol 116 (4) ◽  
pp. 1225-1229 ◽  
Author(s):  
Gilles Alcaraz ◽  
Antoine Baceiredo ◽  
Francoise Dahan ◽  
Guy Bertrand
Keyword(s):  
Lewis Acid ◽  
Lewis Acid Adducts
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