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.

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.

scholarly journals The Role of Carbonium Ions in Color Reception

1965 ◽  
Vol 48 (5) ◽  
pp. 753-760 ◽  
Author(s):  
Paul E. Blatz
Keyword(s):  
Lewis Acid ◽  
Lewis Acids ◽  
Benzene Solution ◽  
Fundamental Property ◽  
Conjugated Systems ◽  
Carbonium Ion ◽  
Carbonium Ions ◽  
Ion Treatment ◽  
Good Agreement

It is a fundamental property of conjugated systems to accept a proton or Lewis acid and form a stable carbonium ion. Polyenes that are protonated or add Lewis acids in this manner undergo substantial red shifts. For example, vitamin A1 acetate absorbs at 350 mµ in neutral and at 650 mµ in acidic benzene solution. The fundamental basis for absorption of polyene systems was described in detail in quantum mechanical terms. Applying the carbonium ion treatment to the visual chromophores retinal1 and retinal2 gives a very satisfactory explanation why these polyenes can be made to absorb in the visual region. Furthermore, by proper placement of the Lewis acid several absorption maxima can be gained from the carbonium ions which result. This treatment can be applied to explain experimental results. Individual cones from the frog are now known to absorb at 455, 537, and 625 mµ. If the value for the green cone (537 mµ) is used to calculate the Vo value in Kuhn's equation, the other two wave lengths may then be calculated. The calculated values are 460 and 600 mµ; this is in good agreement with the results from experiment.

INFRARED SPECTRA OF XANTHONE: LEWIS ACID COMPLEXES

1963 ◽  
Vol 41 (2) ◽  
pp. 522-526 ◽  
Author(s):  
Denys Cook
Keyword(s):  
Lewis Acid ◽  
Lewis Acids ◽  
Quantitative Estimate ◽  
Donor Site ◽  
Carbonyl Oxygen ◽  
Acid Strength ◽  
Carbonyl Groups ◽  
Wide Range ◽  
Stretching Vibration ◽  
Solid Complexes

Xanthone, a member of the γ-pyrone species, which have basic carbonyl groups, forms an excellent series of solid complexes with Lewis acids. In these complexes the carbonyl oxygen atom is the donor site, and the carbonyl stretching vibration moves to progressively lower frequency as the Lewis acid strength increases. The carbonyl frequency in the BI3 complex, 1400 cm−1, is one of the lowest encountered in complexes of this type.The wide range of Lewis acids used to form these complexes has enabled a quantitative estimate of the Lewis acid strength to be made, which compares reasonably well with previous estimates.

Article

1998 ◽  
Vol 76 (4) ◽  
pp. 490-497
Author(s):  
Okba Saied ◽  
Benoit Bachand ◽  
James D Wuest
Keyword(s):  
Carbonyl Group ◽  
Carbonyl Compounds ◽  
Lewis Acids ◽  
Carbonyl Oxygen ◽  
The Other ◽  
Keto Group ◽  
Carbonyl Groups ◽  
Lone Pairs ◽  
Related Compounds ◽  
Oxygen Atoms

Carbonyl oxygen atoms have two formal lone pairs of electrons. In principle, both can be used simultaneously to form complexes with two or more Lewis acids. This multiple coordination promises to have a variety of interesting consequences; unfortunately, however, complexes of carbonyl compounds with multiple Lewis acids are extremely rare. To promote multiple coordination, we have made a series of symmetric ketodiesters and related compounds in which the carbonyl group of a ketone is flanked by two additional sites of Lewis basicity. In such compounds, the flanking bases and both lone pairs of the central ketone are available for binding two equivalents of suitable Lewis acids, thereby producing symmetric double chelates in which the central ketone interacts with two Lewis acids at the same time. As expected, treatment of 3-oxoglutarates and 4-oxopimelates with TiCl4 in a 1:1 ratio yielded unsymmetric single chelates in which the carbonyl groups of the ketone and one ester bind TiCl4, while the other ester remains free. Unfortunately, treatment of the same ketodiesters with TiCl4 in a 1:2 ratio did not produce the desired symmetric double chelates. Instead, 2:4 complexes were formed in which the free esters of the unsymmetric single chelates bind TiCl4 in the normal way, without assistance from the keto group. We attribute this observation to the inherent reluctance of ketones to bind multiple Lewis acids, as well as to unfavorable Cl · · ·Cl interactions created in the hypothetical double chelates by the simultaneous attachment of two octahedrally coordinated atoms of titanium to a single carbonyl oxygen atom.Key words: Lewis acids, chelation, ketodiesters, TiCl4.

The Lewis acid complexes of α,β-unsaturated carbonyl and nitrile compounds. A nuclear magnetic resonance study

1982 ◽  
Vol 60 (6) ◽  
pp. 801-808 ◽  
Author(s):  
Ronald F. Childs ◽  
D. Lindsay Mulholland ◽  
Alan Nixon
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Nmr Spectroscopy ◽  
Magnetic Resonance ◽  
Chemical Shift ◽  
Lewis Acid ◽  
Lewis Acids ◽  
Acid Group ◽  
Nuclear Magnetic Resonance Study ◽  
Magnetic Resonance Study ◽  
C Nmr

1:1 Complexes of a range of Lewis acids with crotonaldehyde (1) have been systematically investigated by 1H and 13C nmr spectroscopy. Lewis acids employed were: BF3, BCl3, BBr3, SnCl4, TiCl4, SbCl5, AlCl3, EtAlCl2, Et2AlCl, Et3Al2Cl3, and Et3Al. Chemical shift changes in 1H nuclei remote from the Lewis acid group were found to be remarkably regular and consistent. The study has been extended to tiglaldehyde (2), pent-3-en-2-one (3), cyclohexenone (4), methyl crotonate (5), and crotonitrile (6) and the relationships between the chemical shift differences associated with complexation of these have been explored.

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.

scholarly journals Theoretical Insight into the Reversal of Chemoselectivity in Diels-Alder Reactions of α,β-Unsaturated Aldehydes and Ketones Catalyzed by Brønsted and Lewis Acids

Organics ◽  
2021 ◽  
Vol 2 (1) ◽  
pp. 38-49
Author(s):  
Lakhdar Benhamed ◽  
Sidi Mohamed Mekelleche ◽  
Wafaa Benchouk
Keyword(s):  
Lewis Acids ◽  
Major Product ◽  
Diels Alder ◽  
Unsaturated Ketone ◽  
Unsaturated Aldehydes ◽  
Aldehydes And Ketones ◽  
Theoretical Insight ◽  
Insight Into ◽  
Good Agreement

Experimentally, a reversal of chemoselectivity has been observed in catalyzed Diels–Alder reactions of α,β-unsaturated aldehydes (e.g., (2E)-but-2-enal) and ketones (e.g., 2-hexen-4-one) with cyclopentadiene. Indeed, using the triflimidic Brønsted acid Tf2NH as catalyst, the reaction gave a Diels–Alder adduct derived from α,β-unsaturated ketone as a major product. On the other hand, the use of tris(pentafluorophenyl)borane B(C6F5)3 bulky Lewis acid as catalyst gave mainly the cycloadduct of α,β-unsaturated aldehyde as a major product. Our aim in the present work is to put in evidence the role of the catalyst in the reversal of the chemoselectivity of the catalyzed Diels–Alder reactions of (2E)-but-2-enal and 2-Hexen-4-one with cyclopentadiene. The calculations were performed at the ωB97XD/6-311G(d,p) level of theory and the solvent effects of dichloromethane were taken into account using the PCM solvation model. The obtained results are in good agreement with experimental outcomes.

Lewis Acid-Promoted Suzuki Reaction using Palladium Chloride Anchored on a Polymer as a Catalyst

2008 ◽  
Vol 61 (8) ◽  
pp. 610 ◽  
Author(s):  
Guozhi Fan ◽  
Hanjun Zhang ◽  
Siqing Cheng ◽  
Zhandong Ren ◽  
Zhijun Hu ◽  
...  
Keyword(s):  
Catalytic Activity ◽  
Lewis Acid ◽  
Lewis Acids ◽  
Heterogeneous Catalysts ◽  
Suzuki Reaction ◽  
Cross Coupling ◽  
Palladium Chloride ◽  
Coupling Reactions ◽  
Cross Coupling Reactions ◽  
Recoverable Catalyst

Palladium chloride anchored on polystyrene modified by 5-amino-1,10-phenanthroline was prepared and used as an efficient recoverable catalyst for Suzuki cross-coupling reactions. The heterogeneous catalysts can be easily separated from the reaction mixture and reused for five cycles without significant Pd leaching and loss of catalytic activity. Rate enhancement in the Suzuki reaction by Lewis acids was also studied.

Synthesis of pyrrolo[1,2-a]naphthyridines by Lewis acid mediated cycloisomerization

2017 ◽  
Vol 15 (15) ◽  
pp. 3216-3231 ◽  
Author(s):  
Anika Flader ◽  
Silvio Parpart ◽  
Peter Ehlers ◽  
Peter Langer
Keyword(s):  
Lewis Acid ◽  
Lewis Acids

Functionalized pyrrolo[1,2-a]naphthyridines were synthesized by application of PtCl2 and Bi(OTf)3 as simple Lewis acids in a cycloisomerization reaction.

ChemInform Abstract: Novel Silicon- and Tin-Containing Ferrocenophanes and Related Compounds as Lewis Acids.

ChemInform ◽  
2010 ◽  
Vol 31 (17) ◽  
pp. no-no
Author(s):  
Reiner Altmann ◽  
Olivier Gausset ◽  
Dagmar Horn ◽  
Klaus Jurkschat ◽  
Markus Schuermann ◽  
...  
Keyword(s):  
Lewis Acids ◽  
Related Compounds
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