The preparation and rearrangements of some 8,8-dimethylhomotropylium cations and their iron tricarbonyl complexes

1985 ◽  
Vol 63 (2) ◽  
pp. 418-425 ◽  
Author(s):  
Ronald F. Childs ◽  
Aravamuthan Varadarajan
Keyword(s):  
Low Temperatures ◽  
Chemical Shifts ◽  
Major Product ◽  
Membered Ring ◽  
Tricarbonyl Complex ◽  
Nmr Spectrum ◽  
H Nmr ◽  
Free Energy Of Activation ◽  
Iron Tricarbonyl ◽  
Proton Chemical Shifts

The circumambulatory rearrangements of some 8,8-dimethylhomotropylium cations and their corresponding iron tricarbonyl complexes have been examined. 8,8-Dimethylhomotropylium cation, 4, has been prepared by protonation of 8,8-dimethyl-bicyclo[5.1.0]octa-3,5-dien-2-ol in FSO3H/SO2ClF. Evidence for homoaromatic delocalization in 4 was found in its characteristic 1H nmr spectrum, particularly when this was compared to that of the non-cyclically delocalized 8,8-dimethyl-bicyclo[5.1.0]octadienyliron tricarbonyl complex 7. Cation 4 was found to be stable at low temperatures but to isomerize to isopropyltropylium ion, 8, at −50 °C, [Formula: see text] The specifically deuterated cation 4D was prepared and a slow circumambulation of C8 around the basal 7-membered ring of this cation was found to occur at −90 °C. The free energy of activation for this circumambulation is 14.5 kcal/mol. Homotropylium cation 4 was also prepared by protonation of 8,8-dimethylbicyclo[3.2.1]octa-3,6-dien-2-ol, 14, at −120 °C. No evidence for the presence of the corresponding bicyclo[3.2.1]octadienyl ion 12 was obtained. The 2,8,8-trimethylhomotropylium cation, 17, was prepared and shown to undergo a circumambulatory rearrangement to give the 4,8,8-trimethyl substituted cation 20 as the major product. In this trimethyl series it also proved possible to generate the 2,8,8-trimethylbicyclo[3.2.1]octadienyl cation, 18, and observe its 1H nmr spectrum at very low temperatures (−116 °C). The proton chemical shifts of 18 suggest that the charge is predominantly located on the 3-carbon bridge. Cation 18 isomerized to 17, 20, and other products at temperatures above −100 °C. The 2,8,8-trimethylbicyclo[5.1.0]octadienyliron tricarbonyl complex 22 was also shown to undergo a circumambulatory rearrangement in which both C8 and the Fe(CO)3 grouping migrate.

1H nuclear magnetic resonance spectral parameters of toluene. Implications for conformational analysis and isotope shifts

1985 ◽  
Vol 63 (10) ◽  
pp. 2597-2600 ◽  
Author(s):  
Ted Schaefer ◽  
Rudy Sebastian ◽  
Glenn H. Penner
Keyword(s):  
Chemical Shifts ◽  
Low Frequency ◽  
Spectral Parameters ◽  
Nmr Spectrum ◽  
H Nmr ◽  
Conformational Preferences ◽  
Precise Analysis ◽  
1H Nuclear Magnetic Resonance ◽  
Direct Measures ◽  
Proton Chemical Shifts

A precise analysis of the 1H nmr spectrum of toluene as a dilute solution in carbon disulfide yields a revised set of spectral parameters. The chemical shift of the para proton lies 12.6 ppb to low frequency of that of the ortho protons at 300 K. The ring proton chemical shifts are discussed and compared with 1H and 3H shifts observed in carbon tetrachloride. The long-range couplings between methyl and ring protons can be said to be quantitatively understood in terms of σ and σ–π electron transmitted mechanisms. The changes observed in these three couplings in phenylacetaldehyde can be quantitatively reproduced in terms of these mechanisms and also illustrate how these changes are direct measures of the conformational preferences in this molecule.

Dimethylhalonium-Ionen in Aluminiumhalogenid/Methylhalogenid-Lösungen / Dimethylhalonium-Ions in Aluminium Halide/Methyl Halide Solutions

1979 ◽  
Vol 34 (7) ◽  
pp. 896-899 ◽  
Author(s):  
Peter Brüggeller ◽  
Erwin Mayer
Keyword(s):  
Time Scale ◽  
Low Temperatures ◽  
Room Temperature ◽  
Chemical Shifts ◽  
Ion Concentration ◽  
Molar Ratio ◽  
Lower Field ◽  
Nmr Spectrum ◽  
H Nmr ◽  
Methyl Halide

Abstract Evidence for the formation of (CH3)2Br+ and (CH3)2I+ in CH3Br and CH3I solutions saturated with AlBr3 comes from the appearance of a second singlet in the 1H NMR spectrum. The (CH3)2Br+ ion is formed at -40 °C to about 5 mol%, the (CH3)2I+ ion at -12 °C with 50 mol% yield. At higher temperatures the concentration of the halonium ions decreases rapidly. The (CH3)2Br+ ion is not detectable at room temperature, the concentration of (CH3)2I+ decreases to about 30 mol%. Dilution of the saturated solutions with methyl halide also reduces the halonium ion concentration. An AlBr3/CH3Br solution with a molar ratio of 1:3 at -40 °C shows no sign of (CH3)2Br+ formation in the XH NMR spectrum. Both effects are best explained by formation of dimethylhalonium ions from the adduct CH3X-AIX3 and by dependence of adduct concentration on temperature and dilution. Exchange of (CH3)2Br+ and (CH3)2I+ with methyl halide is slow on the NMR time scale at low temperatures similar to the results in SbF5/SO2. The 1H NMR singlets of (CH3)2Br+ and (CH3)2I+ are shifted to lower field by 1.32 and 1.68 ppm in comparison with the chemical shifts in SbF5/SO2 solution

scholarly journals Synthesis, Characterization, and Biological Studies of a Piperidinyl Appended Dipicolylamine Ligand and Its Rhenium Tricarbonyl Complex as Potential Therapeutic Agents for Human Breast Cancer

2016 ◽  
Vol 2016 ◽  
pp. 1-10 ◽  
Author(s):  
Amali Subasinghe ◽  
Inoka C. Perera ◽  
Svetlana Pakhomova ◽  
Theshini Perera
Keyword(s):  
Breast Cancer ◽  
Anticancer Agents ◽  
Human Breast Cancer ◽  
Human Breast ◽  
Tricarbonyl Complex ◽  
Nmr Spectrum ◽  
H Nmr ◽  
Biological Studies ◽  
Visible Spectra ◽  
Uv Visible

A novel ligand bearing a central piperidinyl sulfonamide group, N(SO2pip)dpa, and its corresponding Re tricarbonyl complex, [Re(CO)3(N(SO2pip)dpa)]+, have been synthesized in good yield. The methylene CH2signal seen as a singlet (4.54 ppm) in a1H NMR spectrum of the ligand in DMSO-d6appears as two doublets (5.39, 5.01 ppm) in a spectrum of the [Re(CO)3(N(SO2pip)dpa)]+complex and confirms the presence of magnetically nonequivalent protons upon coordination to Re. Structural results revealed that the Re–N bond lengths fall within the normal range establishing coordination of ligand to metal. The presence of intraligandπ→π⁎andn→π⁎transitions is indicated by the absorption peaks around 200–250 nm in UV-visible spectra. Absorption peaks in UV-visible spectra around 300 nm for metal complexes were identified as MLCT transitions. The S–N stretch observed as a strong peak at 923 cm−1for N(SO2pip)dpa appeared at a shorter frequency, at 830 cm−1in an FTIR spectrum of the [Re(CO)3(N(SO2pip)dpa)]+. The intense fluorescence displayed by the N(SO2pip)dpa ligand has quenched upon coordination to Re. Relatively low IC50values given by human breast cancer cells, MCF-7, (N(SO2pip)dpa = 139 μM, [Re(CO)3(N(SO2pip)dpa)]+= 360 μM) indicate that N(SO2pip)dpa and [Re(CO)3(N(SO2pip)dpa)]+are promising novel compounds that can be further investigated on their usage as potential anticancer agents.

Studies related to antitumor antibiotics. Part XXIV. High field 1H nmr analysis and conformations of saframycins A and C

1981 ◽  
Vol 59 (20) ◽  
pp. 2945-2952 ◽  
Author(s):  
J. William Lown ◽  
Alummoottil V. Joshua ◽  
Hsiao-Hsiung Chen
Keyword(s):  
High Field ◽  
Chemical Shifts ◽  
Molecular Geometry ◽  
Coupling Constants ◽  
Cytotoxic Action ◽  
Antitumor Antibiotics ◽  
Dna Templates ◽  
H Nmr ◽  
Proton Chemical Shifts ◽  
Unambiguous Assignment

A detailed analysis of the high field (400 MHz) 1H nmr spectra of the basic antitumor antibiotics saframycin A and C in CDCl3, C6D6, and in aqueous DMSO solutions has been carried out. Selective double irradiation experiments permitted the unambiguous assignment of all the proton chemical shifts and coupling constants. Consideration of the magnitudes of the latter together with specific nOe experiments permits assignment of molecular geometry and average conformations in solution. Selective shifts occurring in DMSO–D2O solutions upon addition of CF3COOD identified the 12-N atom as the site of protonation which result bears directly on the acid promoted binding of these antibiotics to DNA templates as part of their cytotoxic action.

Controlled oxidations of benzo[a]pyrene

1986 ◽  
Vol 64 (7) ◽  
pp. 1247-1253 ◽  
Author(s):  
E. Lee-Ruff ◽  
H. Kazarians-Moghaddam ◽  
M. Katz
Keyword(s):  
Singlet Oxygen ◽  
High Field ◽  
Chemical Shifts ◽  
Product Distribution ◽  
Major Product ◽  
Nuclear Overhauser Enhancement ◽  
Nuclear Overhauser ◽  
Singlet Oxygen Reaction ◽  
Proton Chemical Shifts ◽  
Oxygen Reaction

The four diones derived from benzo[a]pyrene oxidation have been characterized by high-field nuclear magnetic resonance techniques including 2-D COSY and selective nuclear Overhauser enhancement. All the proton chemical shifts for these four quinones have been uneqivocally assigned. The direct photoxidation of benzo[a]pyrene gives a product distribution very similar to the TPP photosensitized oxygenation, suggesting singlet oxygen is involved in the former. A major product, which was characterized as the 6-seco derivative 6 and not previously reported, was detected in the singlet oxygen reaction. The presence of this product suggests a possible mechanism for quinone formation in the singlet oxygen reaction. One-electron oxidations of benzo[a]pyrene were carried out using tris(p-bromophenyl)aminium hexachloroantimonate and quenching of the radical cation with superoxide or water. The product distribution in this case was quite different from that obtained in the direct photooxidation.

Restricted rotation about arene–oxygen bonds in some 1,3-di-tert-butyl-2-methoxyarenedicarbonylphosphorus(III)chromium compounds

1984 ◽  
Vol 62 (11) ◽  
pp. 2566-2569 ◽  
Author(s):  
Eva M. Campi ◽  
Bryan M. K. Gatehouse ◽  
W. Roy Jackson ◽  
Ian D. Rae ◽  
Margaret G. Wong
Keyword(s):  
Crystal Structure ◽  
Low Temperatures ◽  
Nmr Spectra ◽  
Hindered Rotation ◽  
Methyl Group ◽  
Tert Butyl ◽  
H Nmr ◽  
Free Energy Of Activation ◽  
Chromium Compounds ◽  
Related Compounds

The 1H nmr spectra of 1,3-di-tert-butyl-2-methoxybenzenedicarbonyltriphenylphosphinechromium (5) and some related compounds at low temperatures show the presence of two species which interconvert with free energy of activation near 50 kJ mol−1. The species differ in the orientation of the methoxy with respect to the chromium, since the same type of process is observed in a chelate complex in which a phosphinite ligand on chromium is also attached to the arene. Hindered rotation about the arene–chromium axis is not involved. The crystal structure of 5 shows the Ph3P anti to the methoxy and the O-methyl group proximal to chromium.

Addition of the nitroxyl radical TEMPO to 1-naphthylketene: formation of an unusual adduct

1999 ◽  
Vol 77 (5-6) ◽  
pp. 806-809 ◽  
Author(s):  
Jennifer Carter ◽  
Michael H Fenwick ◽  
Wen-wei Huang ◽  
Vladimir V Popik ◽  
Thomas T Tidwell
Keyword(s):  
Nitroxyl Radical ◽  
Chemical Shifts ◽  
Wolff Rearrangement ◽  
Nmr Spectrum ◽  
X Ray ◽  
H Nmr ◽  
Naphthyl Ring ◽  
Nmr Signals ◽  
Very High

1-Naphthylketene (2), generated by thermal Wolff-rearrangement, is trapped in situ by 2,2,6,6-tetramethylpiridinyloxy radical (TEMPO, TO·) to form the adduct 1-naphthCH(OT)CO2T (4), whose structure is confirmed by an X-ray determination. The 1H NMR spectrum of 4 displays three CH3 groups with very high field chemical shifts (δ 0.10-0.47), and this is attributed to the location of these groups in the shielding region above the π system of the naphthyl ring. At -40°C, doubling of most of the 1H NMR signals occurs, and this is attributed to a freezing out of two conformations differing by rotation around the naphthyl—CH bond.Key words: ketene, TEMPO, restricted rotation, 1H NMR, conformational analysis, free radicals.

Ring currents, local anisotropy, and the problem of the out-of-plane protons: a reinvestigation of the nuclear magnetic resonance spectrum of [10]-paracyclophane

1977 ◽  
Vol 55 (13) ◽  
pp. 2575-2581 ◽  
Author(s):  
Arvind Agarwal ◽  
John A. Barnes ◽  
John L. Fletcher ◽  
Michael J. McGlinchey ◽  
Brian G. Sayer
Keyword(s):  
Ring Current ◽  
Chemical Shifts ◽  
Current Model ◽  
Classical Model ◽  
Local Anisotropy ◽  
Nmr Spectrum ◽  
H Nmr ◽  
Out Of Plane ◽  
Mechanical Approach ◽  
Quantum Mechanical Approach

The1H nmr spectrum of [10]-paracyclophane has been recorded at 220 MHz and the methylene protons assigned on the basis of homonuclear decoupled spectra. Local anisotropic contributions to chemical shifts for protons sited above or near the aromatic ring of [10]-paracyclophane have been calculated using a classical model previously proposed by Grant. The residual incremental shift was shown to follow the Waugh–Fessenden–Johnson–Bovey classical ring current model, but the loop separation originally invoked was shown to be unnecessary. These corrected ring current contributions also correlate very well with the quantum-mechanical approach of Haigh and Mallion.

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