Acidity measurements in THF. III. Aldimines and ketimines

1983 ◽  
Vol 61 (12) ◽  
pp. 2729-2734 ◽  
Author(s):  
Robert R. Fraser ◽  
Monique Bresse ◽  
Noemi Chuaqui-Offermanns ◽  
K. N. Houk ◽  
N. G. Rondan
Keyword(s):  
Nmr Spectroscopy ◽  
Methyl Iodide ◽  
Quantitative Estimation ◽  
Steric Effects ◽  
Alkyl Substitution ◽  
C Nmr ◽  
Abinitio Calculations

The relative acidities of fiteen aldimines and ketimines have been measured in THF using either 13C nmr spectroscopy or trapping experiments with methyl iodide. The pKA's are found to vary over a range of more than four pK units. The effects of structure on acidity indicate the acid-weakening effect of alkyl substitution in ketimines to be due to steric effects. This interpretation is supported by the results of abinitio calculations. The data also permit a quantitative estimation of the preference for the syn configuration of lithiated imines to be at least four kcal/mol. The anti selectivity previously reported for the lithiation of endocyclic imines can be accounted for by angular constraints, as indicated by both abinitio calculations and pKa data on this class of imine.

Méthylhalogénocyclopropanation des éthoxy-alcènes diversement alkylés. Identification stéréochimique des adduits et étude de la stéréosélectivité

1982 ◽  
Vol 60 (15) ◽  
pp. 1933-1941 ◽  
Author(s):  
Roger Barlet ◽  
Raymond Le Goaller ◽  
Claude Gey
Keyword(s):  
Nmr Spectroscopy ◽  
Methyl Iodide ◽  
Intermediate Stage ◽  
Complex Salt ◽  
Carbene Complex ◽  
Iodide Ion ◽  
Halogen Exchange ◽  
C Nmr

Ethoxy-alkenes act as excellent carbene acceptors in the methylmonohalogenocyclopropanation reaction mediated by 1,1-dichloroethane and iodide-ion free methyl iodide. As well as chlorinated adducts, a large proportion of brominated products are obtained by means of halogen exchange at the carbene complex – salt intermediate stage. Adduct stereochemistry is determined by 1H and 13C nmr spectroscopy. The syn-stereoselectivity of the reaction is discussed in electronic and steric terms. [Journal Translation]

(9H-Fluoren-9-ylidene)fluoromethyllithium, a Stabilized Fluoroalkenyl Carbanion. Preparation, Reactions, 13C and 19F NMR Spectra

2001 ◽  
Vol 66 (10) ◽  
pp. 1508-1520 ◽  
Author(s):  
Jaroslav Kvíčala ◽  
Andrew Pelter
Keyword(s):  
Nmr Spectroscopy ◽  
Low Temperature ◽  
Methyl Iodide ◽  
Nmr Spectra ◽  
19F Nmr ◽  
19F Nmr Spectra ◽  
13C And 19F Nmr ◽  
C Nmr

(9H-Fluoren-9-ylidene)fluoromethyllithium (1) was prepared by a low-temperature transmetallation of bromo(9H-fluoren-9-ylidene)fluoromethane (2). Whereas the synthesis of unlabeled bromofluoroalkene 2a was based on Wittig-Horner reaction of fluorenone (3) with ethyl (diethoxyphosphoryl)fluoroacetate (4), (1-13C)-labeled compound 2b was obtained via an addition of labeled lithium 1-ethoxy-2-fluoro(2-13C)ethen-1-olate (5) to ketone 3. Fluoroethenyllithium 1 was found by a low-temperature 19F NMR spectroscopy to be stable up to -40 °C; it was reacted with the series of electrophiles, e.g. benzaldehyde (6), methyl iodide (7) or chloro(trimethyl)silane (8). 13C NMR experiments with (1-13C)-labeled 1a proved that fluorocarbenoid 1 is probably monomeric in THF solution in analogy to other halocarbenoids.

10B-, 11B-, 13C-NMR-Untersuchungen von closo-Pentaalkyl-1.5-dicarbapentaboranen(5) / 10B-, 11B-, 13C NMR Studies of closo-Pentaalkyl-1,5-dicarbapentaboranes(5)

1981 ◽  
Vol 36 (6) ◽  
pp. 704-707 ◽  
Author(s):  
Roland Köster ◽  
Bernd Wrackmeyer
Keyword(s):  
Nmr Spectroscopy ◽  
13C Nmr ◽  
Chemical Shifts ◽  
Parent Compound ◽  
Coupling Constants ◽  
Mo Calculations ◽  
Nmr Studies ◽  
Nmr Parameters ◽  
Alkyl Substitution ◽  
C Nmr

AbstractNMR parameters [chemical] shifts (δ11B, δ13C) and coupling constants (1J(13C1H), 1J(13C11B), 1J(13C13C), 1J(11B11B) of closo-pentaalkyl-1,5-dicarbapentaboranes(5) were determinated by 10B, 11B, and 13C NMR spectroscopy. The magnitudes of 1J(13C11B) and 1J(13C13C) correspond to 1J(11B1H), 1J(13C11B) and 1J(13C1H) in the parent compound 1,5-C2B3H5 . According to predictions from MO calculations 1J(11B11B) was found to be < 10 Hz. Together with these data the δ11B and δ13C values show that neither the structure nor the bonding situation in the polyhedron are significantly affected by alkyl substitution.

The mechanism of formation of 2,7-dimethyl-2,6-octadiene in the synthesis of 3-methylene-7-methyl-1,6-octadiene

1983 ◽  
Vol 48 (7) ◽  
pp. 1864-1866
Author(s):  
Jan Bartoň ◽  
Ivan Kmínek
Keyword(s):  
Mass Spectrometry ◽  
Nmr Spectroscopy ◽  
Alkali Metal ◽  
Chromatographic Analysis ◽  
Solid Phase ◽  
Reaction Pathway ◽  
Mechanism Of Formation ◽  
Gas Chromatographic Analysis ◽  
C Nmr ◽  
Visual Observations

2,7-Dimethyl-2,6-octadiene is formed in the catalytic solution for the dimerization of 2-methyl-1,3-butadiene to β-myrcene (3-methylene-7-methyl-1,6-octadiene), as revealed by mass spectrometry and 13C NMR spectroscopy. Visual observations together with the results of gas chromatographic analysis of the catalytic solution suggest that the formation of 2,7-dimethyl-2,6-octadiene is associated with the transition of the alkali metal (sodium) from the solid phase into the solution. A reaction pathway is suggested accounting for the formation of 2,7-dimethyl-2,6-octadiene in the system.

Non-cyclol (lactame) ergot alkaloids

1982 ◽  
Vol 47 (12) ◽  
pp. 3312-3317 ◽  
Author(s):  
Josef Stuchlík ◽  
Alois Krajíček ◽  
Ladislav Cvak ◽  
Jiří Spáčil ◽  
Petr Sedmera ◽  
...  
Keyword(s):  
Nmr Spectroscopy ◽  
Ergot Alkaloids ◽  
C Nmr

Two new alkaloids were isolated from the field ergot. Their structures, N-(D-lysergyl-L-valyl)cyclo(L-valyl-D-prolyl) (IV) and N-(D-lysergyl-L-valyl)cyclo(L-leucyl-D-prolyl) (V), were assigned by mass, 1H and 13C NMR spectroscopy.

An unusual reaction of a bridged triterpenoid α-diketone with acetic anhydride

1991 ◽  
Vol 56 (12) ◽  
pp. 2917-2935 ◽  
Author(s):  
Eva Klinotová ◽  
Václav Křeček ◽  
Jiří Klinot ◽  
Miloš Buděšínský ◽  
Jaroslav Podlaha ◽  
...  
Keyword(s):  
Acetic Acid ◽  
Nmr Spectroscopy ◽  
Acetic Anhydride ◽  
Spectral Methods ◽  
X Ray Diffraction ◽  
X Ray ◽  
Mild Conditions ◽  
Condensation Products ◽  
Unsaturated Lactones ◽  
C Nmr

3β-Acetoxy-21,22-dioxo-18α,19βH-ursan-28,20β-olide (IIIa) reacts with acetic anhydride in pyridine under very mild conditions affording β-lactone IVa and γ-lactones Va and VIIa as condensation products. On reaction with pyridine, lactones Va and VIIa undergo elimination of acetic acid to give unsaturated lactones VIIIa and IXa, respectively. Similarly, the condensation of 20β,28-epoxy-21,22-dioxo-18α,19βH-ursan-3β-yl acetate (IIIb) with acetic anhydride leads to β-lactone IVb and γ-lactone Vb; the latter on heating with pyridine affords unsaturated lactone VIIIb and 21-methylene-22-ketone Xb. The structure of the obtained compounds was derived using spectral methods, particularly 1H and 13C NMR spectroscopy; structure of lactone IVa was confirmed by X-ray diffraction.

A New Dimeric Derivative of Ethoxyquin from Its Reaction with Alkylperoxy Radicals

1993 ◽  
Vol 58 (8) ◽  
pp. 1914-1918 ◽  
Author(s):  
Jaroslav Kříž ◽  
Luděk Taimr
Keyword(s):  
Mass Spectrometry ◽  
Nmr Spectroscopy ◽  
Peroxy Radicals ◽  
Methyl Group ◽  
Alkylperoxy Radicals ◽  
C Nmr

The structure of a new compound formed in the reaction of ethoxyquin with alkylperoxy radicals was resolved by 1H and 13C NMR spectroscopy (including COSY, NOESY, HHC RCT and SSLR INEPT techniques) and confirmed by mass spectrometry. The structure suggest participation of 4-methyl group of ethoxyquin in the deactivation of peroxy radicals. A mechanism of this reaction is proposed.

Reactivity of Sodium Hexaethyl-2,4-dicarba-nido-hexaborate(1-)

1999 ◽  
Vol 64 (6) ◽  
pp. 977-985 ◽  
Author(s):  
Bernd Wrackmeyer ◽  
Hans-Jörg Schanz ◽  
Wolfgang Milius ◽  
Catherine McCammon
Keyword(s):  
Mössbauer Spectroscopy ◽  
Nmr Spectroscopy ◽  
Structural Analysis ◽  
Hydrogen Atom ◽  
Mossbauer Spectroscopy ◽  
Sandwich Complex ◽  
X Ray ◽  
Bromo Derivative ◽  
Boron Tribromide ◽  
C Nmr

Sodium hexaethyl-2,4-dicarba-nido-hexaborate(1-) (6), available from hexaethyl-2,4-dicarba- nido-hexaborane(8) (4) by deprotonation, reacts with deuterated methanol, CD3OD, to give back 4 without H/D exchange of the B-H-B hydrogen atom. The reaction of 6 with diethylboron chloride, Et2BCl, affords hexaethyl-2,4-dicarba-closo-hexaborane(6) (7), the first example of a peralkylated carborane of this type. In contrast, the reaction of 6 with boron tribromide, BBr3, leads mainly to 2,3,4,5,6,7-hexaethyl-2,4-dicarba-closo-heptaborane(7) (8), together with the corresponding 1-bromo derivative (9) and the closo-carborane 7 as side products. The reaction of two equivalents of 6 with FeCl2 gives the air-stable sandwich complex bis[hexaethyl-2,4-dicarba-nido-hexaborate(1-)]iron 10 which was characterised by X-ray structural analysis. All products were characterised by 1H, 11B and 13C NMR spectroscopy, and 57Fe Mössbauer spectroscopy was used to study 10.

Formation of spiro adduct from N-methyl-N-(2,4,6-trinitrophenyl)glycine anion

1989 ◽  
Vol 54 (2) ◽  
pp. 440-445 ◽  
Author(s):  
Vladimír Macháček ◽  
Alexandr Čegan ◽  
Miloš Sedlák ◽  
Vojeslav Štěrba
Keyword(s):  
Nmr Spectroscopy ◽  
Dimethyl Sulfoxide ◽  
Equilibrium Constant ◽  
Mole Fraction ◽  
Nucleophilic Addition ◽  
Adduct Formation ◽  
First Case ◽  
C Nmr

The intramolecular nucleophilic addition of N-methyl-N-(2,4,6-trinitrophenyl)glycine anion in methanol-dimethyl sulfoxide mixtures produces spiro[(3-methyl-5-oxazolidinone)-2,1'-(2',4',6'-trinitrobenzenide)]. The spiro adduct has been identified by means of 1H and 13C NMR spectroscopy. This is the first case when the formation of a Meisenheimer adduct with carboxylate ion is observed. Logarithm of the equilibrium constant of adduct formation increases linearly with the mole fraction of dimethyl sulfoxide in its mixture with methanol.

Alterations in Molecular Composition of Humic Substances from Eucalypt Plantation Soils Assessed by 13 C-NMR Spectroscopy

2012 ◽  
Vol 77 (1) ◽  
pp. 293-306 ◽  
Author(s):  
Emanuelle Mercês Barros Soares ◽  
Ivo Ribeiro Silva ◽  
Roberto Ferreira de Novais ◽  
Yan-Yan Hu ◽  
Klaus Schmidt-Rohr
Keyword(s):  
Nmr Spectroscopy ◽  
Humic Substances ◽  
Molecular Composition ◽  
Eucalypt Plantation ◽  
C Nmr
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