Dicyclohexylethyleneglycol, -diethyleneglycol, -triethyleneglycol, and related monosubstituted cyclohexanes. Conformational analysis using low-temperature 13C and 1H NMR spectroscopy

1995 ◽  
Vol 73 (4) ◽  
pp. 566-572 ◽  
Author(s):  
G.W. Buchanan ◽  
A. Moghimi ◽  
V.M. Reynolds ◽  
K. Bourque
Keyword(s):  
Free Energy ◽  
Nmr Spectroscopy ◽  
1H Nmr Spectroscopy ◽  
Ring Inversion ◽  
Ethylene Glycols ◽  
Axial Conformer ◽  
Conformational Equilibria ◽  
Single Ring ◽  
Conformational Free Energy ◽  
C Nmr

Two conformations of each of the title molecules have been detected by 100 MHz 13C NMR at 210 K. For the dicyclohexyl systems, the conformations are related via a single ring inversion. In each case the equatorial–axial conformer is 4.7 ± 0.4 kJ/mol less stable than the diequatorially substituted form in CD2Cl2 solution. For monosubstituted models, the conformational free energy (−ΔG0) values of the -O-CH2-CH2-OCH3, -OCH2-CH2-O-CH2-CH3, and -O-CH2-CH2-O-CH-(CH3)2 groups have been determined to be 5.4,6.1, and 6.1 ± 0.2 kJ/mol, respectively. In methanol, the latter equilibria are slightly more biased towards the axially substituted conformers. Keywords: substituted ethylene glycols, conformational equilibria.

Novel stereochemical equilibria in crown ethers. Detection of additional conformations of cis-syn-cis- and cis-anti-cis-dicyclohexano-18-crown-6 by 100.6-MHz 13C nuclear magnetic resonance at 173 K

1985 ◽  
Vol 63 (10) ◽  
pp. 2747-2751 ◽  
Author(s):  
G. W. Buchanan ◽  
K. Bourque ◽  
J. W. Bovenkamp ◽  
A. Rodrigue
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Free Energy ◽  
Magnetic Resonance ◽  
Low Temperature ◽  
Crown Ethers ◽  
High Field ◽  
13C Nuclear Magnetic Resonance ◽  
Conformational Equilibria ◽  
Conformational Free Energy ◽  
C Nmr

High field, 13C nmr has been utilized for the analysis of new conformational equilibria in each of the title crown ethers at low temperature. Evidence indicates that these equilibria arise from restricted rotation in the macrocyclic portions of these molecules. The conformational free energy differences between the isomers are small (0.1–0.3 kcal/mol) while barriers to their interconversion are of the order of 8.5–9.0 kcal/mol. Comparisons are made with the degenerate equilibria involving inversion of the cyclohexane rings.

Interactions gauches et chemins réactionnels. Etudes conformationnelles d'hydroxyalkyl-4 cyclohexènes contraints

1981 ◽  
Vol 59 (5) ◽  
pp. 859-864
Author(s):  
Jeanine Bouteiller-Prati ◽  
Jean-Claude Bouteiller ◽  
Jean-Pierre Aycard
Keyword(s):  
Free Energy ◽  
Reaction Path ◽  
High Energy ◽  
Nmr Study ◽  
Conformational Equilibria ◽  
The Stability ◽  
Cis And Trans ◽  
Conformational Free Energy

From J and δ values determined by the nmr study of alcohols obtained by addition of CH3Li and LiAlH4 to the exocyclic carbonyl of cis and trans 3-alkyl 4-carbomethoxy (or acetyl) cyclohexenes (alkyl = H, CH3, C(CH3)3), we have deduced the conformational free energy values (ΔG0X) of the CH(CH3)OH and C(CH3)2OH substituents (0.62 and 2.08 kcal mol−1 respectively) as well as the values for some related conformational equilibria. For transtert-butyl derivatives the stability of the diaxial conformer agrees with a reaction path involving high energy conformers.

The conformational free energy difference for the trideuteromethyl substituent in cyclohexane

1980 ◽  
Vol 58 (23) ◽  
pp. 2714-2719 ◽  
Author(s):  
Harold Booth ◽  
Jeremy Ramsey Everett
Keyword(s):  
Free Energy ◽  
Room Temperature ◽  
Energy Difference ◽  
Axial Orientation ◽  
Free Energy Difference ◽  
Nmr Spectrum ◽  
Enthalpy Difference ◽  
Methyl Cyclohexane ◽  
Conformational Free Energy ◽  
C Nmr

Studies at 169 K to 194 K of the 13C nmr spectrum of cis-1-ethyl-[4-Me-2H3]-4-methylcyclohexane show that the conformational enthalpy difference −ΔH°(C2H3) is 1.82 ± 0.07 kcal mol−1 and the conformational entropy difference ΔS°(C2H3) is −0.28 ± 0.4 cal K−1 mol−1, values which do not differ significantly from the values for CH3. However, analysis of the room temperature 13C nmr spectrum of a mixture of cis-1-ethyl-4-methylcyclohexane and cis-1-ethyl-[4-Me-2H3]-4-methylcyclohexane showed that −ΔG°(C2H3) at 298 K is 11.89 ± 1.46 cal mol−1less than that for CH3, i.e. C2H3 has a slightly greater preference than CH3 for the axial orientation. The 13C nmr spectrum of a mixture of trans-1-ethyl-4-methylcyclohexane and trans-1-ethyl-[4-Me-2H3]-4-methyl-cyclohexane indicates that deuterium-induced 13C nmr isotope shifts, all upfield, occur across 1,2, 3, and 5 bonds.

Synthesis and nuclear magnetic resonance study of the compounds (2-X-1,3-dithiane) (X = H, Me, SiMe3, GeMe3, SnMe3, PbMe3) and their tetracarbonyliron complexes

1978 ◽  
Vol 56 (11) ◽  
pp. 1538-1544 ◽  
Author(s):  
David J. Cane ◽  
William A. G. Graham ◽  
Liviu Vancea
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Nmr Spectroscopy ◽  
Magnetic Resonance ◽  
Energy Barrier ◽  
Nmr Spectra ◽  
Nuclear Magnetic Resonance Study ◽  
Carbonyl Groups ◽  
Magnetic Resonance Study ◽  
Ring Inversion ◽  
C Nmr

A series of (1,3-dithiane)Fe(CO)4 complexes, (2-X-1,3-dithiane)Fe(CO)4, X = H, Me, SiMe3, GeMe3, SnMe3, PbMe3, has been prepared and characterized, and both the complexes and the free ligands studied by 1H and 13C nmr spectroscopy. The energy barrier to ring inversion in (1,3-dithiane)Fe(CO)4, ΔG298†, is 14.7 ± 0.2 kcal mol−1, some 4.4 kcal mol−1 higher than in free 1,3-dithiane.13C nmr spectra showed that within the Fe(CO)4 moiety, rapid averaging of carbonyl groups occurs down to at least −80 °C.

Asymetrical Dimer - allyl-palladiu Complexes II. Data from Infrared Spectra and Chemical Behaviour

2008 ◽  
Vol 59 (7) ◽  
Author(s):  
Maria Maganu ◽  
Filip Chiraleu ◽  
Constantin Draghici ◽  
Gheorghe Mihai
Keyword(s):  
Carbon Monoxide ◽  
Nmr Spectroscopy ◽  
1H Nmr ◽  
Infrared Spectra ◽  
Analytical Methods ◽  
1H Nmr Spectroscopy ◽  
Chemical Behaviour ◽  
The Asymmetry ◽  
Pd Complexes

The previous data obtained by 1H-NMR spectroscopy established the existence of an asymmetry of the bond between Pd and p-allylic groups, even in the p-allyl-Pd complexes dimers which are considered usually symmetric dimers. The asymmetry of the bond depends by the substitutes of the allylic group. Other analytical methods were investigated for additional proof of the obtained results. Thus, this paper discusses how this asymmetry would be reflected in the infrared spectra and in the reaction of the complexes with carbon monoxide.

Diastereoselective Reduction of Selected α-substituted β-keto Esters and the Assignment of the Relative Configuration by 1H-NMR Spectroscopy

2020 ◽  
Vol 07 ◽  
Author(s):  
Christian Trapp ◽  
Corinna Schuster ◽  
Chris Drewniok ◽  
Dieter Greif ◽  
Martin Hofrichter
Keyword(s):  
Nmr Spectroscopy ◽  
1H Nmr ◽  
1H Nmr Spectroscopy ◽  
Selective Reduction ◽  
Reducing Agents ◽  
Relative Configuration ◽  
Curtius Rearrangement ◽  
Keto Esters ◽  
Hydroxy Esters ◽  
Diastereoselective Reduction

Background:: Chiral β-hydroxy esters and α-substituted β-hydroxy esters represent versatile building blocks for pheromones, β-lactam antibiotics and 1,2- or 1,3-aminoalcohols. Objective:: Synthesis of versatile α-substituted β-keto esters and their diastereoselective reduction to the corresponding syn- or anti-α-substituted β-hydroxy esters. Assignment of the relative configuration by NMR-spectroscopy after a CURTIUS rearrangement of α-substituted β-keto esters to 4-substituted 5-methyloxazolidin-2-ones. Method:: Diastereoselective reduction was achieved by using different LEWIS acids (zinc, titanium and cerium) in combination with complex borohydrides as reducing agents. Assignment of the relative configuration was verified by 1H-NMR spectroscopy after CURTIUS-rearrangement of α-substituted β-hydroxy esters to 4-substituted 5-methyloxazolidin-2-ones. Results:: For the syn-selective reduction, titanium tetrachloride (TiCl4) in combination with a pyridine-borane complex (py BH3) led to diastereoselectivities up to 99% dr. High anti-selective reduction was achieved by using cerium trichloride (CeCl3) and steric hindered reducing agents such as lithium triethylborohydride (LiEt3BH). After CURTIUS-rearrangement of each α-substituted β-hydroxy ester to the corresponding 4-substituted 5-methyloxazolidin-2-one, the relative configuration was confirmed by 1H NMR-spectroscopy. Conclusion:: We have expanded the procedure of LEWIS acid-mediated diastereoselective reduction to bulky α-substituents such as the isopropyl group and the electron withdrawing phenyl ring.

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.

Conformational study on ribonucleoside O-phosphonylmethyl derivatives by 1H NMR spectroscopy

1985 ◽  
Vol 50 (8) ◽  
pp. 1899-1905 ◽  
Author(s):  
Milena Masojídková ◽  
Jaroslav Zajíček ◽  
Miloš Buděšínský ◽  
Ivan Rosenberg ◽  
Antonín Holý
Keyword(s):  
Nmr Spectroscopy ◽  
1H Nmr ◽  
1H Nmr Spectroscopy ◽  
Conformational Study ◽  
H Nmr ◽  
Conformational Properties

Conformational properties of ribonucleoside 5'-O-phosphonylmethyl derivatives have been determined by 1H NMR spectroscopy and compared with those of natural nucleosides and 5'-nucleotides.

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