Ab initio studies of the conformations of ethynyl formate, cyano formate and related ethynyl and cyano compounds

Langley, Charles H.; Pawar, Diwakar M.; Noe, Eric A.

doi:10.1016/j.theochem.2005.06.027

Cited by 3 publications

(2 citation statements)

References 19 publications

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“…The E − Z energy differences for formic acid esters decrease in the order R‘ = methyl > vinyl > ethynyl. , The hybridization of carbon in the corresponding hydrocarbons R‘H changes from sp 3 to sp 2 to sp in the series, suggesting that the electron-withdrawing abilities of the groups may be important in enhancing the populations of the E -isomers. However, even with very highly electronegative R‘ groups such as trifluoromethyl, the Z conformations of esters are still generally preferred, although by smaller amounts.…”

Section: Introductionmentioning

confidence: 98%

Conformational Equilibria in Formic Acid and the Adduct of Formic Acid and Hexafluoroacetone, HCO₂C(CF₃)₂OH

2007

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Low-temperature 1H and 13C NMR spectra of formic acid (1) showed separate signals for the E and Z conformations in solvents containing a hydrogen bond acceptor, dimethyl ether. The population of E-1 (6.2% in 3:1:1 CHClF2/CHCl2F/(CH3)2O) was larger than that for 13C-labeled methyl formate in the same solvent (0.2%), which indicated that the relative populations are not determined by steric effects. The free-energy difference between the E and Z conformations of 1 was 0.9 kcal/mol. In a 1:3 CD2Cl2/(CH3)2O solvent mixture, peaks for E and Z conformations were found at low temperatures by 1H and 13C NMR for both formic acid and an adduct with hexafluoroacetone, HCO2C(CF3)2OH (2). The population of E-1 in this solvent mixture was 4.3% by 13C NMR. The carbon spectrum showed two peaks in the carbonyl carbon region of nearly equal intensities at -151.6 degrees C, with E-2 (48%) absorbing downfield of the major Z-2 (52%). The large population of E-2 confirms that electron-withdrawing groups R' in RCO2R' enhance the populations of the E-isomers. The free-energy barriers for 2 of 6.24 (E-to-Z) and 6.26 kcal/mol (Z-to-E) were determined from rate constants obtained by line shape analysis at -143.2 degrees C.

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Section: Introductionmentioning

confidence: 98%

Conformational Equilibria in Formic Acid and the Adduct of Formic Acid and Hexafluoroacetone, HCO₂C(CF₃)₂OH

2007

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“…-(Glyco)sphingolipids and more specifically ceramides (Cers) adopt a parallel orientation of the lipid chains in the cell membrane, requiring a (Z)-configuration of the amide moiety, while the (E)-configuration of amides is preferred in solution and in the solid state by a free-energy difference of ca. 1.2 kcal/mol [1] [2]. There is no a priori reason why the amide moiety of a Cer complexed to a receptor should either adopt the (E)-or the (Z)-configuration.…”

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4,5,6‐Trisubstituted Piperidinones as Conformationally Restricted Ceramide Analogues: Synthesis and Evaluation as Inhibitors of Sphingosine and Ceramide Kinases and as NKT Cell‐Stimulatory Antigens

Mathew

Cavallari²,

Billich

et al. 2009

Chemistry & Biodiversity

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The conformationally based piperidinone sphingosine analogues 7, 8, 15, and 16 were synthesized from allylic alcohol 34 via lactams 31 and 32. The L-arabino diol 7 and the L-ribo diol 8 were transformed into the amino alcohols 17-24. The L-gluco ceramide analogues 43, 46a, and 47, and the L-altro ceramide analogues 51a and 52 were synthesized from either 31 or 32. The L-ribo diols 8 and 16, and the amino alcohols 19 and 20 inhibit sphingosine kinase 1 (SPHK1), while the L-arabino analogues 7, 15, 17, and 18 are inactive. The L-arabino and the L-ribo dimethylamines 21-24, the L-gluco ceramide analogues 43, 46a, and 47, and the L-altro ceramide analogues 51a and 52 did not block SPHK1. Neither the L-arabino diol 7 nor the L-ribo diol 8 inhibited SPHK2 or ceramide kinase. The L-arabino diols 7 and 15 stimulate invariant natural killer T (iNKT) cells when presented by living antigen-presenting cells (APC) and also by plate-bound human CD1d, whereas the L-ribo diols 8 and 16, the L-arabino amino alcohols 17-18, and the dimethylamines 21-22 did not activate iNKT cells. The L-gluco ceramide analogues 43, 46a, and 47 had strongly stimulatory effects on iNKT cells when presented by living APC and also by plate-bound human CD1d, whereas the L-altro ceramide analogue 52 activated only weakly. All activatory compounds induced preferentially the release of pro-inflammatory cytokines, indicating the formation of a stable CD1d--lipid--T-cell receptor complex.

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Salts and Ionic Liquids of Resonance Stabilized Amides

Brand

Martens

Mayer

et al. 2009

Chemistry An Asian Journal

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The synthesis, structure, and bonding of alkali salts of resonance stabilized amides, such as diformylamide (dfa), formylcyanoamide (fca), nitrocyanoamide (nca), and for comparision, the well-known dicyanoamide (dca), are discussed on the basis of experimental and theoretical data. The first structural reports of K(18-crown-6)+dfa-, K(18-crown-6)+fca-, Na+nca-, and Li(TMEDA)+dca- are presented. Examination of the X-ray data reveals almost planar anions with strong cation-anion interactions resulting in network-like structures in the solid state. For comparison, the X-ray structures of covalently bound phenyldicyanoamide and diformamide are also discussed. The thermal behavior of the alkali salts of these amides is studied by thermoanalytical experiments. Moreover, several novel ionic liquids based on resonance stabilized amides have been prepared and were fully characterized, namely the dfa, fca, and nca salts of EMIM (1-ethyl-3-methyl-imidazolium), BMIM (1-butyl-3-methyl-imidazolium), and HMIM (1-hexyl-3-methyl-imidazolium). Most of them are liquid at room temperature, except BMIM+fca- that melts at 32 degrees C. These ionic liquids are neither heat nor shock sensitive, are thermally stable up to over 200 degrees C, and can be prepared easily in large quantities.

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Ab initio studies of the conformations of ethynyl formate, cyano formate and related ethynyl and cyano compounds

Cited by 3 publications

References 19 publications

Conformational Equilibria in Formic Acid and the Adduct of Formic Acid and Hexafluoroacetone, HCO₂C(CF₃)₂OH

Conformational Equilibria in Formic Acid and the Adduct of Formic Acid and Hexafluoroacetone, HCO₂C(CF₃)₂OH

4,5,6‐Trisubstituted Piperidinones as Conformationally Restricted Ceramide Analogues: Synthesis and Evaluation as Inhibitors of Sphingosine and Ceramide Kinases and as NKT Cell‐Stimulatory Antigens

Salts and Ionic Liquids of Resonance Stabilized Amides

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Ab initio studies of the conformations of ethynyl formate, cyano formate and related ethynyl and cyano compounds

Cited by 3 publications

References 19 publications

Conformational Equilibria in Formic Acid and the Adduct of Formic Acid and Hexafluoroacetone, HCO2C(CF3)2OH

Conformational Equilibria in Formic Acid and the Adduct of Formic Acid and Hexafluoroacetone, HCO2C(CF3)2OH

4,5,6‐Trisubstituted Piperidinones as Conformationally Restricted Ceramide Analogues: Synthesis and Evaluation as Inhibitors of Sphingosine and Ceramide Kinases and as NKT Cell‐Stimulatory Antigens

Salts and Ionic Liquids of Resonance Stabilized Amides

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Conformational Equilibria in Formic Acid and the Adduct of Formic Acid and Hexafluoroacetone, HCO₂C(CF₃)₂OH

Conformational Equilibria in Formic Acid and the Adduct of Formic Acid and Hexafluoroacetone, HCO₂C(CF₃)₂OH