- Gas-phase NMR studies of N,N-dimethylthioamides. Influence of the thiocarbonyl substituent on the internal rotation activation energies
-
Temperature-dependent gas-phase 1H NMR spectra of seven thiocarbonyl-substituted N,N-dimethylthioamides (YCSN(CH3)2) obtained at 300 MHz are consistent with the following free activation energies ΔG?298 (kcal mol-1): Y = H, 22.5 (0.1); CH3, 18.0 (0.1); F, 18.3 (0.1); Cl, 16.9 (0.2); CF3, 17.2 (0.1); CH2CH3, 17.6 (0.1); CH(CH3)2, 16.3 (0.1). The results are compared to condensed-phase values and to the corresponding gas-phase oxoamides.
- Neugebauer Crawford,Taha,True,LeMaster
-
-
Read Online
- Primary and Secondary Binding Sites for Lanthanide Shift Reagents with Amides. Differential Behavior of cis vs trans Amide Isomers with LSR
-
Lanthanide induced shifts (LIS) were measured for four dimethylamides, RCON(CH3)2, and four monomethyl amides, RCONHCH3, R=H, CH3, CF3 and CCl3, using Eu(fod)3 in CCl4 and benzene (C6D6) solution.Structural correlations for HCON(CH3)2 and CH3CON(CH3)2 in both solvents yield a preferred binding site for the Eu(fod)3 on one of the lone-pair orbitals of the oxygen atom, with a probable site of secondary importance on the other lone-pair orbital.The cis vs trans isomers of HCONHCH3 and CH3CONHCH3 exhibit remarkably different chemical shift behavior upon addition of Eu(fod)3.
- LaPlanche Graham, Laurine
-
-
Read Online
- Amide bond formation in aqueous solution: Direct coupling of metal carboxylate salts with ammonium salts at room temperature
-
Herein, we report a green, expeditious, and practically simple protocol for direct coupling of carboxylate salts and ammonium salts under ACN/H2O conditions at room temperature without the addition of tertiary amine bases. The water-soluble coupling reagent EDC·HCl is a key component in the reaction. The reaction runs smoothly with unsubstituted/substituted ammonium salts and provides a clean product without column chromatography. Our reaction tolerates both carboxylate (which are unstable in other forms) and amine salts (which are unstable/volatile when present in free form). We believe that the reported method could be used as an alternative and suitable method at the laboratory and industrial scales. This journal is
- Nielsen, John,Tung, Truong Thanh
-
supporting information
p. 10073 - 10080
(2021/12/10)
-
- Conformational analysis. Part 33. An NMR, solvation and theoretical investigation of conformational isomerism in N,N-dimethylfluoroacetamide and N,N-dimethyl-α-fluoropropionamide
-
The solvent and temperature dependence of the 1H and 13C NMR spectra of N,N-dimethylfluoroacetamide (DMFA) and N,N-dimethyl-α-fluoropropionamide (DMFP) are reported and the 5JCF, 1JCF and 4JCF couplings analysed by solvation theory. Density function theory (DFT) at the B3LYP/6-311 +G(d,p) level with ZPE (zero point energy) corrections was used to obtain the conformer geometries. In DMFA, the DFT method gave only two minima for the cis (F-C-C=O, 0°) and gauche (F-C-C=O, 140.6°) rotamers. The trans rotamer was not a minimum in the energy surface. Assuming only the cis and gauche forms, the observed couplings when analysed by solvation theory gave the energy difference (Ecis - Eg) of 2.5 kcal mol-1 in the vapour phase, (cf. the ab initio value of 2.3 kcal mol-1) decreasing to 0.87 kcal mol-1 in CCl4 and to -1.29 kcal mol-1 in DMSO. In DMFP the ab initio calculations gave three minima; the cis (F-C-C=O, 30.4°), gauche-1 (F-C-C=O, 144.7°) and gauche-2 (F-C-C=O, -124.1°) rotamers with (Ecis - Eg2) equal to 2.5 kcal mol-1 and (Eg1 - Eg2) equal to 0.3 kcal mol-1. The observed couplings were analysed by solvation theory assuming one "average" gauche conformer to give (Ecis - Eg(AV)) equal to 2.1 kcal mol-1 in the vapour phase, decreasing to 0.83 kcal mol-1 in CCl4 and to -1.11 kcal mol-1 in DMSO.
- Tormena, Claudio F.,Rittner, Roberto,Abraham, Raymond J.,Basso, Ernani A.,Pontes, Rodrigo M.
-
p. 2054 - 2059
(2007/10/03)
-
- Synthesis and reactivity of trifluorodithioacetates derived from trifluorothioacetamides
-
A general synthesis of trifluorodithioacetates is described by thiolysis of trifluorothioamidium salts, derived from trifluorothioacetamides. The reactivity of these CF3 bearing C2 building blocks has been investigated towards nucleophiles and in cycloaddition reactions. Trifluorodithioacetates react with dienes to give thiopyrans and with diazo compounds to give trifluoromethyl vinyl sulphides via thiirane intermediates. With amines, trifluorodithioacetates give rise to trifluorothioacetamides while thiols add by thiophilic attack leading to new trifluoroethane dithioacetal disulphide. Two equivalents of phosphite furnish one equivalent of thiophosphate and one of phosphorylated trifluoroethane.
- Laduron, Frederic,Nyns, Claire,Janousek, Zdenek,Viehe, Heinz G.
-
p. 697 - 707
(2007/10/03)
-
- Gas-Phase NMR Investigation of Internal Rotation in N,N-Dimethyltrifluoroacetamide. Phase Dependence of Kinetic Parameters
-
Exchange-broadened 1H NMR spectra of gaseous N,N-dimethyltrifluoroacetamide (DMTFA) obtained between 30 and 70 deg C are consistent with the following kinetic parameters: Eact(), 16.7(5) kcal mol-1; ΔG298, 16.4(5) kcal mol-1; ΔH298, 16.1(5) kcal mol-1; and ΔS, -1.1(3) eu.These values may be compared to the higher values obtained for a 10percent solution of DMTFA in CCl4: Eact, 18.3(4) kcal mol1-, ΔG298, 17.8(4) kcal mol-1, ΔH298, 17.6(6) kcal mol-1; and ΔS, -0.6(2) eu.The phase dependence of these parameters is compatible with solvent internal pressure effects on a process which has a large positive activation volume.A large positive activation volume is expected for an internal rotation process proceeding through a freely rotating transition state.
- Ross, Brian D.,True, Nancy S.,Decker, Debra L.
-
-