Hydrogen bonding solvent effect on the basicity of primary amines CH3NH2, C2H5NH2, and CF3CH2NH2

1981 ◽  
Vol 59 (1) ◽  
pp. 151-155 ◽  
Author(s):  
Yan K. Lau ◽  
P. Kebarle
Keyword(s):  
Free Energy ◽  
Energy Difference ◽  
Ion Source ◽  
Primary Amines ◽  
Hydration Free Energy ◽  
Ion Hydration ◽  
Free Energy Difference ◽  
Source Pressure ◽  
Pulsed Electron Beam ◽  
Good Agreement

The equilibria RNH3+(H2O)n−1 + H2O = RNH3+(H2O)n were measured for R = CH3, C2H5, and CF3CH2 from n = 1 to n = 3 with a pulsed electron beam high ion source pressure mass spectrometer. The proton and hydrate transfer equilibria CH3NH3+(H2O)n + C2H5NH2 = CH3NH2 + C2H5NH3+(H2O)n were measured for n = 0 to n = 3. These data allow the evaluation of ΔH0 and ΔG0 for the reactions: R0NH3+(H2O)n + RNH3+ = R0NH3+ + RNH3+(H2O)n. ΔH0 = δΔH00,n(RNH3+), ΔG = δΔG00,n(RNH3+). These data are compared with δΔE0,3 (STO-3G) evaluated by Hehre and Taft. In general good agreement is observed at n = 3. The δΔH00,3(RNH3+) ≈ δΔE0,3(RNH3+) are also found close to the ion hydration free energy difference in aqueous solutions.

UV photoelectron spectroscopic and computational study of 7-substituted cycloheptatrienes

2008 ◽  
Vol 86 (5) ◽  
pp. 444-450 ◽  
Author(s):  
T Bajorek ◽  
N H Werstiuk
Keyword(s):  
Free Energy ◽  
Photoelectron Spectroscopy ◽  
Computational Study ◽  
Energy Difference ◽  
Spectral Simulation ◽  
Free Energy Difference ◽  
Conformational Isomers ◽  
Conformational Isomer ◽  
Good Agreement ◽  
Equatorial Conformer

The He(I) photoelectron (PE) spectra of cycloheptatriene (1), 7-methylcycloheptatriene (2), 7-methoxycycloheptatriene (3), 7-methylthiocycloheptatriene (4), and 7-diemthylaminocycloheptatriene (5) were recorded and interpreted using MO energies and ionization potentials acquired from B3PW91 calculations. Partial simulated PE spectra were in good agreement with the experimental results. The axial and equatorial conformers have distinct PE spectra as illustrated by simulation. The PE spectra of 2, 3, and 5 are representative of the equatorial conformers, while the PE spectrum of 4 was in accord with a 1:1 mixture of equatorial and axial conformational isomers based on spectral simulation. The calculated free energy differences between the equatorial and axial conformers are in the order of 2 kcal mol–1 (1 cal = 4.184 J) for compounds 2, 3, and 5, where the equatorial conformational isomer is lowest in energy. In the case of 4, the equatorial conformer was only marginally lower in energy than its axial counterpart, where the free energy difference is 0.1 kcal mol–1.Key words: 7-substituted cycloheptatrienes, He(I) photoelectron spectroscopy, B3PW91, spectral simulation.

scholarly journals Entropic bonding of the type 1 pilus from experiment and simulation

2020 ◽  
Vol 7 (4) ◽  
pp. 200183
Author(s):  
Fabiano Corsetti ◽  
Alvaro Alonso-Caballero ◽  
Simon Poly ◽  
Raul Perez-Jimenez ◽  
Emilio Artacho
Keyword(s):  
Free Energy ◽  
Energy Difference ◽  
Quantitative Comparison ◽  
Free Energy Difference ◽  
Force Microscopy ◽  
Atomic Force ◽  
Experiment And Simulation ◽  
Dynamics Simulations ◽  
Good Agreement

The type 1 pilus is a bacterial filament consisting of a long coiled proteic chain of subunits joined together by non-covalent bonding between complementing β -strands. Its strength and structural stability are critical for its anchoring function in uropathogenic Escherichia coli bacteria. The pulling and unravelling of the FimG subunit of the pilus was recently studied by atomic force microscopy experiments and steered molecular dynamics simulations (Alonso-Caballero et al. 2018 Nat. Commun . 9 , 2758. (doi:10.1038/s41467-018-05107-6)). In this work, we perform a quantitative comparison between experiment and simulation, showing a good agreement in the underlying work values for the unfolding. The simulation results are then used to estimate the free energy difference for the detachment of FimG from the complementing strand of the neighbouring subunit in the chain, FimF. Finally, we show that the large free energy difference for the unravelling and detachment of the subunits which leads to the high stability of the chain is entirely entropic in nature.

Gas phase ion equilibria: heats of formation of acylium ions RCO+ and protonated acids RC(OH)2+; gas phase catalysis of proton shift RC(OH)2+ → RCO(OH2)+

1979 ◽  
Vol 57 (24) ◽  
pp. 3205-3215 ◽  
Author(s):  
W. R. Davidson ◽  
S. Meza-Höjer ◽  
P. Kebarle
Keyword(s):  
Gas Phase ◽  
Negative Temperature ◽  
Ion Source ◽  
Activation Energy Barrier ◽  
Third Order ◽  
Source Pressure ◽  
Pulsed Electron Beam ◽  
Proton Shift ◽  
Gas Phase Ion ◽  
Good Agreement

The equilibria [2]: [Formula: see text] for R = CH3, C2H5, and C6H5 were studied in a pulsed electron beam high ion source pressure mass spectrometer. van't Hoff plots led to ΔH2 values: (CH3), 24.6; (C2H5), 22.7; (C6H5), 21.9 kcal/mol. ΔHf(RC(OH)2+) were obtained from gas phase basicity ladders combined with the new ΔHf(t-butyl+) = 163 kcal/mol (Beauchamp). The ΔHf(RC(OH)2+) were: (CH3), 71.3; (C2H5), 63.6; (C6H5), 95.5 kcal/mol. Combination of ΔH2 with ΔHf(RC(OH)2+) leads to ΔHf(RCO+): (CH3), 153.7; (C2H5), 144; (C6H5), 174.6 kcal/mol. These results are in agreement with selected data from appearance potentials. The energies and structures of the participants in reaction [2] were calculated by MINDO/3 and STO-3G. MINDO/3 gave good agreement with ΔH2. The establishment of the equilibria [2] was unusually slow. A study of the kinetics revealed that k2f is approximately third order, unusually small, and has an unusually large negative temperature coefficient. Furthermore, reaction [2] was found to be catalyzed by RCOOH. An explanation of these observations is given by assuming that the proton shift RCO(OH2)+ → RC(OH)2+ has a large activation energy barrier in the gas phase. This barrier is removed by formation of a hydrogen bonded complex with RCOOH.

Sign in / Sign up

Export Citation Format

Share Document