Variable-Temperature Ultraviolet Photoelectron-Spectroscopy of the Keto-Enol Tautomers of Pentane-2,4-Dione

1987 ◽  
Vol 40 (3) ◽  
pp. 599 ◽  
Author(s):  
NS Hush ◽  
MK Livett ◽  
JB Peel ◽  
GD Willett
Keyword(s):  
Photoelectron Spectroscopy ◽  
Energy Region ◽  
Variable Temperature ◽  
Photoelectron Spectra ◽  
Ultraviolet Photoelectron Spectroscopy ◽  
Molecular Orbital Calculations ◽  
Electronic Relaxation ◽  
Relaxation Effects ◽  
Enol Tautomer ◽  
Scf Calculations

The HeI photoelectron spectra of pentane-2,4-dione measured at various temperatures have been subjected to a spectrum-stripping technique to enable isolation of the complete HeI photoelectron spectra of the keto and enol tautomers. The resulting spectrum-stripping coefficients allow evaluation of the enolization equilibrium constant at each temperature and subsequently the enthalpy of enolization. Interpretation of the photoelectron spectra is achieved with the use of ab initio molecular orbital calculations. Photoionization of non-bonding oxygen, and π -type electrons, contribute to the low ionization energy region of the spectrum, with a πCC < no- <πCO ordering for the enol tautpmer , and no- < no+ < πCO+ for the keto tautomer . Because of different electronic relaxation effects, ∆SCF calculations are required to predict correctly the observed πCC/no- spacing for the enol tautomer.

Gas-Phase Tautomerism in the Triazoles and Tetrazoles: A Study by Photoelectron Spectroscopy and ab Initio Molecular Orbital Calculations

1981 ◽  
Vol 36 (11) ◽  
pp. 1246-1252 ◽  
Author(s):  
Michael H. Palmer ◽  
Isobel Simpson ◽  
J. Ross Wheeler
Keyword(s):  
Ab Initio ◽  
Gas Phase ◽  
Molecular Orbital ◽  
Photoelectron Spectroscopy ◽  
Relative Stability ◽  
Photoelectron Spectra ◽  
Equilibrium Geometry ◽  
Molecular Orbital Calculations ◽  
Methyl Derivatives

The photoelectron spectra of the tautomeric 1,2,3,- and 1,2,4-triazole and 1,2,3,4-tetrazole systems have been compared with the corresponding N-methyl derivatives. The dominant tautomers in the gas phase have been identified as 2 H-1,2,3-triazole, 1 H-1,2,4-triazole and 2H-tetrazole.Full optimisation of the equilibrium geometry by ab initio molecular orbital methods leads to the same conclusions, for relative stability of the tautomers in each of the triazoles, but the calculations wrongly predict the tetrazole tautomerism.

Tautomerism of pyrazoline-5-thione and triazoline-5-thione studied by variable temperature photoelectron spectroscopy

1983 ◽  
Vol 61 (6) ◽  
pp. 1197-1203 ◽  
Author(s):  
Claude Guimon ◽  
Geneviève Pfister-Guillouzo ◽  
Mlkael Begtrup
Keyword(s):  
Gaseous Phase ◽  
Photoelectron Spectroscopy ◽  
Variable Temperature ◽  
Thermal Isomerization ◽  
Photoelectron Spectra ◽  
Planar Form ◽  
Mndo Calculations

Photoelectron spectra at variable temperatures demonstrate that the rate of thermal isomerization of pyrazoline-5-thione (1a) into methylthiopyrazole(s) in the gaseous phase is metal catalysed. Similar isomerizations of triazolethione (2a and 3a) are at best only slightly so.Furthermore, photoelectron spectra and MNDO calculations show that gaseous methylthiopyrazoles (1b and 1c) and methylthiotriazoles (2b and 2c) exist predominantly in planar form for the b isomer and in nonplanar form for the c isomer. The ΔH0 for the rotameric equilibria is 2.7–4.2 kJ•mol−1.

Application of photoelectron spectroscopy to intramolecularly hydrogen-bonded systems. Part III. The photoelectron spectra of cis and trans 2-substituted cyclopentanols and cis and trans 2-substituted cyclohexanols

1976 ◽  
Vol 54 (12) ◽  
pp. 1929-1937 ◽  
Author(s):  
R. S. Brown
Keyword(s):  
Hydrogen Bonding ◽  
Photoelectron Spectroscopy ◽  
Intramolecular Hydrogen Bonding ◽  
Photoelectron Spectra ◽  
Molecular Orbital Calculations ◽  
Cis And Trans Isomers ◽  
Koopmans Theorem ◽  
Hydrogen Bonded Systems ◽  
Intramolecular Hydrogen ◽  
Cis And Trans

The photoelectron spectra of several well defined molecules exhibiting intramolecular hydrogen bonding has been determined and the analysis of the spectra is in accord with recent molecular orbital calculations of related systems. The experimentally determined enthalpies of the hydrogen bonds in cis-2-aminocyclopentanol and cis- and trans-2-aminocyclohexanol do not correlate in any simple fashion with the shifts in the ionization energies of the nO and nN orbitals compared to a model which precludes hydrogen bonding. The spectral differences attributed to hydrogen bonding in the cis and trans 2-substituted cyclanols cannot be attributed to differences in the through-bond interaction of the n orbitals on either atom since the cis and trans isomers of 1,2-dimethoxycyclopentane and 1,2-dimethoxycyclohexane show virtually identical pe spectra. A discussion of the applicability of Koopmans' theorem and the effect of the hydrogen bond in both the ion and ground states is presented.

Gas-liquid chromatography/ultraviolet photoelectron spectroscopy and the photoelectron spectra of nitrosamines

1976 ◽  
Vol 48 (7) ◽  
pp. 1078-1084 ◽  
Author(s):  
D. Betteridge ◽  
Syed K. Hasanuddin ◽  
David I. Rees
Keyword(s):  
Liquid Chromatography ◽  
Photoelectron Spectroscopy ◽  
Photoelectron Spectra ◽  
Ultraviolet Photoelectron Spectroscopy ◽  
Gas Liquid Chromatography

scholarly journals X-ray Emission Spectra of Some Carbon-containing Molecules

1986 ◽  
Vol 39 (5) ◽  
pp. 717 ◽  
Author(s):  
RA Phillips ◽  
FP Larkins
Keyword(s):  
Transition Probabilities ◽  
Emission Spectra ◽  
Fluorescence Yield ◽  
Total Carbon ◽  
Molecular Orbital Calculations ◽  
Electronic Relaxation ◽  
X Ray ◽  
Hartree Fock ◽  
Relaxation Effects ◽  
Absolute Transition

Ab initio molecular orbital calculations for the energy and intensity of X-ray transitions associated with the carbon monoxide, hydrogen cyanide and carbon dioxide molecules have been calculated at the Hartree-Fock level. It is demonstrated that in general the absolute transition probabilities are sensitive to the inclusion of electronic relaxation effects and interatomic transition moment contributions. It is concluded that calculations for molecular X-r!ly emission henomena should be undertaken at least at the multicentre relaxed Hartree-Fock level to achieve a realistic basis for comparison with experiment. Total carbon-K X-ray rates do not show a strong variation with changes in the molecular environment. The total rates are of a similar magnitude to those reported for the atom. The calculated carbon-K fluorescence yield is also similar in both the carbon atom and the CO2 molecule.

Structure électronique et réactivité des pyridyl-isothiocyanates. Étude quantique et photoélectronique

1986 ◽  
Vol 64 (8) ◽  
pp. 1467-1473 ◽  
Author(s):  
C. Guimon ◽  
G. Pfister-Guillouzo ◽  
D. Ilavsky ◽  
M. Marchalin ◽  
A. Martvon
Keyword(s):  
Molecular Orbital ◽  
Photoelectron Spectroscopy ◽  
Ultraviolet Photoelectron Spectroscopy ◽  
Molecular Orbital Calculations ◽  
Frontier Orbitals ◽  
Secondary Interactions ◽  
Made In ◽  
Structure Electronique

On the basis of molecular orbital calculations made in association with ultraviolet photoélectron spectroscopy (ups), it is demonstrated that the regioselectivity of the cycloadditions of pyridyl-2-isothiocyanate with 1,3-dipoles is directed by frontier orbitals. The different cycloadditions (4 + 2, 2 + 3, 2 + 2) vary with the overlap of these orbitals and this shows the importance of secondary interactions, namely the localization of the orbitals on the atoms adjacent to the bonds that are formed during the addition.

Thermolysis of trimethylsilyl esters: an ultraviolet photoelectron spectroscopy study

1988 ◽  
Vol 66 (6) ◽  
pp. 1430-1439 ◽  
Author(s):  
Nick Henry Werstiuk ◽  
Michael A. Brook ◽  
Peter Hülser
Keyword(s):  
Acetic Acid ◽  
Molecular Orbital ◽  
Photoelectron Spectroscopy ◽  
Small Extent ◽  
Starting Material ◽  
Photoelectron Spectra ◽  
Ultraviolet Photoelectron Spectroscopy ◽  
Spectroscopy Study ◽  
Primary Products ◽  
Trimethylsilyl Trifluoromethanesulfonate

The thermolytic behaviour of trimethylsilyl trifluoromethanesulfonate, 1, trimethylsilyl trifluoroacetate, 2, and trimethylsilyl acetate, 3, has been investigated by ultraviolet photoelectron spectroscopy. Acetate 3 undergoes decomposition only to a small extent at 800 °C via the mechanism shown in Scheme 1 (X = Si); only acetic acid and starting material are detected. In contrast[Formula: see text]with this result, 1 and 2 decompose completely at 725–800 °C and yield products which cannot be derived via the mechanism shown in Scheme 1. Evidence is presented to support our proposal that the thermolysis of 1 yields trimethylsilyl fluoride, 6, and difluorooxathirane dioxide, 7, as primary products. The photoelectron spectra of 1, 2, 3, 6 and trimethylsilanol, 9, are presented. Molecular orbital eigenvalues of dimethylsilene, 4, dimethylsilanone, 5 (calculated using AMPAC and Gaussian 82), 6 and 9 (AMPAC) are reported. Molecular orbital contour diagrams are given for selected MOs of 6 and 9.

The ultraviolet photoelectron spectra of C6F5X compounds, X = (F, Cl, Br, I, H, CH3)

1979 ◽  
Vol 57 (17) ◽  
pp. 2256-2259 ◽  
Author(s):  
Barry C. Trudell ◽  
S. James W. Price
Keyword(s):  
Photoelectron Spectroscopy ◽  
Photoelectron Spectra ◽  
Ultraviolet Photoelectron Spectroscopy

This work provides a study of the 1a2uπ, 2e2gσ, and 1e1gπ levels of a series of C6F5X compounds (X = F, Cl, Br, I, H, CH3) using ultraviolet photoelectron spectroscopy or more simply PES. The three levels are assigned from the PES spectra using the perfluoro effect. A correlation between the energies of these levels and the energies predicted by CNDO/2 and INDO is presented.

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