Photoelectron spectra of substituted oxiranes and thiiranes. Substituent effects on ionization potentials involving σ orbitals

1977 ◽  
Vol 55 (2) ◽  
pp. 318-332 ◽  
Author(s):  
E. J. McAlduff ◽  
K. N. Houk
Keyword(s):  
Ionization Potential ◽  
Substituent Effects ◽  
Great Sensitivity ◽  
Ionization Potentials ◽  
Photoelectron Spectra ◽  
Ethyl Vinyl ◽  
Alkyl Groups ◽  
Koopmans Theorem ◽  
Opposite Order ◽  
The Subject

The state assignments corresponding to the second and third ionization potentials of oxirane have been the subject of some uncertainty due to the great sensitivity of Koopmans' theorem predictions to the type of calculation performed for this molecule. In this study, the assignments made by Basch et al. for oxirane are confirmed through measurement of the photoelectron spectra of methyl-, 1,1-dimethyl-, 1,2-dimethyl, ethyl-, vinyl-, phenyl-, chloromethyl-, and fluoromethyloxirane. The second and third ionizations of thiirane are confirmed to be of the opposite order from those in oxirane by correlations of these values with those reported here for methyl-, vinyl, and methoxymethylthiirane.In these compounds, mono-substitution by alkyl groups causes a decrease in ionization potential not obviously related in a simple way to the type of orbital involved. Thus, assignments cannot be made straightforwardly by observing ionization potential changes caused by hyper-conjugating or inductive substituents. Alkyl group substitution in both oxirane and thiirane lowers IP's in the same order: a2 > b2 > a1 > b1. The effects of alkyl and heteroalkyl groups on the four lowest IP's of oxirane are linearly related to the electronegativities of the groups, and to the influence of alkyl and heteroalkyl substituents on the π IP of ethylene.Comparisons of the IP's of ethylheteranes and dimethylheteranes are quite useful in determining the site of localization of orbital density in the various orbitals.Conjugating substituents, which for symmetry reasons, selectively interact with only a few orbitals make definite assignments possible. Comparisons of experimental ionization potential changes and those predicted by Koopmans' theorem using ab initio STO-3G calculations are in good agreement.

Photoelectron Spectra and Molecular Properties, XLVIII Carbonates and Thiocarbonates

1975 ◽  
Vol 30 (11-12) ◽  
pp. 862-874 ◽  
Author(s):  
K. Wittel ◽  
E. E. Astrup ◽  
H. Bock ◽  
G. Graeffe ◽  
H. Juslén
Keyword(s):  
Ionization Potential ◽  
Substituent Effects ◽  
Lone Pair ◽  
Emission Spectra ◽  
Low Energy ◽  
Photoelectron Spectra ◽  
Energy Bands ◽  
Open Chain ◽  
First Ionization Potential ◽  
Cndo Calculations

Photoelectron (PE) spectra of ethylene and vinylene carbonates and thiocarbonates as well as of methylene trithiocarbonate and some open-chain derivatives are reported.The low energy bands, well separated in the unsaturated compounds, are assigned to lone pair and π type ionizations. The assignment is based on comparison of PE spectra, modified CNDO calculations, and sulfur Κβ emission spectra. The pronounced substituent effects due to which the first ionization potential varies from 8.4 eV to 11.1 eV are discussed.

Spectres photoélectroniques de cyclohexène-2 ones-1 diversement substituées en position 3. Correlations avec la réactivité

1982 ◽  
Vol 60 (10) ◽  
pp. 1163-1172 ◽  
Author(s):  
Geneviève Pfister-Guillouzo ◽  
Serge Geribaldi ◽  
Jean-François Gal
Keyword(s):  
Linear Relationship ◽  
Ionization Potential ◽  
Methylene Chloride ◽  
Substituent Effects ◽  
Lone Pair ◽  
Carbonyl Oxygen ◽  
Ionization Potentials ◽  
Aromatic Ketones ◽  
Different Types ◽  
Oxygen Lone Pair

We have recorded the photoelectronic spectra of 32 differently 3-substituted 2-cyclohexen-1-ones as well as those of 10 para-substituted acetophenones. Assignment of most of the cyclohexenone bands is made and the substituent effects on the π-electron ionization potentials and of the oxygen lone pair are discussed. The linear relationship between the ionization potential of the carbonyl oxygen lone pair and σp-type constants as well as those between the ionization potentials and the enthalpies of complexation (ΔH0) of the ketones with BF3 in methylene chloride allows us to propose that the direct conjugative interaction between the substituents and the carbonyl group is weak in the free ketone but becomes very strong in the complexed or protonated state. The existence of two distinct relationships (ΔH0 = f(PI n0) for 3-substituted cyclohexenones and the aromatic ketones indicates that this type of expression cannot be used for the comparison of the Lewis basicities of different types of ketones; on the contrary, these expressions do allow for the comparison of the relative basicities of the same type. [Journal Translation]

The photoelectron spectra of some molecules containing the C≡N group

1970 ◽  
Vol 317 (1529) ◽  
pp. 187-198 ◽  
Keyword(s):  
Cyanogen Bromide ◽  
Lone Pair ◽  
Vibrational Structure ◽  
Ionization Potentials ◽  
Photoelectron Spectra ◽  
Spin Orbit Coupling ◽  
Ethyl Vinyl ◽  
Cyanogen Chloride ◽  
Nitrogen Lone Pair ◽  
Cyanogen Iodide

The photoelectron spectra of a number of molecules containing the C≡N group have been measured over the range 6 to 21 eV. For cyanogen chloride, cyanogen bromide and cyanogen iodide, ionization potentials have been determined and assigned to particular molecular orbitals on the basis of the vibrations coupled with the ionization processes, and of the splitting due to spin-orbit coupling. Differences in these features among the three compounds have been discussed in terms of the delocalization of electrons in these molecules. From the spectra of methyl, ethyl, vinyl and allyl cyanides, potentials have been determined for ionization from the C=C π, C≡N π and nitrogen lone pair orbitals, and other higher ionization potentials have been determined but not assigned explicitly. A number of ionization potentials have been determined for mono-, di-, and tri-chloro-methyl cyanides, but absence of accompanying vibrational structure and the additional complexity caused by the levels derived from 3p electrons in the chlorine atoms make specific assignments impossible.

Correlations of substituent effects on proton and fluorine chemical shifts with inverse ionization potentials

1967 ◽  
Vol 45 (24) ◽  
pp. 3143-3151 ◽  
Author(s):  
T. Schaefer ◽  
F. Hruska ◽  
H. M. Hutton
Keyword(s):  
Electric Fields ◽  
Chemical Shifts ◽  
Substituent Effects ◽  
Group Iv ◽  
The Other ◽  
Ionization Potentials ◽  
Time Dependent ◽  
Practical Application ◽  
Methyl Proton ◽  
Proton Chemical Shifts

The fluorine and proton chemical shifts in some geminally disubstituted vinylidene fluorides and ethylenes are discussed. For these compounds, at least, there are difficulties with an interpretation based on intramolecular time-dependent electric fields. On the other hand, the shifts correlate with the inverse ionization potentials of the substituents, indicating a paramagnetic effect arising from the second term in Ramsey's expression. It is suggested that the effect operates via the bonds and not across space. Methyl proton shifts in a series of substituted methyl compounds of group IV, V, and VI elements show similar correlations. A practical application of the correlation to spectral analysis problems is given.

A Discussion on photoelectron spectroscopy - Orderings of π and σ ionization potentials in carbocyclic and heterocyclic aromatic compounds

1970 ◽  
Vol 268 (1184) ◽  
pp. 131-140 ◽  
Keyword(s):  
Photoelectron Spectroscopy ◽  
Aromatic Compounds ◽  
Lone Pair ◽  
Ionization Potentials ◽  
Photoelectron Spectra ◽  
Light Sources ◽  
Orbital Energies ◽  
Substituted Pyridines ◽  
Nitrogen Lone Pair ◽  
Electron Correlation Effects

Data on calculated orbital energies and experimentally measured ionization potentials of carbocyclic and heterocyclic aromatic compounds are compared and contrasted. The ordering or orbital energies and ionization potentials do not always seem to parallel one another, probably owing to either electron correlation effects, or to deviations from Koopman’s theorem. The effects on photoelectron spectra of using different light sources and analysers are discussed in relation to their bearing on the orbital orderings of aromatic compounds. The high resolution He 584 A. photoelectron spectrum of pyridine is shown to be open to two interpretations regarding the ordering of the ionization potentials of the π orbitals and the ‘nitrogen lone pair’ (n). One of the interpretations involves the three lowest pyridine ionization potentials being π (9.2 eV), π L (9.5 eV) and n (10.5 eV) whilst the other has the first three ionization potentials being the order π , n, π . The photoelectron spectra of substituted pyridines and diazines are discussed in the light of the two possible explanations for the pyridine spectrum.

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