The conjugation and effective charges of the atoms at the triple bond in germylacetylenes

Egorochkin, A. N.; Skobeleva, S. E.; Mushtina, T. G.; Bogoradovsky, E.T.

doi:10.1007/bf02495603

Cited by 5 publications

(13 citation statements)

References 11 publications

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“…The experimental (E b ) and calculated (E´b) carbon 1s binding energies for all compounds of the series I-XVIII obey the three parameter equation of type (11). Two pa rameter equations (9) have poorer statistical characteris tics.…”

Section: Resultsmentioning

confidence: 99%

“…The Ind contribution varies from 37 to 83%, and only for series XIV, it is close in magnitude to the Res contribution (see Table 11). The coefficients b of all three parameter equations of type (11) are posi tive (see Table 10). This means that enhancement of the acceptor inductive -I effect (donor +I effect) of the substituent X causes the C1s energy to increase (decrease).…”

Section: Resultsmentioning

confidence: 99%

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Carbon 1s binding energy and substituent effects in C-centered radical cations

et al. 2009

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The carbon 1s binding energies (E b ) measured by X ray photoelectron spectroscopy or obtained from quantum chemical calculations for 18 series of compounds in which the reaction center is the C atom are analyzed. It was established for the first time that E b values in carbon centered radical cations depend on the inductive, resonance, and polarizability effects of sub stituents.Key words: carbon 1s binding energy, inductive effect, conjugation, polarizability effect of substituents.The photoelectron and X ray electron spectroscopies (PES and XES, respectively) are widely used to study the ionization energies E of the electronic levels of molecules (see, for example, Refs 1-10). The gas phase PES and XES are based on the reaction ,where R C BX is a neutral molecule, R C •+ BX is a radical cation, X is substituent, and е -is an electron.The ionization energy E is equal to the total energy difference between the radical cation and the moleculeWithout loss of generality, we consider that the R C BX molecules form reaction series. Each series contains an invariable reaction center R C , the bridge В, and variable substituents X (in the R C X series, there is no bridge be tween R C and X). Detachment of an electron by reaction (1) occurs only from R C . Therefore, the formation of R C •+ BX or R C •+ X radical cations does not involve direct photoionization of orbitals of the substituents X.Photoelectron spectroscopy is used to determine the energy E (ionization potentials I) of valence electrons. The radical cation R C •+ BX is formed upon detachment of an outer (valence) electron from R C under the action of photoelectrons hν with energy of about tens of electron

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Carbon 1s binding energy and substituent effects in C-centered radical cations

et al. 2009

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“…Until recently, + R values for organometallic substituents (which are arbitrarily referred to as primary) were known only for phenyl and benzyl derivatives (D = Ph, Table 1) which were extensively studied by chemical and spectral methods [1,2]. The corresponding values for other D became accessible only as a result of our studies [3][4][5][6][7][8][9] ( Table 1). Let us consider general relations holding in variation of + R for MMe 3 and CH 2 MMe 3 , depending on the nature of M and D.…”

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“…We are now capable of studying donor resonance effect in derivatives with D other than Ph. This is favored by accumulation of data (though poorly analyzed) on resonance effects in radical cations Me 3 MD + · and Me 3 MCH 2 D + · [3][4][5][6][7][8][9] having a large positive charge on various D centers. We anticipated that study of such radical cations will make it possible to analyze donor effects of , and ,n conjugation (which are the main factor responsible for nongeneral character of resonance parameters of organometallic substituents) provided that acceptor effects of d, and d,n conjugation (in Me 3 SnD + · ) or *, and *,n conjugation (in Me 3 MCH 2 D + · ) are less important.…”

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“…Conjugation in molecules like DMMe 3 and DCH 2 MMe 3 (M = Si, Ge, Sn) which possess a large positive charge on the D center (e.g., in radical cations Me 3 MD + · and Me 3 MCH 2 D + · ) is quantitatively characterized by electrophilic resonance parameters + R of MMe 3 and CH 2 MMe 3 substituents [1][2][3][4][5][6][7][8][9]. Until recently, + R values for organometallic substituents (which are arbitrarily referred to as primary) were known only for phenyl and benzyl derivatives (D = Ph, Table 1) which were extensively studied by chemical and spectral methods [1,2].…”

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Nongeneral Character of the Resonance Parameters Σ R + of Silicon-, Germanium-, and Tin-Containing Substituents in Radical Cations

Egorochkin

Кузнецова

2005

Russ J Org Chem

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The resonance parameters + R of substituents Y in radical cations YD + · [where D is a -or n-type center, and Y = MMe 3 , CH 2 MMe 3 (M = Si, Ge, Sn), C(SiMe 3 ) 3 ] depend on the nature of both Y and D. Using radical cations YD + · (Y = CH 2 SiMe 3 , SnMe 3 ) as examples, it was found that the two conjugation parameters, constants + R of substituents Y and perturbation energy calculated by the modified molecular orbital perturbation method, are linearly related to each other. The energies of donor and acceptor components of the overall resonance effect of CH 2 SiMe 3 and SnMe 3 with respect to radical cation centers D + · were estimated for the first time. The donor energy constituent in YD + · is considerably greater than in neutral DY molecules.In keeping with the modern views [1, 2], conjugation in DMMe 3 and DCH 2 MMe 3 molecules is determined by properties of both MMe 3 or CH 2 MMe 3 substituent (M = Si, Ge, Sn) and reaction center D; the latter may be an , -unsaturated or aromatic hydrocarbon radical (R ), as well as an atom (X) possessing unshared electron pairs. Therefore, the ability of substituents like MMe 3 and CH 2 MMe 3 to be involved in conjugation with D cannot be described by universal resonance parameters like R which are invariant from D. The absence of universality is closely related to the mechanism of conjugation in molecules like DMMe 3 and DCH 2 MMe 3 , which is more complex than in analogous carbon derivatives (M = C).The mechanism of conjugation is based on the concept involving dual (acceptor and donor simultaneously) resonance properties of MMe 3 substituents (M = Si, Ge, Sn) with respect to D in DMMe 3 molecules [1,2]. Acceptor resonance effect (d, or d,n conjugation) implies interaction between vacant nd orbitals of atoms M and antibonding * orbitals of the M-C bonds in MMe 3 , on the one hand, and R group (or X atom), on the other. This effect becomes weaker as the atomic number of M rises in the series Si > Ge > Sn; when M = C, acceptor resonance effect is absent. Donor resonance effect ( , or ,n conjugation) is interaction between orbitals of the M-C bond in MMe 3 and R group (or X atom), and it becomes stronger as the atomic number of M rises (C < Si < Ge < Sn); i.e., the effect is minimal for M = C.The CH 2 MMe 3 substituents in DCH 2 MMe 3 molecules act as weak acceptors and strong donors with respect to D [1]. Clearly predominating donor resonance effect of , and ,n conjugation originates from interaction between orbitals of the C-M bonds in CH 2 MMe 3 and R group (or X) [1, 2]. As with MMe 3 , the effect increases in the M series C < Si < Ge < Sn.Weak and poorly studied [1] acceptor resonance effect of CH 2 MMe 3 substituents originates from *, (or *,n) conjugation, i.e., interaction between antibonding * orbitals of the CH 2 -M bond and R (or X). It will be shown below that effects of *, and *,n conjugation in DCH 2 MMe 3 , despite their lesser importance as compared to donor , and ,n conjugation, are not negligible. Of the two opposite constituents of the overall resonance...

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