Charge Distributions and Chemical Effects. IX. On the Charge Dependence of C-13 Chemical Shifts in Alkylcyclohexanes and Cyclopropane

1975 ◽  
Vol 53 (16) ◽  
pp. 2400-2405 ◽  
Author(s):  
Réal Roberge ◽  
Sándor Fliszár
Keyword(s):  
Ab Initio ◽  
Chemical Shifts ◽  
Significant Extent ◽  
Charge Distributions ◽  
Chemical Effects ◽  
Charge Dependence ◽  
Net Charges ◽  
The Relationship

The analysis of ab initio charge distributions in cyclohexane and selected methylcyclohexanes indicates that no effect other than that described by the relationship δC = −237.1 qC + 242.64 between C-13 chemical shifts and C net charges (as determined for the alkanes) contributes to any significant extent to the shielding of the carbon atoms. This is no longer true for cyclopropane.

Charge Distributions and Chemical Effects. VIII. Ionization Potentials of Normal and Branched Alkanes

1974 ◽  
Vol 52 (22) ◽  
pp. 3799-3802 ◽  
Author(s):  
Hervé Henry ◽  
Sándor Fliszár
Keyword(s):  
Standard Error ◽  
Chemical Shifts ◽  
Binding Energies ◽  
Ionization Potentials ◽  
Electron Population ◽  
Charge Distributions ◽  
Chemical Effects ◽  
Branched Alkanes ◽  
Net Charges

The comparison of adiabatic ionization potentials of normal and branched alkanes with carbon net charges indicates a lowering of the i.p.'s with increasing electron population of the electron-richest pair of bonded C—C atoms in the molecules. In terms of "inductive charges", it is found that n = −4.4083, i.e., precisely the same ordering of charges previously determined from l3C n.m.r. shifts. The relative C charges can thus be calculated from 13C chemical shifts and used in the equation [Formula: see text], where [Formula: see text] one half the sum of charge on the pair of electron-richest bonded C atoms, to give i.p.'s with a standard error of 0.044 eV. The relevance of these charges with respect to carbon 1s binding energies is discussed.

Charge distributions and chemical effects. XLVII. Density matrix contribution to the charge distribution in hydrocarbons, arising from singly excited configurations in CI calculations

1992 ◽  
Vol 70 (1) ◽  
pp. 68-73 ◽  
Author(s):  
Claude Mijoule ◽  
Jean-Marie Leclercq ◽  
Michel Comeau ◽  
Sándor Fliszár ◽  
Maud Picard
Keyword(s):  
Density Matrix ◽  
Charge Density ◽  
Charge Distribution ◽  
Configuration Interaction ◽  
Mulliken Charge ◽  
Charge Distributions ◽  
Chemical Effects ◽  
Net Charges ◽  
Ci Calculations

The involvement of excited configurations in Mulliken charge analyses is examined for ethylene and acetylene, using an optimized 4-31G basis. The net charges of carbon, −346.4 × 10−3 (C2H4) and −335.3 × 10−3 e (C2H2) at the SCF level, are reduced to −269.9 × 10−3 and −271.2 × 10−3 e, respectively. Double excitations appear to contribute little to these corrections. In acetylene, three single σ → σ* type excitations are responsible for ~83% of the charge correction whereas, as expected, the role of π → π* type excitations is small. Similarly, four σ → σ* configurations account for ~76% of the correction in ethylene. These effects are particularly important in comparisons with alkanes, whose charges are relatively little affected by CI corrections. Theoretical charges obtained from CI calculations appear to converge toward their empirical counterparts in a generalization of Mulliken's scheme, which allows for an uneven partitioning of CH overlap populations. Keywords: charge density, configuration interaction.

Charge distributions and chemical effects. X. Enthalpies of formation of alkanes, a calculation from 13C nuclear magnetic resonance shifts

1976 ◽  
Vol 54 (13) ◽  
pp. 2085-2088 ◽  
Author(s):  
Hervé Henry ◽  
Sándor Fliszár ◽  
André Julg
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Linear Combination ◽  
Enthalpies Of Formation ◽  
Chemical Effects ◽  
13C Nuclear Magnetic Resonance ◽  
Net Charges ◽  
The Relationship ◽  
Two Parameter ◽  
C Nmr

An analysis of the molecular energy in terms of bond contributions indicates that the latter (εij) can be approximated by a linear combination of the changes in net charges qi and qj. From the equation ΔH(atomization) = ∑εij, and the relationship between 13C chemical nmr shifts and C net charges, it is then possible to derive a two-parameter equation, ΔHf0 = ΔHf0(C2H6) + ν(N–2) + λ∑(Ncc + 1)δeth, which enables the calculation of enthalpies of formation of alkanes CNH2N+2 from 13C nmr shifts (δeth = shift relative to ethane, Ncc = number of CC bonds formed by the C atom whose shift is δeth).

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