THE USE OF GLOBAL AND LOCAL MOLECULAR-PARAMETERS FOR THE ANALYSIS OF THE GAS-PHASE BASICITY OF AMINES
THE USE OF GLOBAL AND LOCAL MOLECULAR-PARAMETERS FOR THE ANALYSIS OF THE GAS-PHASE BASICITY OF AMINES
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DOI：
10.1021/ja00279a008
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发表时间：
1986-09-17
影响因子：
15
通讯作者：
MORTIER, WJ
中科院分区：
文献类型：
--
作者：
YANG, W;MORTIER, WJ
It is demonstrated that the variationof the gas-phase basicities of amines can be analyzed by using two parameters: one global and one local (that is, site-dependent). Two global quantities (the average “effective” electronegativity and the geometric average of the isolated-atom electronegativities) and two local quantities (the fukui function and the residual charges) are tested. A two-parameter linear model containing one global and one local quantity produces satisfactory correlations with the experimental gas-phase basicities. It is shown how to express the fukui function, which reflectsthe site reactivity in density functional theory (f {7)=[dp (r)/dN] v^), in terms of the variation of the Mulliken gross charges (<?,) of an atom in a molecule, which is accompanied with a change in the total number of electrons (N) in this molecule: ff= q¡(N+ 1)-q¡(N); f~= qt (N)-q,(N-1) and/, 0= f2 [g¡(N+ 1)-q,{N-1)].The electron density distribution is fundamental for understanding chemical reactivity and naturally leads to explaining nucleophylic and electrophylic attack on the basis of electrostatic interactions. However, the electron density by itself does not explain everything, and it was recognized that thechange in electron density under the influence of an approaching reagent is also of importance. The frontier-electron theory of chemical reactivity by Fukui1, 2 recognizes the key role of thevalence electrons in forming molecules and considers therefore the dis-tribution of the highest energy orbital electron density as being most important for electrophilic attack and the lowest energy vacant orbitals in nucleophilic substitution reactions. In reactions with radicalsboth orbitals become important. The highest oc-cupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) are in this way considered as the principal factors governing the easiness of chemical reactions and the stereoselective path.
