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Strain Energies of Inorganic Rings

Benjamin M. Gìmarc ; Department of Chemistry and Biochemistry, University of South Carolina, Columbia, SC 29208, U.S.A.
D. Scott Warren ; Department of Chemistry and Biochemistry, University of South Carolina, Columbia, SC 29208, U.S.A.

Puni tekst: engleski pdf 39.448 Kb

str. 125-141

preuzimanja: 143



Strain energy, an important concept in organic chemistry, can also be applied to inorganic ring systems. Deviations of bond angles and torsional angles from preferred valence values at ring vertices implies a strained structure with increased energy. Strain energy is the energy difference between the energy change for a process as determined by experiment and as determined by a model that does not include strain. In practice, the experimental energy change can be approximated by differences in energies of products and reactants as obtained from ab initio SCF MO calculations. The bond additivity model can be used to describe the process that neglects the effects of strain. Strain energies for monocycles On and Sn, n = 3-8, will be compared with those for cycloalkanes. The surprise here is that four- membered rings of sulfur and of oxygen have greater strains than do three- membered rings. Strain energies of polycyclic clusters *4, **6> Eg, As4, and As6 are small compared to those of analogous hydrocarbons. The conventional concepts of strain energy, resonance energy, and average bond energy can be combined to rationalize differences in relative energy trends among isomeric structures of C6H6, P6 and As6. The rule of additivity of ring strain energies, useful in the estimation of polycyclic hydrocarbons, may also be applicable to polycyclic inorganic clusters. The concepts of average bond energies, resonance stabilization, and strain energy and the rules of bond additivity and ring strain energy are usefiil in understanding properties of inorganic molecules when we know how the inorganic parameters differ from the better known organic values.

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