Theoretical justification of empirical additivity schemes for conformational energies

Abstract

Additivity of conformational energy of saturated molecules has been studied using the perturbation theory for density matrix. Analytical expressions for both total and conformational energies have been obtained and analyzed up to the third-order members. It is shown that the conformational energy of compounds under investigation can be presented as a sum of transferable increments corresponding to the energies of separate conformational segments and their sequences. The role of end groups in determination of energies of conformational segments is revealed. The influence of substitution has been investigated. The dependence of subtle conformational effects on common structural peculiarities of Hamiltonians of saturated molecules has been concluded.

Unbranched n-Alkanes

“…This leads to the second problem: How much does each gauche conformation contribute to the total energy of a conformer? Several theoretical investigations focused on this question [2,[21][22][23] and found that the energy is essentially additive provided that the gauche conformations are sufficiently separated by trans segments. Cumulated gauche sequences deviate from additivity as local interactions can have either a stabilizing or destabilizing effect.…”

Ramanspektroskopische Untersuchung der Esterfaltung in Überschallexpansionen, Oder: Wie man bei der Suche nach der Haarnadel im Esterhaufen fünf auf einmal findet

“…Für Decan hingegen führt jede Faltung durchschnittlich zu einer Strafe von 2,5 kJ mol −1 , was gut zur allgemein bei Alkanen assoziierten Faltungsstrafe von 2 kJ mol −1 passt. [4,98] Die Stabilität der gefalteten Ester könnte dadurch erklärt werden, dass die gauche-Faltung die Bildung von stabilisierenden, intramolekularen H-Brücken zwischen dem Carbonyl-O und den H in γ-Position begünstigt.…”