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How Can Rotaxanes Be Modified by Varying Functional Groups at the Axle?—A Combined Theoretical and Experimental Analysis of Thermochemistry and Electronic Effects
Author(s) -
Spickermann Christian,
Felder Thorsten,
Schalley Christoph A.,
Kirchner Barbara
Publication year - 2008
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200700479
Subject(s) - thermochemistry , chemistry , hydrogen bond , solvent , covalent bond , axle , gibbs free energy , computational chemistry , molecule , solvent effects , standard enthalpy of formation , thermodynamics , organic chemistry , physics
We present theoretically as well as experimentally determined thermochemical data of the non‐covalent interactions in different axle‐substituted pseudorotaxanes. The overall interaction energy lies in the region of 35 kJ mol −1 , independent of the substitution pattern at the axle. Because rearrangement energies of 7 and 3 kJ mol −1 are required for wheel and axle, respectively, the sum of the net interactions of individual non‐covalent bonds must exceed 10 kJ mol −1 to achieve a successful host–guest interaction. The geometrical analysis shows three hydrogen bonds, and the close inspection of the individual dipole moments as well as the individual hydrogen bonds reveals trends according to the different functional groups at the axle. The individual trends for the different hydrogen bonds almost lead to a cancellation of the substitution effects. From solvent‐effect considerations it can be predicted that the pseudorotaxane is stable in CHCl 3 and CH 2 Cl 2 , whereas it would dethread in water. Comparing experimentally and theoretically calculated Gibbs free enthalpies, we find reasonable agreement if an exchange reaction of one solvent molecule instead of the direct formation reaction is considered.