期刊
CHEMICAL SCIENCE
卷 8, 期 1, 页码 405-410出版社
ROYAL SOC CHEMISTRY
DOI: 10.1039/c6sc02727j
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资金
- Deutsche Forschungsgemeinschaft, Priority Program Dispersion [SPP 1807, Schr 597/27-1]
The structure and dynamics of enigmatic hexa(3,5-di-tert-butylphenyl) ethane was characterized via NMR spectroscopy for the first time. Our variable temperature NMR analysis demonstrates an enthalpyentropy compensation that results in a vanishingly low dissociation energy (Delta G(d)(298) = -1.60(6) kcal mol(-1)). An in silico study of increasingly larger all-meta alkyl substituted hexaphenylethane derivatives (Me, Pr-i, Bu-t, Cy, 1-Ad) reveals a non-intuitive correlation between increased dimer stability with increasing steric crowding. This stabilization originates from London dispersion as expressed through the increasing polarizability of the alkyl substituents. Substitution with conformationally flexible hydrocarbon moieties, e. g., cyclohexyl, introduces large unfavourable entropy contributions. Therefore, using rigid alkyl groups like tertbutyl or adamantyl as dispersion energy donors (DED) is essential to help stabilize extraordinary bonding situations.
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