873964-27-3Relevant academic research and scientific papers
Probing the Delicate Balance between Pauli Repulsion and London Dispersion with Triphenylmethyl Derivatives
R?sel, S?ren,Becker, Jonathan,Allen, Wesley D.,Schreiner, Peter R.
supporting information, p. 14421 - 14432 (2018/10/26)
The long-known, ubiquitously present, and always attractive London dispersion (LD) interaction was probed with hexaphenylethane (HPE) derivatives. A series of all-meta hydrocarbyl [Me, iPr, tBu, Cy, Ph, 1-adamantyl (Ad)]-substituted triphenylmethyl (TPM) derivatives [TPM-H, TPM-OH, (TPM-O)2, TPM?] was synthesized en route, and several derivatives were characterized by single-crystal X-ray diffraction (SC-XRD). Multiple dimeric head-to-head SC-XRD structures feature an excellent geometric fit between the meta-substituents; this is particularly true for the sterically most demanding tBu and Ad substituents. NMR spectra of the iPr-, tBu-, and Cy-derived trityl radicals were obtained and reveal, together with EPR and UV-Vis spectroscopic data, that the effects of all-meta alkyl substitution on the electronic properties of the trityl scaffold are marginal. Therefore, we concluded that the most important factor for HPE stability arises from LD interactions. Beyond all-meta tBu-HPE we also identified the hitherto unreported all-meta Ad-HPE. An intricate mathematical analysis of the temperature-dependent dissociation constants allowed us to extract δGd298(exptl) = 0.3(5) kcal mol-1 from NMR experiments for all-meta tBu-HPE, in good agreement with previous experimental values and B3LYP-D3(BJ)/def2-TZVPP(C-PCM) computations. These computations show a stabilizing trend with substituent size in line with all-meta Ad-HPE (δGd298(exptl) = 2.1(6) kcal mol-1) being more stable than its tBu congener. That is, large, rigid, and symmetric hydrocarbon moieties act as excellent dispersion energy donors. Provided a good geometric fit, they are able to stabilize labile molecules such as HPE via strong intramolecular LD interactions, even in solution.
London Dispersion Enables the Shortest Intermolecular Hydrocarbon H···H Contact
R?sel, S?ren,Quanz, Henrik,Logemann, Christian,Becker, Jonathan,Mossou, Estelle,Ca?adillas-Delgado, Laura,Caldeweyher, Eike,Grimme, Stefan,Schreiner, Peter R.
supporting information, p. 7428 - 7431 (2017/06/14)
Neutron diffraction of tri(3,5-tert-butylphenyl)methane at 20 K reveals an intermolecular C-H···H-C distance of only 1.566(5) ?, which is the shortest reported to date. The compound crystallizes as a C3-symmetric dimer in an unusual head-to-hea
