Intramolecular London Dispersion Interaction Effects on Gas-Phase and Solid-State Structures of Diamondoid Dimers

Abstract

The covalent diamantyl (CH) and oxadiamantyl (CHO) dimers are stabilized by London dispersion attractions between the dimer moieties. Their solid-state and gas-phase structures were studied using a multitechnique approach, including single-crystal X-ray diffraction (XRD), gas-phase electron diffraction (GED), a combined GED/microwave (MW) spectroscopy study, and quantum chemical calculations. The inclusion of medium-range electron correlation as well as the London dispersion energy in density functional theory is essential to reproduce the experimental geometries. The conformational dynamics computed for CHO agree well with solution NMR data and help in the assignment of the gas-phase MW data to individual diastereomers. Both in the solid state and the gas phase the central C-C bond is of similar length for the diamantyl [XRD, 1.642(2) Å; GED, 1.630(5) Å] and the oxadiamantyl dimers [XRD, 1.643(1) Å; GED, 1.632(9) Å; GED+MW, 1.632(5) Å], despite the presence of two oxygen atoms. Out of a larger series of quantum chemical computations, the best match with the experimental reference data is achieved with the PBEh-3c, PBE0-D3, PBE0, B3PW91-D3, and M06-2X approaches. This is the first gas-phase confirmation that the markedly elongated C-C bond is an intrinsic feature of the molecule and that crystal packing effects have only a minor influence.

Flexibility at the Fringes: Conformations of the Steroid Hormone β‐Estradiol

“…It can be used to unambiguously identify the low energy conformers present in the cold environment of a supersonic jet and to determine the energy order by their intensities, as demonstrated in the present work. This study is also important to further evaluate the applicability of rotational spectroscopy to larger molecular systems . It can be expected that the estradiol conformers corresponding to different orientations of the two hydroxy groups will have only small differences in the rotational constants because of the large overall molecular mass of 272 g/mol.…”

A Rational Approach to Tetra‐Functional Photo‐Switches

“…As a characteristic for photo‐dimers and photo‐cyclomers, the new bonds formed by cycloaddition, C(3)−C(21) [1.606(1) Å] and C(10)−C(28) [1.662(2)], are very long compared to the standard C−C single bond with 1.52 Å . They are in the range of very long C−C bonds like those in diamantoid dimers and longer than the central bond in diamantyl‐diamantane [solid state, XRD: 1.647(4), gas‐phase, GED: 1.630(5) Å] …”

Exceptionally Long C−C Single Bonds in Diamino‐o‐carborane as Induced by Negative Hyperconjugation

“…However,t he measured C À Cb ond lengths in the nitrogensubstituted o-carboranes 1-4 significantly exceed this value. [14,17] This CÀCdistance is also longer than the 1,2-dithiolato-, 1,2diphosphono-, and mono-amino o-carborane derivatives (180.3 pm, [35] 172.2 pm, [36] and 185.2 pm, [21] respectively). This value exceeds that of the bis-diamondoids,and those of the dispiro(acridan)-substituted acenaphthenes.…”

“…[4] There are many exceptions to this relationship for CÀCb onds in more complex situations. Recently,F okin, Schreiner, and co-workers reported the synthesis of hydrocarbons with extremely long CÀCbonds,stabilized by attractive London dispersion forces between two large diamondoid substituents [12][13][14] (Figure 1). [6][7][8] Fore xample,u ltra-long C À C bonds have been found in tetra-substituted 3,8-dihalobuta-[b]naphthalenes prepared by Toda, Herges,a nd co-workers, with CÀCd istances ranging from 168.6 pm to 173.4 pm [9][10][11] (Figure 1).…”

“…[6][7][8] Fore xample,u ltra-long C À C bonds have been found in tetra-substituted 3,8-dihalobuta-[b]naphthalenes prepared by Toda, Herges,a nd co-workers, with CÀCd istances ranging from 168.6 pm to 173.4 pm [9][10][11] (Figure 1). Recently,F okin, Schreiner, and co-workers reported the synthesis of hydrocarbons with extremely long CÀCbonds,stabilized by attractive London dispersion forces between two large diamondoid substituents [12][13][14] (Figure 1). Ishigaki, Suzuki, and co-workers obtained aseries of dispiro-(acridan)-substituted pyracene and acenaphthenes with C À C bond lengths of up to 180.6 pm.…”