The Bent Bonds of Cubane

Abstract

The carbon–carbon bonding in cubane is shown not to be along the C–C vectors between carbon atoms at the corners of a cube. Instead, the bonding is “bent” as seen in a new single‐crystal X‐ray structure of cubane at 93 K. The bent bond angles and lengths are compared with the geometric angles and with predictions. The distortions from the tetrahedral angle of the sp3‐hybridized carbon atoms are shown to be relatively small in cubane, unlike those in cyclopropane, which are large. Despite this and other differences, cubane and cyclopropane have similar reactivity, a fact that has not been widely recognized. It is suggested that cubane might mimic the chemistry of the cyclopropane ring in the pharmacology of some cyclopropane‐containing drugs.

Not Your Usual Bioisostere: Solid State Study of 3D Interactions in Cubanes

“…As highlighted by Fleischer et al. the bent bonds of cubane scaffold allow for the acidic hydrogen atoms to be presented in several directions which are unavailable for its benzene counter‐part . However, this effect is only seen in certain cubane carboxylic acids ( 3 – 6 , 9 and 10 ).…”

“…As highlighted by Fleischer et al the bent bonds of cubane scaffold allow for the acidic hydrogen atomst ob ep resented in severald irections which are unavailable for its benzene counter-part. [15] However,t his effect is only [6,12] seen in certain cubane carboxylic acids (3-6, 9 and 10). It can be seen that the 4-substituted position to the cubanes caffold plays an important role in the formation of catemers.…”

“…In the 1,4-substituted cubane carboxamide derivatives structures shown in Figure 7( for bond lengths and angless ee Ta ble S2)a na lternate hydrogen-bonding network is observed. [6a, 7] Due to the nature of these groups (8,(13)(14)(15)a nd the strong hydrogen bondingp roperties of carboxamides, the dimer formationi sm uch more prevalent and thus, there is no formationo ft he syn/anti catemers resulting in ag reater number of interactions between the 4-position and the cubane scaffold. As shown by Kuduva et al this class of structure adopts ad imer formation combined with as hallow glide motif, which is unusual for carboxamides.…”

“…When alternate functionalities are incorporated ontot he 1positiono ft he cubane scaffold, as seen with carboxylic acids (2-5), methyl esters (19)(20)(21)(22), or primary carboxamides (15)(16)(17), the hydrogen bond donor/acceptor groups form the primary interactions in these complexes with the halogen functionality secondary in terms of directing packing. [6, 7, 16h] In the carboxylic acid group, the 4-fluorocubane (2)f orms dimers, complementary to the head-to-head dimer of the acid, through an overlap of H···F contacts resulting in as taggered hydrogen bondinghalogenb ondings ystem ( Figure S17).…”

Nonconjugated Hydrocarbons as Rigid‐Linear Motifs: Isosteres for Material Sciences and Bioorganic and Medicinal Chemistry

“…In addition, further hyperconjugation,v icinal throughb ond s CaCb !p* could be the reason for the notable stabilityo ft he cubane cation. [122] Furthermore, Eaton et al pointedo ut another consideration: the internuclearl ine between the individualc arbon bondsr epresents af alse pictureo ft he actually bent bond ("banana bond"), [123] since the endocyclic interorbital angle is rather 101-1048 than 908, [124] reducing the actual pyramidalization angle. [122] Further influences on the solvolysis rate are reported for substituted cubanes.…”