Non-covalent Interactions and Their Effects on Chemical Reactivity

Non-covalent interactions play significant role across a variety of scientific fields including molecular self-assembly and supramolecular chemistry. Over the past few decades, different types of non-covalent interactions have been investigated through experimental and computational means. Yet, many aspects of these interactions are still rather unexplored. Additionally, studies involving application of close spatial interactions to influence chemical reactivity are rare. This research not only explores certain physical aspects of non-covalent interactions but also investigates their effects on chemical reactivity of some important organic functional groups. For instance, we expand the current understandings of conventional (amide NH···F) and non-conventional OH···p hydrogen bonding interactions. An inverse correlation was observed between the strength of amide NH···F hydrogen bond and electronic density of aromatic rings in 1,8-disubstituted naphthalenes, wherein the 1H–19F coupling constants are among the largest observed so far. Crystallographic analysis of a few substituted analogues based on fused 9,10-dihydroanthracene-bicycloheptane scaffold revealed a stepwise switch of a HO···p interaction to a strong non-conventional OH···p hydrogen bond by increasing the electronic density on the aromatic ring. Additionally, we were able to isolate and crystallize an indefinitely stable ring unsubstituted aliphatic para quinone methide (p-QM) which portrayed chemical transformations contrary to the traditional QM chemistry. For example, it resisted all attempts at aromatization by reduction (both catalytic and hydride based) whereas nucleophilic addition resulted in an unanticipated rearrangement of the molecular framework to yield an overall hydrogenation reaction placing each hydrogen nine heavy atoms apart. Protonation with a strong acid resulted in a crystallizable cation stabilized by a combination of partial aromatization of the QM moiety and cation-p interactions. Most importantly, the p-QM fragment facilitated an unprecedented photochemical oxygen insertion with the earth abundant dioxygen gas into the proximate aromatic ring while remaining intact itself. Mechanistic investigation, both experimental and computational, points to the criticality of the QM fragment to this important, yet unexplored metal free oxygen insertion into a pure organic scaffold. Finally, we present the first ever X-ray crystal structure of a symmetrical organic fluoronium cation, thereby providing an ultimate existential proof of the last missing piece of the halonium ion family