NMR investigation of substituent effects on strength of π-π stacking and hydrogen bonding interactions to supports the formation of [2 + 2] photodimerization in (para-X-ba):::(bpe)||(bpe):::(para-X-ba) complexes

Abstract

We have investigated the ability of para-X-phenylboronic acid (para-X-ba) to enable reactivity of trans-1,2-bis(4-pyridyl)ethylene (bpe) to direct intermolecular [2 + 2] photodimerization via computational chemistry. Para-X-ba would support the formation of discrete four component hydrogen bonded molecular assemblies wherein π-π stacking of a pyridyl-functionalized alkene would conform to undergo [2 + 2] photodimerization.We have demonstrated by computational 1H NMR data the effect of electron-withdrawing and donating substituents in (para-X-ba):::(bpe)||(bpe):::(para-X-ba) complexes to assemble bpe into π-π stacking via –(B)O − H···N– hydrogen bonds to react to afford (para-X-ba):::tpcb:::(para-X-ba) complexes (X = NO2, CN, F, Cl, Br, C(O)CH3, OCH3, OH, NH2 and H where || and ∙∙∙ denote π-π stacking and hydrogen bonds).Also, these interactions have been investigated at M05-2X/6-311++G** level of theory in detail in terms of the energetic, geometrical parameters and electron density properties to characterize and to examine the strengthening of the interactions. There are good relationships between the NMR, AIM, energy data and Hammett constants.

Keywords

• Photodimerization
• Computational chemistry
• Hammett constants
• π-π Stacking
• Hydrogen bonding