Computational investigation on the intramolecular resonance-inhibited hydrogen bonding: a new type of interaction versus the RAHB model

A Direct Proof of the Resonance‐Impaired Hydrogen Bond (RIHB) Concept

“…Among the stereoisomers, 2 is the most stable stereoisomer, followed by 4 which is less stable by 28.5 kJ mol −1 . Isomer 3 is the least stable stereoisomer and the energy difference between 3 and 4 reaches 52.8 kJ mol −1 at the M06‐2X/6‐311+G(d,p) level, compared with 54.4 kJ mol −1 at the MP2/aug‐cc‐pVTZ level by Masumian and Nowroozi . Clearly, the energy differences among 2 – 4 largely result from the different strengths of H‐bonds, as at least for 3 and 4 , flipping the H‐bond donor by 180° leads to the same open molecule (see Figure ).…”

“…With the confirmation of the RIHB concept in the ionic system 1 , we continued to study a neutral system, namely ( z )‐3‐imino‐1‐propen‐1‐ol, a tautomer of β‐aminoacrolein which has three different stereoisomers ( 2 – 4 ) with different intramolecular H‐bonds. Isomers 2 and 3 contain H‐bonds of the NH⋅⋅⋅O type while 4 has a N⋅⋅⋅HO H‐bond, but in all three isomers H‐bonds are coupled with π‐resonance . The major results are shown in Table and Figure .…”

“…[10c, 13] M06-2X densityf unctionalt heory (DFT)c alculationsw itht he basis seto f6-311 + G(d,p) were performedthroughoutt he work as results at this level of theory are comparable with MP2/6-311 + G(d,p) results. [8] All computations were performed with the GAMESS software, [14] where the BLWc ode was ported to in our laboratory.…”

“…Isomers 2 and 3 contain H-bonds of the NH···O type while 4 has aN ···HO H-bond, but in all three isomers H-bonds are coupled with p-resonance. [8,12] The major results are shown in Table 1a nd Figure 1. Amongt he stereoisomers, 2 is the most stable stereoisomer,f ollowed by 4 which is less stable by 28.5 kJ mol À1 .I somer 3 is the least stable stereoisomer andt he energy difference between 3 and 4 reaches 52.8 kJ mol À1 at the M06-2X/6-311 + G(d,p) level, compared with 54.4 kJ mol À1 at the MP2/aug-cc-pVTZ level by Masumian and Nowroozi.…”

“…In contrast, there is ap ossibility that p-resonance occurs in the opposite direction and diminishes the positive charge on the donor side (with dÀ)a nd negative chargeo nt he acceptor side (with d +), leading to the weakening of the H-bond (right in Scheme 1). This alternative scenarior ecently has been called resonance-inhibited H-bond by Masumiana nd Nowroozi, [8] or resonance-impairedH -bond (RIHB)b yG uevara-Vela et al [9] Considering the great potentials of this new phenomenon in the interpretation of molecular structures and interaction as well as rational designs of novel materials, herew ei ntend to elucidate the exact impacto fpconjugation on RIHB systemsb yc omparing the structurala nd spectralc hanges with the quenching of resonance within the very same conjugated systems. This is achieved by using the block-localized wavefunction( BLW) method, [10] which is the simplest variant of ab initio valence bond (VB) theory [11] and can self-consistently derive the wavefunction forastrictly electron-localized (usually the most stable resonance)s tate.…”