Structure and NMR spectra of cyclophanes with unsaturated bridges (cyclophenes)

Abstract

The calculated structures of several known and hypothetical cyclophanes with ethylene bridges (cyclophenes) are reported together with experimental and calculated values of their NMR parameters. Of the exchange-correlation functionals and basis sets used in this work, only the ωB97X-D/6-311++G(2d,2p) and ωB97X-D/cc-pVQZ yielded values of the C(sp3)-C(sp3) bond length close to the experimental data, although significant differences still remain. As far as the NMR parameters are concerned, except for close-lying signals, chemical shifts and coupling constants calculated at the ωB97X-D/cc-pVQZ level reproduce in most cases the experimental trends. Contrary to the calculations of geometries, an agreement between the values of the NMR parameters obtained at ωB97X-D/cc-pVQZ level and the experimental ones is the poorest compared with that of the ωB97X-D/6-311++G(2d,2p) one. Taking into account that the results of the different calculations show the same qualitative trends in most cases, we believe that they correctly describe the structure and properties of the hypothetical molecules studied here.

Structure, NMR and Electronic Spectra of [m.n]Paracyclophanes with Varying Bridges Lengths (m, n = 2–4)

“…Understandably, the C4···C10 distances of 3 , 5 and 6 are longer than 3.4 Å, unlike those of 1 , 2 and 4 . In our previous study as well as the study by Grimme et al, the dispersion-uncorrected B3LYP functional has been found to overestimate the inter-ring separation distance, as well as the C sp 3 –C sp 3 bond length of 1 , due to its over-repulsive nature. In contrast, dispersion-corrected functionals ( e. g. ωB97X-D) give results close to the experimental values. ,, Overall, the ωB97X-D functional gives somewhat shorter inter-ring distances than B3LYP, with larger differences for the molecules with the longest bridges.…”

“…Understandably, the C4•••C10 distances of 3, 5 and 6 are longer than 3.4 Å, unlike those of 1, 2 and 4. In our previous study 23 separation distance, as well as the C sp 3 −C sp 3 bond length of 1, due to its over-repulsive nature. In contrast, dispersioncorrected functionals (e. g. ωB97X-D) give results close to the experimental values.…”

“…Keeping in mind that the comparison of experimental and computed geometries is often very difficult (since the latter refer to isolated molecules in the gas phase while the former to the solid state), we note that the functionals that correctly reproduce the inter-ring separations (vide inf ra) do not necessarily give reliable values of the bridge torsional angles. For instance, our reported bond lengths and bond angles of 1 (studied together with other cyclophanes with unsaturated bridges) 23 calculated using ωB97X-D are in excellent agreement with the experimental geometry obtained by Lyssenko et al 11 The C1C13C14C7 twist angle of 1 determined using the same functional is 14.9°(Table 1) while the experimental twist angle obtained by Lyssenko et al at 100 K is 0.0°1 1 and that by Hope et al is 6.4°at room temperature. 24 However, this calculated value agrees well with the very low-temperature twist angle reported by Wolf et al, 12.83(4) o at 15 K. 29 Also Shirai et al 44 and Bachrach 7 on the basis of MP2 and ωB97X-D calculations reported values of 21.8°and 15.4°, respectively, for the C1C13C14C7 twist angle.…”

“…10,15−18 They have also been shown to have antibacterial efficacy, 19 to be inhibitors of HIV proteinase, 20 and to act as catalysts and sensors. 21,22 Until very recently, as discussed in detail in our previous studies, 23 different experimental studies of [2.2]paracyclophane 1 gave conflicting structural information, with X-ray data measured at 100 K yielding an eclipsed D 2h geometry 11 and a D 2 geometry at room temperature. 24 Also the C sp 2 C sp 3 C sp 3 C sp 2 twist angle for the D 2 symmetry has been the subject of controversy in both experimental 11,24 and theoretical studies.…”

Theoretical study of substituent effects on the geometry and strain enthalpy in [2,2]paracyclophanes

“…3.4 Å. Until very recently, as discussed in detail in previous studies (Dodziuk et al, 2012), different experimental studies of [2,2]paracyclophane gave conflicting structural information, with X-ray data measured at 100 K yielding an eclipsed D 2h geometry (Lyssenko et al, 2003) and a D 2 geometry at room temperature (Demissie et al, 2016). Also the C1-C2-C9-C10 twist angle for the D 2 symmetry has been the subject of controversy in both experimental and theoretical studies.…”