Ab initio and density functional studies of cooperative hydrogen bonding in calix[4]-and calix[6]arenes

Abstract

The cone conformation of 4 symmetry is shown by the Hartree-Fock method (3-21G basis) to be the predominant conformer of calix [4]arene; the compressed cone of 2 symmetry is the major conformer of calix [6] [7-9, 12, 13] and density functional [6-9, 14] methods, and only one work deals with investigation of calix [6]arenes by these methods [13]. None of these works dealing with calixarenes has reported on hydrogen bond energy calculations, although this energy is the key factor of conformational stability and conformational lability of calixarenes with free hydroxyl groups [12] and their reactivity [11].The stability of the hydrogen bond in calixarene was correlated with the reaction route involving this compound when dialkoxydihydroxycalix[4]arene was synthesized from monoalkoxytrihydroxycalix[4]arene [11] (Fig. 1). Similar alkylation and acylation reactions with intermediate phenoxide anions stabilized by the maximum number of stable hydrogen bonds were also reported for calixarenes having larger rings [11]. In his review [11] D. Rudkevich demonstrated in detail that intramolecular hydrogen bonds are as important as intermolecular hydrogen bonds for molecular void formation. Therefore further investigation of intramolecular hydrogen bonding in "guest-host" complexes (in particular, investigation of the energy parameters of hydrogen bonds) is of great importance in view of the influence of intramolecular hydrogen bonds on the route and rate of transformations involving cleavage and formation of covalent bonds and on the complexation ability of cavitands.I. I. Mechnikov Odessa National University; andrej_novikov@mail.ru, andrej_novikov@ukr.net.

Energy and Geometry of Cooperative Hydrogen Bonds in p-Substituted Calix[n]- and Thiacalix[n]arenes: A Quantum-Chemical Approach

“…The relevant values of the hydrogen bonding energy for calix[4]-and thiacalix[4]arenes are represented in Table 1S of the Supporting Information. As was shown earlier, 16,17 this effect is manifested in a decrease in the distances between oxygen atoms of hydroxyl groups, involved in the formation of hydrogen bonds, along with an increase in the chain length of these bonds (see also Tables 2S and 3S for psubstituted thiacalix[4]-and thiacalix [6]arenes of the Supporting Information). Cooperative effects in the hydrogen bond chains are due to the mutual polarization of H-bonds.…”

“…The relevant values of the hydrogen bonding energy for calix[4]- and thiacalix[4]arenes are represented in Table 1S of the Supporting Information. As was shown earlier, , this effect is manifested in a decrease in the distances between oxygen atoms of hydroxyl groups, involved in the formation of hydrogen bonds, along with an increase in the chain length of these bonds (see also Tables 2S and 3S for p -substituted thiacalix[4]- and thiacalix[6]arenes of the Supporting Information). Cooperative effects in the hydrogen bond chains are due to the mutual polarization of H-bonds. , For the quantitative estimation of the mutual effect of hydrogen bonds in compounds 17, 18, 19, 20, 22, 24, and 26 ( n = 6, R = F, Cl, Br, I, NO 2 , OCH 3 , and COCH 3 ), we applied multiple correlation between the H-bond energy values and the average values of Mulliken partial charges on oxygen atoms of the considered and neighboring H-bonds based on the calculations by the RHF/3-21G approach.…”

“…At the same time, B3LYP/6-31G predicts that the energy of the winged cone conformer (Figure 1, c) of p-methylthiacalix [6]arene (41) exceeds that of the compressed cone C 2 on 18.9 kcal/mol. According to the RHF/ 3-21G calculations, in calix [6]arene (16) and p-fluorocalix- [6]arene (17) the total energy of the winged cone conformers is, respectively, 23.1 and 23.6 kcal/mol above that of the compressed cone C 2 . Earlier, Kim and Choe 34 identified with B3LYP/ 6-31G(d,p) only two cone conformers of calix [6]arene and p-tertbutylcalix [6]arene, the compressed cone C 2 , and the winged cone C 2 .…”

“…It is known 16,17 that the number and strength of the intramolecular hydrogen bonds, as well as their capability to form chains, significantly affect the relative stability of conformers of calix- [6]arenes and thiacalix [6]arenes. As seen from Chart 2, the most stable compressed cone C 2 is capable of forming a closed chain from six intramolecular hydrogen bonds like the standard cone conformer.…”

“…Cooperative effects in the hydrogen bond chains are due to the mutual polarization of H-bonds. 16,17 For the quantitative estimation of the mutual effect of hydrogen bonds in compounds 17, 18, 19, 20, 22, 24, and 26 (n = 6, R = F, Cl, Br, I, NO 2 , OCH 3 , and COCH 3 ), we applied multiple correlation between the H-bond energy values and the average values of Mulliken partial charges on oxygen atoms of the considered and neighboring H-bonds based on the calculations by the RHF/ 3-21G approach. The obtained multiple correlation coefficient 55 The Journal of Physical Chemistry A ARTICLE is rather large and equals 0.988.…”