π−π-Interactions in Pentacyclo- [8.2.1.1.^2,51.^4,71^8,11]hexadeca-1,7-diene

Abstract

If two π-systems, such as two triple or two double bonds, are separated by ethano or propano bridges, a considerable difference between the energy splitting of the molecular π orbitals is encountered. This difference is apparent in comparing the photoelectron spectra of 1,5cyclooctadiyne (1) and 1,6-cyclodecadiyne (2). 1 The splitting of the ionization energies of the "in-plane" π-orbitals in these diynes was found to be 0.4 eV for 1 and 1.5 eV for 2. 1 A similar difference is expected in dienes in which the double bonds are connected by four ethano and four propano bridges. An example of the former type of diene is provided by tricyclo[4.2.2.2 2,5 ]dodecadiene-1(2),5(6) (3), 2 and pentacyclo [8.2.1.1 2,5 1. 4,7 1 8,11 ]hexadeca-1,7-diene (4a) 3 and its 4,5,10,11-tetramethyl derivative 4b 4 provided examples of the latter. To demonstrate the existence of the predicted difference in the π-orbital energies in 3 and 4, we have recorded the He(I) photoelectron (PE) spectra of 4a and 4b and compared the spectra with that of 3. 5 The PE spectrum of 4a ( Figure 1) shows two bands at 7.43 and 8.97 eV (see Table 1) which are well separated from strongly overlapping bands at higher energies. The PE spectrum of 4b looks very similar, and the first two bands appear at 7.32 and 8.79 eV.To interpret the PE spectra of 4a and 4b, we have carried out quantum chemical calculations on 4a. The geometry of 4a was optimized in D 2h symmetry at the Hartree-Fock level of theory, using the 6-31G* basis set. 6 A frequency calculation showed that the optimized D 2h geometry is a minimum on the potential energy surface for 4a. The predicted ionization energies were obtained, both from application of Koopmans's theorem 7 and by ∆SCF and ∆MP2 calculations (see Table 1). In the ∆SCF energy calculations we used the RHF method for the neutral molecule, and the UHF methology for the radical cation and its excited states. Thus, ∆MP2 uses the RMP2 method for 4a but its unrestricted version (UMP2) for the cations. All these single-point calculations were carried out at the RHF geometry of the neutral molecule 4a. The electronic structure of 4a was further investigated by partitioning the interactions between the localized π bonds into those through-space (TS) and those through-bond (TB). 8 We make use of a methodology, first suggested by Heilbronner and Schmelzer, 9 which is based on the Fock matrix in a localized basis. For a quantitative treatment we applied the procedure of Imamura et al. 10 It is based on subsequent diagonalization steps of those parts of the Fock matrix which correspond to the relevant localized orbitals. As a

Intramolecular π–π Interactions in Diethanodihydronaphthalene and Derivatives: Dynamic and Static Behavior of the Interactions Elucidated by QTAIM Dual Functional Analysis

“…The π–π interactions are extremely important, due to the indispensable role in physical, chemical, and biological sciences. Various types of the π–π interactions have been investigated structurally and energetically, so far . We have been much interested in the π–π interactions as a factor to control the fine details of structures and to create delicate properties in materials.…”

Laticyclic conjugated double bonds within the framework of oligocondensed bicyclo[2.2.2]octenes

“…Rigid molecules with two double bonds facing each other in close proximity represent the simplest laticyclic conjugated systems. Many of them are known and in, for example, isodrine, 2 seco-pagodadiene, 3 hypostrophene, 4 tricyclo-[6.2.2.2 2,5 ]dodeca-1,5-diene 5 and pentacyclo[8.2.1.1 2,5 .1 4,7 .1 8,11 ]hexadeca-1,7-diene 6 the through space interaction has been studied. We have developed a general method for the synthesis of oligocondensed bicyclo[2.2.2]octenes with all-syn configuration and here describe a series of them with up to five laticyclic conjugated etheno bridges.…”

A Benchmark Study of Electronic Couplings in Donor–Bridge–Acceptor Systems with the FMR-B Method

“…Molecules 2 (4 a,b ) are dienes connected by four propyl chains with and without additional substitutes. The couplings are similar and large (0.77 and 0.74 eV, respectively), given that the electron has multiple through-bond pathways for the transfer. Molecule 3 (3) has an interesting cage structure that allows the D/A groups to be in relatively close proximity.…”