Benzene stacked dimer

Fig. 7 The benzene stacked dimer filled squares, total energy open squares, atom-atom Coulombic energy triangles, correct Coulombic energy. The ever increasing trend of the atom-atom energy is obviously insensitive to the choice of point charges...

Finally, in the benzene dimer (Fig. 18.4c), there is an area of non-bonded overlap located at the center of each benzene ring, resembling the isosurface for bicyclo[2,2,2]octene. There is another lower-density surface between the overlapping portions of the benzenes, where r-stacking is expected. It is important to compare this image to the ones displayed in Table 18.1. The intermolecular interaction in benzene dimer appears very clearly with NCI as a surface that highlights the benzene to benzene stacking interaction, well beyond the pair interactions found with AIM. 

Although the benzene dimer has been extensively studied as a prototype for the tt/tt interaction, its relevance to general properties of aromatic residues in proteins was questioned. The toluene dimer was instead proposed as a better prototype for the tt/tt interaction in proteins [65]. MP2 calculations show that the stacked dimers are substantially stabler than the T-shaped one [65,66] and that the antiparallel dimer is 0.9 kcal/mol stabler than the parallel dimer [66]. Recently reported CCSD(T) calculations of the toluene dimer show that the cross dimer (- 4.08 kcal/mol) is slightly stabler than the antiparallel and parallel dimers (- 3.77 and - 3.41 kcal/mol, respectively), as shown in Table 4 [10]. These stacked dimers are substantially stabler than the T-shape dimer (- 2.62 kcal/mol). Spectroscopic measurements show that the toluene dimer consists of at least two isomers [67,68). The interaction energy of the toluene dimer ( e) obtained from a CCSD(T) calculation (- 4.1 kcal/mol) is not very different from the experimental Eg value (- 3.6 kcal/mol) [69]. 

The theory had never been tested on a logical model system. Let us consider in detail one representative case, the superimposable stacking of the two benzene rings, one from each triplet diphenylcarbene molecule. These are considered to represent idealized modes of dimeric interaction of the aromatic ring parts of open-shell molecules in ordered molecular assemblies like crystals, liquid crystals and membranes. 

While the water dimer serves as the prototype system for studying hydrogen-bonding interactions, the benzene dimer serves this same purpose for tt-tt stacking. The latter may also be relevant for technological applications, but it is mainly associated with... 

Computational studies on the n-n stacking problem began with the simplest model the benzene dimer. While not the only possible configurations, the benzene dimer structures most studied are the sandwiches 77s (D f) and 77s (T>6 ), the parallel displaced 77pd, and the T-shaped configurations 77t and 77t. ... 

B3LYP and B3P86 fail to locate a face-to-face dimer of benzene, leading to the standard thought that DPT fails to appropriately treat dispersion. This would make DFT unsuitable for computing the stacked nucleic acid bases. In fact, both B3LYP/6-31+G(d,p) and X3LYP/cc-pVTZ fail to locate any stacked A-T, C-G, C-C, or U-U pairs. 

A study investigating the influence of the stacking <7- tt and tt- tt interactions on the shielding tensors has also been discussed recently. However, only the model systems of benzene and formamidine dimers were investigated. ... 

The 5.10-dihydro-5-methyl-10-ethylphenazine (MEP) complex of TCNQ has been prepared but not characterized in detail. We anticipate the MEP-TCNQ structure and physical properties to resemble MjP-TCNQ and E2P-TCNQ. The 5.10-dihydro-5.10-diethylphenazine (E2P)-TCNQ complex s structure has been determined. The E2P moeities are folded along the N-N axis, as shown in Fig. 11 for MjP-TCNQ the two benzene halves have a dihedral angle of 12.7°. The mixed stack is again dimerized. Both ethyls are bent to one side of the average phenazine plane, a configuration that reinforces the dimerization or is reinforced by the dimerization. 

R. Parthasarathi and V. Subramanian, Stacking interactions in benzene and cytosine dimers from molecular electron density perspective. Struct. Chem. 16, 243-255 (2005). 

The 1,2,4,5-tetrazine-benzene dimer has a geometry in which the rings are stacked and parallel to each other.32,33... 

---