Comments on ‘‘Shape-selective diisopropylation of naphthalene in H-mordenite: Myth or reality?’’

Recently, the reaction system of isopropylation of naphthalene over USY and H-mordenite zeolites was comprehensively treated experimentally as well as computationally by Buijs et al. [1]. Results from both sources were used to discard shape selectivity as an explanation for the observed product distribution. In this contribution, it is shown that their computational argument cannot be used for this purpose, since after the improvement of their orthogonal projection method, it gives very similar results to those criticised in their paper. 2011 Elsevier Inc. All rights reserved. In a very recent paper, Buijs et al. [1] set out to clear up the chemical events occurring during the isopropylation of naphthalene in USY and H-mordenite. The reaction chosen for experimental and computational scrutiny is an important one, since 2,6diisopropylnaphthalene can be an important intermediate in the way of producing 2,6-naphthalene dicarboxylic acid. The experimental treatment of this complex reaction system stirred much controversy in recent years, especially because of the ambiguity in the analysis of the reacting mixture [2]. A continuous improvement in the analytical method changed or at least modified the interpretation of the experimental findings [3]. In the paper, being commented the analytical technique was superb; thus, no one has any reason to doubt the validity of the experimental results obtained. Furthermore, the whole experimental work, not just the analytical part, is quite comprehensive and very convincing. Obviously, the results provide more than adequate ammunition for meaningful and detailed rationalisation of the entire reaction system. However, the computational part of the paper is a somewhat different matter. The authors have chosen the B3LYP/6-31G method for the full geometry optimisation of the possible diisopropylnaphthalene (DIPN) isomers and calculated the isomer composition at thermodynamic equilibrium at 200 C. They have related these results to their experimental findings and to the calculated composition based on fully optimised geometric data comll rights reserved. nkó). puted at MP2(full)/6-31G level at 25 C published in one of our earlier papers [4]. They claimed that contrary to our results (we have stated that 2,6-DIPN is smaller than 2,7-DIPN; thus, it fits better to the main channel of H-Mordenite), the dimensions of 2,6-DIPN were equal to those of 2,7-DIPN. Since a complete set of geometric data on the isomers is not published in the commented work (only those of 2,6-DIPN and, of course, those of 2,7-DIPN being equal with those of 2,6-DIPN are communicated), after the appearance of the manuscript in the ScienceDirect database, we have asked the authors about the geometries of the isomers and the method of obtaining molecular dimensions. They were kind enough to provide with the geometries as well as the way of obtaining the dimensions. The latter was as follows: after geometry optimisation (and checking whether it was a minimum or not), the molecule was orthogonally projected, and dimensions and the cross-section dimensions were measured with a ruler. The geometries received from the authors allowed us to crosscheck our results. We have found that applying our method [4] for determining molecular dimensions for the most stable conformers (3D grids consisting of 400 400 400 points were taken around each molecule, the electron density was calculated, and for each conformer, a sequence of molecular shapes and dimensions was generated using a set of cut-off values {0.0005, 0.001, 0.002, 0.003, 0.004, 0.005}), but using the B3LYP/6-31G method for electron density calculations, gave nearly identical results to our previously published data (compare MP2 and B3LYP data in Table 1). The minor differences experienced for 1,2 and 1,4 isomers may be accounted for easily. For these molecules, the most stable con-