Theoretical study of the hydrogen bonding interaction in the hydration of the tetrahydropyran molecule.

VALLEJOS, M.; ANGELINA, EMILIO; PERUCHENA, N. M.

Los Cocos, Cordoba, Argentina.

Conferencia; 9th Latin American Conference on Physical Organic Chemistry- CLAFCO; 2007

Latin American Society of Physical Organic Chemistry

In the present work, the distribution of the electronic charge density in the THP/H2O complex is studied within the framework of the Density Functional Theory and the Atoms in Molecules Theory. First, thirty four hydration structures obtained with AGOA program were used as the initial guess for a full geometry optimization for the THP/H2O complex (1:1) in gas phase. Six configurations corresponding to local minima were found (A-F) using the B3LYP functional hybrid and 6-31G** basis set. Two different intermolecular interactions are found, namely conventional hydrogen bonding or proper HB and improper HB. In contrast with a more traditional point of view in which a hydrogen bond O…Hw-Ow (w=water) could be assumed as the preferential interaction for the formation of this complex, it is the bifunctional HB >O...Hw-Ow...H-C, which yields the most stable conformation. Weak interactions that correspond to improper HB C-H...Ow have been verified in four configurations (A-D). A strong interaction that correspond to a proper HB Ow-Hw…OTHP, was found in only one (E). Finally, in the latter configuration (F) which shown to be the most stable, a bifuctional HB was involved where both molecules (THP and H2O) take part as hydrogen donor Ow-Hw…OTHP and hydrogen acceptor C(3,5)-Ha…Ow simultaneously. In A, B and E configurations the electronic charge transfer (ECT) in large proportion is directed to the ó∗ antibonding orbital (electron acceptor) of the X-H bond (X= C in A and B, X= O in E). In the other hand, in C and D configurations, a small portion of ECT goes to the ó∗ antibonding orbital of the C-H bond of the electron acceptor and great part is transferred to remote part of the electron acceptor. Cooperative effects between proper and improper HB are suggested to play a significant role in this stabilization of the latter complex. Attention is focused on topological parameters at the bond critical points (BCP) in all bonds involved in the formation of the complex, from Atoms in molecules (AIM) theory, in all minima obtained. The bifunctional HB is a result of significant electron density redistribution effect over whole molecules. In addition, the average atomic properties are determined on the all atoms (average electron population N(Ù), atomic net charge q(Ù), atomic energy E(Ù), atomic volume v(Ù), and first moment of the atomic charge distribution M(Ù)) and their changes are analyzed in deep form.