Der Zweifel ist der Beginn der Wissenschaft. Wer nichts anzweifelt, prüft nichts. Wer nichts prüft, entdeckt nichts. Wer nichts entdeckt, ist blind und bleibt blind." Teilhard de Chardin (1881-1955) "Ein Mensch ohne Wissenschaft ist wie ein Soldat ohne Degen, wie ein Acker ohne Regen; er ist wie ein Wagen ohne Räder, wie ein Schreiber ohne Feder; Gott selbst mag die Eselsköpfe nicht leiden." Abraham a Santa Clara (1644-1709) "Não há nada que atrapalhe mais o desenvolvimento científico do que o

more »

... esejo de que ele aconteça rápido demais". Georg Christoph Lichtenberg (1742-1799) "O trabalho espanta três males: o vício, a pobreza e o tédio". Voltaire, François-Marie Arouet (1694-1778) "Quando o trabalho é prazer, a vida é uma grande alegria. Quando o trabalho é dever, a vida é escravidão". Máximo Gorki (1868-1936) I AGRADECIMENTOS A Deus, que me deu forças e saúde para que pudesse realizar este trabalho. Ao Prof. Dr. Sérgio E. Galembeck, pela orientação, paciência, transmissão de conhecimentos e pela participação na minha formação. Aos meus pais: Benedito Suavinho Caramori e Ana Maria Finoto Caramori, pelo apoio e compreensão. Aos meus irmãos Eliana e Ronaldo e ao meu cunhado Viana, pelos bons momentos de convivência. À minha esposa Renata, pela compreensão e pelo amor que se multiplica. e Mariana pela amizade e pelos momentos de convivência. Aos amigos Kleber T. Oliveira, Renato T. Parreira e Ricardo Vessecchi, pelas valorosas discussões. À Profa. Dra. Maria Teresa do Prado Gambardella, pela colaboração com as estruturas de raios-x dos [2.2]ciclofanos. À FAPESP pelo apoio financeiro (processo: 02/03753-5) e pela competência. Ao LCCA, pelos recursos computacionais. À Universidade pública, gratuita e de qualidade. A todas as pessoas que direta ou indiretamente contribuíram para a realização deste trabalho. IV Abstract In this work, the [2.2]cyclophanes ([2.2]paracyclophane (1), anti-[2.2]metacyclophane (2a), syn-[2.2]metacyclophane (2b) e [2.2]metaparacyclophane (3)), which are the simplest [2 n ] cyclophanes that contain two phenyl rings connected by two ethanediyl linkages, were studied computationally. 1 2a 2b 3 Cyclophanes have presented several important applications, such as auxiliary in asymmetric synthesis, catalysts that simulate enzymatic functions, presenting selectivity in relation to the substrates. They are employed either in supramolecular chemistry or in biomedical areas. Studies that apply electron spin resonance or that investigate the non-linear optical properties of [2.2]cyclophanes, indicate that these compounds present transannular interactions, which occur through direct overlap of orbitals lying in different rings, throughspace, or through overlap between orbitals from rings and bridges, through-bond. The transannular interactions have a fundamental role in cyclophane chemistry, changing the reactional behavior of these compounds, and the spectroscopic transitions. Despite the fact that the well known methods of preparation, from the simplest to the most complex cyclophanes, have been studied intensively, computational studies that intent to comprehend the correlations between tension and aromaticity, electronic structure, and the mechanism of the transannular interactions are rarely found in the literature. Therefore, the aim of this work was not only to study the transannular interactions, correlating the structural differences, tension in rings and bridges, atomic charges, aromaticity, and chemical shifts of the [2.2]cyclophanes isomers but also to extent a similar treatment to the fluorinated derivatives. In addition, the effects of substituents such as (CN, Cl, C=O, NH 2 , and NO 2 ) and the protonation on the electronic structure of [2.2]paracyclophane were also evaluated. The geometry optimizations of 1, carried out by using different methods and basis set, showed that the models MP2/6-31+G(d,p) and B3PW91/6-31+G(d,p) provide the best results in comparison with the x-ray data. Conformational searches showed that 2a and 2b are the conformers that present the same energy and the isomer 3 has two degenerated conformers. V The strain energies of the bridges followed the same tendency as the relative energies, indicating that the tension on the bridges and the repulsions between the π clouds of the aromatic rings are the key factors that determine the [2.2]cyclophane stabilities. The isodesmic reactions indicated that the rings are absorbents of tension. NICS and HOMA showed that the aromaticity of the rings is preserved despite the changes on the planarity. The NBO method confirmed that all [2.2]cyclophanes present through-bond interactions, but only 2a and 2b exhibit noteworthy through-space interactions. The AIM analysis pointed out that the transannular interactions behave as closed shell interactions (ionic or hydrogen bond), stabilizing the [2.2]cyclophanes. The main geometric changes, observed to the fluorinated derivatives, were those related with the dihedral angle of bridges. The isodesmic reactions pointed out that the tensions of bridges and the relative energies are affected by the fluorination. In addition, the fluorinated rings absorb more tension than the non-fluorinated rings. NICS and HOMA showed that the substitution by fluorine increases the aromaticity of the [2.2]cyclophanes. The NBO analysis indicated that the number of through-space interactions increase with the fluorination, but it is restrict to the derivatives of 2a and 2b. In addition, the same analysis pointed out a conjugation of the fluorine lone pairs with the π system. On the other hand, the AIM analysis suggested that the substitution do not increase the number of through-space interactions, but confirmed the conjugation of the fluorine lone pairs. The other substituents can affect the geometric parameter of 1 noticeably. The partitioned analysis of isodesmic reactions showed that the tensions in bridges and rings not only depend on the substituents employed but also on the position of substitution. NICS and HOMA pointed out that the aromaticity is bigger in the non-substituted rings of [2.2]paracyclophane derivatives than in 1. The NBO analysis showed that the substitution and protonation increase the number of through-space interactions. AIM method indicated the transannular interactions occur only to the derivate substituted by NH 2 and CN, and to the protonated specie. However, these interactions presented features of closed shell interactions with small stabilizations. The atomic charges and the chemical shifts confirmed the changes of the electronic density, observed through the AIM method. VI