A Study On Molecular Studies - 1517 Words

Cyclopropenyl cation (1), the smallest hydrocarbon molecule is a centro-symmetric molecule with a D_3h symmetry. It’s the simplest aromatic species demonstrating aromatic features linked to the delocalization of the two Ï€ electrons. It follows the Hà ¼ckel’s rule, (4n+2) Ï€ electron with n = 0. Aromaticity cannot directly be experimentally measured. However, various methods were performed such as computational studies from the Schleyer group^1, which address the energy, structural changes and magnetic properties of cyclic conjugated system. Computational studies were performed using the Gaussian 94 computational package with ab initio method and the complete basis set amended by Peterson and co-workers was used for calculations.^2 The†¦show more content†¦Ã£â‚¬â€"ã€â€"(CH)ã€â€"_3ã€â€"^++cyclopropane →cyclopropyl cation (1) Reaction Different substituents have different effects on the stability of 1. Effect of these substituents were studied on the relative stability of 1. Either these substituents have an electron withdrawing effect or electron donating effect on the ring. Electron withdrawing group such as trialkylsilyl groups attached directly to the carbenium ion centre have a destabilizing effect. However, tris(trimethylsilyl)cyclopropenylium hexachloroantimonate (2) could be synthesize from readily available materials as shown in figure 2 and it’s relatively stable.^4 As shown in figure 3, C-C bond lengths for the tris(trimethylsilyl)cyclopropenylium cation are not equal. The ring is significantly distorted from its ideal D_3h symmetry since one of the carbon atoms in the ring system is close to the chlorine atoms in the hexachloroantimonate. This distortion shows that it is caused by the counterion and lattice effects.^4 Using the isodesmic hydride transfer reaction, the effect of trisilyl and trismethyl substitution was calculated. Three sillyl groups stabilize 1 by 22.4 kcal/mol while three methyl groups has a larger effect and more stable than 1 by 31.4 kcal/mol. Thus, Me Si H was found as the order of the