The monosilacyclopropenium cation

The cyclopropenium cation (45, M = C) is a well established aromatic system with a high aromatic stabilization energy of 58.7 kcalmol [equation 18, M = C, at B3LYP/6-311++G(2d,2p)] °. What happens when one carbon atom is substituted by sihcon At HF/STO-2G the monosilacyclopropenium cation, 46, has a rather delocalized structure with r(C—C) = 1.393 A, r(C—Si) = 1.722 A and with CSiC and SiCC bond angles of 46.3° and 66.9°, respectively° . However, according to equation 19 which measures the effect of delocalization, 46 is destabilized by 11 kcalmol (HF/3-21G//HF/STO-2G) while 45, M = C is stabilized by 36 kcalmol . Unfortunately, this study used a very low computational level and should be repeated using more reliable methods. 

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