Monosilicon‐substituted cyanoacetylene: A computational study

A detailed theoretical investigation of the [H,Si,C2,N] potential energy surfaces including 28 minimum isomers and 65 interconversion transition states is reported at the Gaussian‐3//B3LYP/6‐31G(d) level. Generally, the triplet species lie energetically higher than the singlet ones. The former three low‐lying isomers are linear HCCNSi 1 (0.00 kcal/mol), branched SiC(H)CN 12 (7.09 kcal/mol), and bent HNCCSi 7 (14.22 kcal/mol), which are separated by rather high barriers from each other and are kinetically very stable with the least conversion barriers of 32.6–70.5 kcal/mol. Two energetically high‐lying isomers HCNCSi 3 (42.99 kcal/mol) and SiC(H)NC 13 (36.05 kcal/mol) are also kinetically stable with a barrier of 49.19 and 21.42 kcal/mol, respectively. Additionally, five high‐lying isomers, that is, three chainlike isomers, HCCSiN 2 (55.17), HCSiNC 6 (47.80), HSiNCC 11 (78.83), and one three‐membered ring isomer HNcSiCC 19 (51.21), and one four‐membered ring isomer cSiCN(H)C 27 (50.6 kcal/mol), are predicted to each have lower conversion barriers of 12–18 kcal/mol and can be considered as meta‐stable species. All of the predicted 10 isomers could exist as stable or meta‐stable intermediates under suitable conditions. Finally, the structural and bonding analysis indicate that the [H,Si,C2,N] molecule contains various properties that are of chemical interest (e.g., silylene, SiC triple bonding, and conjugate SiN triple bonding and CC triple bonding, charge–transfer specie, planar aromatic specie, cumulate double bonding). This is the first detailed theoretical study on the potential energy surfaces of the series of hydrogenated Si,C,C,N‐containing molecules. The knowledge of the present monohydrogenated SiC2N isomerism could provide useful information for more highly hydrogenated or larger Si,C2,N‐containing species. © 2006 Wiley Periodicals, Inc. J Comput Chem 27: 578–595, 2006

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