Departamento de Química, C-9. Universidad Autónoma de Madrid. Cantoblanco. 28049-Madrid. Spain, and Laboratoire de Chimie Théorique, UMR-CNRS-7616, Université de Paris 06, F-94000 Ivry, France.
J Chem Theory Comput. 2008 Oct 14;4(10):1593-9. doi: 10.1021/ct800178x.
The structure, bonding, and protonation of NCSeX and XNCSe (X = Me, F, Cl, Br) derivatives has been investigated at the B3LYP/6-311++G(3df,2p)//B3LYP/6-31+G(d,p) level of theory. Three different approaches, namely, ELF, AIM, and NBO indicate that three main factors are responsible for the enhanced stability of the selenocyanates with respect to the isoselenocyanates when the substituents are halogens, whereas for alkyl substituents, it is the other way around: (a) the Se-X (X = F, Cl, Br) bonds are much stronger than the Se-X (X = Me); (b) the N-X (X = F, Cl, Br) bonds are much weaker than the N-X (X = Me) ones; (c) on going from the selenocyanates to the isoselenocyanates, when the substituents are halogen atoms, there is a significant weakening of the CN bond, which becomes essentially a double bond, whereas upon methyl substitution the CN bond retains its triple bond character. The same stability trends are observed for the corresponding N-protonated species. More importantly, the calculated stability differences are rather similar to those obtained for the neutral compounds, so that selenocyanates and isoselenocyanates exhibit rather similar basicities in the gas phase. Both types of isomers behave as gas-phase nitrogen bases.
采用 B3LYP/6-311++G(3df,2p)//B3LYP/6-31+G(d,p) 理论水平研究了 NCSeX 和 XNCSe（X = Me、F、Cl、Br）衍生物的结构、键合和质子化。三种不同的方法，即 ELF、AIM 和 NBO，表明当取代基为卤素时，三种主要因素导致硒氰酸盐相对于异硒氰酸盐的稳定性增强，而对于烷基取代基，则反之：（a）Se-X（X = F、Cl、Br）键比 Se-X（X = Me）键强得多；（b）N-X（X = F、Cl、Br）键比 N-X（X = Me）键弱得多；（c）从硒氰酸盐到异硒氰酸盐，当取代基为卤素原子时，CN 键明显减弱，实质上变成双键，而当取代基为甲基时，CN 键保留其叁键特征。相应的 N-质子化物种也表现出相同的稳定性趋势。更重要的是，计算出的稳定性差异与中性化合物的稳定性差异相当相似，因此在气相中硒氰酸盐和异硒氰酸盐表现出相当相似的碱性。这两种异构体都表现为气相氮碱。
