Department of Chemistry, Southern Methodist University , 3215 Daniel Avenue, Dallas, Texas 75275-0314, United States.
J Phys Chem A. 2013 Sep 12;117(36):8981-95. doi: 10.1021/jp406200w. Epub 2013 Aug 30.
Increasing the effective electronegativity of two atoms forming a triple bond can increase the strength of the latter. The strongest bonds found in chemistry involve protonated species of hydrogen cyanide, carbon monoxide, and dinitrogen. CCSD(T)/CBS (complete basis set) and G4 calculations reveal that bond dissociation energies are misleading strength descriptors. The strength of the bond is assessed via the local stretching force constants, which suggest relative bond strength orders (RBSO) between 2.9 and 3.4 for heavy atom bonding (relative to the CO bond strength in methanol (RBSO = 1) and formaldehyde (RBSO = 2)) in HCNH((1)Σ(+)), HCO((1)Σ(+)), HNN((1)Σ(+)), and HNNH((1)Σg(+)). The increase in strength is caused by protonation, which increases the electronegativity of the heavy atom and thereby decreases the energy of the bonding AB orbitals (A, B: C, N, O). A similar effect can be achieved by ionization of a nonbonding or antibonding electron in CO or NO. The strongest bond with a RBSO value of 3.38 is found for HNNH using scaled CCSD(T)/CBS frequencies determined for CCSD(T)/CBS geometries. Less strong is the NN bond in FNNH and FNNF.
形成三键的两个原子的有效电负性增加可以增强后者的强度。化学中发现的最强键涉及质子化的氢氰酸、一氧化碳和二氮物种。CCSD(T)/CBS（完全基组）和 G4 计算表明，键离解能是误导性的强度描述符。通过局部拉伸力常数评估键的强度，这表明重原子键的相对键强度顺序（RBSO）在 2.9 到 3.4 之间（相对于甲醇中的 CO 键强度（RBSO = 1）和甲醛（RBSO = 2））在 HCNH((1)Σ(+))、HCO((1)Σ(+))、HNN((1)Σ(+)) 和 HNNH((1)Σg(+))中。强度的增加是由质子化引起的，质子化增加了重原子的电负性，从而降低了键合 AB 轨道（A、B：C、N、O）的能量。CO 或 NO 中的非键或反键电子的电离也可以产生类似的效果。使用针对 CCSD(T)/CBS 几何形状确定的缩放 CCSD(T)/CBS 频率，在 HNNH中发现具有 RBSO 值 3.38 的最强键。FNNH和 FNNF中 NN 键较弱。
