Ring Strain Energies of Three-Membered Homoatomic Inorganic Rings El₃ and Diheterotetreliranes El₂Tt (Tt = C, Si, Ge): Accurate versus Additive Approaches

Abstract

Accurate ring strain energies (RSEs) for three-membered symmetric inorganic rings El 3 and organic dihetero-monocycles El 2 C and their silicon El 2 Si and germanium El 2 Ge analogues have been computed for group 14–16 “El” heteroatoms using appropriate homodesmotic reactions and calculated at the DLPNO-CCSD-(T)/def2-TZVPP//B3LYP-D4/def2-TZVP(ecp) level. Rings containing triels and Sn/Pb heteroatoms are studied as exceptions to the RSE calculation as they either do not constitute genuine rings or cannot use the general homodesmotic reaction scheme due to uncompensated interactions. Some remarkable concepts already related to the RSE such as aromaticity or strain relaxation by increasing the s-character in the lone pair (LP) of the group 15–16 elements are analyzed extensively. An appealing alternative procedure for the rapid estimation of RSEs using additive rules, based on contributions of ring atoms or endocyclic bonds, is disclosed.

Ring Strain Energy of Diheteropnictogeniranes El2Pn (Pn=N, P, As, Sb)– Accurate versus Additive Approaches

“…Homodesmotic reactions offer a powerful framework for precisely assessing thermochemical properties in both saturated [5,7] and unsaturated [6] cyclic 3‐, 4‐, 5‐, or 6‐membered rings, such as the accurate quantification of ring strain, stability, and reactivity trends, by systematically altering the ring size or formal conversion into acyclic derivatives while maintaining structural integrity. For instance, the significance of homodesmotic reactions in elucidating the intricate interplay of ring size and thermochemical properties was underscored, providing valuable insights for chemical design and prediction [22] .…”

“…The already reported fifty-eight different bond strain contributions B, for thirteen ElÀ El and forty-five additional ElÀ Tt (Tt = C, Si, Ge) bonds allowed the additive estimation of RSE for 388 of these 3MRs, which represents 40.0 % of the total amount, with a rather good Root Mean Square Error, RMSE = 1.168 kcal/mol. [32] The natural extension of this study would be to address PnEl 2 -type rings (Pn = N, P, As, Sb) in such a way that the method could be expanded to include the contribution of ElÀ Pn bonds to the additively estimated RSE (RSE B add ). Excluding In, Th and Pb, as mentioned beforehand, and taking into account the previously used rings [32] plus the new fifty-seven rings reported herein, a first approximation would use a set of 136 equations (1) with seventeen unknowns (A 1 ) corresponding to the number of atoms.…”

“…[32] The natural extension of this study would be to address PnEl 2 -type rings (Pn = N, P, As, Sb) in such a way that the method could be expanded to include the contribution of ElÀ Pn bonds to the additively estimated RSE (RSE B add ). Excluding In, Th and Pb, as mentioned beforehand, and taking into account the previously used rings [32] plus the new fifty-seven rings reported herein, a first approximation would use a set of 136 equations (1) with seventeen unknowns (A 1 ) corresponding to the number of atoms.…”

“…In this regard, RSE data with high reliability and accuracy have been recently reported, for a large set of rings including the most important three‐membered families of parent (unsubstituted) saturated [5] ( I ) and unsaturated [6] ( II ) heterocycles, where X is a group 13–16 element (“El”) with its typical covalency completed with H‐bonds (X=ElH n ), together with a comprehensive analysis of the main factors affecting strain (Figure 1). The study was also extended to rings with three ( III ) or two or identical heteroatoms ( IVa ) as well as the heavier tetreliranes ( IVb,c ,) [7] …”

“…The study was also extended to rings with three (III) or two or identical heteroatoms (IVa) as well as the heavier tetreliranes (IVb,c,). [7] In addition, a new fast RSE estimation method, based on the additivity of endocyclic bond contributions B El-El' , was proposed, thus providing an attractive and efficient alternative approach (called RSE add ) to the higher-quality (but more tedious) RSE calculation by evaluating homodesmotic reactions. [7] This method can currently be applied to any saturated threemembered ring (3MR) containing only ElÀ El and ElÀ Tt bonds (Tt = C, Si, Ge).…”