Theoretical Insights into the Structural Differences between Organic and Inorganic Amines/Ethers

Abstract

The contrasting geometrical features between organic and inorganic counterparts of amines and oxanes are explained in terms of an offset between attractive (donor–acceptor) and repulsive (donor–donor) interactions. Natural bond orbital (NBO) calculations carried out at the density functional theory level of theory reveal that hyperconjugative effects in the organic amines and ethers are overcome by repulsive interactions occurring between the lone pair on the nitrogen/oxygen atom and the adjacent σ­(C–R) bond orbitals. Although displaying lower energies than in the corresponding organic derivatives, the LP­(X) → σ*­(E–R) (X = N, O; E = Si, Ge, Sn) interactions in heavier counterparts overcome the LP­(X)···σ­(E–R) repulsions, impacting thus their structural behavior. In addition, NBO deletion optimizations emphasize that among hyperconjugations, back-bonding effects of the LP­(X) → d­(E) type dictate to a lesser extent the anomalous structures of the inorganic amines and oxanes.

Bonding in Barium Boryloxides, Siloxides, Phenoxides and Silazides: A Comparison with the Lighter Alkaline Earths

“…Note that, in the four structures, the terminal nitrogen atoms (N t ) retain their trigonal planar bonding mode (Σ θ (N t )=360°; Table 4). This is in line with the planarity of N(SiR 3 ) 3 , [74] where hyperconjugation exists between the nitrogen lone pair and the three silyl groups. The N t planarity also allows for π donation to the Ae metal.…”

Offsets between hyperconjugations, p→d donations and Pauli repulsions impact the bonding of E–O–E systems. Case study on elements of Group 14

“…NBO S4, ESI †). Moreover, the present NBO DEL analyses reinforce previous conclusions on ethers, 51,63 S3 and S4, ESI †).…”

“…As recalled in the Introduction, special attention was paid to understand the distinctive properties of organic and inorganic counterparts, while a recent paper addressed this issue in terms of offsets between LP(O)-s*(E-R), LP(O)-d(E) and LP(O)Á Á Ás(E-H) effects. 63 These are analogous interactions that motivate the structural features of oxonium cations as well. However, the bonding picture in ethers is more complex compared to oxonium species, for the reason that in ethers such secondary interactions originate from two different LPs, and not just one as in oxonium cations.…”

“…62 Regardless of the previous efforts to explain the structural differences between C-O-C units and those of heavier analogues, the development of a unifying bonding theory has remained a challenge. 3 However, in our latest paper, 63 carried out on hydrogenated/methylated models of amines and ethers (i.e. (R 3 E) 3 N and (R 3 E) 2 O derivatives, respectively), we have suggested that not only attractions (i.e.…”

“…3,68 Therefore, given the analogy between the LP(X)Á Á Ás(EÀR) repulsions (X = O, N) occurring within ethers/amines and the LP(D)Á Á Ás(AÀH) ones, we will henceforth adopt the 'Pauli repulsion' term for the LP(X)Á Á Ás(EÀR) effects. Although the bonding patterns reported by Moraru et al have shown promising results on simplistic models such as the (R 3 E) 3 N and (R 3 E) 2 O derivatives (E = C, Si, Ge, Sn; R = H, Me), 63 further clarifications are still required. Given the complexity of more realistic systems, i.e.…”