Substituent Effects in Cation−π Interactions: A Unified View from Inductive, Resonance, and Through-Space Effects

Abstract

The quantification of inductive (I), resonance (R), and through-space (TS) effects of a variety of substituents (X) in cation-π interactions of the type C₆H₅X···Na⁺ is achieved by modeling C₆H₅-(Φ₁)(n)-X···Na⁺ (1), C₆H₅-(Φ₂)(n)-X···Na⁺ (2), C₆H₅-(Φ(2perpendicular))(n)-X···Na⁺ (2'), and C₆H₆ ···HX···Na⁺ (3), where Φ₁ = -CH₂CH₂-, Φ₂ = -CHCH-, Φ(2perpendicular) indicates that Φ₂ is perpendicular to the plane of C₆H₅, and n = 1-5. The cation-π interaction energies of 1, 2, 2', and 3, relative to X = H and fitted to polynomial equations in n have been used to extract the substituent effect E₀¹, E₀², E₀(2'), and E₀³ for n = 0, the C₆H₅X···Na⁺ systems. E₀¹ is made up of inductive (E(I)) and through-space (E(TS)) effects while the difference (E₀² - E₀(2')) is purely resonance (E(R)) and E₀³ is attributed to the TS contribution (E(TS)) of the X. The total interaction energy of C₆H₅X···Na⁺ is nearly equal to the sum of E(I), E(R), and E(TS), which brings out the unified view of cation-π interaction in terms of I, R, and TS effects. The electron-withdrawing substituents contribute largely by TS effect, whereas the electron-donating substituents contribute mainly by resonance effect to the total cation-π interaction energy.

Accurate Prediction of Cation−π Interaction Energy Using Substituent Effects

“…1,4,9,15,28−32 For instance, in the case of C 6 H 5 X···Na + systems, compared to X = H, electron-donating (ED) substituents show stronger cation−π binding whereas electron-withdrawing (EW) substituents show weaker cation−π binding. [22][23][24]33 Recently, we have shown that the total substituent effect experienced by the C 6 H 5 X···Na + system is equal to the sum of the contributions of inductive, resonance and through-space effects of X. 22 Further, in a series of studies we have shown that molecular electrostatic potential (MESP) topographical analysis provides accurate quantification of substituent effect in organic and inorganic systems.…”

Substituent Effects on Non‐Covalent Interactions with Aromatic Rings: Insights from Computational Chemistry

“…More recently, Sayyed and Suresh [75] attempted to separate induction, resonance, and through-space (field) effects of substituted arenes in cation/p interactions. In their model, the substituents are linked to the benzene ring by a variety of spacers, and interaction energies were derived using an extrapolation procedure.…”

“…In their model, the substituents are linked to the benzene ring by a variety of spacers, and interaction energies were derived using an extrapolation procedure. Sayyed and Suresh concluded [75] that in cation/p interactions, electron-withdrawing groups mainly operate via through-space effects, whereas the effects of electron donating substituents are transmitted through p resonance effects.…”

“…The preferred binding mode was found to be a triScheme 4. Model cation/p complexes of Li + and Na + with monosubstituted benzenes (left) studied by Suresh and Gadre, [73] Lewis and coworkers, [74] Wheeler and Houk, [6c] and Sayyed and Suresh, [75] as well as the Na + /dipole complex (right) studied by Lewis et al [74] Scheme 5. Substituted 1,3,5-tris(ethynyl)benzenes studied by Deyà and coworkers [76] to quantify the role of ethynyl spacer groups on the effects of substituents (X) on cation/p and anion/p interactions.…”

Theoretical vs. Experimental Ir Frequency Shifts Upon Π- Hydrogen Bonding: Complexes of Substituted Phenols With Hexamethylbenzene

“…In a number of studies from our laboratory, we have established that EPN is a remarkably accurate descriptor of the abilities of specific atomic centers in molecules to form hydrogen bonds [42][43][44][45][46][47] and also in quantifying chemical reactivity [48][49][50][51]. In later years, EPN values have been successfully employed by other authors in examining reactivity trends [52][53][54][55][56][57][58][59][60]. Politzer and Thruhlar [61] defined the electrostatic potential at nuclei Y (V Y ) by Eqn.…”