Comparative analysis of blue‐shifted hydrogen bond versus conventional hydrogen bond in methyl radical complexes

Abstract

ABSTRACT:Methyl radical complexes H 3 C . . . HCN and H 3 C . . . HNC have been investigated at the UMP2(full)/aug-cc-pVTZ level to elucidate the nature of hydrogen bonds. To better understand the intermolecular H-bond interactions, topological analysis of electron density at bond critical points (BCP) is executed using Bader's atoms-in-molecules (AIM) theory. Natural bond orbital (NBO) analysis has also been performed to study the orbital interactions and change of hybridization. Theoretical calculations show that there is no essential difference between the blue-shift H-bond and the conventional one. In H 3 C . . . HNC complex, rehybridization is responsible for shortening of the NOH bond. The hyperconjugative interaction between the single electron of the methyl radical and NOH antibonding orbital is up to 7.0 kcal/mol, exceeding 3.0 kcal/mol, the upper limit of hyperconjugative n(Y)3*(X-H) interaction to form the blue-shifted H-bond according to Alabugin's theory.

Theoretical study of the interaction mechanism of single-electron halogen bond complexes H3C⋯Br-Y (Y = H, CN, NC, CCH, C2H3)

“…Single-electron halogen bonds are very rare and have been much less studied than single-electron hydrogen bonds such as CH 3 ⋅⋅⋅HF [11], CH 3 ⋅⋅⋅HX (X = Cl, Br) [12], CH 3 ⋅⋅⋅H 2 O [13], CH 3 ⋅⋅⋅ CH 4 [14], CH 3 ⋅⋅⋅HCN and CH 3 ⋅⋅⋅HNC [15]. The few theoretical studies of single-electron halogen bonds that have been reported to date have concentrated on the structure-activity relationships between the strength of interaction and the nature of the substituents.…”

“…However, previous studies of unusual lithium and halogen bonds, especially the latter, have been very limited [10]. Most recently, the concept of single-electron weak interactions has been introduced to characterize several special weak bonds, including single-electron hydrogen bonds [11][12][13][14][15], single-electron lithium bonds [16], single-electron sodium bond [17] and singleelectron halogen bonds [18,19].…”

A theoretical analysis of the weakly bound complexes HM ··· HXY (M=O and S; XY=CN and NC): comparison with H2M ··· HXY complexes

“…The weakly hydrogen-bonded H 3 C-HF complex has been detected in the reaction of methane with F 2 in low-temperature noble gases using spectroscopic methods [13][14][15]. The structures, frequency shifts, and interaction energies of H 3 C-HF, H 3 C-HCCH, H 3 C-HCN, H 3 C-HNC, and H 3 C-H 2 O complexes have been investigated using quantum chemical calculations [8,[16][17][18][19][20][21]. The results show that the methyl radical can participate in singleelectron hydrogen bonding, but the bonding is relatively weak.…”

A novel single‐electron sodium bond system of H3C···NaY (YH, OH, F, CCH, CN, and NC)

“…Most recently, the concept of single‐electron H bond, i.e, the interaction between the unpaired electron in the radical molecule and the proton donor, has been introduced to characterize several special hydrogen bond complexes11–20. As sodium is a congener of hydrogen, it is a logical isomorphic replacement to substitute the hydrogen with sodium in single‐electron hydrogen bond.…”