Nonadditivity of methyl group in single‐electron hydrogen bond of methyl radical‐water complex

Abstract

ABSTRACT:The nonadditivity of methyl group in the single-electron hydrogen bond of the methyl radical-water complex has been studied with quantum chemical calculations at the UMP2/6-311ϩϩG(2df,2p) level. The bond lengths and interaction energies have been calculated in the four complexes: CH 3 OH 2 O, CH 3 CH 2 OH 2 O, (CH 3 ) 2 CHOH 2 O, and (CH 3 ) 3 COH 2 O. With regard to the radicals, tert-butyl radical forms the strongest hydrogen bond, followed by iso-propyl radical and then ethyl radical; methyl radical forms the weakest hydrogen bond. These properties exhibit an indication of nonadditivity of the methyl group in the single-electron hydrogen bond. The degree of nonadditivity of the methyl group is generally proportional to the number of methyl group in the radical. The shortening of the C⅐⅐⅐H distance and increase of the binding energy in the (CH 3 ) 2 CHOH 2 O and (CH 3 ) 3 COH 2 O complexes are less two and three times as much as those in the CH 3 CH 2 OH 2 O complex, respectively. The result suggests that the nonadditivity among methyl groups is negative. Natural bond orbital (NBO) and atom in molecules (AIM) analyses also support such conclusions.

A σ-hole interaction with radical species as electron donors: does single-electron tetrel bonding exist?

“…Hence, the hydrogen atoms in the methyl radical are substituted stepwise by 1-3 methyl groups, respectively. 11 As is expected, with the increase of the number of methyl groups in the methyl radical, the interaction energy becomes more negative. 7 with the interaction energies listed in Table 5.…”

“…The single-electron halogen bond shows a positive nonadditivity of the methyl group, 22 which is different from the negative one in the hydrogen-bonded complex CH 3 Á Á ÁH 2 O. 11 An ab initio study was performed to compare the singleelectron hydrogen, lithium, and halogen bonds by applying HBe, H 2 B, and H 3 C radicals as the electron donors, and the results showed that the interactions become stronger in order of H 3 C o HBe o H 2 B. 23 Single-electron halogen and pnicogen bonds belong to the s-hole interaction, which is an attractive interaction between the Lewis bases and the s-hole, a region of positive electrostatic potential on the outer side of the halogen and pnicogen atoms.…”

Regular/abnormal variation in the strength and nature of the halogen bond between H2Te and the dihalogens: Prominent effect of methyl substituents

“…For instance, the interaction energy is −8.7 kcal/mol in FCl‐CNH, but becomes −17.2 kcal/mol in FCl‐CNH‐CNLi, doubled by the combination of cooperativity between halogen and hydrogen bonds and Li substitution . Due to its extensive presence in biology and chemistry, attention has been given to the effect of the methyl group on the strength of non‐covalent interactions . For most hydrogen bonds, the methyl group on the electron donor is electron‐donating and that on the proton donor is electron‐withdrawing, both enhancing the strength of hydrogen bonding .…”

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.…”