A Theoretical Study of the Effects of Protonation and Deprotonation on Bond Dissociation Energies

Abstract

Ab initio molecular orbital calculations indicate that the bond dissociation energies (BDE) for homolytic cleavage of CX bonds (X = C, N, 0, F) are increased by protonation of the corresponding alkyl, amine, alcohol, or fluoride functional groups; the effect of deprotonation of these groups is rather small for saturated species, whereas for unsaturated ones deprotonation leads to large increases in the CX BDEs. The effects on the CC BDEs in CCX compounds are quite systematic: protonation of X increases the CC BDE, while the converse holds for deprotonation. Two types of correlation between bond lengths and homolytic bond dissociation energies are observed. Firstly, protonation and deprotonation lead to a normal correlation for the adjacent CC bonds: the bond length decreases as the BDE increases. Protonation, however, results in an anomalous correlation for the CX bonds: the bond length increases as the BDE increases. These observations stabilization, and competing heterolytic dissociation.

Reaction path analysis for 1-butanol dehydration in H-ZSM-5 zeolite: Ab initio and microkinetic modeling

“…The protonation of the alcohol molecule weakens the strength of the C-O bond and facilitates the heterolytic cleavage of the C-O bond. Similar results have been reported for alkyl halides (R-X), where the protonation was found to favor the heterolytic scission of the C-X bond [65]. As inferred by the elongation of the C-O bond, the protonated alcohol molecule is a more suitable candidate for the elimination and substitution reactions that follow.…”

Supramolecular Multiblock Polystyrene–Polyisobutylene Copolymers via Ionic Interactions

“…The weak, broad peak at 1070 cm −1 in Figure 2a is from the C−N stretching vibration of the primary amine end groups from the H 2 N-PIB-NH 2 sample. 54 That peak shifted to 1080 cm −1 in the blend sample due to the protonation of the primary amine by the sulfonic acid, 55 which provides additional proof of the ionic bond formation.…”

Switching radical stability by pH-induced orbital conversion

“…Radical stability is influenced by polar effects 12,13 , which, at long range, act primarily through-space rather than through-bond 14 . For example, the stability of the aminoxyl radical is affected by resonance between its two forms, I and II (Fig.…”