Remote substituent effects on bond dissociation energies of para-substituted aromatic silanes

Computational Study on N-N Homolytic Bond Dissociation Enthalpies of Hydrazine Derivatives

The hydrazine derivatives have been regarded as the important building blocks in organic chemistry for the synthesis of organic N-containing compounds. It is important to understand the structure-activity relationship of the thermodynamics of N-N bonds, in particular, their strength as measured by using the homolytic bond dissociation enthalpies (BDEs). We calculated the N-N BDEs of 13 organonitrogen compounds by eight composite high-level ab initio methods including G3, G3B3, G4, G4MP2, CBS-QB3, ROCBS-QB3, CBS-Q, and CBS-APNO. Then 25 density functional theory (DFT) methods were selected for calculating the N-N BDEs of 58 organonitrogen compounds. The M05-2X method can provide the most accurate results with the smallest root-mean-square error (RMSE) of 8.9 kJ/mol. Subsequently, the N-N BDE predictions of different hydrazine derivatives including cycloalkylhydrazines, N-heterocyclic hydrazines, arylhydrazines, and hydrazides as well as the substituent effects were investigated in detail by using the M05-2X method. In addition, the analysis including the natural bond orbital (NBO) as well as the energies of frontier orbitals were performed in order to further understand the essence of the N-N BDE change patterns.

Theoretical study on homolytic B–B cleavages of diboron(4) compounds

The B–B BDEs of diboron(4) compounds and the Pt–B and Cu–B BDEs of their corresponding complexes were investigated by SOGGA11-X method.

Computational study on C–B homolytic bond dissociation enthalpies of organoboron compounds

The theoretical study of three hybridized C–B BDEs with different substituents can provide corresponding guidance to experimental research studies.

Computational study on alkenyl/aryl C(sp2)–O homolytic cleavage of carboxylates and carbamates

The alkenyl/aryl C(sp²)–O cleavage and the substituent effect in both carboxylates/carbamates and corresponding Ni complexes were investigated in detail by wB97 method.

Theoretical study on homolytic C(sp2)–O cleavage in ethers and phenols

The C(sp²)–O BDEs and the substituent effect of ethers/phenols were investigated in detail by the wB97 method.

The alternating of substituent effect on the ¹³C NMR shifts of all bridge carbons in cinnamyl aniline derivatives

Bridge carbon (13)C NMR shifts of a wide set of substituted cinnamyl anilines p-XC(6)H(4)CHCHCHNC(6)H(4)Y-p (XNO(2), Cl, H, Me, MeO, or NMe(2); YNO(2), CN, CO(2)Et, Cl, F, H, Me, MeO or NMe(2)) had been used as a probe to study the change of substituent effect in the conjugated system. The goal of this work was to study the difference among the substituent effect on SCS of all bridge carbons, and find the alternating of substituent effect in this model compounds. In this study, it was found that the change of the inductive effect and the conjugative effect on different bridge carbons is related to the bond number (m) from the substituent to the corresponding carbon, and the adjusted parameters σ(F(rel))(∗) and σ(R(ver))(∗) can be suitable to scale the difference of the inductive effect and the conjugative effect on bridge carbons. Moreover, because of the difference of substituent effect on bridge carbons, the substituent cross-interaction item Δσ(2)(Δσ(2) = (σ(F(rel))(∗)(X) + σ(R(ver))(∗)(X) - σ(F(rel))(∗)(Y) - σ(R(ver))(∗)(Y))(2)) was not suitable simply to scale the interaction between substituents X and Y for all bridge carbons, so the Δσ(2) was recommended to be divided into two parts: Δσ(F(rel))(2) (Δσ(F(rel))(2) = σ(F(rel))(∗)(X) - σ(F(rel))(∗)(Y))(2)) and Δσ(R(ver))(2) (Δσ(R(ver))(2) = (σ(R(ver))(∗)(X) - σ(R(ver))(∗)(Y))(2)). With σ(F(rel))(∗), σ(R(ver))(∗), Δσ(F(rel))(2), Δσ(R(ver))(2), and δ(C,parent), the obtained correlation equation can be used to correlate with the 159 sorts of SCS of the different bridge carbon in cinnamyl aniline derivatives. The correlation coefficient is 0.9993, and the standard deviation is only 0.53 ppm. The multi-parameter correlation equation can be recommended to predict well the corresponding bridge carbons SCS of disubstituted cinnamyl anilines.

THEORETICAL STUDY ON OXYGEN–OXYGEN HOMOLYTIC BOND DISSOCIATION ENTHALPIES OF PEROXIDES

Seven theoretical methods (B3LYP, B3P86, X3LYP, BMK, MP2, CBS-QB3, G3B3) were employed to calculate oxygen–oxygen homolytic bond dissociation enthalpies of 13 peroxides. Comparison of the performances of these methods with the available experimental data showed that ROBMK method is suitable and economical for calculating O–O homolytic bond dissociation enthalpies of peroxides. Then ROBMK method was used to calculate O–O homolytic bond dissociation enthalpies of a series of peroxides. Meanwhile, the α-substituent effect and Hammett relationship were also discussed.

Theoretical Prediction of the Hydride Affinities of Various p- and o-Quinones in DMSO

The hydride affinities of 80 various p- and o-quinones in DMSO solution were predicted by using B3LYP/6-311++G (2df,p)//B3LYP/6-31+G* and MP2/6-311++G**//B3LYP/6-31+G* methods, combined with the PCM cluster continuum model for the first time. The results show that the hydride affinity scale of the 80 quinones in DMSO ranges from -47.4 kcal/mol for 9,10-anthraquinone to -124.5 kcal/mol for 3,4,5,6-tetracyano-1,2-quinone. Such a long scale of the hydride affinities (-47.4 to -124.5 kcal/mol) indicates that the 80 quinones can form a large and useful library of organic oxidants, which can provide various organic hydride acceptors that the hydride affinities are known for chemists to choose in organic syntheses. By examining the effect of substituent on the hydride affinities of quinones, it is found that the hydride affinities of quinones in DMSO are linearly dependent on the sum of the Hammett substituent parameters sigma: DeltaGH-(Q) approximately -16.0Sigmasigmai - 70.5 (kcal/mol) for p-quinones and DeltaGH-(Q) approximately -16.2Sigmasigmai - 81.5 (kcal/mol) for o-quinones only if the substituents have no large electrostatic inductive effect and large ortho-effect. Study of the effect of the aromatic properties of quinone on the hydride affinities showed that the larger the aromatic system of quinone is, the smaller the hydride affinity of the quinone is, and the decrease of the hydride affinities is linearly to take place with the increase of the number of benzene rings in the molecule of quinones, from which the hydride affinities of aromatic quinones with multiple benzene rings can be predicted. By comparing the hydride affinities of p-quinones and the corresponding o-quinones, it is found that the hydride affinities of o-quinones are generally larger than those of the corresponding p-quinones by ca. 11 kcal/mol. Analyzing the effect of solvent on the hydride affinities of quinones showed that the effects of solvent (DMSO) on the hydride affinities of quinones are mainly dependent on the electrostatic interaction of the charged hydroquinone anions (QH-) with solvent (DMSO). All the information disclosed in this work should provide some valuable clues to chemists to choose suitable quinones or hydroquinones as efficient hydride acceptors or donors in organic syntheses and to predict the thermodynamics of hydride exchange between quinones and hydroquinones in DMSO solution.