Thermal and photochemical Wallach rearrangement of azoxybenzene in zeolite cages

Acidic zeolites HY and CaY catalyse the Wallach rearrangement of azoxybenzene (I) leading mainly to the formation of para-hydroxyazobenzene (II) and ortho-hydroxyazobenzene (III). In this transformation, increasing the loading level of I results in the formation of a larger amount of para-isomer. As observed in isotropic media, photochemical Wallach rearrangement in the presence of various cation-exchanged faujasites results in the predominant formation of the ortho-isomer from the S₁ state and this rules out any appreciable heavy atom effect.     

Conformational Analyses of Glycinal and Alaninal: A Computational Study

We present computational results from detailed gas-phase conformational analyses of the -substituted aldehydes, glycinal and alaninal. A synplanar conformer of glycinal and a synperiplanar conformer of alaninal in which the C=O and C–N bonds are in an eclipsing orientation are found to be lowest in energy; the two amino hydrogen atoms in these conformers are both directed over the C–C bond, i.e., in a compact arrangement. For the Group VA analogs, H₂P–CH₂–CHO and H₂P–CH(CH₃)–CHO, skew conformers in which the C–H and C–Me groups, respectively, are in an eclipsing orientation with the C=O bond are found to be lower in energy than the syn(peri)planar conformers. The results of various self-consistent reaction-field calculations suggest that the lowest-energy conformer of glycinal in 1, 2-dichloroethane is still synperiplanar, although the orientation of the amino hydrogen atoms may be different from that in the gas phase. Similar reaction-field calculations for alaninal raise the possibility that in this solvent a skew conformer, in which the C–H bond is nearly eclipsing the C=O bond, is energetically competitive with synperiplanar conformers.     

Rearrangement of azoxybenzocrowns into chromophoric hydroxyazobenzocrowns and the use of hydroxyazobenzocrowns for the synthesis of ionophoric biscrown compounds

The Wallach rearrangement was used as a method for preparing p-hydroxyazobenzocrown ethers starting from different azoxybenzocrowns as substrates. Synthesis of a series of p-hydroxyazobenzocrowns under modified conditions and characterization of the obtained products are presented. o-Hydroxyazobenzocrowns were identified among the products of the photochemical rearrangement of azoxybenzocrowns. Novel biscrowns were synthesized from p-hydroxyazobenzocrown ethers. The synthesized host molecules, differing in the size of the macrocycles and in the substituents in the aromatic rings, have the same dioxymethylene linkers. They were used as potential sodium or potassium ionophores in classic and miniature (screen-printed) ion-selective electrodes. The properties (tautomerism, acid–base equilibrium) of newly prepared o-hydroxyazobenzocrown ethers and their p-substituted analogs were studied using spectroscopic methods and compared.     

A Computational Study of Conformers of 2-Thiaoxacyclohexane (1,2-Oxathiane)

Ab initio molecular orbital theory with the 6-31G(d), 6-31G(2d), 6-31+G(d), 6-31G(d,p), 6-31+G(d,p), and 6-311G(d,p) basis sets and the hybrid density functionals B3LYP, B3P86, and B3PW91 have been used to calculate the optimized geometries and relative energies of the chair, half-chair, sofa, twist, and boat structures of 2-thiaoxacyclohexane (1,2-oxathiane). The values of the energy difference (E, kcal/mol) between the chair and 3,6-twist structures of 1,2-oxathiane were 4.92 (HF), 4.73 (MP2), and 4.66 (DFT). The HF chair–twist energy difference (G _c–t ^o) for 1,2-oxathane was 5.16 kcal/mol. Intrinsic reaction coordinate (IRC) calculations connected a transition state (TS-A) between the chair conformation and the less stable 2,5-twist form and connected two transition states (TS-B, TS-C) between the chair conformation and the more stable 3,6-twist conformer. The DFT energy differences between the chair and TS-A, TS-B, and TS-C were 11.4, 10.8, and 12.6 kcal/mol, respectively. Hyperconjugative stereoelectronic interactions were observed in the chair (n _o and ) and 3,6-twist (n _S and n _O ) conformers of 1,2-oxathiane. The chair conformation of 1,2-oxthiane is 9.6 and 10.0 kcal/mol, respectively, less stable than the chair conformations of 3-thiaoxacyclohexane (1,3-oxathiane) and 4-thiaoxacyclohexane (1,4-oxathiane, thioxane).     

Rearrangement Reactions of Tritylcarbenes: Surprising Ring Expansion and Computational Investigation

As a rule, acetylides and sulfonyl azides do not undergo electrophilic azide transfer because 1,2,3‐triazoles are usually formed. We show now that treatment of tritylethyne with butyllithium followed by exposure to 2,4,6‐triisopropylbenzenesulfonyl azide leads to products that are easily explained through the generation of short‐lived tritylethynyl azide and its secondary product cyanotritylcarbene. Furthermore, it is demonstrated that tritylcarbenes generally do not produce triphenylethenes exclusively, as was stated in the literature. Instead, these carbenes always yielded also (diphenylmethylidene)cycloheptatrienes (heptafulvenes) as side products. This result is supported by static DFT, coupled cluster, and ab initio molecular dynamics calculations. From these investigations, the fused bicyclobutane intermediate was found to be essential for heptafulvene formation. Although the bicyclobutane is also capable of rearranging to the triphenylethene product, only the heptafulvene pathway is reasonable from the energetics. The ethene is formed straight from cyanotritylcarbene.     

Theoretical Study on the Bicyclo[4.1.0]heptatriene Rearrangement in a Molecular Container

The conversion process from bicyclo[4.1.0]heptatriene （BCT） to 1,2,4,6-cycloheptatetraene （CHTE） within a molecular container was studied with AM1 method, and single point energies for all stationary points were evaluated by B3LYP and HF methods. The conversion potential barrier for the encapsulation complex became smooth when compared with that for the rearrangement in free state. The influences of the inner phase of the molecular container on the conversion process were discussed.     

Computational Study of the Release of H2 from Ammonia Borane Dimer (BH3NH3)2 and Its Ion Pair Isomers.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.     

环丙基卡宾重排为环丁烯机理的密度泛函研究

采用 B3LYP 方法,用 6-311G(d)基组计算了环丙基卡宾重排为环丁烯的反应物、过渡态和产物的能量和振动频率,并用 IRC 计算验证了过渡态。结果表明环丙基卡宾的重排机理不同于通常碳正离子重排采用的亲核重排机理,而是一个亲电重排机理。     

Computational and Theoretical Chemistry in Structure-Reactivity Studies of Organophosphorus Compounds

Computational multivariation analysis, molecular orbital calculation as well as molecular mechanics study were used for the qualitative and quantitative evaluation of the relationship between chemical structure and reactivity of organophosphorus compounds.     

ChemInform Abstract: Azidopentazole is Probably the Lowest-Energy N8 Species - A Theoretical Study.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.     

Density Functional Study on the Mechanism of Amadori Rearrangement Reaction

The reaction mechanism of amadori rearrangement in the initial stage of Maillard reaction has been investigated by means of density functional theory calculations in the gaseous phase and aqueous solution.Cyclic ribose and glycine were taken as the model in the amadori rearrangement.Reaction mechanisms have been proposed,and possibility for the formation of different compounds has been evaluated through calculating the relative energy changes for different steps of the reaction by following the total mass balance.The calculations reveal that the amadori rearrangement initialized via the intramolecular rearrangement,transferring one proton from N(3) to O(4) atom.In the next step,the second proton is also transferred from N(3) to O(4) atom,corresponding to the cleavage of C(4)-O(4) bond and the release of one water molecule.Then another proton is transferred from N(3) to C(5) atom via TS3 with the reaction barrier of 58.3 kcal·mol-1 after tunneling the effect correction calculated at the B3LYP/6-31+G(d) level of theory,and this step is rate limiting for the whole catalytic cycle.Ultimately,the product is generated via keto-enolic tautomerization.Present calculation could provide insights into the reaction mechanism of Maillard reaction since experimental evaluation of the role of intermediates in the Maillard reaction is quite complicated.     

ChemInform Abstract: A Density Functional Study of the Various Forms of UN4O12 Containing Uranyl Nitrate

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.     

ChemInform Abstract: Polyamidoimidonitride Clusters of Zirconium. - A Molecular Orbital Study

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.     

ChemInform Abstract: A Theoretical Study of NH- 4 and PH- 4.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.     

A Combined QM/MM Molecular Dynamics Simulations Study of Nitrate Anion (NO3‐) in Aqueous Solution.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.     

Reply to the comment on MORT treatment of bond length alternation in conjugated hydrocarbons

It is shown that in treating bond distortions in the framework of the approach suggested by Nakajima, the contributions of different terms to the total energy are highly sensitive to the choice of parameters and to variations in the functional dependence of the resonance integral as a function of bond length. Hence one can not unambiguously attribute the overall effect to any particular term or terms, and sometimes one has to make a rather careful adjustment in order to avoid qualitatively erroneous results. Though the simple molecular orbital resonance theory (MORT) approach is rather naive, it correctly predicts relative bond lengths in a range of molecules with essentially no parameter adjustment. This approach is hence a rather successful first order approximation to more sophisticated models which progressively incorporate missing contributions. The variation of the resonance integral with bond length and the -bond compression energy should be in these more sophisticated models undoubtedly taken into account. However, the contribution of the charge polarisation can not be totally disregarded, especially in the case of conjugated compounds containing small rings.Theoretica Chimica Acta 65, 77–80 (1984)