Orientational effect of aryl groups on 77Se NMR chemical shifts: experimental and theoretical investigations

The orientational effect of p-YC6H4 (Ar) on delta(Se) is elucidated for ArSeR, based on experimental and theoretical investigations. The effect is examined in the cases in which Se--CR in ArSeR is either in the Ar plane (pl) or is perpendicular to the plane (pd). 9-(Arylselanyl)anthracenes (1) and 1-(arylselanyl)anthraquionones (2) are employed to establish the effect in pl and pd, respectively. Large upfield shifts are observed for Y=NMe2, OMe, and Me, and large downfield shifts for Y=COOEt, CN, and NO2 in 1, relative to Y=H, as is expected. Large upfield shifts are brought by Y=NMe2, OMe, Me, F, Cl, and Br, and downfield shifts by Y=CN and NO2 in 2, relative to Y=H, with a negligible shift by Y=COOEt. Absolute magnetic shielding tensors of Se (sigma(Se)) are calculated for ArSeR (R=H, Me, and Ph), assuming pl and pd, based on the DFT-GIAO method. Observed characters are well explained by the total sigma(Se). Paramagnetic terms (sigmap(Se)) are governed by (sigmap(Se)xx+sigmap(Se)yy), in which the direction of np(Se) (constructed by 4pz(Se)) is set to the z axis. The main interaction in pl is the np(Se)-pi(C6H4)-pz(Y) type. The Y dependence in pl occurs through admixtures of 4pz(Se) in pi(SeC6H4Y) and pi*(SeC6H4Y), modified by the conjugation, with 4px(Se) and 4py(Se) in sigma(CSeX) and sigma*(CSeX) (X=H or C) under a magnetic field. The main interaction in pd is the sigma(CSeX)-pi(C6H4)-px(Y) type, in which Se-X is nearly on the x axis. The Y dependence in pd mainly arises from admixtures of 4pz(Se) in np(Se) with 4px(Se) and 4py(Se) in modified sigma*(CSeX), since np(Se) is filled with electrons. It is demonstrated that the effect of Y on sigmap(Se) in the pl conformation is the same regardless of whether Y is an electron-donor or electron-acceptor, whereas for pd conformations the effect is greater when Y is an electron donor, as observed in 1 and 2, respectively. Contributions of each molecular orbital and each transition on sigmap(Se) are evaluated, which enables us to recognize and visualize the effect clearly.     

Insertion of Amides into a Polyoxometalate

POM alert : The incorporation of an amide oxygen atom into the framework of the Dawson‐type polyoxometalate (POM) cluster [P₂V₃W₁₅O₆₂]^9? (see picture) allows the communication of electronic effects between the organic and the inorganic parts of the molecule, including fine‐tuning of the redox properties of the entire hybrid POM by the organic components, and transmission of the POM's electron‐attracting properties to the organic moiety.

     

Boratabenzene Anions C5B(CN)6− and C5B(CF3)6− and the Superacidic Properties of their Conjugate Acids

Designing superacids: A computational study of protonated boratabenzenes and the gas‐phase acidity of their conjugate acids is presented. Conjugate acids of boratabenzenes substituted with CN or CF₃ groups (see figure) are highly acidic species; the protonated hexacyanoboratabenzene and hexakis(trifluoromethyl)boratabenzene have computational gas‐phase acidities of 250.5 and 276.8 kcal mol^?1, respectively.

     

2,7‐Di‐tert‐butylnaphtho[1,8‐cd][1,2]dithiole 1,2‐dioxides: Thermally Stable,Photochemically Active vic‐Disulfoxides

Bulking up: The thermal barrier to rearrangement of a vic‐disulfoxide is significantly increased through steric buttressing about the (O)S? S(O) bond. Whereas the title compounds represent the most thermally stable vic‐disulfoxides known to date, they also undergo a novel photomediated epimerization at room temperature (see scheme).

     

N4H4分子取代基效应的量子化学研究

本文计算了甲基（-CH₃）,羟基（-OH）对1-丁氮烯和2-丁氮烯的取代基效应.1-丁氮烯引入取代基后.N=N双键的键长变短,而N-N单键的键长增长.异构体2-丁氮烯的键长变化较小.引入甲基或羟基后,N原子的孤对电子会与相应的N-C（N-O）键之间发生相互作用,使整个分子的超共轭作用增强.随着取代基数目的增多,总能量和生成热就会降低,取代基数目与分子能量（生成热）之间具有很好的相关性.     

Experimental study on the reaction pathway of α‐haloacetophenones with nucleophiles: direct substitution or carbonyl addition?

The reaction of PhCOCH₂Cl with OH^– gave the expected α‐substituted alcohol (PhCOCH₂OH) in addition to three dimer products. To clarify whether the substitution product is formed by direct S_N2 or via carbonyl addition, the reaction of PhCOCH₂Cl and OMe^– was examined. The reaction gave two products, PhCOCH₂OH as the major product after acid hydrolysis and PhCOCH₂OMe as the minor product. An electron‐withdrawing substituent on the phenyl ring enhanced the overall reactivity and gave more alcohol than ether. It was concluded that the alcohol was formed via carbonyl addition‐epoxidation route, whereas the ether was formed by the direct substitution route. Copyright © 2012 John Wiley & Sons, Ltd.     

Photoswitchable “Turn‐on” Fluorescence Diarylethenes: Substituent Effects on Photochemical Properties and Electrochromism

A series of “turn‐on” fluorescence diarylethenes derived from 2,3‐bis(2‐methylbenzo[b]thiophen‐3‐yl)‐5,6‐dihydro‐4H‐thieno[2,3‐b]thiopyran‐4‐one ( 1 ) with alkyl and acetyl substituents were synthesized. The photochemical and photophysical properties of these derivatives, including the photoreaction of crystalline 1 , were thoroughly investigated to reveal substituent effects on their properties. The results indicated that alkyl substituents did not significantly affect the absorption and emission spectra of the diarylethenes. However, large absorption and emission wavelength shifts were observed for the diarylethene with an acetyl substituent due to extension of π–π conjugation. Significantly, all of the fluorescent ring‐closed forms of the compounds isomerized to their ring‐open forms in the presence of Cu²⁺ in the dark. EPR results provide clear evidence for the formation of the compound 1 radical cation intermediate that might be generated in the reaction between c‐ 1 and Cu²⁺. DFT calculations found that the ground‐state activation energy for ring‐opening of 1^.+ was approximately 9.2 kcal mol^?1 lower than that of 1 without Cu²⁺, such that a Cu²⁺‐catalyzed oxidative cycloreversion reaction at room temperature might be possible.     

Single‐Point Remote Control of Flapping Motion in Clothespin‐Shaped Bimetallic Palladium Complexes Based on the N(sp2)–N(sp3) Interconversion in Amide Functionalities

The synthesis, structure, and flapping motion of clothespin‐shaped binuclear trans‐bis(salicylaldiminato)palladium(II) complexes (anti‐ 1 ) with 4‐azaheptamethylene linkers bearing amide ( a – g ), urethane ( h ), or urea ( i ) functionalities are described in this report. Various 2D ¹H NMR experiments and XRD analyses indicate that the amide‐ and urethane‐linked anti‐ 1 a , b , d – h complexes exist as equilibrated mixtures of major and minor conformers I and II in CDCl₃, whereas the complexes anti‐ 1 c and i were observed as a single species. The mapping of NOESY cross‐peaks between conformers I and II revealed that the equilibration of the major and minor conformers of anti‐ 1 a , b , d – h proceeds by two pathways, namely a nonrotatory flapping motion of the coordinated blades and a nonflapping rotation of C?N bonds, whereas the equilibration of anti‐ 1 c proceeds by simultaneous flapping and rotation motions. Kinetic studies carried out by means of ¹H–¹H EXSY experiments revealed that 1) the ΔG^≠_298K values for the flapping motion are controlled remotely by the steric and electronic effects of the RCON functionalities and 2) the activation parameters for the nonrotatory flapping process are identical to those for the nonflapping peptide rotation in the complexes anti‐ 1 a,b,d – h , which indicates that the present multistep conformational transformation induced by the flapping motion is controlled by the rate‐determining pyramidalization/depyramidalization (i.e., sp²/sp³ interconversion) of the nitrogen atoms of the functionalities. The static and controllable molecular mobility of anti‐ 1 bearing peptide linkers has been discussed by comparison with the dynamic behavior of its analogues anti‐ 2 – 4 with flexible polymethylene linkers.     

Effect of Methyl,Hydroxyl, and Chloro Substituents in Position 3 of 3′,4′,7‐Trihydroxyflavylium: Stability,Kinetics, and Thermodynamics

The effect of methyl, hydroxyl, and chloride substituents in position 3 of the 3′,4′,7‐trihydroxyflavylium core structure was studied. The stability, relative energy of each of chemical species (thermodynamics), and their rates of interconversion (kinetics) are very dependent on these substituents. By comparing the mole fraction distribution at equilibrium of the three multistate systems with the parent 3′,4′,7‐trihydroxyflavylium, introduction of a methyl substituent in position 3 increases the mole fraction of hemiketal at the expense of the trans‐chalcone and increases the hydration rate very significantly; a hydroxyl substituent in position 3 gives rise to a degradation process, as observed in anthocyanidins. In the case of 3‐chloro‐3′,4′,7‐trihydroxyflavylium, a dramatic increase of the flavylium cation acidity was observed and a photochromic system can be operated upon irradiation of the respective trans‐chalcone in 1 m HCl. According to the photochromic response of 3,3′,4′,7‐tetrahydroxyflavylium and 3′,4′,7‐trihydroxyflavylium, some requirements for a good photochromic performance are discussed.