Understanding the Reactivity of Endohedral Metallofullerenes: C78 versus Sc3N@C78

The physical factors behind the reduced Diels–Alder reactivity of the Sc₃N@C₇₈ metallofullerene as compared with free C₇₈ have been investigated in detail by means of computational tools. To this end, the reactions between 1,3‐butadiene and free C₇₈ and endohedral Sc₃N@C₇₈ have been analysed in terms of regioselectivity and reactivity by using the activation strain model of reactivity in combination with the energy decomposition analysis method. Additional factors such as the molecular orbital overlap or the aromaticity of the corresponding transition states have been also explored. Our results indicate that the lower reactivity of the metallofullerene finds its origin mainly in the less stabilizing interaction between the deformed reactants along the reaction coordinate induced by the triscandium nitride moiety.     

Beiträge zur Chemie der Pyrrolpigmente, 78. Mitt.: Die Eigenschaften desb-Nor-bilatrien-abc-b-Nor-biladien-ac-Systems

The redox coupleb-nor-biladiene-ac (2)/b-nor-bilatriene-abc (3) exhibits an oxidative half wave potential of 800 mV in acetonitrile solution. It is demonstrated that it can be used as an extremely efficient electron carrier through bulk membranes. Whereas2 is not suitable as a ligand in carrier mediated cation transport,3 is a medium suited carrier for Cu(II) or Zn(II) ions, however, it is the most efficient one found so far for transport of Hg(II) ions. A 1:1 zinc chelate of3 is isolated and characterized. it is deduced to represent a polymer consisting of about 73 monomer units.

     

《化学学报》2020年(78卷)总目录

《化学学报》 第七十八卷      

Electrolytic partial fluorination of organic compounds. Part 78: Regioselective anodic fluorination of 2-oxazolidinones

Various 2-oxazolidinones were galvanostatically electrooxidized in the presence of various fluoride salts. It was found that a fluorine atom was introduced to the α-position of the nitrogen atom of N-acyl- and N-alkoxycarbonyl-2-oxazolidinones to provide the corresponding α-fluorinated products in moderate to good yields. In the case of N-phenoxycarbonyl derivative, fluorination took place on the phenyl group selectively.     

Über die Struktur der Acrylnitril-Guanidin-Kondensate Über Heterocyclen, 78. Mitt.

Repetition of the work ofSugino andTamaka ¹ showed that acrylonitrile and guanidine react inDMF to yield not only 3,4,6,7-tetrahydro-2H-pyrimido[1,2—a]pyrimidine-2,8(1H)-diimine (1), but a mixture (F) of1 (as a main product) and 2-amino-4-imino-1,4,5,6-tetrahydropyrimidine-1-propionitrile (7) besides one or two bases not identified so far.1 and7 were isolated as picrates. For the prove of their structures,1- and7-picrate were also prepared by an unequivocal synthesis starting from iminodipropionitrile hydrochloride8 · HCl: The latter on reaction with cyanamide gave9 which cyclized to afford a mixture of1,7 and 2-amino-4-oxo-1,4,5,6-tetrahydropyrimidine-1-propionitrile (10). The picrates of1 and7 were identical with those prepared from the acrylonitrileguanidine-condensateF. This result supports the prior proposed¹ structures of pyrimidopyrimidine1 and of4,5 and6, obtained by hydrolysis of1. Nmr-, ir-and some of the mass spectra of1,4,7–10 (and their salts) are reported.

     

Monometallic cyanide cluster fullerene YCN@C78: A theoretical prediction

Stimulated by the recent experimental success in production and characterization of YCN@C_s(6)‐C₈₂, the possibility of encapsulating YCN cluster in the C₇₈ fullerene has been performed using density functional theory. Six isomers of YCN@C₇₈ are considered based on six lowest energy C₇₈^2? isomers. The results reveal that YCN@D_3h(24109)‐C₇₈ and YCN@C_2v(24107)‐C₇₈, both of which satisfy the isolated‐pentagon rule, present excellent thermodynamic stability with very small energy differences. Moreover, the large HOMO‐LUMO gaps (1.55 and 1.47 eV for YCN@D_3h(24109)‐C₇₈ and YCN@C_2v(24107)‐C₇₈, respectively) indicate their high kinetic stabilities. Significantly, in both the structures, the encapsulated YCN cluster is triangular, similar to the cases of YCN@C_s(6)‐C₈₂ and TbCN@C₂(5)‐C₈₂. In addition, electronic absorption spectra, infrared spectra, and ¹³C nuclear magnetic resonance spectra of two stable structures have also been explored to further disclose the molecular structures and properties. © 2015 Wiley Periodicals, Inc.     

Vibrational structure of endohedral fullerene Sc3N@C78 (D3h'): evidence for a strong coupling between the Sc3N cluster and C78 cage.

The vibrational structure of the endohedral cluster fullerene Sc(3)N@C(78) is studied by FTIR spectroscopy, Raman spectroscopy and DFT-based quantum chemical calculations. Remarkably good agreement between experimental and calculated spectra is achieved and a full assignment of the Sc(3)N-based vibrational modes is given. Significant differences in the vibrational structure of the endohedral cluster fullerene Sc(3)N@C(78) and the empty, charged C(78) (6-): 5 (D(3h)') are rationalized by the strong coupling between the Sc(3)N cluster and the fullerene cage. This coupling has its origin in a significant overlap of the Sc(3)N and C(78) molecular orbitals, and causes atomic-charge and bond-length redistributions compared to the neutral C(78) and the C(78) (6-) anion. An ionic model is not sufficient to describe the electronic, geometric and vibrational structure of the Sc(3)N@C(78) nitride cluster fullerene.     

Conformational studies by dynamic NMR. 78. Stereomutation of the helical enantiomers of trigonal carbon diaryl-substituted compounds: dimesitylketone, dimesitylthioketone, and dimesitylethylene.

The free energies of activation for the enantiomerization of the title compounds (Mes2C = X, Mes = 2,4,6-trimethylphenyl) were determined by dynamic NMR to be 4.6, 6.5, and 9.2 kcal mol-1 for X = O, S, and CH2, respectively. Single-crystal X-ray diffraction showed that the structure of dimesitylketone is that of a propeller (C2 symmetry) with the mesityl rings twisted by 50 degrees with respect to the plane of carbonyl. The same structure was predicted by molecular mechanics calculations, which also produced good agreement between computed and experimental barriers for a dynamic process where a disrotatory one-ring flip pathway reverses the helicity of the conformational enantiomers. Solid-state NMR spectra indicated that the enantiomerization barrier in the crystal must be much higher (at least 19 kcal mol-1) than that in solution. Contrary to the case of dimesitylketone, the calculated barrier of dimesitylethylene agrees better with the experimental value if the enantiomerization process is assumed to be a conrotatory two-ring flip pathway.     

UPLC-MS/MS测定葡萄籽提取物中78种农药残留

建立了超高效液相色谱串联质谱法(UPLC-MS/MS)检测葡萄籽提取物中78种农药残留物的分析方法。样品用乙腈振荡提取,经乙二胺-N-丙基甲硅烷(PSA)和石墨化炭(GCB)固相萃取柱串联净化,乙腈-甲苯(V/V3:1)洗脱,洗脱液浓缩至约0.5 mL后,于45℃下氮气吹干,1.0 mL乙腈定容,UPLC-MS/MS测定,外标法定量。葡萄籽提取物中,78种农药在0.001～0.2μg/mL范围内线性关系均良好;所有农药的方法定量限(LOQ)均低于17.0μg/kg;在5,25,50μg/kg的添加水平下,葡萄籽提取物中78种农药的平均回收率处于72.6%～113.5%之间,相对标准偏差不大于11%。方法适用于葡萄籽提取物中78种农药残留的快速筛查测定。     

A C78 fullerene precursor: toward the direct synthesis of higher fullerenes

A C78 fullerene related structure (of C78:1 and C78:4, the last undiscovered C78 IPR isomer) has been synthesized and investigated as a pyrolytic precursor. The pyrolysis of precursor containing all 78 carbon atoms in the required positions and 93 of the 117 C-C bonds, needed for fullerene formation, showed selectivity for C78 fullerene formation. In independent experiments it has been shown that the flash pyrolysis of C78 fullerene is not affected by Stone-Wales rearrangement and loss of C2 fragments and, thus, is very promising for the synthesis of individual isomers of higher fullerenes.