Computational structure-activity relationships in H2 storage: how placement of N atoms affects release temperatures in organic liquid storage materials

DFT(B3PW91) calculations show that release of H2 is greatly favored thermodynamically in five membered rings over six and by the incorporation of N atoms into the rings, either as ring atoms or as ring substituents, particularly in 1,3 positions.     

两种杂原子复配对Y型分子筛结晶性能的影响

分子筛作为催化剂或催化剂的载体材料广泛应用于各种催化反应过程中,将杂原子引人分子筛骨架中形成杂原子分子筛,可在较大的范围内调节分子筛表面的酸性中心和氧化还原催化活性中心.     

Reaction of tert-Butylcyanoketene with 2′-Cyclohexylspiro [Fluorene-9,3′-Oxaziridine]

Although the reactions of ketenes and three-membered heterocycles containing one hetero atom are well known,^1,2 only one investigation of similar recations with three-membered rings containing two hetero atoms has been reported.³ The reaction of 2-ethyl-3-phenyloxaziridine with diphenylketene was found to afford among other minor products an oxazolidinone derivative (1) and benzaldehyde in yields of 38% and 50% respectively.     

Conformational Flexibility of Benzannelated Derivatives of Six-Membered 1,2- and 1,4-Dihydroaromatic Rings Containing No Saturated Carbon Atoms

The effect of benzannelation on the conformational flexibility of the six-membered 1,2- and 1,4-dihydroaromatic rings containing no saturated carbon atoms is studied by the ab initio HF/6-31G(d, p) method. It is shown that replacement of the C=C bond by the benzene ring leads to enhanced conformational flexibility of the ring due to weaker conjugation interactions involving the bridging carbonyl group or the heteroatom. The dihydro ring remains flexible even when included in the tetracene fragment. In all cases, the 1,2-dihydroaromatic rings are less rigid than their 1,4-dihydroanalogs.     

Nematogens incorporating a lateral flexible ring

A lateral flexible ring can be introduced on a mesogenic core containing four rings. Lateral aliphatic rings containing up to 12 atoms have been synthesized. Despite this large lateral protruding substituent, a large nematic range is obtained. A compound with a benzo15-crown-5 lateral ring has been successfully obtained and shows the possibility of designing nematic liquid crystals with a crown ether moiety at a lateral position.     

Nematogens incorporating a lateral flexible ring

A lateral flexible ring can be introduced on a mesogenic core containing four rings. Lateral aliphatic rings containing up to 12 atoms have been synthesized. Despite this large lateral protruding substituent, a large nematic range is obtained. A compound with a benzo15-crown-5 lateral ring has been successfully obtained and shows the possibility of designing nematic liquid crystals with a crown ether moiety at a lateral position.     

Zur struktur des diethylgermanium-diphenylsiliciumoxids und zur konformation von achtringen mit silicium und germanium

Diethylgermanium-diphenylsilicon oxide [(Et₂Ge)O(Ph₂Si)O]₂ has been prepared by reaction of diethylgermanium dichloride and diphenyldihydroxysilane. Spectra and X-ray analysis showed the presence of a puckered eight-membered silicon—germanium—oxygen ring. The ethyl groups of the germanium atoms are disordered. A procedure is proposed for eight-membered rings with low symmetry to obtain a classification into clearly explaining ring forms based on exact or approximated planes put through as many ring atoms as possible. All of the 42 published eight-membered rings with silicon or germanium and oxygen, nitrogen or carbon could be classified by this method.     

Zur Lokalisierung funktioneller Gruppen in Steroiden mit Hilfe der Massenspektrometrie: XIII—Massenspektren von 3,7,17-Trihydroxyandrostanen und 7,17-Dihydroxyandrostan-3-onen

Androstanes with a trans connected A/B ring system and hydroxy groups in positions 3, 7 and 17 show in their mass spectra key ions of mass 99 and 178. The ion of mass 99 contains the carbon atoms of ring D, and the ion of mass 178 those of the A/B ring system and C-11. If the rings A and B are cis connected, the ion of mass 178 is produced with much lower abundance and the ion of mass 99 is almost absent. The α or β position of a hydroxy group in position 7 can be deduced from the spectra of corresponding trimethylsilyl derivatives: a fragment of [M ? 131] dominated by presence of a 7α-trimethylsilyl ether group and trans connection of the A/B ring system. Determination of the configuration of the hydroxy group in position 3 is very difficult. Analogous fragments are observed in the spectra of the corresponding 7, 17-dihydroxyandrostan-3-ones.     

一种新型包含平面四配位碳二硼有机化合物的理论研究

采用B3LYP/6-311+G**方法, 研究了一种新型的包含平面四配位碳(ptC)二硼有机化合物C9B2H6的结构、稳定性和振动频率. 计算结果表明, C9B2H6结构的稳定性和两个硼原子的位置有很大关系, 硼原子起给予σ电子和接受π电子的作用. 在C9B2H6的15个异构体中, 最稳定的结构是具有C2v对称性的异构体(1,5), 在异构体(1,5)中, 两个硼原子位于同一个六元环中且与ptC相邻. 而且占据的π轨道说明异构体(1,5)具有10个π电子, 满足4n+2规则. 计算的核独立化学位移(NICS)值显示异构体(1,5)强的芳香性位于C9B2H6的两个三元环而不是两个六元环上.     

Total Synthesis of Potent Antitumor Agent (−)‐Lasonolide A: A Cycloaddition‐Based Strategy

A detailed account of the enantioselective total synthesis of (?)‐lasonolide A is described. Our initial synthetic route to the top tetrahydropyran ring involved Evans asymmetric alkylation as the key step. Initially, we relied on the diastereoselective alkylation of an α‐alkoxyacetimide derivative containing an α′ stereogenic center and investigated such an asymmetric alkylation reaction. Although alkylation proceeded in good yield, the lack of diastereoselectivity prompted us to explore alternative routes. Our subsequent successful synthetic strategies involved highly diastereoselective cycloaddition routes to both tetrahydropyran rings of lasonolide A. The top tetrahydropyran ring was constructed stereoselectively by an intramolecular 1,3‐dipolar cycloaddition reaction. The overall process constructed a bicyclic isoxazoline, which was later unravelled to a functionalized tetrahydropyran ring as well as a quaternary stereocenter present in the molecule. The lower tetrahydropyran ring was assembled by a Jacobsen catalytic asymmetric hetero‐Diels–Alder reaction as the key step. The synthesis also features a Lewis acid catalyzed epoxide opening to form a substituted ether stereoselectively.     

Concise synthesis of 2-amino-4(3H)-quinazolinones from simple (Hetero)aromatic amines

A novel and simple method of preparation of 2-alkylaminoquinazolin-4-ones with fused heteroaromatic rings from easily accessible (hetero)aromatic amines is described. The method is very efficient, and the 2-alkylaminoquinazolinone derivatives are obtained in three steps without chromatographic purification. The key step is the ring closure of the N-protected guanidine intermediates by intramolecular Friedel-Craft's type substitution.     

Core-modified porphyrin based assemblies

Core-modified porphyrins, resulting from the replacement of one or two pyrrolic nitrogens with other hetero atoms such as O, S, Se, and Te possess very interesting and distinct properties compared to tetrapyrrolic porphyrins. Specially, the singlet state energy levels can be fine tuned with suitable modification of porphyrin core by substituting pyrrolic “N” with hetero atoms such as “O” and “S”. In this review, we discuss the synthesis of various core-modified porphyrin building blocks containing one, two, three and four functional groups by following various synthetic methodologies developed in the past decade and the use of these core-modified porphyrin building blocks in the construction of several covalently and non-covalently linked hetero porphyrin dyads, triads, tetrads and pentads containing one or more different types of porphyrin sub-units. The photophysical studies are also described to show the possibility of singlet–singlet energy transfer from one porphyrin sub-unit to another in these hetero porphyrin arrays.     

Distribution of aluminum and boron in the periodical building units of boron-containing Beta zeolites

Various boron only ([B]-BEA) as well as aluminum- and boron-containing beta zeolites ([Al,B]-BEA) have been prepared and modified by ion exchange of ammonium, sodium, and nickel ions. The zeolite samples have been characterized by 11B, 27Al, and 29Si MAS as well as three of them by 11B and 27Al 3Q-MAS NMR spectroscopy. The quantitative contributions of defect-free Si(nX) (n = 2, 1, 0; X = Al, B) and Si(OH)x (x = 2, 1) sites to the NMR signal intensities were calculated from the various Si/(Al + B) ratios and relative 11B, 27Al, and 29Si NMR signal intensities using the special distribution of aluminum and boron in different periodical building units of the zeolite framework. The boron atoms are sitting exclusively in diagonal positions in the four-membered rings of [B]-BEA zeolites, while the aluminum atoms are situated both in diagonal and lone positions in the four-membered rings of [Al,B]-BEA zeolites. A higher part of boron atoms are positioned in framework-related deformed tetrahedral boron species than in lattice positions in the [B]-BEA than in the [Al,B]-BEA zeolites. All extraframework octahedral aluminum species are transformed back to lattice positions due to ion exchange from the protonated form to ammonium-, sodium-, or nickel-ions containing zeolites. Oppositely, trigonal boron leaves the zeolite structure completely during ion exchange.     

A theoretical prediction of stability in hydrogen-bonded complexes formed between oxirane and oxetane rings with HX (X=F and Cl)

The optimised geometries of heterocyclic hydrogen-bonded complexes, C2H4O...HX and C3H6O...HX, where X=F or Cl, were determined at DFT/B3LYP/6-311++G(d,p) computational level. Structural, electronic and vibrational properties of these complexes are used in order to compare the strained ring, which confer the great reactivity of these heterocyclic rings with monoprotic acids, forming a primary hydrogen bond. A secondary hydrogen bond between the hydrogen atoms of the CH2 groups and the halide species also takes place, thus causing a nonlinearity (characterized by the theta angle), in the primary hydrogen bond.     

Preparation and structure of a solid-state hypervalent-iodine polymer containing iodine and oxygen atoms in fused 12-atom hexagonal rings

The treatment of dilute aqueous solutions of [hydroxy(tosyloxy)iodo]benzene with aqueous Mg(ClO4)2 produced thin elongated-hexagonal plates exhibiting a supramolecular structure in which tetra-mu-oxopentaiodanyl dication repeat units are joined to each other by significantly ionic bonds and each unit is associated with two perchlorate ions. The linearly extended cationic structure is formed from the 12-atom hexagonal rings of alternating iodine and oxygen atoms, a novel structure. Each 12-membered ring forms a nearly planar hexagonal shape with sides defined by almost linear O-I-O segments (175.7+/-1.6) degrees. The apexes are occupied by bridging oxide ligands where the I-O-I angles deviate only slightly from an ideal 120 degrees hexagonal angle (116.8+/-1.2) degrees, consistent with sp2 hybridization of the bridging oxygen atoms that participate in three-center four-electron bonds with iodine. These 12-atom hexagons are slightly "chair" distorted at the oxygen atoms. The planes of the rings are separated by layers containing the phenyl rings. The perchlorate ions reside in void spaces created by the three-up, three-down arrangement of the phenyl rings around each 12-membered I-O ring and are positioned directly above and below the I-O rings.     

Cycloaddition reactions of 1.3-benzothiazines v synthesis of new tetracyclic ring systems

New tetracyclic derivatives (3a,$\text{b}$, 5, 8) similar to protoberberines, but containing a lactam structural element and other hetero atoms besides the bridge-head nitrogen in rings B and C, were prepared by cycloaddition of 6,7-dimethoxy-2H-1,3-benzothiazine (1a) with $\text{o}$-substituted aromatic carboxylic acid derivatives (2a,$\text{b}$, 4) and from 4- methyl-6,7-dimethoxy-2$\text{H}$-1,3-benzothiazine (1b) with 3.5-dinitrobenzoyl chloride.     

A novel highly stereoselective multi-component synthesis of N-substituted β-amino ketone derivatives using copper(II) phthalocyanine as reusable catalyst

Stereoselective synthesis of N-substituted β-amino ketone derivatives with substituents include one or two polar hetero atoms on benzene rings in many cases has been achieved by a one-pot multi-component process using copper(II) phthalocyanine as catalyst. The new process is suitable for the inclusion of a wide variety of substrates for the construction of highly functionalized Mannich-type structural scaffolds. The catalyst used is recycled and reused for repeating the reactions.     

The gas phase structure of ethynylferrocene using microwave spectroscopy

Gas phase structural parameters for ethynylferrocene have been determined using microwave spectroscopy. Rotational transitions due to a- and b-type dipole moments were measured. Twenty four rotational constants have been determined by fitting the measured transitions of various isotopomers using a rigid rotor Hamiltonian with centrifugal distortion constants. Least-squares fits to determine structural parameters and Kraitchman analyses have been used to determine the gas phase structural parameters and the atomic coordinates from the rotational constants. The distance between the Fe atom and the C atoms of the cyclopentadienyl rings is r(Fe-C1) = 2.049(5) A, and the distance between the carbon atoms of the cyclopentadienyl ring is r(C-C) = 1.432(2) A. The ethynyl group is bent away from the Fe atom and out of the plane of the carbon atoms in the adjacent cyclopentadienyl ring by 2.75(6) degrees. Structural parameters were also obtained from DFT calculations and Kraitchman analyses, and the results are compared. Analysis of fit results for 13C isotopic substitution data indicates that the carbon atoms of the two cyclopentadienyl rings are in an eclipsed conformation in the ground vibrational state. Trends in microwave experimental values for the distance from the Fe atom to the center of the cyclopentadienyl ring for a series of substituted ferrocenes have been analyzed. This analysis provides an estimate of the gas phase distance from the Fe atom to the centers of the cyclopentadienyl rings for ferrocene of 1.65(1) A.     

Fullerene‐Based Macro‐Heterocycle Prepared through Selective Incorporation of Three N and Two O Atoms into C60

A 14‐membered heterocycle is created on the C₆₀ cage skeleton through a multistep procedure. Key steps involve repeated PCl₅‐induced hydroxylamino N?O bond cleavage leading to insertion of nitrogen atoms, and also piperidine‐induced peroxo O?O bond cleavage leading to insertion of oxygen atoms. The hetero atoms form one pyrrole, two pyran, and one diazepine rings in conjunction with the C₆₀ skeleton carbon atoms. The fullerene‐based macrocycle showed unique reactivities towards fluoride ion and copper salts.     

Dielectric properties of three‐ring fluorinated compounds

Four three‐ring compounds, consisting of two cyclohexyl rings and one mono‐ or difluorinated phenyl ring, were studied using dielectric spectroscopy methods over a broad frequency range (1 kHz–3 GHz). They exhibit a nematic phase in a broad temperature interval, enriched by a smectic B phase in one case. The static and dynamic dielectric properties were analysed. It was established that the bridging CH₂CH₂ group placed between cyclohexyl and phenyl rings considerably changes the reference frame of the molecule, unlike the situation when it links two cyclohexyl rings. In the nematic and smectic B phases the motion around the short axis is a Debye process, whereas the rotation around the long axis is split into two processes: independent rotation of the whole molecule and its fluorophenyl part.