Syntheses of ketonated disulfide-bridged diruthenium complexes via C-H bond activation and C-S bond formation

The alpha-C-H bonds of 3-methyl-2-butanone, 3-pentanone, and 2-methyl-3-pentanone were activated on the sulfur center of the disulfide-bridged ruthenium dinuclear complex [(RuCl(P(OCH3)3)2)2(mu-S2)(mu-Cl)2] (1) in the presence of AgX (X = PF6, SbF6) with concomitant formation of C-S bonds to give the corresponding ketonated complexes [(Ru(CH3CN)2(P(OCH3)3)2)(mu-SSCHR1COR2)(Ru(CH3CN)3(P(OCH3)3)2)]X3 ([5](PF6)3, R1 = H, R2 = CH(CH3)2, X = PF6; [6](PF6)3, R1 = CH3, R2 = CH2CH3, X = PF6; [7](SbF6)3, R1 = CH3, R2 = CH(CH3)2, X = SbF6). For unsymmetric ketones, the primary or the secondary carbon of the alpha-C-H bond, rather than the tertiary carbon, is preferentially bound to one of the two bridging sulfur atoms. The alpha-C-H bond of the cyclic ketone cyclohexanone was cleaved to give the complex [(Ru(CH3CN)2(P(OCH3)3)2)(mu-SS-1- cyclohexanon-2-yl)(Ru(CH3CN)3(P(OCH3)3)2)](SbF6)3 ([8](SbF6)3). And the reactions of acetophenone and p-methoxyacetophenone, respectively, with the chloride-free complex [(Ru(CH3CN)3(P(OCH3)3)2)2(mu-S2)]4+ (3) gave [(Ru(CH3CN)2(P(OCH3)3)2)(mu-SSCH2COAr)(Ru(CH3CN)3(P(OCH3)3)2)](CF3SO3)3 ([9](CF3SO3)3, Ar = Ph; [10](CF3SO3)3, Ar = p-CH3OC6H4). The relative reactivities of a primary and a secondary C-H bond were clearly observed in the reaction of butanone with complex 3, which gave a mixture of two complexes, i.e., [(Ru(CH3CN)2(P(OCH3)3)20(mu-SSCH2COCH2CH3)(Ru(CH3CN)3(P(OCH3)3)2)](CF3SO3)3 ([11](CF3SO3)3) and [(Ru(CH3CN)2(P(OCH3)3)2)(mu-SSCHCH3COCH3)(Ru(CH3CN)3(P(OCH3)2)](CF3SO3)3 ([12](CF3SO3)3), in a molar ratio of 1:1.8. Complex 12 was converted to 11 at room temperature if the reaction time was prolonged. The relative reactivities of the alpha-C-H bonds of the ketones were deduced to be in the order 2 degrees > 1 degree > 3 degrees, on the basis of the consideration of contributions from both electronic and steric effects. Additionally, the C-S bonds in the ketonated complexes were found to be cleaved easily by protonation at room temperature. The mechanism for the formation of the ketonated disulfide-bridged ruthenium dinuclear complexes is as follows: initial coordination of the oxygen atom of the carbonyl group to the ruthenium center, followed by addition of an alpha-C-H bond to the disulfide bridging ligand, having S=S double-bond character, to form a C-S-S-H moiety, and finally completion of the reaction by deprotonation of the S-H bond.     

Reduction reactions of a 1,3,5-triphosphabenzene

The reactions of the triphosphabenzene, 1,3,5-P3C3But3, with LiMH4, M = Al or Ga, lead to the triphosphabicyclo[3.1.0]hexanediyl metallate complexes, [[[Li(OEt2)][MH2(P3C3But3H2)]]2], which give exo- and endo-isomers of a triphosphabicyclo[3.1.0]hexane, P3C3But3H4 upon quenching. The related reaction of [AlH3(NMe3)] with 1,3,5-P3C3But3 affords three identifiable products, viz. a triphosphabicyclo[3.1.0]hexenyl complex, [AlH2(P3C3But3H)(NMe3)], and two triphosphabicyclo[3.1.0]hexanediyl complexes, [AlH(P3C3But3H2)(NMe3)] and [Al2H4(P3C3But3H2)(NMe3)]. In contrast, the reactions of 1,3,5-P3C3But3 with either [GaH3(quin)], quin = quinuclidine, or Me3SnH lead only to the triphosphabicyclo[3.1.0]hexenyl complexes, [GaH2(P3C3But3H)(quin)] and [Me3Sn(P3C3But3H)]. Quenching of the former affords a triphosphabicyclo[3.1.0]hexene, P3C3But3H2, while quenching the latter gives its triphosphacyclohexa-1,4-diene valence isomer. Treatment of 1,3,5-P3C3But3 with "GaI" yields a GaI3 complex of the triphosphahexa-1,4-diene, [GaI3(P3C3But3H2)], whilst treatment with the anionic Ga(I) heterocycle, [:Ga[N(Ar)C(H)]2]-, Ar = C6H3Pri2-2,6, affords the known diphospholyl anion, [1,3-P2C3But3]- via a P-abstraction from the triphosphabenzene. Finally, reaction of the 1,3,5-triphosphacyclohexane, [P(OEt)C(H)(But)]3, with thionyl chloride yields the unusual lambda5, lambda5, lambda5-1,3,5-triphosphacyclohexane, [P(O)(Cl)C(H)(But)]2[P(OEt)(S)C(H)(But)]. Suggestions as to the mechanisms of a number of these reduction reactions are made and the crystal structures of seven compounds are reported.     

Bond additivity corrections for G3B3 and G3MP2B3 quantum chemistry methods

We have developed bond additivity correction (BAC) procedures for the G3-based quantum chemistry methods, G3B3 and G3MP2B3. We denote these procedures as BAC-G3B3 and BAC-G3MP2B3. We apply the procedures to compounds containing atoms from the first three rows of the periodic table including H, B, C, N, O, F, Al, Si, P, S, and Cl atoms. The BAC procedure applies atomic, molecular, and pairwise bond corrections to theoretical heats of formation of molecules. The BAC-G3B3 and BAC-G3MP2B3 procedures require parameters for each atom type but not for each bond type. These parameters have been obtained by minimizing the error between the BAC-G3B3 and BAC-G3MP2B3 predictions and the experimental heats of formation for a 155 molecule reference set, containing open and closed shell molecules representing various functional groups, multireference configurations, isomers, and degrees of saturation. As compared to former BAC-MP4, BAC-G2, and BAC-hybrid methods, BAC-G3B3 provides better agreement with experiment for a wider range of chemical moieties, including highly oxidized species involving SOx s, NOx s, POx s, and halogens. The BAC-G3B3 and BAC-G3MP2B3 procedures are applied to an extended test suite involving 273 compounds. We assess the overall quality of BAC-G3B3 with experiments and other theoretical approaches. For the reference set, the average error for the BAC-G3B3 results is 0.44 kcal/mol as compared to 0.82 kcal/mol for the raw G3B3. For the extended test set, the average error for the BAC-G3B3 results is 0.91 kcal/mol as compared to 1.38 kcal/mol for the raw G3B3. As compared to the other BAC procedures, the improved predictive capability of BAC-G3B3 and BAC-G3MP2B3 procedures is, to a large extent, due to the improved quality of G3-based methods resulting in much smaller BAC correction terms.     

An Easy Access to Benzofurans via DBU Induced Condensation Reaction of Active 2‐Hydroxy Acetophenones with Phenacyl Chlorides: A Novel Class of Antioxidant Agents

A convenient and efficient one‐pot synthesis of benzofurans 3a , 3b , 3c , 3d , 3e , 3f , 3g , 3h , 3i , 3j , 3k , 3l , 3m , 3n , 3o , 3p , 3q , 3r , 3s , 3t has been described from 2‐hydroxy acetophenones and phenacyl chlorides in the presence of DBU. The procedure was applicable for a variety of phenacyl chlorides and provides a variety of benzofurans with higher yields. DBU acts as a base and as well as nucleophiles. All the derivatives were subjected to in vitro antioxidant screenings against representative 2,2′‐diphenyl‐1‐picryl‐hydrazyl and 2,2′‐azino‐bis(3‐ethylbenzthiazoline‐6‐sulfonic acid) radicals and results worth for further investigations.     

Cation-anion interactions in 1-ethyl-3-methylimidazolium trifluoromethanesulfonate-based ionic liquid electrolytes

An important step in developing ionic-liquid-based electrolytes for lithium rechargeable batteries is obtaining a molecular-level understanding of the ionic interactions that occur in these systems. In this study, 1-ethyl-3-methylimidazolium trifluoromethansulfonate ([C2mim]CF3SO3) is complexed with LiCF3SO3, and the local structures of the CF3SO3- and [C2mim]+ ions are investigated with infrared and Raman spectroscopy. The isolation and subsequent refinement of a Li[C2mim](CF3SO3)2 crystal provides further insight into the structure of the [C2mim]CF3SO3-LiCF3SO3 solutions. Minor changes are observed in the infrared and Raman spectra of dilute [C2mim]CF3SO3-LiCF3SO3 solutions compared to pure [C2mim]CF3SO3. However, a suspension of very small Li[C2mim](CF3SO3)2 crystallites forms at a solution composition of [C2mim]CF3SO3:LiCF3SO3 = 10:1 (mole ratio), placing an upper limit on the solubility of LiCF3SO3. Essentially no changes are observed in the vibrational modes of the [C2mim]+ cations over the entire range of LiCF3SO3 compositions studied, suggesting that the addition of these compounds does not significantly perturb the local structure of the [C2mim]+ cations. The salt used in this study has a common anion with the ionic liquid; thus, the ion cloud surrounding the [C2mim]+ ions, which must be primarily composed of CF3SO3- anions, is not significantly altered with the addition of LiCF3SO3.     

Detailed characterization of (3 x 3) iodine adlayer on Pt(111) by unequal-sphere packing model

A simple unequal-sphere packing model is applied to study the iodine (3x3) adlayer on the Pt(111) surface. By using a newly introduced parameter, defined as the average adsorbate height, three characteristic adlattices, (3x3)-sym, (3x3)-asym, and (3x3)-lin, have been selected and characterized in great detail, including the exact adatom registry. The (3x3)-sym iodine adlattice, observed in many experimental studies, appears to be, on average, the closest one to the substrate surface. A special contour plot of average adsorbate height vs X and Y positions of the (3x3) iodine unit cell indicates the existence of two local minima, which are related to preferential formation of (3x3)-sym and (3x3)-asym iodine adlattices. Our model gives good agreement with experimental findings, and explains the mechanism of preferential appearance of (3x3)-sym and (3x3)-asym structures.     

Synthesis of 2‐Arylquinazolin‐4(3H)‐ones by N‐Aryl Benzamidines with Aromatic Carbonates

The reaction of N‐aryl benzamidines 1a , 1b , 1c , 1d , 1e , 1f , 1g , 1h , 1i , 1j , 1k , 1l , 1m , 1n with diphenyl carbonate 2a or ethyl phenyl carbonate 2b synthesized 2‐arylquinazolin‐4(3H)‐ones 3a , 3b , 3c , 3d , 3e , 3f , 3g , 3h , 3i , 3j , 3k , 3l , 3m , 3n in simple and safe process with good yields (71–90%). It was suggested that different electron‐donating substituent in N‐aryl benzamidines 1a , 1b , 1c , 1d , 1e , 1f , 1g , 1h , 1i , 1j , 1k , 1l , 1m , 1n afforded similar effect to the yields of 2‐arylquinazolin‐4(3H)‐ones 3a , 3b , 3c , 3d , 3e , 3f , 3g , 3h , 3i , 3j , 3k , 3l , 3m , 3n . In these reactions, N‐aryl benzamidines 1a , 1b , 1c , 1d , 1e , 1f , 1g , 1h , 1i , 1j , 1k , 1l , 1m , 1n built up intermediate compounds by nucleophilic addition to carbonates 2 to give annulation products 3a , 3b , 3c , 3d , 3e , 3f , 3g , 3h , 3i , 3j , 3k , 3l , 3m , 3n , following to cyclization involving the elimination of ethanol/phenol.     

Synthesis of β‐Methoxyacrylate Natural Products Based on Box‐PdII‐Catalyzed Intermolecular Methoxycarbonylation of Alkynoles

Bis(oxazoline)‐palladium(II) catalyzed carbonylation of homopropargyl alcohols afforded acyclic methoxyacrylate 2 and 6‐membered lactone 3a , 3b , 3d , 3e , 3f , 3g , 3h , 3i , 3j , 3k in good combined yield. In the case of propargyl alcohols, 5‐membered lactones 3p , 3q , 16 were obtained in moderate yields. The one‐pot synthesis of kawa lactones 3a , 3r , 3s and formal synthesis of dihydroxycystothiazole A and dihydroxycystothiazole C are presented. To elucidate the stereochemistry of (+)‐annularin G and (?)‐annularin H, the first asymmetric syntheses of these natural products were achieved.     

二甲基甲酰胺中四种钕盐的电导

通过电导测量研究了四种钕盐：Nd(CF3SO3)3、Nd(ClO4)3、Nd(NO3)3和NdCl3在极性非质子溶剂DMF中的电导性质.利用线性拟合方法求得在25 ℃下Nd(CF3SO3)3和Nd(ClO4)3的极限摩尔电导率分别为278.8和 280.7 S•cm2•mol－1.用间接方法求得Nd(NO3)3 与NdCl3 的极限摩尔电导率分别为297.2和287.3 S•cm2 •mol－1.在25～65 ℃温度范围内，Nd(CF3SO3)3和Nd(ClO4)3的电导率随温度呈线性变化. Nd(NO3)3和NdCl3的电导行为表现出明显的离子缔合.     

Synthesis of Dithiocarbamates Containing Disulfide Linkage Using Cyclic Trithiocarbonate and Amines under Solvent–Catalyst Free Condition

A green and facile synthesis of dithiocarbamate derivatives containing disulfide linkage by the ring opening reaction of trithiocarbonate with amines under solvent and catalyst‐free condition with excellent yields is being reported. Environmental benignity, easy work up, smaller reaction time, and lack of column chromatography are the significant features of this protocol. The cyclic trithiocarbonate ( 1 ) has been used as a starting material for the first time to synthesize compounds of biological interest ( 3a , 3b , 3c , 3d , 3e , 3f , 3g , 3h , 3i , 3j , 3k , 3l , 3m , 3n , 3o , 3p , 3q ).     

REBO3中Ce3+和Bi3+对Sm3+光致发光的影响

在紫外光(UV)激发下,系统地研究了REBO_3(RE=La,Gd,Y)中Sm~(3+),Ce~(3+)和Bi~(3+)的发射光谱、激发光谱及其发光强度与组成、结构的关系.结果表明:Ce~(3+)、Bi~(3+)均可敏化LaBO_3中Sm~(3+)的发光;而在GdBO_3和YBO_3中,只有Bi~(3+)能敏化Sm~(3+)的发光,Ce~(3+)猝灭Sm~(3+)的发光.本文还探讨了三种基质中Sm~(3+)发光浓度猝灭的机理.     

Fluorotrimethylsilane affinities of anionic nucleophiles: A study of fluoride-induced desilylation

In this study, preparation and decomposition of five novel pentavalent fluorosiliconates, RSi(CH3)3F- (R = CH3CH2O, CF3CH2O, (CH3)2CHO, (CH3)3SiO, and (CH3)3SiNH) is used to investigate the process of fluoride-induced desilylation. The siliconates were characterized by collision-induced dissociation and energy-resolved mass spectrometry. Decomposition of RSi(CH3)3F- leads to loss of the nucleophile R- and FSi(CH3)3, except in the case of (CH3)3SiNHSi(CH3)3F-, where HF loss is also observed. Ion affinities for FSi(CH3)3 have been measured for all five nucleophiles, and compare well with computational predictions. The observed trend of the bond dissociation energies resembles the trend of deltaH(acid) values for the corresponding conjugate acids, RH. Additionally, this data has been incorporated with existing thermochemistry to derive fluoride affinities for four of the silanes (R = CH3CH2O, (CH3)2CHO, (CH3)3SiO, and (CH3)3SiNH). We use the fluoride affinity of the silanes and the FSi(CH3)3 affinity of the departing nucleophilic anion to assess the feasibility of fluoride-induced desilylation of the silanes examined in this work.     

Si(CH3)3Cl分子电离电势和化学键能的测定

The photoionization spectroscopy of Si(CH3)3Cl in the range of 50 -130 nm was studied with synchrotron radiation source. The adiabatic ionization potentials of molecule Si(CH3)3Cl and radical Si(CH3)3 are 10.06 ±0.02 eV and 7.00±0.03 eV respectively. In addition, the appearance potentials of Si(CH3)2Cl+, Si(CH3)3+, SiCl+ and SiCH3+ were determined:
AP(Si(CH3)2Cl+) ＝10.49±0.02eV, AP(Si(CH3)3+) ＝ 11.91 ±0.02eV
AP(SiCl+) ＝ 18.64 ±0.06eV, AP(SiCH3+)＝ 18.62 ±0.02eV
From these, some chemical bond energies of Si(CH3)3Cl+ were calculated:
D(Si(CH3)2Cl+ - CH3) ＝0.43 ±0.02eV, D(Si(CH3)3+ - Cl) ＝ 1.85 ± 0.02eV
D(SiCH3+ - (2CH3 ＋ Cl)) ＝ 8.56 ± 0．06eV, D(SiCH3+ - 2CH3) ＝6.71±0．06eV
D(SiCl+ - 3CH3) ＝ 8.58 ± 0.06eV, D(SiCl＋- 2CH3) ＝ 8.15 ±0.06eV
D(SiCH3+- (CH3 ＋ Cl)) ＝8.13 ±0.06eV     

KMgF3:Ce3+,Tb3+纳米粒子中Ce3+→Tb3+的发光及能量传递

利用微乳液方法,合成了铈、铽共掺杂的氟镁钾纳米粒子,研究了体系中Ce3+→Tb3+的发光特性以及它们之间的相互作用,结果表明KMgF3:Ce3+Tb3+纳米粒子中存在Ce3+→Tb3+的能量传递过程,即Ce3+可以将吸收的能量直接传递给Tb3+离子,使得Tb3+的绿色发光强度大为增加.     

Gold as hydrogen: structural and electronic properties and chemical bonding in Si3Au3(+0-) and comparisons to Si3H3(+0-)

A single Au atom has been shown to behave like H in its bonding to Si in several mono- and disilicon gold clusters. In the current work, we investigate the AuH analogy in trisilicon gold clusters, Si3Au3(+0-). Photoelectron spectroscopy and density functional calculations are combined to examine the geometric and electronic structure of Si3Au3-. We find that there are three isomers competing for the ground state of Si3Au3- as is the case for Si3H3-. Extensive structural searches show that the potential energy surfaces of the trisilicon gold clusters (Si3Au3-, Si3Au3, and Si3Au3+) are similar to those of the corresponding silicon hydrides. The lowest energy isomers for Si3Au3- and Si3Au3 are structurally similar to a Si3Au four-membered ring serving as a common structural motif. For Si3Au3+, the 2pi aromatic cyclotrisilenylium auride ion, analogous to the aromatic cyclotrisilenylium ion (Si3H3+), is the most stable species. Comparison of the structures and chemical bonding between Si3Au3(+0-) and the corresponding silicon hydrides further extends the isolobal analogy between Au and H.     

Trinuclear silver(I) complexes of fluorinated pyrazolates

Silver pyrazolates [[3-(CF3)Pz]Ag]3, [[3-(CF3),5-(CH3)Pz]Ag]3, [[3-(CF3),5-(Ph)Pz]Ag]3, [[3-(CF3),5-(But)Pz]Ag]3, and [[3-(C3F7),5-(But)Pz]Ag]3 have been synthesized by treatment of the corresponding pyrazole with a slight molar excess of silver(I) oxide. This economical and convenient route gives silver pyrazolates in high (>80%) yields. X-ray crystal structures of [[3-(CF3),5-(CH3)Pz]Ag]3, [[3-(CF3),5-(But)Pz]Ag]3, and [[3-(C3F7),5-(But)Pz]Ag]3 show that these molecules have trinuclear structures with essentially planar to highly distorted Ag3N6 metallacycles. [[3-(CF3),5-(CH3)Pz]Ag]3 forms extended columns via intertrimer argentophilic contacts (the closest Ag...Ag separation between the neighboring trimers are 3.355 and 3.426 A). The trinuclear [[3-(CF3),5-(But)Pz]Ag]3 units crystallize in pairs, basically forming "dimers of trimers", with the six silver atom core of the adjacent trimers adopting a chair conformation. However, in these dimers of trimers, even the shortest intertrimer Ag...Ag distance (3.480 A) is slightly longer than the van der Waals contact of silver (3.44 A). [[3-(C3F7),5-(But)Pz]Ag]3, which has two bulky groups on each pyrazolyl ring, shows no close intertrimer Ag...Ag contacts (closest intertrimer Ag...Ag distance = 5.376 A). The Ag-N bond distances and the intratrimer Ag...Ag separations of the silver pyrazolates do not show much variation. However, their N-Ag-N angles are sensitive to the nature (especially, the size) of substituents on the pyrazolyl rings. The pi-acidic [[3,5-(CF3)2Pz]Ag]3 and [[3-(C3F7),5-(But)Pz]Ag]3 form adducts with the pi-base toluene. X-ray data show that they adopt extended columnar structures of the type [[Ag3]2.[toluene]]infinity and [[Ag3]'.[toluene]]infinity ([[3,5-(CF3)2Pz]Ag]3 = [Ag3],[[3-(C3F7),5-(But)Pz]Ag]3 = [Ag3]'), in which toluene interleaves and makes face-to-face contacts with [[3-(C3F7),5-(But)Pz]Ag]3 or dimers of [[3,5-(CF3)2Pz]Ag]3.     

1H, 13C, and 73Ge NMR spectral analysis of substituted aryltrimethylgermanes

NMR chemical shifts of 1H, 13C, and 73Ge are reported for a series of monosubstituted aromatic trimethylgermanes of the type XC6H4Ge(CH3)3; X = p-N(CH3)2, p-OCH3, p-OC2H5, p-C(CH3)3, p-Si(CH3)3, p-Ge(CH3)3, p-Sn(CH3)3, p-CH3, m-CH3, -H, m-OCH3, p-Cl, p-Br, m-F, m-CF3, p-CF3, o-OCH3, and o-CH3. The relatively narrow 73Ge resonances show a strong correlation with Hammett sigma constants, with a correlation coefficient of 0.976 and 0.876 for 73Ge chemical shifts in meta- and para-substituted derivatives, respectively. The 13C chemical shifts of the methyl carbons bonded to germanium also display a relationship, with correlation coefficients of 0.904, 0.993, and 0.911 for para-, meta- and all derivatives, respectively. Comparisons of the Hammett plots for the homologous series XC6H4M(CH3)3; M = C, Si, Ge, Sn, show that, in general, correlation coefficients decrease while slopes increase significantly down the group, presumably reflecting the corresponding increase in chemical shift range of the group 14 atom. The Hammett constant derived for the p-Ge(CH3)3 group of +0.13 compares with the NMR-derived constants of -0.12 for p-C(CH3)3, +0.14 for p-Si(CH3)3, and -0.14 for p-Sn(CH3)3. The indication of electron release by carbon and tin can be rationalized through traditional hyperconjugative arguments for carbon and by the low electronegativity and consequent inductive effect of tin. The small electron attraction suggested by the positive constants for silicon and germanium can be simply, and perhaps naively, attributed to pi-acceptor interactions with the benzene ring.     

Cholesterol levels and plasma membrane fluidity in 3T3 and SV101-3T3 cells.

Polyene antibiotics such as filipin selectively inhibit wheat germ agglutinin-induced agglutination of transformed and malignant cells compared to normal cells (Hatten ME, Burger MM: Biochemistry 18: 739, 1979). Since filipin binds specifically to cholesterol, we measured cholesterol levels in 3T3 cells and SV101-3T3 cells. SV101-3T3 cells contained 50-100% more cholesterol per cell than 3T3 cells. Both cell types were starved for cholesterol by growth in lipid-depleted medium plus 25-hydroxycholesterol. The cholesterol level of SV101-3T3 cells decreased by 30-50%, while the level in 3T3 cells remained constant. Filipin-stained SV101-3T3 cells revealed bright patches of filipin under fluorescence microscopy. These patches were absent in 3T3 cells and in SV101-3T3 and 3T3 cells starved for cholesterol. We selectively labeled plasma membranes of these cells with a spin label analog of phosphatidylcholine. The spin label indicated differences in plasma membrane fluidity that may be related to the different cholesterol levels in 3T3 and SV101-3T3 cells.     

Pros and cons of σ -aromaticity

A discussion of σ-aromaticity requires a distinction between σ-conjugation, σ-electron delocalization, and σ-bond delocalization, all of which can be considered as prerequisites of σ-aromatic character. All molecules with three or more atoms encounter σ-conjugative interactions. Also, all σ-electrons are delocalized if the term delocalization is taken in its quantum theoretical meaning. However, σ-conjugation and σ-electron delocalization do not necessarily imply σ-bond delocalization. - One can distinguish between three different modes of σ-delocalization: ribbon delocalization in acyclic molecules and larger rings, surface delocalization in small rings, and volume delocalization in cage compounds. Surface delocalization of σ-electrons is found to lead to σ-bond delocalization. An example is cyclopropane. Bonding in cyclopropane can only be described in terms of nonclassical 2-electron 3-center and 4-electron 3-center bonds. Application of the criteria used to define π-aromaticity reveals that the properties of cyclopropane are in line with these criteria and that the term σ-aromaticity cannot be rejected on the grounds that aromaticity is restricted to π-electrons. The pros and cons of using the term σ-aromaticity in chemical discussions are presented.     

NF3 decomposition over some metal oxides in the absence of water

NF3 decomposition in the absence of water over Al2O3, Fe2O3, Co3O4 and NiO, and transition metal oxides (Fe2O3, Co3O4 and NiO) coated Al2O3 reagents was investigated. The results show that Al2O3 is an active reagent for NF3 decomposition with 100% conversion lasting for 8.5 h at 400 ℃. Fe2O3, Co3O4 and NiO coated Al2O3 reagents are superior to bare Al2O3, and 5%Co3O4/Al2O3 has a high reactivity with NF3 full conversion maintaining for 10.5 h. It is suggested that the presence of transition metal oxide is beneficial to the reactivity of Al2O3, and results in a significant enhancement in the fluorination of Al2O3.