共查询到20条相似文献,搜索用时 62 毫秒
1.
The photochemistry of 1,2‐dihydro‐1,2‐azaborinine derivatives was studied under matrix isolation conditions and in solution. Photoisomerization occurs exclusively to the Dewar valence isomers upon irradiation with UV light (>280 nm) with high quantum yield (46 %). Further photolysis with UV light (254 nm) results in the formation of cyclobutadiene and an iminoborane derivative. The thermal electrocyclic ring‐opening reaction of the Dewar valence isomer back to the 1,2‐dihydro‐1‐ tert‐butyldimethylsilyl‐2‐mesityl‐1,2‐azaborinine has an activation barrier of (27.0±1.2) kcal mol −1. In the presence of the Wilkinson catalyst, the ring opening occurs rapidly and exothermically (Δ H=(−48±1) kcal mol −1) at room temperature. 相似文献
2.
The photochemistry of 1,2‐dihydro‐1,2‐azaborinine derivatives was studied under matrix isolation conditions and in solution. Photoisomerization occurs exclusively to the Dewar valence isomers upon irradiation with UV light (>280 nm) with high quantum yield (46 %). Further photolysis with UV light (254 nm) results in the formation of cyclobutadiene and an iminoborane derivative. The thermal electrocyclic ring‐opening reaction of the Dewar valence isomer back to the 1,2‐dihydro‐1‐ tert‐butyldimethylsilyl‐2‐mesityl‐1,2‐azaborinine has an activation barrier of (27.0±1.2) kcal mol ?1. In the presence of the Wilkinson catalyst, the ring opening occurs rapidly and exothermically (Δ H=(?48±1) kcal mol ?1) at room temperature. 相似文献
3.
Vacuum ultraviolet (VUV) dissociative photoionization of isoprene in the energy region 8.5–18 eV was investigated with photoionization mass spectroscopy (PIMS) using synchrotron radiation (SR). The ionization energy (IE) of isoprene as well as the appearance energies (AEs) of its fragment ions C 5H 7+, C 5H 5+, C 4H 5+, C 3H 6+, C 3H 5+, C 3H 4+, C 3H 3+ and C 2H 3+ were determined with photoionization efficiency (PIE) curves. The dissociation energies of some possible dissociation channels to produce those fragment ions were also determined experimentally. The total energies of C 5H 8 and its main fragments were calculated using the Gaussian 03 program and the Gaussian‐2 method. The IE of C 5H 8, the AEs for its fragment ions, and the dissociation energies to produce them were predicted using the high‐accuracy energy model. According to our results, the experimental dissociation energies were in reasonable agreement with the calculated values of the proposed photodissociation channels of C 5H 8. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
4.
The dissociative photoionization of molecular‐beam cooled CH 2CO in a region of ?10–20 eV was investigated with photoionization mass spectrometry using a synchrotron radiation as the light source. Photoionization efficiency curves of CH 2CO + and of observed fragment ions CH 2+, CHCO +, HCO +, C 2O +, CO +, and C 2H 2+ were measured to determine their appearance energies. Relative branching ratios as a function of photon energy were determined. Energies for formation of these observed fragment ions and their neutral counterparts upon ionization of CH 2CO are computed with the Gaussian‐3 method. Dissociative photoionization channels associated with six observed fragment ions are proposed based on comparison of determined appearance energies and predicted energies. The principal dissociative processes are direct breaking of C=C and C‐H bonds to form CH 2+ + CO and CHCO + + H, respectively; at greater energies, dissociation involving H migration takes place. 相似文献
5.
A general method of generating radicals in cold supersonic expansions in the gas phase is presented. The method relies on excimer laser photolysis of suitable precursor molecules in a thin quartz capillary mounted at the orifice of a pulsed gas nozzle and can easily be combined with vacuum‐UV photoionization mass spectrometry and high‐resolution photoelectron spectroscopy to study the reactivity and the rovibronic energy level structure of neutral radicals and their ions, as well as to determine highly accurate adiabatic ionization energies. The characteristics of the radical source are described in detail, and its performance is illustrated by mass spectrometric and high‐resolution photoelectron spectroscopic investigations of NH 2, CH 2, CH 3, C 2H, C 2H 3, and C 2H 5. The radical source is not only suitable to produce cold samples (rotational temperature of ca. 30 K) of radicals of moderate reactivity, such as NH 2, CH 3, or C 2H 5, but it is also useful to prepare highly reactive radicals ( e.g., C 2H) for spectroscopic investigations. 相似文献
6.
The photoionization and dissociative photoionization of Im( iPr) 2, 1,3‐diisopropylimidazolin‐2‐ylidene, was investigated by imaging photoelectron photoion coincidence (iPEPICO) with vacuum ultraviolet (VUV) synchrotron radiation. A lone‐pair electron of the carbene carbon atom is removed upon ionization and the molecular geometry changes significantly. Only 0.5 eV above the adiabatic ionization energy, IE ad=7.52±0.1 eV, the carbene cation fragments, yielding propene or a methyl radical in parallel dissociation reactions with appearance energies of 8.22 and 8.17 eV, respectively. Both reaction channels appear at almost the same photon energy, suggesting a shared transition state. This is confirmed by calculations, which reveal the rate‐determining step as hydrogen‐atom migration from the isopropyl group to the carbene carbon center forming a resonance‐stabilized imidazolium ion. Above 10.5 eV, analogous sequential dissociation channels open up. The first propene‐loss fragment ion dissociates further and another methyl or propene is abstracted. Again, a resonance‐stabilized imidazolium ion acts as intermediate. The aromaticity of the system is enhanced even in vertical ionization. Indeed, the coincidence technique confirms that a real imidazolium ion is produced by hydrogen transfer over a small barrier. The simple analysis of the breakdown diagram yields all the clues to disentangle the complex dissociative photoionization mechanism of this intermediate‐sized molecule. Photoelectron photoion coincidence is a promising tool to unveil the fragmentation mechanism of larger molecules in mass spectrometry. 相似文献
7.
The reaction of thionyl chloride with the semicarbazone 2 gave 4,5‐dihydro‐6,9‐dihydroxynaphtho‐[1,2‐ d][1,2,3]thiadiazole ( 3 ) instead of 4,5‐dihydro‐6,9‐dimethyoxynaphtho[1,2‐ d][1,2,3]thiadiazole ( 4 ). Selenium dioxide oxidation of compound 2 gave 4,5‐dihydro‐6,9‐dimethyoxynaphtho[1,2‐ d][1,2,3]selenadiazole ( 5 ). Oxidation of compound 5 with 2,3‐dichloro‐5,6‐dicyano‐1,4‐benzoquinone afforded 6,9‐dimethyoxynaphtho[1,2‐ d][1,2,3]selenadiazole ( 6 ). 相似文献
8.
The photoionization and dissociative photoionization of m-xylene (C8H10) were researched by using synchrotron radiation vacuum ultraviolet (SR-VUV) and supersonic expanding molecular beam reflectron time-of-flight mass spectrometer (RFTOF-MS) system. The photoionization efficiency spectra (PIEs) of parent ion C8H10+ and main fragment ions C8H9+ and C7H7+ were observed, and the ionization energy (IE) of m-xylene and appearance energies (AEs) of main fragment ions C8H9+ and C7H7+ were determined to be 8.60 ± 0.03 eV, 11.76 ± 0.04 eV and 11.85 ± 0.05 eV, respectively. Structures of reactant, transition states (TSs), intermediates (INTs), and products involved in two dominant dissociation channels were optimized at the B3LYP/6-311++G(d,p) level, and the relative energies were calculated at the G3 level. Based on the results, two major dissociative photoionization channels, C7H7++CH3 and C8H9++H were calculated at the B3LYP/6-311++G(d,p) level. On the basis of theoretical and experimental results, the dissociative photoionization mechanisms of m-xylene were proposed. The C–H or C–C bond dissociation and hydrogen migration are the main processes in the dissociation channels of m-xylene cation. 相似文献
10.
Cyclocondensation of 5‐amino‐6‐methyl‐2‐morpholinopyrimidine‐4‐thiol ( 1 ) and 2‐bromo‐5,5‐dimethylcyclohexane‐1,3‐dione ( 2 ) under mild reaction condition afforded 4,7,7‐trimethyl‐2‐morpholino‐7,8‐dihydro‐5 H‐benzo[ b ]pyrimido[5,4‐ e ][1,4]thiazin‐9(6 H )‐one ( 3 ). The 1H and 13C NMR data of compound ( 3 ) are demonstrated that this compound exists primarily in the enamino ketone form. Reaction of compound ( 3 ) with phosphorous oxychloride gave 4‐(9‐chloro‐4,7,7‐trimethyl‐7,8‐dihydro‐6 H‐benzo[ b ]pyrimido[5,4‐ e ][1,4]thiazin‐2‐yl)morpholine ( 4 ). Nucleophilic substitution of chlorine atom of compound ( 4 ) with typical secondary amines in DMF and K 2CO 3 furnished the new substituted derivatives of 4‐(4,7,7‐trimethyl‐7,8‐dihydro‐6 H‐benzo[ b ]pyrimido[5,4‐ e ][1,4]thiazin‐2‐yl)morpholine ( 5a , 5b , 5c , 5d , 5e , 5f , 5g , 5h ). All the synthesized products were characterized and confirmed by their spectroscopic and microanalytical data. 相似文献
11.
Ring closing metathesis of 8‐allyl‐9‐butenylpurines or N,9‐diallyl‐ N‐methyl‐9 H‐purin‐8‐amines with the Grubbs second generation catalyst resulted in fused 9,10‐dihydro‐6 H‐azepino[1,2‐e]purines or 9,10‐dihydro‐6 H‐[1,3]diazepino[1,2‐ e]purines, respectively. The 8‐allyl‐9‐butenylpurines were prepared from 8‐bromo‐9‐butenylpurines after Stille coupling with allyltributyltin. The N,9‐diallyl‐ N‐methyl‐9 H‐purin‐8‐amines were synthesized from 9‐allyl‐8‐bromopurines after treatment with allylamine in H 2O under MW irradiation, followed by methylation with MeI in KOH. The new compounds were tested as inhibitors of lipid peroxidation. 6‐Methyl‐4‐(morpholin‐4‐yl)‐7,10‐dihydro‐6 H‐[1,3]diazepino[1,2‐ e]purine presents interesting results and could serve as a lead compound. 相似文献
12.
Molecules of the title compound, C 18H 20N 2O 3, are linked into ribbons by N—H·O and N—H·N hydrogen bonds. Stereochemical comparison with Ro 15‐1788 ( viz. ethyl 8‐fluoro‐5,6‐dihydro‐5‐methyl‐6‐oxo‐4 H‐imidazo[1,5‐ a][1,4]benzodiazepine‐3‐carboxylate) has identified three electronegative N and O atoms in the molecule as features likely to be responsible for its activity as a benzodiazepine‐receptor antagonist. 相似文献
13.
The most remarkable aspect of the crystal structure of the title compound (systematic name: 3,4‐dihydro‐2,2‐dimethyl‐2 H‐naphtho[1,2‐ b]pyran‐5,6‐dione), C 15H 14O 3, is that a π‐stacking interaction is present between the two naphthalene ring systems of symmetry‐related molecules. Apart from these π–π interactions, different molecules are held together by weak C—H⋯O hydrogen‐bonding interactions. 相似文献
14.
A convenient approach to 2,2′‐(1,4‐phenylene)bis[1‐acetyl‐1,2‐dihydro‐4 H‐3,1‐benzoxazin‐4‐one] derivatives 4 was explored employing the one‐pot condensation of anthranilic acids (=2‐aminobenzoic acids) 1 with terephthalaldehyde (=benzene‐1,4‐dicarboxaldehyde; 2 ) under ultrasound‐irradiation conditions ( Scheme 1). The reactions proceeded smoothly in the presence of excess Ac 2O in the absence of any other catalyst and solvent to afford the respective products in high yields. 相似文献
15.
Crystals of 1,4‐diethyl‐ and 1,2‐diethylbenzene, both C 10H 14, and ethylbenzene, C 8H 9, have been grown in situ. The molecules of 1,4‐diethyl‐ and 1,2‐diethylbenzene are located about a centre of inversion and across a twofold axis, respectively. In both molecules, the terminal methyl groups are located on opposite sides of the plane of the aromatic ring. In the crystal structures of all three compounds, molecules are linked together by (Ar)C—H...π and CH 2...π contacts. The methyl H atoms do not form close contacts with any of the aromatic π systems. 相似文献
16.
The facile and convenient access by a conventional procedure in ethanol as solvent to a new series of succinyl‐spaced pyrazoles including 1,4‐bis[5‐(trichloromethyl)‐5‐hydroxy‐4,5‐dihydro‐1 H‐pyrazol‐1‐yl]butane‐1,4‐diones (64–82%) and the respective dehydrated derivatives as 1,4‐bis[5‐(trichloromethyl)‐1 H‐pyrazol‐1‐yl]butane‐1,4‐diones in 57–82% yields, from the regioselective cyclocondensation reactions of 4‐substituted 4‐methoxy‐1,1,1‐trichloroalk‐3‐en‐2‐ones with succinic acid dihydrazide, where the 4‐substituents are Me, Ph, 4‐FC 6H 4, 4‐ClC 6H 4, 4‐NO 2C 6H 4, 2‐furyl, and 2‐thienyl, is reported. J. Heterocyclic Chem., 2011. 相似文献
17.
The photoionization and dissociation photoionization of toluene have been studied using quantum chemistry methods.The geometries and frequencies of the reactants,transition states and products have been performed at B3LYP/6-311++G (d,p) level,and single-point energy calculations for all the stationary points were carried out at DFT calculations of the optimized structures with the G3B3 level.The ionization energies of toluene and the appearance energies for major fragment ions,C 7H 7+,C 6H 5+,C 5H 6+,C 5H 5+,are determined to be 8.90,11.15 or 11.03,12.72,13.69,16.28 eV,respectively,which are all in good agreement with published experimental data.With the help of available published experimental data and theoretical results,four dissociative photoionization channels have been proposed:C 7H 7++H,C 6H 5++CH 3,C 5H 6++C 2H 2,C 5H 5++C 2H 2+H.Transition structures and intermediates for those isomerization processes are determined in this work.Especially,the structures of C 5H 6+ and C 5H 5+ produced by dissociative photoionization of toluene have been defined as chain structure in this work with theoretical calculations. 相似文献
18.
The Diels–Alder reaction between 5‐hydroxy‐1,4‐naphthoquinone and 5,5‐dimethyl‐3‐vinyl‐1,2‐cyclohexadienyl acetate by endo addition gives the title compound, C 22H 22O 5, in 68% yield. This racemic diastereoisomer has the opposite regiochemistry to ochromycinone analogues produced previously and may allow access to a new type of anticancer‐active saquayamycin analogue. 相似文献
19.
When 2,3‐dichloro‐1,4‐naphthoquinone (DCHNQ) ( 1 ) is allowed to react with 1‐phenylbiguanide (PBG) ( 2 ), 4‐chloro‐2,5‐dihydro‐2,5‐dioxonaphtho[1,2‐ d]imidazole‐3‐carboxylic acid phenyl amide ( 4 ), 6‐chloro‐8‐phenylamino‐9 H‐7,9,11‐triaza‐cyclohepta[ a]naphthalene‐5,10‐dione ( 5 ) and 4‐dimethyl‐amino‐5,10‐dioxo‐2‐phenylimino‐5,10‐dihydro‐2 H‐benzo[ g]quinazoline‐1‐carboxylic acid amide ( 6 ) were obtained. While on reacting 1 with 2‐guanidinebenzimidazole (GBI) ( 3 ) the products are 3‐(1 H‐benzoimidazol‐2‐yl)‐4‐chloro‐3 H‐naphtho[1,2‐ d]imidazole‐2,5‐dione ( 7 ) and 3‐[3‐(1 H‐benzoimidazol‐2‐yl)‐ureido]‐1,4‐dioxo‐1,4‐dihydronaphthalene‐2‐carboxylic acid dimethylamide ( 8 ). 相似文献
20.
The title compounds, namely 6‐methoxy‐3,3‐dimethyl‐3 H‐benzo[ f]chromene, C 16H 16O 2, (III), and racemic 3‐bromo‐2,2,6,6‐tetramethyl‐3,4‐dihydro‐2 H,6 H‐1,5‐dioxatriphenylene, C 20H 21BrO 2, (IV), were both synthesized in one‐step regioselective Wittig reactions from substituted 1,2‐naphthoquinones. The new ring in both compounds adopts a screw‐boat conformation. A single π–π stacking interaction links the molecules of (III) into centrosymmetric dimeric aggregates, and a single C—H...π(arene) hydrogen bond links the molecules of (IV) into centrosymmetric dimers. 相似文献
|