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121.
Premamoy Ghosh Tapas Kumar Ghosh 《Journal of polymer science. Part A, Polymer chemistry》1984,22(10):2295-2303
Photopolymerization of methyl methacrylate (MMA) was studied at 40°C using a macromolecular C.T. Complex between poly(N-vinyl carbazole) and bromine, expressed in brief as (PNVC–Br2) complex, as the photoinitiator. Initiator exponent was 0.40 for [PNVC–Br2] ≤ 2.5 × 10?3 mol L?1 and practically zero for [PNVC–Br2] > 2.5 × 10?3 mol L?1. Monomer exponent in different diluent systems such as benzene, carbon tetrachloride, and acetone was close to 1.0. Low initiator exponent (<0.5) is explained on the basis of an initiator-dependent termination mechanism, in addition to the usual bimolecular termination. Analysis of kinetic data indicates that the initiator-dependent termination is primarily due to degradative initiator transfer and that due to primary radicals is considered inconsequential in view of monomer exponent being close to unity. The non-ideal termination process assumes over-whelming prominence at high [PNVC–Br2]. 相似文献
122.
123.
Joy Md. Tuhinur R. Uddin Md. Miaz Bhoumik Nikhil C. Ghosh Shishir Kabir Shariff E. 《Transition Metal Chemistry》2021,46(2):149-157
Reactions of unsaturated [HOs3(CO)8{µ3-Ph2PCH(R)P(Ph)C6H4}] (R?=?H, Me) with Bu3SnH are examined. [HOs3(CO)8{µ3-Ph2PCH(R)P(Ph)C6H4}] reacts with Bu3SnH at room temperature to afford [H2Os3(CO)8(SnBu3){µ3-Ph2PCH(R)P(Ph)C6H4}] (1) via oxidative addition of the Sn?H bond to the parent cluster. Heating 1 in refluxing toluene leads to the formation of [H2Os3(CO)7(SnBu3){µ3-Ph2PCH(R)P(Ph)C6H4}] (2) through decarbonylation. Cluster 2 exists in two isomeric forms in solution which has been probed by VT NMR spectroscopy. The new Os-Sn bimetallic clusters have been characterized by a combination of analytical and spectroscopic data together with single-crystal X-ray diffraction analysis.
Graphic abstract 相似文献124.
The ambido-, stereo- and enantioselectivity of the phosphoramide-promoted aldol reactions of α-oxy aldehyde trichlorosilyl enolates with benzaldehyde has been investigated. Analysis of the products from α-tert-butyldimethylsilyloxy α-deuterioacetaldehyde trichlorosilyl enolate confirmed that this 1,2-bis-silyloxyethene derivative reacted as a tert-butyldimethylsilyl enolate rather than trichlorosilyl enolate in the aldol reaction with very high ambidoselectivity. The phosphoramide-coordinated trichlorosilyl group acted as an organizing center for the aldol reaction. From the aldol process, excellent anti-diastereoselectivity could be achieved. The enantioselectivity remained moderate to low for both anti- and syn-diastereomer with a wide range of phosphoramide catalysts. α-Triisopropylsilyloxy, phenoxy and benzyloxy acetaldehyde trichlorosilyl enolates also reacted in a similar fashion with benzaldehyde to give aldol products with varying degrees of selectivities. 相似文献
125.
A novel method for the synthesis of chiral α-amino acids has been developed where the acid functionality was constructed by oxidizing a hydroxymethyl group introduced by Evans’ method in the α-position of an appropriate acid substrate and the amino part came from the amide of the original carboxyl group following a modified Hofmann rearrangement reaction. 相似文献
126.
Soumen Ghosh Rupa Mukhopadhyay Madeleine Helliwell Alok K. Mukherjee 《Acta Crystallographica. Section C, Structural Chemistry》2007,63(8):o496-o500
The pyrazine ring in two N‐substituted quinoxaline derivatives, namely (E)‐2‐(2‐methoxybenzylidene)‐1,4‐di‐p‐tosyl‐1,2,3,4‐tetrahydroquinoxaline, C30H28N2S2O5, (II), and (E)‐methyl 2‐[(1,4‐di‐p‐tosyl‐1,2,3,4‐tetrahydroquinoxalin‐2‐ylidene)methyl]benzoate, C31H28N2S2O6, (III), assumes a half‐chair conformation and is shielded by the terminal tosyl groups. In the molecular packing of the compounds, intermolecular C—H...O hydrogen bonds between centrosymmetrically related molecules generate dimeric rings, viz. R22(22) in (II) and R22(26) in (III), which are further connected through C—H...π(arene) hydrogen bonds and π–π stacking interactions into novel supramolecular frameworks. 相似文献
127.
S. K. Ghosh E. Tettamanti P. L. Indovina 《Zeitschrift für Physik B Condensed Matter》1976,24(2):227-233
Contributions to the spin-lattice relaxation time (T
1) and the spin-spin relaxation time (T
2) due to critical fluctuations (CF) have been determined in para-azoxyanisole (PAA) from the corresponding proton relaxation times measured at 60 MHz over a temperature range of about 35 °K above the nematic-isotropic transition temperatureT
C
.In determining the CF contributions, the procedure followed here is the same as the present authors used earlier for a similar study in p-methoxybenzylidene p-n butylaniline (MBBA). Like that in MBBA at 14 MHz, a maximum in the CF contribution toT
1, has been observed. Following a recent theory we identify this contribution toT
1 arising from the nonlocal part of CF, and we call thisT
1)CFN. The correlation time associated with this nonlocal part of CF,
CFN, has been determined at different temperatures fromT
1)CFN. The temperature dependence of
CFN is in good agreement with the Landau-de Gennes theory and is consistent with that observed earlier in MBBA. The temperature dependence ofT
2)CF is also in reasonable agreement with the above behavior of
CFN. However, ourT
2)CF data can also be fitted to a temperature dependence expected from a contribution toT
2)CF arising from the local part of CF, such a fitting is comparatively poorer than the former. Since ourT
2)CF data are neither sufficiently accurate nor elaborate, no attempt has been made here to separate these two contributions, nonlocal and local parts of CF, which have been predicted from theoretical considerations. A behavior similar to that of ourT
2)CF is also shown by the earlier data of Cabane and Clark obtained from14N resonance when their data are processed properly.Work done with the financial support of the Consiglio Nazionale delle Ricerche granted through the Gruppo Nazionale di Struttura della Materia to the Istituto di Fisica, Università dell' AquilaA preliminary report of this work was presented at the Fifth International Symposium on Magnetic Resonance held at Bombay, India, January 14–18, 1974 相似文献
128.
Reactivity of [M2(μ‐Cl)2(cod)2] (M=Ir,Rh) and [Ru(Cl)2(cod)(CH3CN)2] with Na[H2B(bt)2]: Formation of Agostic versus Borate Complexes 下载免费PDF全文
K. Bakthavachalam K. Yuvaraj Mohammad Zafar Prof. Dr. Sundargopal Ghosh 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(48):17291-17297
Treatment of [M2(μ‐Cl)2(cod)2] (M=Ir and Rh) with Na[H2B(bt)2] (cod=1,5‐cyclooctadiene and bt=2‐mercaptobenzothiazolyl) at low temperature led to the formation of dimetallaheterocycles [(Mcod)2(bt)2], 1 and 2 ( 1 : M=Ir and 2 : M=Rh) and a borate complex [Rh(cod){κ2‐S,S′‐H2B(bt)2}], 3 . Compounds 1 and 2 are structurally characterized metal analogues of 1,5‐cyclooctadiene. Metal–metal bond distances of 3.6195(9) Å in 1 and 3.6749(9) Å in 2 are too long to consider as bonding. In an attempt to generate the Ru analogue of 1 and 2 , that is [(Rucod)2(bt)2], we have carried out the reaction of [Ru(Cl)2(cod)(CH3CN)2] with Na[H2B(bt)2]. Interestingly, the reaction yielded agostic complexes [Ru(cod)L{κ3‐H,S,S′‐H2B(bt)2}], 4 and 5 ( 4 : L=Cl; 5 : L=C7H4NS2). One of the key differences between 4 and 5 is the presence of different ancillary ligands at the metal center. The natural bond orbital (NBO) analysis of 1 and 2 shows that there is four lone pairs of electrons on each metal center with a significant amount of d character. Furthermore, the electronic structures and the bonding of these complexes have been established on the ground of quantum‐chemical calculations. All of the new compounds were characterized by IR, 1H, 11B, 13C NMR spectroscopy, and X‐ray crystallographic analysis. 相似文献
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130.