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Fu N Allen AD Kobayashi S Tidwell TT Vukovic S Matsuoka T Mishima M 《The Journal of organic chemistry》2008,73(5):1768-1773
Cyclobutenediones 5 disubstituted with HO (a), MeO (b), EtO (c), i-PrO (d), t-BuO (e), PhO (f), 4-MeOC6H4O (g), 4-O2NC6H4O (h), and 3,4-bridging OCH2CH2O (i) substituents upon laser flash photolysis gave the corresponding bisketenes 6a-i, as detected by their distinctive doublet IR absorptions between 2075 and 2106 and 2116 and 2140 cm-1. The reactivities in ring closure back to the cyclobutenediones were greatest for the group 6b-e, with the highest rate constant of 2.95 x 10(7) s-1 at 25 degrees C for 6e (RO = t-BuO) in isooctane, were less for 6a (RO = OH, k = 2.57 x 10(6) s-1 in CH3CN), while 6f-i were the least reactive, with the lowest rate constant of 3.8 x 10(4) s-1 in CH3CN for 6h (RO = 4-O2NC6H4O). The significantly reduced rate constants for 6f-i are attributed to diminution of the electron-donating ability of oxygen to the cyclobutenediones 5f-h by the ArO substituents compared to alkoxy groups and to angle strain in the bridged product cyclobutenedione 5i. The reactivities of the ArO-substituted bisketenes 6f-h in CH3CN varied by a factor of 50 and gave an excellent correlation of the observed rate constants log k with the sigma p constants of the aryl substituents. Computational studies at the B3LYP/6-31G(d) level of ring-closure barriers are consistent with the measured reactivities. Photolysis of squaric acid (5a) in solution provides a convenient preparation of deltic acid (7). 相似文献
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Nanyan Rena Zhang Sean Yu Philip Tiller Suzie Yeh Elizabeth Mahan William Bart Emary 《Rapid communications in mass spectrometry : RCM》2009,23(7):1085-1094
The quantitative capabilities of a linear ion trap high‐resolution mass spectrometer (LTQ‐Orbitrap™) were investigated using full scan mode bracketing the m/z range of the ions of interest and utilizing a mass resolution (mass/FWHM) of 15000. Extracted ion chromatograms using a mass window of ±5–10 mmu centering on the theoretical m/z of each analyte were generated and used for quantitation. The quantitative performance of the LTQ‐Orbitrap™ was compared with that of a triple quadrupole (API 4000) operating using selected reaction monitoring (SRM) detection. Comparable assay precision, accuracy, linearity and sensitivity were observed for both approaches. The concentrations of actual study samples from 15 Merck drug candidates reported by the two methods were statistically equivalent. Unlike SRM being a tandem mass spectrometric (MS/MS)‐based detection method, a high resolution mass spectrometer operated in full scan does not need MS/MS optimization. This approach not only provides quantitative results for compounds of interest, but also will afford data on other analytes present in the sample. An example of the identification of a major circulating metabolite for a preclinical development study is demonstrated. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
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对气、固两相正激波松弛流动进行了数值研究,方程中考虑了压力梯度及非匀速运动引起的附加质量力。给出了完整的计算方法,对三种不同固相容积比、不同固相颗粒直径和不同马赫数分别进行了数值计算,所得计算结果给出了气、固两相的速度、温度、压力、密度、固相容积比及熵值沿流向分布情况。文章对气、固两相参数在松弛区中的变化规律进行了讨论。 相似文献
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Aguilar-Aguilar A Allen AD Cabrera EP Fedorov A Fu N Henry-Riyad H Leuninger J Schmid U Tidwell TT Verma R 《The Journal of organic chemistry》2005,70(23):9556-9561
[Structure: see text]. Ferrocenylketene (1) is calculated to be destabilized by 1.6 kcal/mol relative to phenylketene (10) by B3LYP isodesmic comparison to the corresponding alkenes. Ketene 1 generated by Wolff rearrangement in CH3CN is identified by the IR band at 2119 cm(-1) and has a rate constant for reaction with n-BuNH2 less than that for 10 by a factor of 5. 1,2-Bisferrocenyl-1,2-bisketene 18 and 1-ferrocenyl-2-trimethylsilyl-1,2-bisketene 21 were prepared by photochemical ring opening of the corresponding cyclobutenediones, and 18 undergoes rapid ring closure 67 times faster than the corresponding 1,2-diphenyl-1,2-bisketene, while bisketene 21 is longer lived than 18 by a factor of 3.2 x 10(4). 相似文献
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N-protected 1-amino-alkylphosphonamidates were synthesized using one-pot reactions of benzyl carbamate, aldehydes and alkoxyphosphine dichlorides and then with amines in the presence of triethylamine. 相似文献