共查询到19条相似文献,搜索用时 140 毫秒
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为弄清聚芳醚酮单体在硫酸中变色(红)现象,通过13C NMR研究了它们在CDCl3、CDCl3+DMSO-d6和H2SO4的13C谱化学位移及氟端基偶合情况.研究表明:这些单体溶于硫酸时,羰基碳弛豫时间缩短化学位移增加,而与羰基相连的季碳弛豫时间减小化学位移也减少.据此,首次提出硫酸使这些单体极化的机理为正极性磺酸基使羰基发生电子离城,变温13C谱对此进行了验证. 相似文献
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利用离子性指数(INI)和立体效应参数(α、β、γ)对100个膦化合物中磷原子进行结构表征,并与其核磁共振磷谱(31P NMR)建立了优良的定量构谱相关(QSSR)模型:δP=-163.695 3-1.003 1INI+34.632 7α+13.892 9β-3.331 7γ. 建模的计算值、留一法(Leave-One-Out, LOO)交互校验(Cross-Validation, CV)预测值的复相关系数(R)分别为0.976 5和0.973 9. 所建模型不仅在一定程度上阐明了膦类化合物31P NMR谱化学位移与其分子结构信息之间的关系,同时也提供了一种从理论上计算膦类化合物31P NMR谱化学位移的新方法,并对深入了解膦类化合物结构与性能的关系及解析、预测其31P NMR谱提供了一定的理论依据. 相似文献
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羰基13C NMR化学位移的计算 总被引:1,自引:1,他引:0
根据核外电子云球对称效应原理,建立化学位移统一计算公式,计算了醛、酮、酰氯、羧酸和酯中羰基的13C NMR化学位移,在一定程度上说明了影响13C NMR化学位移的主要结构因素,并对一些反常现象作出了直观合理的解释。 相似文献
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二正丁基锡(IV)基羧酸酯的谱学表征 总被引:10,自引:0,他引:10
合成了10个二正丁基锡(IV)基羧酸酯化合物{[nBu2Sn (O2CR)]2O}2(A1~A5)和nBu2Sn (O2CR)2(B1~B5)(R=1:CCl3;2:CHCl2;3:CH2Cl;4:PhCH=CH;5:2,2,3,3-四甲基环丙基),其中A4、A5和B5为新化合物,对它们进行了元素分析和IR及、1H、13C、119Sn NMR谱表征,重点讨论了13C和119Sn NMR谱的谱学特征及化学位移值与母体酸的PKa值大小的关系,并在此基础上推测了它们分子结构。 相似文献
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利用1H-1H COSY,1H-13C HMQC,HMBC等2D NMR技术对一种新的配体1-(2-羧基苯基甲酰基)氨基硫脲(H3L)进行1H、13C NMR谱数据分析与归属,对于它与Cu+离子配位的化合物[Cu2(H3L)2Cl2](H2O)3也作了1H、13C NMR的测定,简单讨论了它的配位行为,粗略确定了它的结构. 相似文献
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采用1H-1H COSY,HMQC、HMBC等2D NMR技术对化合物(Et4N)2[Pd2(mp)2(μ-mpH)2]进行1H、13C NMR谱数据分析与归属,表明它在DMSO溶液中仍保持原有固体状态的分子结构. 相似文献
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按取代苯甲酰胺、取代N-甲基苯甲酰胺、取代N,N-二甲基苯甲酰胺三类,提出了计算这三类化合物中羰基17O-NMR化学位移的公式:δcal(17O)=δ0n+C×ΣΔ,并通过线性回归法结合最小二乘法得到11种取代基参数,计算结果用以上三类化合物的33个羰基17O-NMR化学位移数据为样本点作回归检验,置信度为99.5%,计算误差Δδ小于1.0(相对误差小于0.1%)的17O-NMR化学位移计算值占90%以上. 相似文献
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提出计算脂肪酮和脂肪酰卤羰基17O-NMR化学位移的公式:δcal=δ0n+C×Δα,通过线性回归法确定了22种取代基参数.经回归检验表明该公式计算结果置信度为99.5%,与实验值的偏差Δδ在10.0以内的羰基17O-NMR化学位移计算值在90%左右. 相似文献
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An earlier study fit calculated dynamic 13C‐NMR spectra in trifluoroacetic acid (TFA) (with added sulfuric acid) to slow exchange between N‐protonated and O‐protonated tautomers of 1‐azabicyclo[3.3.1]nonan‐2‐one. The present study reports simultaneous observation of both carbonyl 13C peaks in 40% sulfuric acid/60% TFA at ?40 °C. This furnishes the only example in which experimental carbonyl 13C chemical shifts may be compared with a neutral lactam (in TFA or CDCl3) with its N‐protonated and O‐protonated derivatives. The seemingly anomalous upfield chemical shifts (experimental and computational) of the 13C carbonyl peaks in this N‐protonated lactam (and other twisted N‐protonated lactams) relative to the free bases are compared with data for unstrained protonated lactams and amides. The results are rationalized through conventional resonance structures. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
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The effect of protonation to formanilides was studied by measurements of 13C-NMR chemical shifts in CDCl3 and methanesulfonic acid. It was found that the 13C shift of the ring carbon, to which the amide group is attached, exhibits an upfield shift by the protonation, whereas the peaks of the rest of ring carbons and carbonyl carbon shift downfield. The protonation-induced shifts of the ring carbons were found to be roughly correlated with the differences of the total electron densities between formanilides and their monocations. From the comparison between the protonation-induced shifts and the differences of the total electron densities at the carbons, especially at the carbonyl carbon, it is suggested that N-protonation is partly involved, although O-protonation seems to be dominant. 相似文献
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The 1H and 13C NMR chemical shift assignments of a series of (E) - and (Z)-N,N-Dialkylacetamides [CH3C(O)NR1R2, with R1/R2=Me/Et (1), Me/n-Bu (2), Et/n-Bu (3), Et/t-Bu (4), Me/Hydrcxyethyl (5)., Et/Hydroxyethyl (6), Et/Acetylhydroxyethyl (7)] are reported. The 1H chemical shifts for the N-substituents of the amides 1–7 recorded in benzene-d6 and in chloroform-d1 are in agreement with the Hatton and Richards (ASIS) and Paulsen-Todt models, respectively. The 13C chemical shifts for the N-substituents of compounds 1–3 were compared with data of the corresponding symmetrical amides, and the results can be explained by the reciprocal steric compression effect of one N-substituent on the other. The validity of this explanation is confirmed by 13C spin-lattice relaxation time (T1) measurements. 相似文献
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NMR and DFT studies on persistent carbocations derived from benzo[kl]xanthene,dibenzo[d,d′]benzo[1,2‐b:4,3‐b′]difuran,and dibenzo[d,d′]benzo[1,2‐b:4,5‐b′]difuran in superacidic media 下载免费PDF全文
Takao Okazaki Madoka Nakagawa Takeshi Futemma Toshikazu Kitagawa 《Journal of Physical Organic Chemistry》2016,29(2):107-111
Persistent carbocations generated by the protonation of hetero‐polycyclic aromatic compounds with oxygen atom(s) were studied by experimental NMR and density function theory calculations. Benzo[kl]xanthene ( 1 ), dibenzo[d,d′]benzo[1,2‐b:4,3‐b′]difuran ( 2 ), and dibenzo[d,d′]benzo[1,2‐b:4,5‐b′]difuran ( 3 ) were synthesized by the annulation of arenediazonium salts. Compound 1 in FSO3H‐SbF5 (4:1)/SO2ClF and 3 in FSO3H‐SbF5 (1:1)/SO2ClF ionized to 1aH+ with protonation at C(4) and to 3aH+ with protonation at C(6), and these cations were successfully observed by NMR at low temperatures. The density function theory calculations indicated that 1aH+ and 3aH+ were the most stable protonated carbocations and that 2 should ionize to 2aH+ with protonation at C(6). According to the changes in 13C chemical shifts (Δδ13C), the positive charge was delocalized into the naphthalene unit for 1aH+ , into one benzo[b,d]furan unit for 2aH+ , and into one benzo[b,d]furan unit for 3aH+ . Copyright © 2015 John Wiley & Sons, Ltd. 相似文献