Fourier Transform 13C NMR Analysis of Some Methaqualone Metabolites

The natural abundance carbon-13 nuclear magnetic resonance spectra of some methaqualone metabolites were recorded using the pulse fourier transform technique. The chemical shift of various carbon resonances have been assigned on the basis of the chemical shift theory, multiplicities observed in SFORD spectrum and comparison with the chemical shifts of the corresponding carbons of methaqualone.     

A Device for Offsetting High Level Electrical Interferences in Low Level Detectors

It is often useful to maintain an analogue output of a signal which has excessive noise. At near D.C. frequencies, this is seldom possible. However, when the noise can be identified, two ways of correcting this situation are immediately available. The first is to eliminate the interference at the source and the second is to supply appropriate offset to this interference. In the case of high-level energy sources, it is virtually impossible to eliminate their interference and it becomes necessary to fabricate electrical offsets to do this. This procedure is well-established in electronics and is used extensively in operational amplifiers.     

Energy Transfer from the Upper Triplet States of Aromatic Molecules

The energy transfer from the upper triplet states of diphenylamine, naphthalene and triphenylene to toluene and hexene-1 is studed. Two mechanisms of dissipation transferred energy in solvents are discussed.     

Investigation of the substituent specific cross‐interaction effects on 13C NMR of the CN bridging group in substituted benzylidene anilines

The substituent effect on ¹³C NMR of the C?N in benzylidene anilines XPhCH?NPhY was investigated, in which the substituents X and Y are in p‐position or in m‐position of the two aromatic rings. The substituent effects including the inductive effects of X and Y, the conjugative effects of X and Y, and the substituent specific cross‐interaction effect were put into one model to quantify the ¹³C NMR chemical shift δ_C(C?N) of the C?N in XPhCH?NPhY. A penta‐parameter correlation equation with correlation coefficient 0.9975 and standard error 0.17 ppm was obtained for 80 samples of compounds. The result shows that the substituents X and Y have an opposite effect on the δ_C(C?N). The electron‐withdrawing effects of X decrease the δ_C(C?N); while the electron‐donating effects of X increase the δ_C(C?N). In contrast, the electron‐withdrawing effects of Y increase the δ_C(C?N); while the electron‐donating effects of Y decrease the δ_C(C?N). A new substituent specific cross‐interaction effect parameter Δσ² was proposed, which indicates that the most substituent specific cross‐interaction effect exists in the pair of max electron‐withdrawing group (EWG) and max electron‐donating group (EDG) or the pair of max EDG and max EWG. Further to verify the obtained correlation equation, 15 samples of model compounds were prepared and their δ_C(C?N) was measured in this work. The predicted δ_C(C?N) values with the obtained equation are in good agreement with the measured ones for these prepared compounds, which confirmed the reliability of the obtained equation. Copyright © 2010 John Wiley & Sons, Ltd.     

Minimization of the pulse's timing jitter in a dispersion-compensated WDM system

We address the problem of the collision-induced crosstalk between pulses in a dispersion-compensated WDM system composed of a periodic array of cells that include two or three fiber segments. Both the cross- and self-phase-modulation nonlinearities are taken into account. A semi-analytical approximation and direct simulations are used to calculate the frequency shift (FS) of colliding pulses, and to search for conditions which provide for minima of the FS and the temporal shift (TS), including the most promising possibility of minimizing both shifts simultaneously. Semi-analytical results, obtained by means of the perturbation theory, are in qualitative agreement with the numerical findings, especially in regimes near the optimum. In searching for the FS and TS minima, we investigate the effect of changing the initial width and chirp of the pulse, position of the amplifier within the dispersion–compensation period, group-velocity difference between the channels, allocation of the group-velocity-dispersion (GVD) inside the cell, and the average GVD. We conclude that a more sophisticated dispersion–compensation map, with three different local values of GVD, may be significantly more efficient than the one based on two different segments. A global FS minimum, with respect to the variation of all the parameters, is found.     

The Prediction of the 13C NMR Signal Positions in Substituted Naphthalenes,Part 2: The Use of Statistical Substituent Chemical Shift (SSCS) Values

The prediction of the ¹³C NMR signals for derivatives of naphthalene has been investigated using statistical Substituent Chemical Shift (SSCS) values. For α-derivatives the model had a correlation coefficient of observed versus predicted line positions of r=.98 with an standard deviation of 2.1ppm while in the β case r=.98 with the standard deviation being 2.0ppm. Prediction of the 9 and 10 positions had an r=.93 with the standard deviation being 1.5ppm. The data base consisted of 5250 signals from 525 naphthalene derivatives.     

取代基效应对二芳基硝酮CH=N(O)桥基1H NMR化学位移的影响

合成一系列取代二芳基硝酮XArCH=N（O）ArY化合物,测定其核磁共振氢谱（¹H NMR）,指认出桥基CH=N（O）上质子的化学位移δH[CH=N（O）],定量研究取代基效应对δH[CH=N（O）]的影响.得到一个4参数定量方程,标准偏差（S）为0.020,较好地表达了δH[CH=N（O）]的变化规律.结果表明,该类化合物的δH[CH=N（O）]主要受4个因素影响：X基团的场/诱导效应[σ_F（X）];Y基团的共轭效应[σ_R（X）];基团X和Y之间的特殊交叉作用（Δσ²）;以及基团X和O^-之间的特殊交叉作用[Δσ²_（X-O^-）].其中,Δσ²_（X-O^-）对δ_{H[CH=N（O）]}变化的贡献超过70%.通过δH[CH=N（O）]与二芳基希夫碱XArCH=NArY桥基CH=N上质子化学位移的δH（CH=N）比较发现,这两类化合物桥基上质子的化学位移之间没有良好的线性关系.因而,在应用NMR谱图解析有机化合物分子结构时,不能简单地用δH（CH=N）的变化去类比δ_{H[CH=N（O）]}的变化.