Simple doublet

The sharp series members are all simple doublets which all show the same splitting, namely, that of the i P n and states. 

Here is the input file for an optimization of the transition structure for the reaction H3CO —t H2COH (a simple 1,2 hydrogen shift reaction). We specify a UHF calculation (open shell) since the molecular system is a doublet ... 

NMR is the method of choice for determining the ratio of EO units to PO units since the analysis is simple to perform, does not require calibration, and is applicable over a wide range of EO-PO ratios. The spectrum contains only two resonances a doublet due to the methylene groups of the PO units, and a composite band, which is due to the CH2O groups of the PO and EO... 

One possibility for this was demonstrated in Chapter 3. If impact theory is still valid in a moderately dense fluid where non-model stochastic perturbation theory has been already found applicable, then evidently the continuation of the theory to liquid densities is justified. This simplest opportunity of unified description of nitrogen isotropic Q-branch from rarefied gas to liquid is validated due to the small enough frequency scale of rotation-vibration interaction. The frequency scales corresponding to IR and anisotropic Raman spectra are much larger. So the common applicability region for perturbation and impact theories hardly exists. The analysis of numerous experimental data proves that in simple (non-associated) systems there are three different scenarios of linear rotator spectral transformation. The IR spectrum in rarefied gas is a P-R doublet with either resolved or unresolved rotational structure. In the process of condensation the following may happen. 

A 90° Gaussian pulse is employed as an excitation pulse. In the case of a simple AX spin system, the delay t between the first, soft 90° excitation pulse and the final, hard 90° detection pulse is adjusted to correspond to the coupling constant JJ x (Fig- 7.2). If the excitation frequency corresponds to the chemical shift frequency of nucleus A, then the doublet of nucleus A will disappear and the total transfer of magnetization to nucleus X will produce an antiphase doublet (Fig. 7.3). The antiphase structure of the multiplets can be removed by employing a refocused ID COSY experiment (Hore, 1983). 

There is still another situation that leads to second order spectra and this one usually cannot be anticipated. For example, take a look at the proton spectrum of 3,3,3-trifluoropropene in Fig. 2.9. This spectrum is not the simple one that one would expect for a monosubstituted ethylene. However, the second order nature of this spectrum can be understood after examining the fluorine-decoupled spectrum, which is given in Fig. 2.10. The decoupled spectrum displays the expected multiplets from the ABC system, each proton appearing as a doublet of doublets. The second order spectrum seen in Fig. 2.9 derives from the fact that the protons at 5.98 and 5.93 are seen from the 19F frequency as... 

Spectrum 5.6 also shows a good example of roofing , which we touched on earlier. If you imagine the simple case of a pair of doublets well separated from each other, then all four of their lines will be of almost equal intensity. But when coupled doublets get closer together, they become distorted so that their inner lines become more intense, and their outer lines less intense. This is the onset of non-first-ordemess . The closer a pair of coupled doublets are to each other, the more extreme the effect becomes. It is worth noting that the phenomenon can sometimes be a useful interpretive tool, as the roofing can indicate which doublet is coupled to which other one, in spectra where you encounter two or more systems of this type doublets which are coupled to each other, always roof towards a point between them, as shown. 

As we have already seen, accidental equivalence could be responsible for the theoretically nonequivalent protons of an AB system presenting as a singlet and for the more complex ABX system presenting as a simple doublet and triplet. But occasionally, even more interesting manifestation of accidental equivalence can be observed. Consider the molecule below (Structure 6.10) and its spectrum (Spectrum 6.6) which shows only the regions of interest to us - expanded and with the intervening region removed. 

Figure 12.8 shows an illustration of the above theory on a very simple model compound the Fe11 ion in (frozen) water. The high-spin ferrous ion is S = 2, and the observed resonance is from the intradoublet transition within the l 2) doublet (alternatively the I2S-VII72 "1") doublet) (Hagen 1982b). The simulation of the experimental... 

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