Mirror image method

MDPM mode dispersion phase matching MIM mirror image method... 

Due to the zero slope at the wall, the mirror image method can be used to find the capillary force the second identical particle (mirror image) floats at the distance 2s from the original one ([19], Figure 3.12(a)). In... 

As in tic, another method to vaUdate a chiral separation is to collect the individual peaks and subject them to some type of optical spectroscopy, such as, circular dichroism or optical rotary dispersion. Enantiomers have mirror image spectra (eg, the negative maxima for one enantiomer corresponds to the positive maxima for the other enantiomer). One problem with this approach is that the analytes are diluted in the mobile phase. Thus, the sample must be injected several times. The individual peaks must be collected and subsequently concentrated to obtain adequate concentrations for spectral analysis. 

To understand how this method of resolution works, let s see what happens when a racemic mixture of chiral acids, such as (+)- and (-)-lactic acids, reacts with an achiral amine base, such as methylamine, CH3NH2. Stereochemically, the situation is analogous to what happens when left and right hands (chiral) pick up a ball (achiral). Both left and right hands pick up the ball equally well, and the products—ball in right hand versus ball in left hand—are mirror images. In the same way, both ( H- and (-)-lactic acid react with methylamine equally... 

When a molecule has two stereogenic centers, each has its own configuration and can be classified (R) or (5) by the Cahn-Ingold-Prelog method. There are a total of four isomers, since the first center may be (R) or (5) and so may the second. Since a molecule can have only one mirror image, only one of the other three can be the enantiomer of A. This is B [the mirror image of an (R) center is always an (5) center). The compounds C and D are a second pair of enantiomers and the rela-... 

In all of our examples so far, we have been comparing two compounds that are mirror images. For them to be mirror images, they need to have different configurations for every single stereocenter. Remember that our first method for drawing enantiomers was to switch all wedges with dashes. For the two compounds to be enantiomers, every stereocenter had to be inverted. But what happens if we have many stereocenters and we only invert some of them ... 

It is possible for a componnd to be its own mirror image. In such a case, the compound will not have a twin. It will be all by itself, and the total number of stereoisomers will be an odd number, rather than an even number. That one lonely compound is called a meso componnd. If you try to draw the enantiomer (using either of the methods we have seen), yon will find fhat your drawing will be the same compound as what yon started with. 

Answer We need to try to draw the mirror image and see if it is j ust the same compound redrawn. If we use the second method for drawing enantiomers (placing the mirror on the side), then we wiU be able to see that the compound we would draw is the same thing ... 

The method is applicable to only solid substances which form well defined crystals. Thus in 1848 Pasteur separated for the first time the active forms of sodium ammonium tartate by evaporating a recemic solution below 27°. Two type of crystals were obtained, which had different shapes and were the mirror images of each other. The crystals were separated under a microscope with the help of forceps. Since the crystals of one type were all d isomer and the crystals of the other type were 1 isomer, their separation led to a separation of the recemic mixture. On dissolving in solution they showed opposite rotation. 

NMR data [95]. This new method requires two sets of dipolar couplings from two different protein orientations. Together with the backbone dipolar couplings that are typically used (i.e., amide NH, C N, CaC, CaHa and the two-bond HNC ), CaCp dipolar couplings are also needed. Provided that the orientation of one peptide plane is known independently, the dipolar coupling data give rise to two possible orientations for the subsequent peptide plane, where the conformations about the alpha carbon in these two orientations are mirror images. One of the conformations can be ruled out because of chirality. 

In order to select the operating conditions for any fluorimetric method, the excitation and emission spectra of the analyte must be determined. Figure 2.9 illustrates the fact that an emission spectrum is an approximate mirror image of the excitation spectrum, the latter being similar to the absorption spectrum of the compound. 

The solutions of these crystal structures of enantiomorphous substances of natural origin give the complete stereochemistry of the molecules concerned, except for one piece of information the normal X-ray methods do not reveal wrhich of the two mirror-image structures is the correct one. There are, however, special X-ray methods that do give this information these are described in a later section. 

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