Molecular equivalence number structural

Johnson, M.A. and Xu, Y.-j. Using molecular equivalence numbers to visually explore structural features that distinguish chemical libraries. 

Fig. 1. Empiric observation that more than approx 20 compounds from any scaffold need to be tested in order to be sure that an active will be found. (A) This shows the results from a whole cell assay in which the compounds have been classified using the Level 1 Ring System of the Structural Browsing Index (SBI) also known as molecular equivalence numbers or meqnums, which is the most-detailed level. The most-populated SBI containing only inactives is labeled 1, it contains 16 compounds. The most populated SBI containing actives is labeled 2. (B) Looking at only the compounds present in the most-populated SBI (2 above) and arranging the compounds in this SBI randomly, the smallest set of compounds in which an active (indicated by +) can be found is approx 30 compounds.

Fig. 4. Comparision of molecular equivalence numbers or structural browsing indices (SBI) containing active molecules from four different sublibraries. This figure shows how, even though the libraries described in Fig. 3 occupy similar chemistry spaces, they still undersample certain areas so that some active classes are only found when screening one particular sublibrary and not the others. This figure takes the active compounds represented in Fig. 3B using structural Browsing Indices and shows which library the actives came from. This serves to emphasize how active compounds with particular structural features may be identified in only one of the three sublibraries, e.g., compounds containing the SBI 7704 are only found in the CAC sublibrary.

Cyclopropene has the correct number of it electrons to be aromatic, namely 4(0) + 2 = 2, but it does not have a continuous closed loop of 2p orbitals. If, however, the CH2 group becomes a CH+ group in which the carbon atom is sp hybridized and has a vacant 2p orbital, thus still containing only two electrons, then the overlap of orbitals is continuous, and according to molecular orbital theory, the cyclopropenyl cation should be aromatic. The cyclopropenyl cation can be drawn as a resonance hybrid of three equivalent contributing structures. The fact that we can draw three equivalent contributing structures is not the key to the aromaticity of this cation the key is that it meets the Hiickel criteria of aromaticity. 

An equivalent way of looking at the conclusion of item (2) is to recall that Eq. (5.40) gives the (number average) number of monomers of both kinds in the polymer and multiply this quantity by the average molecular weight of the two kinds of units in the structure (88 + 112)/2 = 100. 

X-ray diffraction patterns from dendrimers tend to lack sharp features and are similar to those from amorphous linear polymers. This suggests a molecular arrangement in dendrimers that is fairly disordered. There is also the problem that these molecules can exist in a large number of energetically equivalent conformations and that in solution there can be rapid interchange between these conformations. This contributes to the overall amorphous structure of dendrimers. 

One of the key parameters for correlating molecular structure and chemical properties with bioavailability has been transcorneal flux or, alternatively, the corneal permeability coefficient. The epithelium has been modeled as a lipid barrier (possibly with a limited number of aqueous pores that, for this physical model, serve as the equivalent of the extracellular space in a more physiological description) and the stroma as an aqueous barrier (Fig. 11). The endothelium is very thin and porous compared with the epithelium [189] and often has been ignored in the analysis, although mathematically it can be included as part of the lipid barrier. Diffusion through bilayer membranes of various structures has been modeled for some time [202] and adapted to ophthalmic applications more recently [203,204]. For a series of molecules of similar size, it was shown that the permeability increases with octa-nol/water distribution (or partition) coefficient until a plateau is reached. Modeling of this type of data has led to the earlier statement that drugs need to be both... 

In this book, in order that you can concentrate your attention on the NMR spectra, we shall provide you with the molecular formula in all cases. This in turn provides you with information which can be extremely useful during the process of solving the structure if the molecule only contains C, H, N and O then you can use the molecular formula to obtain the number of so-called double bond equivalents, i.e. information on the degree of unsaturation. Though there are various formulas which can be devised to do this, we recommend the calculation using the following formula for a molecule CaHbOcNd, the number of double bond equivalents DBE is calculated as follows... 

The assessment of surfactant structures and optimal mixtures for potential use in tertiary flooding strategies in North Sea fields has been examined from fundamental investigations using pure oils. The present study furthermore addresses the physico-chemical problems associated with reservoir oils and how the phase performance of these systems may be correlated with model oils, including the use of toluene and cyclohexane in stock tank oils to produce synthetic live reservoir crudes. Any dependence of surfactant molecular structure on the observed phase properties of proposed oils of equivalent alkane carbon number (EACN) would render simulated live oils as unrepresentative. 

Geometry errors increase with the size of a system when the number of nonbonded interactions increases, and folded conformations are differently affected than extended ones. That is, MP2-energies calculated at HF-geometries can be inaccurate, because geometry errors are not necessarily the same in different conformations of the same molecule. Regarding the molecular structures it can be shown that, even when differences between MP2 geometries and the HF equivalents are small, they can be significant. 

The main statistical characteristic of the chemical structure of a heteropolymer among those pertaining to the first type is the distribution of molecules f( h, 12) for numbers l and h of their constituent monomeric units Mi and M2. In dealing with a high-molecular weight polymer, these numbers may be taken as continuous variables, uniquely specifying chemical size l=l + h and composition f = li/l of a macromolecule. Under such a consideration, it is more convenient instead of function /(Zi, l2) to use the equivalent function of Size-Composition Distribution (SCD) f(l, < ) This is possible to represent... 

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