Answering questions about structure

What is its molecular symmetry (which determines the possibility of chirahty)  

What is its geometrical structure, i.e. the bond lengths and angles, or the nuclear positions, from which the bond lengths and angles can be deduced  

What is its electronic stracture, how are the electrons distributed over the molecular orbitals, and which of the orbitals are occupied or vacant  

The techniques we can use to try to answer some or all of these questions will depend on the kind of material we are working with. In this introductory chapter, we begin the process of providing some general answers to these questions they will often require a combination of methods. More in-depth responses will be found in the specialized chapters that follow. 

The second question we asked was whether our product was a single, pure compound. The key factors to recognize here are that, first, we should use techniques that give clear distinct peaks. This again brings NMR and vibrational spectroscopy, and possibly mass spectrometry, into focus, and powder X-ray diffraction can tell us how many crystalline phases are present. Second, if possible, we would like to use the peak intensities for quantitative analysis. We pursue this point in Section 2.9, but here we can note that if our compound has been characterized before, any peaks that are present in the new spectrum, but were not recorded for the original sample, may be assigned to impurities. But it is, of course, important to ensure that reference and sample spectra are recorded under the same conditions of phase, temperature, concentration and instrument resolution, so that the comparison can be as detailed and reliable as possible. 

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Molecular modeling seeks to answer questions about molecular properties— stabilities, reactivities, electronic properties—as they are related to molecular structure. The visualization and analysis of such structures, as well as their molecular properties and molecular interactions, are based on some theoretical means for predicting the structures and properties of molecules and complexes. If an algorithm can be developed to calculate a structure with a given stoichiometry and connectivity, one can then attempt to compute properties based on calculated molecular structure and vice versa. 

Answer the following questions about structure and bonding. 

The above examples illustrate how NMR spectra are routinely used to answer questions about reactions and products. Spectra are usually examined in conjunction with other information that permits a broad-based structure identification to be earned out. Outside of structure questions in texts and on exams, one is almost never handed an NMR spectrum and asked to identify die compound in die absence of odier supporting information. 

Bond orders and charge densities in the indigo molecule have been calculated [7] and compared with the results of X-ray analysis [8], These studies confirm the structural formula 1 and answer questions about the basic chromophore of the dye (see Section 2.4). 

In just the last few years, scientists have realized that scans may be powerful, noninvasive allies in the detection and control of post-chemo brain. But not all scans are alike. One of the differences between PET and MRI the way it was used in the Inagaki study is that MRI measures the brain s structure and volume. But PET is different. It answers questions about how we use our brains. 

In this chapter we have attempted to explore some ofthe conceptual and technical issues in using the newly available national datasets in England to answer questions about inclusion and achievement. Notably, file definition of special educational needs, differences in patterns of provision across LAs, and the variable number of children who could be described as having special educational needs make it difficult to collect or meaningfiilly analyse statistics about provision, attainment or the students. However, there is some value in looking at trends as long as file data are used and interpreted cautiously. Because of the enormous scale and file structure of the NPD and the PLASC, file data they contain may be assigned... 

We measure infrared spectra to answer questions about samples. One question we commonly try to answer is, What molecules are present in this sample , otherwise called unknown analysis. The peak positions in an infrared spectrum correlate with molecular structure, which is part of why infrared spectroscopy is useful. Over the last 100-plus years a great number of infrared spectra have been measured, and the peak positions of known molecules derived from these spectra can be used to identify the molecules in an unknown sample [1]. 

The focus of Part B is on the closely interrelated topics of reactions and synthesis. In each of the first twelve chapters, we consider a group of related reactions that have been chosen for discussion primarily on the basis of their usefulness in synthesis. For each reaction we present an outline of the mechanism, its regio- and stereochemical characteristics, and information on typical reaction conditions. For the more commonly used reactions, the schemes contain several examples, which may include examples of the reaction in relatively simple molecules and in more complex structures. The goal of these chapters is to develop a fundamental base of knowledge about organic reactions in the context of synthesis. We want to be able to answer questions such as What transformation does a reaction achieve What is the mechanism of the reaction What reagents and reaction conditions are typically used What substances can catalyze the reaction How sensitive is the reaction to other functional groups and the steric environment What factors control the stereoselectivity of the reaction Under what conditions is the reaction enantioselective ... 

In order to answer questions regarding the therapeutic and cosmetic uses of the myriad dermatological concoctions available, a pharmacist must be knowledgeable about the anatomical structure and physiological functions of the skin and the chemical compositions and physicochemical properties of its constituent tissues. Some understanding of how its properties are affected by disease and damage is a must, as is... 

The project group designed a questionnaire with 286 questions, structured to cover each substep of all the types of major steps encountered in the supply chains. If an enterprise covered more than one major step, this meant that more than one interview was carried out, with more than one person or more interviews with the same person. For each enterprise, the interviewees typically answered 150-200 questions about 1-3 major steps. The questions were designed by experts to describe the principles and intentions of the... 

The ribosome is a unique cellular machine in that its main functional component is RNA whereas proteins seem to play only a structural role. For a long time, it has been debated whether RNA or proteins contribute most to the ribosome s function. With the determination of high-resolution crystal structures, this question could finally be answered. Clearly, these structures have revolutionized the field of ribosome studies. Already in the 1980s, Yonath and coworkers had grown crystals of active ribosomes that diffracted to about 0.6 nm (6 A) (1 A = 0.1nm) resolution. However, owing to the large size of the ribosome of about 2 500 000 Da (lDa=lgmoP), the ribosome structure was not solved to atomic resolution until tbe year 2000. 

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