Bond Formation Studies By Charge Density Measurements and Solid State 17O NMR Spectrometry

这个项目涉及化学键的形成。所选择的反应是富电子基团如胺或含有带负电荷的氧原子的那些与贫电子基团如碳-碳双键的加成反应，所述贫电子基团具有连接的吸电子基团。分子将被制备成具有一对紧密靠近的这样的基团。它们之间的键形成程度将通过测量它们之间的电子密度来检测，并通过对粉末状晶体样品的核磁共振（NMR）测量来检测-检测富电子基团的氮（如15 N）或氧（如17 O）原子。这些测量都是这两种技术的前沿。特定分子上的电子密度分布是通过对小晶体进行非常精确的X射线衍射测量（XRD）来确定的，这将有助于在国际上越来越多地使用这种技术来检查弱键相互作用。特别重要的是确定反应基团之间的电子密度分布的性质如何随着基团之间的距离减小即随着键形成而变化。在粉末状晶体样品上使用NMR测量意味着通过X射线衍射确定的固态结构可以直接与NMR实验中来自N或O的信号的位置相关。使用17 O的NMR测量将是开创性的，因为这只是通过最近的技术发展才变得可行，包括在磁场中的样品的双旋转。然而，对于17 O测量，将需要制备富含17 O同位素的化合物。最后，并且特别重要的是，伴随氧阴离子的阳离子的选择将变化，以确定这如何改变氧阴离子的反应性，这将通过基于早期结果的结构（XRD）和NMR测量来监测。预计氧的反应性会被与其结合更紧密的阳离子降低，我们的测量将提供一种量化这一点的方法。

This project concerns the formation of chemical bonds. The reactions chosen are addition reactions of electron-rich groups such as amines or those containing negatively charged oxygen atoms with electron-poor groups such as carbon-carbon double bonds which have electron attracting groups attached. Molecules will be prepared which have a pair of such groups held in close proximity. The degree of bond formation between them will be detected by measurements of the electron density between them, and by nuclear magnetic resonances (NMR) measurements on powdered crystalline samples - detecting either the nitrogen (as 15N) or oxygen (as 17O) atom of the electron-rich group. These measurements are at the cutting edge of both these techniques. The electron density distribution on a particular molecule is determined from very accurate X-ray diffraction measurements (XRD) on a small crystal, and this will contribute to the growing use of this technique internationally to examine weak bonding interactions. Of particular importance is to determine how the properties of the electron density distribution between the reacting groups changes as the distance between the groups decreases i.e. as the bond forms. Use of NMR measurements on powdered crystalline samples means that the solid state structure determined by X-ray diffraction, can be directly related to the position of the signal from N or O in the NMR experiment. The NMR measurements using 17O will be ground breaking, since this has only become feasible through recent developments of the technique, including double rotation of the sample in the magnetic field. Nevertheless, for the 17O measurements it will be necessary to prepare compounds which are enriched in the 17O isotope. Finally, and of particular importance, the choice of cation accompanying the oxygen anion will be varied to determine how this alters the reactivity of the oxygen anion, which will be monitored by structural (XRD) and NMR measurements building on earlier results. The reactivity of the oxygen would be expected to be decreased by cations which bind more tightly to it, and our measurements will provide an approach to quantify this.