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。选择的反应是富电子基团(如胺)或含负电氧原子的基团与贫电子基团(如碳-碳双键)的加成反应，这些基团带有电子吸引基团。将制备一对这样的基团紧密相连的分子。它们之间的成键程度将通过测量它们之间的电子密度来检测，并通过对粉末晶体样品的核磁共振(核磁共振)测量-检测富电子基团的氮(As 15N)或氧(As 17O)原子。这些测量都处于这两种技术的前沿。特定分子上的电子密度分布是通过对小晶体的非常精确的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项技术来研究弱成键相互作用。尤其重要的是确定随着基团之间的距离减小，即随着键的形成，反应基团之间的电子密度分布的性质如何变化。对粉状晶体样品进行核磁共振测量意味着，X射线衍射确定的固态结构可以直接与核磁共振实验中来自N或O的信号的位置有关。使用17O的核磁共振测量将是开创性的，因为只有通过最近技术的发展，包括样品在磁场中的双旋转，这才变得可行。然而，对于17O测量，必须制备富含17O同位素的化合物。最后，也是特别重要的一点是，伴随氧阴离子的阳离子的选择将有所不同，以确定这如何改变氧阴离子的反应性，这将通过在先前结果的基础上进行结构(X射线衍射)和核磁共振测量来监测。氧的反应性预计会被与它结合得更紧密的阳离子所降低，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.