四卤化锡混合物中受扩散控制的卤原子交换动力学研究

NMR STUDY OF DIFFUSION-CONTROLLED EXCHANGE OF HALOGENS IN THE MIXTURES OF TIN (IV) TETRAHALIDES

以1 1 9SnNMR方法研究了四氯化锡和四溴化锡混合物 (1∶1 ,摩尔比 )交换体系在不同条件下的动力学性质 .测定了在不同浓度的氘代氯仿溶液中 5个交换组份的表观纵向弛豫时间 (T1 )及 5个组份相互间的交换速率常数 (k) ,结果表明交换速率常数与表观纵向弛豫速率成正比关系 ;同时 ,根据1 1 9Sn 1DNMR信号的线宽估测了有效横向弛豫时间 (T 2 ) ,并由T1 /T 2 推断在所研究的体系中分子的运动属NMR慢运动极限 .从实验结果可推断在所研究的复杂交换体系中 5个组份间的交换与分子自扩散运动有关 ,即化学交换与交换主体的扩散运动有必然的联系 .

The dynamics of halogen exchange in the mixtures of SnCl 4 and SnBr 4 at different concentrations were studied by using 119Sn NMR spectroscopy. The spin lattice relaxation times (T 1) and the exchange rate constants (k) were measured. The results show that the magnetization exchange rate constants in this system are proportional to the apparent relaxation rates. It is believed that the system is in the slow motion limit, since the T 1/T 2 ratio is very large. Theories indicate that the spin-lattice relaxation times are proportional to the molecular reorientation correlation time and the correlation time is related to diffusion. It can be concluded that halogen exchange in this system is 'diffusion-related'.