Pseudorotation in XPF4
Pseudorotation in XPF4
复制标题
XPF4 中的赝旋转
DOI：
10.1021/ja00824a013
复制
发表时间：
1974
影响因子：
15
通讯作者：
G. Whitesides
中科院分区：
文献类型：
--
作者：
M. Eisenhut;H. Mitchell;D. Traficante;R. J. Kaufman;J. Deutch;G. Whitesides
本文研究了（CH_3）_2NPF_4（1）、C_1PF_4和CH_3 PF_4的~（81）P核磁共振谱随温度的变化。轴向和赤道氟（CH 3）2NPF 4和C1 PF 4的交换遵循Berry伪旋转预期的置换方案;即，轴向和赤道氟原子同时交换。1的假旋转速率与1的浓度无关，但由THF和（CH 3）20催化。1在CHCl 2F中的假旋转的活化自由能为AG*= 8.8±0.2 kcal/mol（-85），C1 PF 4在CHCl 2F中的假旋转的活化自由能为AG*~ 4.2±0.3 kcal/mol（-177）。将这些速率与由其他人获得的数据相结合表明，具有组成XPF 4的化合物的相对伪旋转速率以（CH 3）2N< SR，H< Cl<CH 3，F的顺序增加。本文提出了一种新的计算方法，它可以计算低浓度的中间体沿着1的赝旋转坐标对光谱的影响。这一过程表明，与两个基态处于平衡状态的单个中间体的影响，一般可以通过在核自旋系统的通常的Kaplan-Alexander运动方程中只加入一个称为“转移算符”的算符A来精确地描述。将该方法应用于1的光谱表明，即使正方形金字塔是沿伪旋转坐标的中间沿着，也不可能在目前可获得的光谱分辨率下通过nmr线形分析检测到它。
The temperaturedependence of the 81P nmr spectra of (CH3) 2NPF4 (1), C1PF4, and CH3PF4has been examined. The interchange of axial and equatorial fluorinesin (CH3) 2NPF4 and C1PF4 follows the permutational scheme expected for Berry pseudorotation; viz., both axial and equatorial fluorine atoms interchange at the same time. The rate of pseudorotation of 1 is independent of the concentration of 1 but is catalyzed by THF and (CH3) 20. The free energy of activation for pseudorotation of 1 in CHC12F is AG*= 8.8±0.2 kcal/mol at—85, and for C1PF4 in CHC12F is AG*~ 4.2±0.3 kcal/mol at—177. Combination of these rates with data obtained by others indicates that the relative rates of pseudorotation of compounds having the composition XPF4 increases in the order (CH3) 2N< SR, H< Cl< CH3, F. A new procedure has been developedwhich permits calculation of the influence of an intermediate present in low concentration along the pseudorotation coordinate for 1 on its spectrum. This procedure establishes that the influence of a single intermediatein equilibrium with two ground states can in general be described exactly by incorporation of only one further operator, called the “transfer opera-tor” A, into the usual Kaplan-Alexander equation of motion of the nuclear spin system. Application of this pro-cedure to the spectrum of 1 indicates that even if a square pyramid were an intermediate along the pseudorotation coordinate, it would not be possible to detect it by nmr line shape analysis at presently accessible spectral resolution.