核遲共振光譜可應用在研究化合物的結構,物理性質及分子運動等三個 領域.本研究分成兩個部分,首先是定量研究於W(CO)5L(L=P Ph3,PPh2Me,PPhMe2,PMe3)系列中,電子回饋到 CO配位基之2p軌域上的電子密度.此物理量可由氧-17的四極偶合 常數x的測定而求得,而x值則由核四極遲緩時間的測定可計算出,至於 相關時間值則由碳-13之化學位移異向遲緩時間求得.由取代基效應證 明配位基均為p-酸性:取代基的s-鹼性與p-酸性對〔2p〕值均有 影響,而前者稍微顯著.〔2p〕ax/〔2p〕rad值很接近理論值 2,p-中性或p-鹼性取代物,則大於此理論值極大值,呈現明顯的反 式效應,亦即具有強列的方向性.第二部分乃從事液態分子動力研究,探 討CCl3CN的再定位運動情形,由翻滾,自旋運動速度兩者加以描述 .翻滾運動速度可由碳-13化學位移異位向遲緩時間及核四極遲緩時間 兩種方法得到.自旋運動速度值可由氯的核四極遲緩時間其求得.結果顯 示此分子是進行非球形運動,而翻滾運動速度比自旋運動速度受溫度的影 響較大.在本實驗由碳-13化學位移異位向遲緩時間及氮的核四極遲緩 時間所求得的翻滾運動速度值相當接近,這說明由化學位移異位向遲緩時 間所求的相關時間的可靠性.然而於高溫下,化學位移異位向遲緩時間的 準確性就降低了,而應採用氮核四極遲緩時間的方法. NMR spectroscopic technique can be applied on structure elucida tion,probeof molecular motion an d determinationof phsical proper ties.The first subjectof this re search is to evaluate electron d ensity dispersed onto the carbon yl’s antibonding pi-orbitalsin t ungsten pentacarbonyl complexes, W(CO)5L{L=PPh3,PPh2Me,PPhMe2,PMe 3}.Experimental results indicate that these phosphines are subst antiallyp-accepting ligands.The p-electrondensity on the rest ca rbonyl groups are affected by su bstituents’ s-basicityand p-acid ity in a competitive manner.Toge ther with earlier studies,it is found that substitution effects on 2p-population for axial and r adial carbonyls are well predict ed by number of metal’s d-orbita ls through which back-bonding pr oceeds.For p-neutral or p-donati ng ligands,,these effects are st rongly directional.The second pa rt of this research is to invest igate reorientational dynamics i nCCl3CN,which is characterized b y thespinning and tumbling diffu sion constant.These two motions can be solved by measuring the r eorientationalcorrelation times, tc,for both the CN and CCl vecto rs. Measurements of the values o f tc were accomplished bynitroge n-14 and chlorine-35 NMR quadrup olar relaxation time(T2q)experim ents.We have also utilized carbo n-13 chemical shift anisotropysp in-lattice relaxation times(T1CS A) todetermine tc(CN).Derived ma gnitudes ofspinning and tumbling diffusion constants reveal this molecule undergoes a significan tly anisotropicreorientation.Reo rientational diffusionconstants obtained from T1CSA(13C) andT2q( 14N)are in good consistence at v arious temperatures. Hence,this studyhas laid foundation for fut ure researchperformed on investi gation of bonding in M-CN comple xes.
|