臺灣博碩士論文加值系統

　　核四極偶合常數（QCC）已經證明是一有力的工具，可用來偵測p鍵變化之情形，最近發展出由核四極弛緩在測定液態中此一物理量，此一新技巧必須要有一精確的電場梯度向量相關時間值（τc）, 在此研究中，由Tlq（14N）實驗和τC值之測定來偵測苯甲睛及其取代物間p電子移動的情形。
　　首先針對苯甲睛之對位碳上的弛緩時間及NOE效應並進而導出其偶極弛緩速率（TIDD），求出這分子的τC值（7.78ps），再經由偵測氮-14核四極弛緩時間（0.482ms），結果得到QCC(14N)=4.25MHz，另外為了證實可以縱化學位移不等方向性之弛緩時間（T1CSA）中求出τC，我們在兩個磁場測量－CN的弛緩時間，從T1CSA得到πc(8.86ps)，而QCC值（3.98MHz），和T1DD所獲得值符合，由此可知T1CSA也是一個可以求出□c的方法，而由上述兩種數據得知pi電子密度是從苯環移動到－CN的pi軌域上，這結果可用以解釋對位碳原子在碳－13NMR圖譜中移向低磁場。
　　同時也以相同的方法做溶劑效應及不同取代基對於QCC的影響，這兩個方法都同時顯示出不同取代基之QCC的增加，則是由於取代基拉電子的特性，故可從QCC的結果中得知兩個pi系統間p電子密度移動的情形，這研究可作為未來氰金屬錯合物及－CN基的p鍵結研究之基礎，因為由T1CSA測定準確的相關時間值已被證實。

　　It has been recently demonstrated that nuclear quadrupolar relaxation time (Tlq) measurements provide a powerful tool for determination of quadrupole coupling constants (QCC) in liquids. This technique, however, requires an accurate value of the correlation time , τc, of the electric field gradient vector. In the research, we investigate the migration of π-electron between benzonitrile and its various substitution from the measured values of QCC(14N). Substitution and solvent effects have also been examined.
　　Measurements of the relaxation time and the nuclear Overhauser effect were first performed on the paracarbon in benzonitrile to extract the dipolar relaxation rate. This permits the determination of the correlation time, τc, of the two-fold molecular symmetry axis. Combining the calculated value of τc, 7.78ps, with the measured nitrogen-14 quadrupolar relaxation time, 0.482ms, the experimental values of QCC(14N), 4.25 MHz was obtained. In order to confirm the validity of extracting □c from TICSA, relaxation times of the cyano carbon were measured at two field strengths. Using the magnitude of τc (8.86 ps) derived from TICSA(21.1 sec), calculated values of QCC, 3.98 MHz, is in good agreement with that obtained from T1DD. The lover QCC, compared to that in HCN, manifests that pi-electron density migrates from benzene ring to the cyano pi-system. This conclusion may be applied to account for the downfield shift of the para-carbon in benzonitrile.
　　In studies of substitution effects on magnitudes of QCC, values of τc determined by both T1DD and T1CSA were in use .Experimental results from both methods reveal that substitution with halogens or methoxyl groups yields increased magnitudes of QCC's These can be rationalized by the electron withdrawing nature of substituents which results in a reversed migration of pi-electron density between the two pi-system. More importantly, the capability for calculating reliable values of correlation times from T1CSA is verified. The research performed here, therefore, has laid the foundation for future studies of pi-bonding variations in organic nitriles, cyano halogens, and cyano metal complexes.