Molecularly Tuning the Radicaloid N–H···O═C Hydrogen Bond

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• 作者：Norman Lu ; Wei-Cheng Chung ; Rebecca M. Ley ; Kwan-Yu Lin ; Joseph S. Francisco ; Ei-ichi Negishi
• 刊名：Journal of Physical Chemistry A
• 出版年：2016
• 出版时间：March 3, 2016
• 年：2016
• 卷：120
• 期：8
• 页码：1307-1315
• 全文大小：357K
• ISSN：1520-5215

文摘

Substituent effects on the open shell N–H···O═C hydrogen-bond has never been reported. This study examines how 12 functional groups composed of electron donating groups (EDG), halogen atoms and electron withdrawing groups (EWG) affect the N–H···O═C hydrogen-bond properties in a six-membered cyclic model system of O═C(Y)–CH═C(X)N–H. It is found that group effects on this open shell H-bonding system are significant and have predictive trends when X = H and Y is varied. When Y is an EDG, the N–H···O═C hydrogen-bond is strengthened; and when Y is an EWG, the bond is weakened; whereas the variation in electronic properties of X group do not exhibit a significant impact upon the hydrogen bond strength. The structural impact of the stronger N–H···O═C hydrogen-bond are (1) shorter H and O distance, r(H···O) and (2) a longer N–H bond length, r(NH). The stronger N–H···O═C hydrogen-bond also acts to pull the H and O in toward one another which has an effect on the bond angles. Our findings show that there is a linear relationship between hydrogen-bond angle and N–H···O═C hydrogen-bond energy in this unusual H-bonding system. In addition, there is a linear correlation of the r(H···O) and the hydrogen bond energy. A short r(H···O) distance corresponds to a large hydrogen bond energy when Y is varied. The observed trends and findings have been validated using three different methods (UB3LYP, M06-2X, and UMP2) with two different basis sets.