title: Molecularly Tuning the Radicaloid N-H···O═C Hydrogen Bond.
abstract: 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.
authors: Department of Chemistry, Purdue University , 1393 Brown Building, West Lafayette, Indiana 47907-1393, United States.|Institute of Organic and Polymeric Materials, National Taipei University of Technology , Taipei 106, Taiwan.
authors: Norman
authors: N
authors: Lu
authors: Institute of Organic and Polymeric Materials, National Taipei University of Technology , Taipei 106, Taiwan.
authors: Wei-Cheng
authors: WC
authors: Chung
authors: Department of Chemistry, Purdue University , 1393 Brown Building, West Lafayette, Indiana 47907-1393, United States.
authors: Rebecca M
authors: RM
authors: Ley
authors: Institute of Organic and Polymeric Materials, National Taipei University of Technology , Taipei 106, Taiwan.
authors: Kwan-Yu
authors: KY
authors: Lin
authors: Department of Chemistry, Purdue University , 1393 Brown Building, West Lafayette, Indiana 47907-1393, United States.|Department of Chemistry, University of Nebraska-Lincoln , Lincoln, Nebraska 68588, United States.
authors: Joseph S
authors: JS
authors: Francisco
authors: Department of Chemistry, Purdue University , 1393 Brown Building, West Lafayette, Indiana 47907-1393, United States.
authors: Ei-Ichi
authors: E
authors: Negishi