Kehoe Zachary R, Woller Garrett R, Speetzen Erin D, Lawrence James B, Bosch Eric, Bowling Nathan P
Department of Chemistry , University of Wisconsin-Stevens Point , 2001 Fourth Avenue , Stevens Point , Wisconsin 54481 , United States.
Department of Chemistry , Missouri State University , 901 South National Avenue , Springfield , Missouri 65897 , United States.
J Org Chem. 2018 Jun 1;83(11):6142-6150. doi: 10.1021/acs.joc.8b01064. Epub 2018 May 11.
The electronic properties of a pyrazine-containing arylene ethynylene unit are influenced by hydrogen bond and halogen bond donors that are held in proximity of the pyrazine rotor. These interactions are evident with iodine- and bromine-centered halogen bonds and O-H- and C-H-based hydrogen bonds. Bathochromic shifts of UV-vis and fluorescence signals are the best indicators of this intramolecular attraction. The effects can be attenuated in solvents that are less favorable for intramolecular halogen or hydrogen bonding, such as 2-propanol, and amplified in solvents that are supportive, such as toluene. Intramolecular attractions promote planarity in the pyrazine ethynylene system, likely increasing the effective conjugation of the unsaturated backbone. Additionally, computations at the B3LYP and M062X levels of theory using 6-311++G(2d,p) and aug-cc-pVTZ basis sets suggest that the Lewis acidity of the halogen and hydrogen atoms influences electronic behavior even in the absence of conformational constraints.
含吡嗪的亚芳基乙炔单元的电子性质受吡嗪转子附近的氢键和卤键供体影响。这些相互作用在以碘和溴为中心的卤键以及基于O-H和C-H的氢键中很明显。紫外可见和荧光信号的红移是这种分子内吸引力的最佳指标。在不利于分子内卤键或氢键的溶剂（如2-丙醇）中，这种效应会减弱，而在支持性溶剂（如甲苯）中会增强。分子内吸引力促进了吡嗪乙炔体系的平面性，可能增加了不饱和主链的有效共轭。此外，使用6-311++G(2d,p)和aug-cc-pVTZ基组在B3LYP和M062X理论水平上的计算表明，即使在没有构象限制的情况下，卤素和氢原子的路易斯酸度也会影响电子行为。
