The effect of fluorine substitution on the hydrogen bonding interaction in the complexes of fluorosubstituted pyridines and acetic acid was examined through theoretical method. Two types of double hydrogen bonding cyclic structures have been predicted, one with O–H···N and C–H···O interactions and the other with O–H···F and C–H···O interactions. The changes of the hydrogen bonding interactions are visualized by the reduced density gradient (RDG) and bond critical point (BCP) parameters analysis. With increasing in fluorination, the C–H···O bond strength increases, and the O–H···N and O–H···F bond strengths decrease. Although the O–H···N and O–H···F hydrogen bond energies decrease, the bond type has not changed in all of the fluorinated complexes. For the same degree of fluorination complexes, fluorine favors the C–H···O hydrogen bonding interaction through the cooperating of O–H···F and C–H···O hydrogen bonds, although fluorine is a weak hydrogen bond acceptor. The natural population analysis (NPA) and molecular electrostatic potentials (ESP) were adopted to further explore the variation characteristics of hydrogen bond strength. We found that the substituent fluorine atom acts as a role of electron withdrawing. The pyridine ring nitrogen atom and 2‐position fluorine atom become less negative, and the remaining H atom(s) become more electropositive with increasing degree of fluorination. The hydrogen bond strength is correlated with the charge redistribution of the proton H and acceptor (N and F) atoms.

中文翻译：

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阐明氟取代对吡啶和乙酸络合物中氢键相互作用的影响

通过理论方法研究了氟取代基对氟代吡啶与乙酸配合物中氢键相互作用的影响。预测了两种类型的双氢键环状结构，一种具有O–H···N和C–H···O相互作用，另一种具有O–H···F和C–H···O相互作用。氢键相互作用的变化可通过降低的密度梯度（RDG）和键临界点（BCP）参数分析来观察。随着氟化作用的增加，C–H···O键强度增加，而O–H···N和O–H···F键强度降低。尽管O·H··N和O·H··F的氢键能降低，但键类型并未在所有氟化配合物中改变。对于相同程度的氟化物，尽管氟是弱氢键受体，但氟通过OH··F和CH···O氢键的相互作用促进了CHH··O氢键相互作用。采用自然种群分析（NPA）和分子静电势（ESP）进一步探讨了氢键强度的变化特征。我们发现，取代基氟原子起着吸电子的作用。吡啶环上的氮原子和2位氟原子的负性变小，并且随着氟化程度的增加，其余的H原子正电性变强。氢键强度与质子H和受体（N和F）原子的电荷再分布相关。采用自然种群分析（NPA）和分子静电势（ESP）进一步探讨了氢键强度的变化特征。我们发现，取代基氟原子起着吸电子的作用。吡啶环上的氮原子和2位氟原子的负性变小，并且随着氟化程度的增加，其余的H原子正电性变强。氢键强度与质子H和受体（N和F）原子的电荷再分布相关。采用自然种群分析（NPA）和分子静电势（ESP）进一步探讨了氢键强度的变化特征。我们发现，取代基氟原子起着吸电子的作用。吡啶环上的氮原子和2位氟原子的负性变小，并且随着氟化程度的增加，其余的H原子正电性变强。氢键强度与质子H和受体（N和F）原子的电荷再分布相关。吡啶环上的氮原子和2位氟原子的负性变小，并且随着氟化程度的增加，其余的H原子正电性变强。氢键强度与质子H和受体（N和F）原子的电荷再分布相关。吡啶环上的氮原子和2位氟原子的负性变小，并且随着氟化程度的增加，其余的H原子正电性变强。氢键强度与质子H和受体（N和F）原子的电荷再分布相关。