In this work, a conceptual DFT investigation is carried out to study the electrophilic aromatic substitution reaction (SEAr) of 1,2-dimethoxybenzene and 3-(p-nitrobenzoyloxy)-but-3-en-2-one (a captodative olefin). Her...In this work, a conceptual DFT investigation is carried out to study the electrophilic aromatic substitution reaction (SEAr) of 1,2-dimethoxybenzene and 3-(p-nitrobenzoyloxy)-but-3-en-2-one (a captodative olefin). Herein, we have studied the regioselectivity of such reactions considering the effect of solvents of different polarities and the presence of BF3 as the catalyst. Understanding the effect of the solvent and the role of the Lewis catalyst on the pathway of Friedel-Crafts reactions is important to further facilitate the introduction of side chains in aromatic rings with captodative olefins, and thus be able to synthesize compounds analogous to natural products, e.g., α-asarone. Global and local reactivity descriptors were obtained, finding a key role when these reactions take place in the presence of nonpolar solvents. In addition, the Intrinsic Reaction Coordinate diagrams (IRCs) were calculated. Such results of the free activation energy (ΔG‡) clearly show that this reaction is entirely regioselective, forming the unique product in the para position, in agreement with our predictions of the local reactivity descriptors obtained from the Parr functions, wherein the first reaction step, the carbon C4 of the aromatic compound 1,2-dimethoxybenzene is favored. Moreover, from the IRCs, we found that the reactivity of the para adduct increases in the presence of nonpolar solvents. Interestingly, considering a polar solvent (MeCN), the intermediate formed (σ-complex) is more stable since it presents a more significant charge transfer with the solvent than the intermediate in the presence of a nonpolar solvent, making a reaction more challenging to reach when the reaction is carried out in the presence of MeCN because of the increasing of the energetic barrier from σ-complex to the TS2 in the intrinsic reactive coordinate diagram. Therefore, the polarity of the solvent plays an important role, particularly in the activation energy of the TS2. Our computational results explained our experimental results quite well, confirming the importance of the solvent’s polarity to this SEAr reaction and explaining why, experimentally, the nonpolar solvent drove the reaction under catalyzed conditions.展开更多
2009年以来,中美直飞航班的运力增加了八倍。2019年上半年的全球航空业,充满变数。波音发生空难事故,全部波音737 MAX 8和MAX 9机型停止执飞,随之带来的运力骤减,考验着航空公司在航班正常率、飞机利用率、营业收入、成本控制等各方面...2009年以来,中美直飞航班的运力增加了八倍。2019年上半年的全球航空业,充满变数。波音发生空难事故,全部波音737 MAX 8和MAX 9机型停止执飞,随之带来的运力骤减,考验着航空公司在航班正常率、飞机利用率、营业收入、成本控制等各方面指标的运营能力。不过,对于机队中没有737MAX的达美航空来说,反而因为这种供需关系的变化而获益。展开更多
目的探讨外生型剖宫产术后瘢痕妊娠患者的微创手术疗效,为该类患者的微创应用提供可参考依据。方法共纳入80例该院外生型剖宫产术后瘢痕妊娠患者作为研究对象,采用随机数字法平均分为观察组与对照组两组,分别给予腹腔镜微创治疗及宫腔...目的探讨外生型剖宫产术后瘢痕妊娠患者的微创手术疗效,为该类患者的微创应用提供可参考依据。方法共纳入80例该院外生型剖宫产术后瘢痕妊娠患者作为研究对象,采用随机数字法平均分为观察组与对照组两组,分别给予腹腔镜微创治疗及宫腔镜微创治疗,观察患者手术过程中失血量、手术时间、月经复潮时间及病灶完全消失时间等,比较两组的差异及术后不良反应。结果 40例宫腔镜患者中1例因术中出血量较大转开腹手术切除治疗,术后7例患者复查彩超示有明显病灶,成功率为82.5%。40例腹腔镜患者均顺利完成手术,术后复查无明显病灶,成功率100.0%。两组成功率比较差异有显著性(P<0.05)。观察组患者术中出血量、术后引流量、住院时间、血清β-h C G正常时间、月经复潮时间及病灶完全消失时间均明显低于对照组患者,两组间比较差异有显著性(P<0.05)。术后观察组患者C R P水平低于对照组患者,差异有显著性(P<0.05)。结论腹腔镜微创治疗对外生型剖宫产术后瘢痕妊娠患者创伤小、恢复快,对瘢痕子宫的修复有更好的疗效。展开更多
文摘In this work, a conceptual DFT investigation is carried out to study the electrophilic aromatic substitution reaction (SEAr) of 1,2-dimethoxybenzene and 3-(p-nitrobenzoyloxy)-but-3-en-2-one (a captodative olefin). Herein, we have studied the regioselectivity of such reactions considering the effect of solvents of different polarities and the presence of BF3 as the catalyst. Understanding the effect of the solvent and the role of the Lewis catalyst on the pathway of Friedel-Crafts reactions is important to further facilitate the introduction of side chains in aromatic rings with captodative olefins, and thus be able to synthesize compounds analogous to natural products, e.g., α-asarone. Global and local reactivity descriptors were obtained, finding a key role when these reactions take place in the presence of nonpolar solvents. In addition, the Intrinsic Reaction Coordinate diagrams (IRCs) were calculated. Such results of the free activation energy (ΔG‡) clearly show that this reaction is entirely regioselective, forming the unique product in the para position, in agreement with our predictions of the local reactivity descriptors obtained from the Parr functions, wherein the first reaction step, the carbon C4 of the aromatic compound 1,2-dimethoxybenzene is favored. Moreover, from the IRCs, we found that the reactivity of the para adduct increases in the presence of nonpolar solvents. Interestingly, considering a polar solvent (MeCN), the intermediate formed (σ-complex) is more stable since it presents a more significant charge transfer with the solvent than the intermediate in the presence of a nonpolar solvent, making a reaction more challenging to reach when the reaction is carried out in the presence of MeCN because of the increasing of the energetic barrier from σ-complex to the TS2 in the intrinsic reactive coordinate diagram. Therefore, the polarity of the solvent plays an important role, particularly in the activation energy of the TS2. Our computational results explained our experimental results quite well, confirming the importance of the solvent’s polarity to this SEAr reaction and explaining why, experimentally, the nonpolar solvent drove the reaction under catalyzed conditions.
文摘2009年以来,中美直飞航班的运力增加了八倍。2019年上半年的全球航空业,充满变数。波音发生空难事故,全部波音737 MAX 8和MAX 9机型停止执飞,随之带来的运力骤减,考验着航空公司在航班正常率、飞机利用率、营业收入、成本控制等各方面指标的运营能力。不过,对于机队中没有737MAX的达美航空来说,反而因为这种供需关系的变化而获益。
文摘目的探讨外生型剖宫产术后瘢痕妊娠患者的微创手术疗效,为该类患者的微创应用提供可参考依据。方法共纳入80例该院外生型剖宫产术后瘢痕妊娠患者作为研究对象,采用随机数字法平均分为观察组与对照组两组,分别给予腹腔镜微创治疗及宫腔镜微创治疗,观察患者手术过程中失血量、手术时间、月经复潮时间及病灶完全消失时间等,比较两组的差异及术后不良反应。结果 40例宫腔镜患者中1例因术中出血量较大转开腹手术切除治疗,术后7例患者复查彩超示有明显病灶,成功率为82.5%。40例腹腔镜患者均顺利完成手术,术后复查无明显病灶,成功率100.0%。两组成功率比较差异有显著性(P<0.05)。观察组患者术中出血量、术后引流量、住院时间、血清β-h C G正常时间、月经复潮时间及病灶完全消失时间均明显低于对照组患者,两组间比较差异有显著性(P<0.05)。术后观察组患者C R P水平低于对照组患者,差异有显著性(P<0.05)。结论腹腔镜微创治疗对外生型剖宫产术后瘢痕妊娠患者创伤小、恢复快,对瘢痕子宫的修复有更好的疗效。
