为什么巴比妥类药物的合成一般是在丙二酸二乙酯的2位引入相应的取代基后再与脲缩合成环？
参考答案：
这是因为丙二酸二酯2位亚甲基上的氢比较活泼，在醇钠催化下易于和卤烃反应。而环合后形成的巴比妥酸，由于4，6-位的羰基与相邻酰亚氮原子上的孤电子对发生p、π共轭，并存在下列平衡。
巴比妥酸单内酰亚胺双内酰亚胺三内酰亚胺因而降低2位亚甲基的活泼性。除少数诸如卤丙烯、3-卤代环己烯等较活泼的卤
烃能与其反应外，一般都很困难，收率极低，无实用价值。所以巴比妥类药物的合成一般是在丙二酸二乙酯的2位引入相应的取代基后再与脲缩合成环，而不采用先合环，再在5位引入取代基的方法。
第二卷（共35分） 第四部分：写作（共两节，满分35分） 任务型读写（共10小题；每空1分，满分10分） 阅读下列短文，根据所读内容在文章后的表格中填入恰当的单词。注意：表格中的每个空格只填1个单词 Can the thought of loved ones help reduce pain? This may indicate the importance of social relationships and staying socially connected. A study was recently conducted by researchers at the University of California in Los Angeles. In the study, the researchers asked 25 women to participate who had boyfriends with whom they had been in a good relationship for more than six months. The women received painful heat stimuli(刺激)to their forearms while they went through a number of different conditions. In one set of conditions, they viewed photographs of their boyfriend, a stranger and a chair. “When the women were just looking at pictures of their partner, they actually reported less pain to the heat stimuli than when they were looking at pictures of an object or pictures of a stranger, ” said study co-author Naomi Eisenberger, director of UCLA’s Social and Affective Neuroscience Laboratory, “Thus, the mere reminder of one’s partner through a simple photograph was capable of reducing pain.” In another set of conditions, each woman held the hand of her boyfriend, the hand of a male stranger and a squeeze ball. The study found that when women were holding their boyfriends’ hands, they reported less physical pain than when they were holding a stranger’s hand or a ball while receiving the same amount of heat stimulation. “This changes our idea of how social support influences people,” Eisenberger said. “This study proves how much of an impact our social ties can have on our experience and fits with other work emphasizing the importance of social support for physical and mental health,” Eisenberger added. The researchers advised that the next time people are going through a stressful or painful experience, if they cannot bring a loved one with them, a photo may do.
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