问题 单项选择题

香豆素类化合物在碱中长时间放置

A.不发生变化
B.生成顺式邻羟基桂皮酸盐
C.生成顺式邻羟基桂皮酸
D.生成反式邻羟基桂皮酸盐
E.生成反式邻羟基桂皮酸

答案

参考答案:D

解析: 本题考查香豆素类与碱的作用。
香豆素的化学结构有内酯性质,易于碱水解反应得顺邻羟桂皮酸。但长时间碱液放置或UV照射,可转变为稳定的反邻羟桂皮酸。某些具有特殊结构的香豆素,如C8取代基的适当位置上有羰基、双键、环氧等结构者,和水解新生成的酚羟基发生缔合、加成等作用,可阻碍内酯的恢复,保留了顺邻羟桂皮酸的结构。

阅读理解

What do you think is the most common illness? Do you get ill sometimes? We are lucky to live now, because there are lots of medicines to make people better.

The most common illness in the world is the cold. It often begins with a sore throat. Then you sneeze and your nose runs. You usually have a headache too. Often you cough later. It’s not a very bad illness, but you can feel quite ill.

There isn’t a cure (治愈) for a cold, but you can take medicines to make you feel better. For instance, aspirin (阿斯匹林) can stop your headache. It is good to rest, and to drink a lot of water too. A doctor once said to me, “With the proper medicine, a cold will continue for seven days. With no medicine, it will continue for a whole week!”

Where does our medicine come from? A long time ago, people knew that some plants made them feel better. They ate the leaves, the roots, the fruit, or the seeds of plants. For instance, the juice of lemons makes a sore throat feel better.

In modern times, scientists have looked at these plants, and found out which chemicals (化学物质) are in them. Many of our medicines today are made from those chemicals.

There are some illnesses which we can’t cure yet. And nobody has found a cure for old age. But because of modern medicines, most people now live longer than their grandparents.

小题1:How does a cold often begin?

______________________________________________________________

小题2:Can aspirin stop a headache?

______________________________________________________________

小题3:How long does a cold usually continue?

______________________________________________________________

小题4:What kind of juice makes a sore throat feel better?

______________________________________________________________

小题5:What are many of our medicines today made from?

______________________________________________________________

单项选择题