问题 问答题 简答题

举例说明紫外吸收光谱在分析上有哪些应用。

答案

参考答案:

(1)定性分析:max:化合物特性参数,可作为定性依据;有机化合物紫外吸收光谱:反映结构中生色团和助色团的特性,不完全反映分子特性;计算吸收峰波长,确定共扼体系等;甲苯与乙苯:谱图基本相同;结构确定的辅助工具;

(2)定量分析:依据:朗伯-比耳定律:吸光度:A=bc。有机化合物结构的辅助解析。

(3)可获得的结构信息.如:(1)200-400nm无吸收峰。饱和化合物,单烯。(2)270-350nm有吸收峰(ε=10-100)醛酮n→π*跃迁产生的R带。(3)250-300nm有中等强度的吸收峰(ε=200-2000),芳环的特征吸收(具有精细解构的B带)。(4)200-250nm有强吸收峰(ε104),表明含有一个共轭体系(K)带。共轭二烯:K带(230nm);不饱和醛酮:K带230nm,R带310-330nm,260nm,300nm,330nm有强吸收峰,3,4,5个双键的共轭体系

单项选择题
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There is a new type of small advertisement becoming increasingly common in newspaper classified columns.It is sometimes placed among “situations vacant”, although it does not offer anyone a job, and sometimes it appears among “situations wanted”, although it is not placed by someone looking for a job, either.What it does is to offer help in applying for a job.

“Contact us before writing your application”, or “Make use of our long experience in preparing your curriculum vitae or job history”, is how it is usually expressed.The growth and apparent success of such a specialized service is, of course, a reflection on the current high levels of unemployment.It is also an indication of the growing importance of the CV, with the suggestion that it may now qualify as an art form in its own right.

There was a time when job seekers simply wrote letters of application.“Just put down your name, address, age and whether you have passed any exams”, was about the average level of advice offered to young people applying for their first jobs when I left school.The letter was really just for openers, it was explained, everything else could and should be saved for the interview.And in those days of full employment the technique worked.The letter proved that you could write and were available for work.Your eager face and intelligent replies did the rest.

There is no doubt, however, that it is increasing number of applicants with university education at all points in the process of engaging staff that has led to the greater importance of the CV.

小题1:The new type of advertisement which is appearing in newspaper column        

A.informs job hunters of the opportunities available

B.informs employers of the people available for work

C.divides available jobs into various types

D.promises to offer useful advice to those looking for employment小题2:Nowadays a demand for this specialized type of service has been created because          .

A.there are so many people out of work

B.there are so many toplevel jobs available

C.there is a lack of jobs available for artistic people

D.the CV is considered to be a work of art小题3:In the past it was expected that first job hunters would        

A.write an initial letter giving their life history

B.keep any detailed information until they obtained an interview

C.have no qualifications other than being able to read and write

D.pass some exams before applying for a job小题4:The CV has become such an important document because           

A.there has been an increase in the number of applicants with degrees

B.there has been an increase in the number of jobs advertised

C.jobs are becoming much more complicated nowadays

D.the other processes of applying for jobs are more difficult to do