现代波普学之UV.ppt

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1、现代波普学第二篇紫外光谱分析法2.1BackgroundA.BasicsofUVLightAbsorptionUltraviolet/visiblespectroscopyinvolvestheabsorptionofultraviolet/visiblelightbyamoleculecausingthepromotionofanelectronfromagroundelectronicstatetoanexcitedelectronicstate.Ultraviolet/Visiblelight:wavelengths(l)betwe

2、en190and800nmfeigeoerRadiationintheultraviolet(UV)andvisibleregionofthespectrumhasthecorrectenergytoexciteelectronsinoneorbitalintoanorbitalofhigherenergyTheelectronsthataremosteasilypromotedarethoseinconjugated-bondsAconjugatedmoleculehasalternatingsingleandmultiplebonds

3、inatleastpartofthemolecule紫外光谱图吸收峰的位置、吸收强度nm横坐标：波长（nm）纵坐标：，log，A，T%最大吸收波长：max最大吸收峰值：max例：丙酮max=279nm(=15)正己烷TypesofTransitionsThereareseveraltypesofelectronictransitionsavailabletoamoleculeincluding:stos*(alkanes)stop*(carbonylcompounds)ptop*(alkenes,carbonylcom

4、pounds,alkynes,azocompounds)htos*(oxygen,nitrogen,sulfur,andhalogencompounds)htop*(carbonylcompounds)Figure1.1Typesofelectronictransitions.提示分子轨道理论：一个成键轨道必定有一个相应的反键轨道。通常外层电子均处于分子轨道的基态，即成键轨道或非键轨道上。Transitionsfromthehighestoccupiedmolecularorbital(HOMO)tothelowestoccupiedmo

5、lecularorbital(LUMO)requiretheleastamountofenergyandarethereforeusuallythemostimportantNotalltransitionsthatarepossiblewillbeobserved.Someelectronictransitionsare"forbidden"bycertainselectionrules.However,evenforbiddentransitionscanbeobserved,buttheseareusuallynotveryinte

6、nse.PeakBroadeningUVabsorptionsaregenerallybroadbecausevibrationalandrotationallevelsare"superimposed"ontopoftheelectroniclevels.Figure1.2PeakbroadeningForthisreason,thewavelengthofmaximumabsorption(lmax)isusuallyreported.ReturnB.TerminologyThefollowingdefinitionsareusefu

7、linadiscussionofUV/Visspectroscopy.chromophoreAnygroupofatomsthatabsorbslightwhetherornotacoloristherebyproduced.auxochromeAgroupwhichextendstheconjugationofachromophorebysharingofnonbondingelectrons.基本术语：生色团与助色团生色团：最有用的紫外—可见光谱是由π→π＊和n→π＊跃迁产生的。这两种跃迁均要求有机物分子中含有不饱和基团。这类含有π键

8、的不饱和基团(能产生颜色的基团)称为生色团。简单的生色团由双键或叁键体系组成，如乙烯基、羰基、亚硝基、偶氮基—N＝N—、乙炔基、腈基—C㆔N等。助色团：有一些含有n电子的基团(如—OH、—OR