1. Chapter 14 Applications of Ultraviolet-Visible Molecular Absorption Spectrometry

2. Constructive and destructive interference of electron waves. Electronic Transitions Between Molecular Orbitals

5. A center of light absorption in a molecule.

6.  *  * Angular Momentum of the Electron is Conserved

7. n  * n  * Angular Momentum of the Electron is Not Conserved Angular Momentum of the Electron is Conserved

8. “forbidden” “allowed”

9. possible transitions? (nm)      * (allowed)  * (allowed) n  * (allowed) n  * (forbidden) 10 5 alkanes alkenes, alkynes, aromatics carbonyls cmpd’s with heteroatoms 10 4 10 3 10 2 10 150300

10. 1,2,4,5-tetrazine

11. 1.Solvent Shifts – is a peak a  * or an n  * transition? 2.Effect of ring substituents on the absorbance spectrum of cpmd’s with aromatic rings 3.Effect of pH on absorbance spectra, e.g. indicators HIn  H + + In -

12.  * "red shift“ in a polar solvent

13.  * energy level is polar and stabilized by a polar solvent

14. n  * “blue shift“ in a polar solvent

15. electron donating (stabilizes ring, lowers energy, red shift): methyl, phenol, R 2 N -, RO- electron withdrawing (destabilizes ring, raises energy, blue shift): : nitro, carboxylic, ester, ketones, aldehydes

16. phenolphthalein crystal violet phenol red

17. 1.Mixture Analysis 2.Sample “matrix” – Standard Addition methods 3.Derivative Spectroscopy – enhancing weak spectral details 4.Enzyme Kinetics

18. 1. Mixture Analysis A = A M + A N e.g. determination of caffeine + sodium benzoate in soft drinks (Ch312)

19. 2. Can be used with any instrumental technique; useful if there is an irreproducible sample “matrix” = all the impurities in the sample, e.g. microorganisms, dissolved metals and organics, particulate matter, humics, etc. (Ch 1, p. 13-17) V spike → Signal → add increasing volumes of known concentration (V spike ) to fixed volume of sample

20. V x, C x "spike" = added analyte of known concentration and volume V x = volume unknown C x = concentration unknown V s = volume "spike" C s = concentration "spike" V t = total volume V s, C s dilute to V t A = A x + A s =  bC dx +  bC ds Plot A vs. V s m =b =C x =

21. Example 1-1 10 mL aliquots of a natural water sample were pipetted into 50.00 mL volumetric flasks. Exactly 0.00, 5.00, 10.00, 15.00 and 20.00 mL of a standard solution containing 11.1 ppm of Fe 3+ was added to each, followed by an excess of SCN - ion to give the red complex Fe(SCN) 2+. After dilution to volume, the instrument response S for each of the 5 solutions, measured with a colorimeter, was found to be 0.240, 0.437, 0.621, 0.809, and 1.009 respectively. What was the concentration of Fe 3+ in the water sample?

22. 3. Derivative Spectroscopy - used to enhance weak spectral features

23. 4. Enzyme Kinetics – “Michaelis-Menten” Mechanism E + S ES  P + E k1k1 k -1 k2k2