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Instrumental

Prof. Zvi C. Koren Topics

Spectrometric Techniques: UV/Vis (ultraviolet/visible) Spectrometry – electronic transitions FTIR (Fourier Transform Infrared) Spectrometry – molecular vibrations NMR (Nuclear Magnetic resonance) Spectrometry – nuclear spins MS () AA (Atomic Absorption) Spectrometry Chromatographic Methods: GC-MS (Gas – Mass Spectrometry) HPLC-PDA (High-Performance Liquid Chromatography – Photodiode Array detection) GPC (Gel Permeation Chromatography) Thermal Analysis: DSC (Differential Scanning ) DMTA (Dynamic Mechanical Thermal Analysis) Others: TOC (Total Organic Carbon) Analyzer = Spectrometry = Spectrophotometry

The study of the interaction between light and matter

UV/Vis Spectroscopy:

Absorption of light leads to a transition of an electron from one level to the next. Wave Theory of Light

l

A The Spectral Regions and Molecular Transitions

Region Wavelengths () Transitions X-ray 10–2 – 10 nm K and L electrons Far UV 10 – 200 nm Mid-shell e’s Near UV 200 – 400 nm Valence e’s Visible 400 – 800 nm Valence e’s Near Infrared, NIR 0.8 – 2.5 m Molecular vibrations IR 2.5 – 50 m Molecular vibrations Far IR 50 – 300 m Molecular rotations Microwave 0.3 mm – 0.5 m Molecular rotations Radiowave 0.5 – 300 m NMR, Nuclear Magnetic Resonance Visible Light

R O Y G. B I V Violet: 400 - 420 nm Indigo: 420 - 440 nm Blue: 440 - 490 nm Green: 490 - 570 nm Yellow: 570 - 585 nm Orange:585 - 620 nm Red: 620 - 780 nm Color Wheel: Complementary Colors Absorbed and Reflected Colors: “What you see is NOT what you got.”

Complementary colors are diametrically opposite each other: color absorbed vs. Color observed

Note: Green is unique in that it can be created by absorption close to 400 nm as well as absorption near 800 nm. UV/Vis Spectrometer: Dual Beam

(multiple l‘s) (prism) mono- chromatic single l Transmittance vs. Absorbance

Transmittance: T = I/Io < 1 (sometimes expressed as a percent, %, and not as a fraction)

Absorbance: A = log10(Io/I) = –log10T If no absorption of light has occurred: A = 0  T = 1

Beer’s Law (or Beer-Lambert Law)

Absorbance: A = a·b·c (but often written as A = bc) a or  = molar absorptivity (or extinction coefficient), l-dependent units of M–1cm–1 b = light path through the (cuvet), typically 1 cm c = concentration of the solute in the solution  A = f(l), and of the material of course A is linear with c, ideally For strongly absorbing compounds:  > 10,000. For weakly absorbing compounds:  = 10 – 100. Typical UV/Vis Spectrum Note the Experimental Conditions: c = 0.142 M (in 95 % ethanol), Homework Assignment 1: b = 1.0 cm (Email the answers to me)

1. What is the color of the solution? Explain. 2. What are the values of

395 and 255? Use the appropriate units. Show the calculation. Do the numbers make sense? 3. What is the name of the compound? (Use the naming tool from the ChemSketch program from the free site www.acdlabs.com.) Why Are Some Organic Colored?

extensively conjugated pi-electrons