Your Name: Question 1. Electromagnetic Spectrum. (10, diagrams adopted from images in the online public domain)

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1 Question 1. Electromagnetic Spectrum. (10, diagrams adopted from images in the online public domain) (a) In the yellow-shaded areas, provide the most appropriate term to describe the wave. (5 points) (b) Provided are the black body radiation curves for our sun and a red hot object (below). Also provided is a graph that shows the light intensity as a function of wave length for an incandescent lamp (a normal light bulb) and for a compact fluorescent (CF) lamp. (5 points) What are the major differences between sun light, an incandescent light bulb, and a compact fluorescent lamp? Why do we refer to incandescent light as being a warm light? Would you describe compact fluorescent light as warm light? Incandescent: continuous, maximum intensity on red edge, lots of red = warm light CF: not continuous, maximum intensity in green, reds to not dominate ( cold light ) Suppose you work at a leading art gallery in San Francisco and have to decide whether you want to replace extant incandescent lighting with CF lighting. Do you recommend the use of CFL? Why, or why not? PRO CFL: Cheaper lighting. Less cost for air-conditioning. Better relative intensities. CON CFL: BUT not continuous!! Neither is really adequate. One needs full spectrum lighting. I.e., Lighting/?gclid=CPfPv_zA_pwCFQ4MDQodPkq-0A -1-

2 Question 2. Spectroscopy Related Simple Calculations. (20 points) (a) For radiation with wave number 4,000 cm -1, provide...its wavelength in nm and its color (if colored). (3) its frequency in Hertz. (3) 2500 nm, no color (b) For radiation with wavelength 2 microns, provide the wavelength in meters (m). (2) the wavelength in nanometers (nm). (2) m 2000 nm (c) Provide the equation for the computation of the percent transmittance based on I S and I 0, where I S is the intensity of radiation measured after the sample and I 0 is the intensity of radiation measured without the sample. T = I S /I 0 100% (2 points) (d) Provide the (very approximate) reduced mass of I H in kg. Molmass(I) = 127 g/mol. Molmass(H) = 1 g/mol. Avogadro s number is N A = (4 points) µ(hi) = /(128 N A ) 1/ (e) Provide the (very approximate) moment of inertia of one molecule of I H in kg m 2. Assume that iodine is not moving, that hydrogen is rotating around the iodine, and that d(h I) = 161 pm. (4 points) Ι(HI) = 10-3 /N A /

3 Question 3. Vibrational and Rotational Energy Levels and Transitions. (30 points) (a) Complete the equations for the energy levels of the quantum-mechanical oscillator (with reduced mass µ, force constant k, and fundamental frequency ν o ) and the quantum-mechanical rigid rotor (with moment of inertia I, where r i is the distance of mass m i from rotational axis n). (16 points) Oscillator Rigid Rotor E vib = (v + 0.5) hν ο E rot = J (J + 1) h 2 / (8π 2 I n ) ν ο = 1/2π (k/µ) I n = m i r i 2 (b) Which scheme best describes the vibrational energy levels of a harmonic oscillator? Circle one. (3 points) E CORRECT: RIGHT (c) Which scheme best describes the vibrational energy levels of an anharmonic oscillator? Circle one. (3 points) E CORRECT: RIGHT -3-

4 (d) The scheme on the right is frequently used to discuss the rotational finestructure of vibrational bands. E J' = 5 Label the energy levels, i.e., provide the vibrational and rotational quantum numbers for the levels. J' = 4 J' = 3 Indicate as vertical arrows all transitions that show up in the R-branch of a vibrational band. J' = 2 J' = 1 J' = 0 (8 points) ΔJ = +1 J = 5 J = 4 J = 3 J = 2 J = 1 J = 0-4-

5 Question 4. IR spectra are shown of butyramide, H 3 C (CH 2 ) 2 CO NH 2, and N-ethylacetamide, H 3 C CO NH CH 2 CH 3. (15 points) Butyramide is shown on TOP_ (top/bottom). Explain your assignment. Two N-H peaks, cm -1 CO stretch, cm -1 Bending, cm -1 for prim. and sec. amides. N-Ethylacetamide is shown on _BOTTOM_ (top/bottom). Explain your assignment. One N-H peak, 3000 cm -1 CO stretch, cm -1 Bending, cm -1 for prim. and sec. amides. -5-

6 Question 5. Structure Determination. (25 points) Mass of molecular ion: 118 [C 7 H 6 N 2 ] IR-Spectrum [Not alcohol! Not acid! Primary amine! Nitrile!] Raman Spectrum Spectrum [Nitrile!!] -6-

7 HNMR-Spectrum Spectrum [Two aromatic H-types! Exchanging Hs.] Draw the structure of the compound and provide its name. Explain your reasoning. Assign all characteristic features directly in the spectra. HNMR and IR: Must have amine. IR: Amine is primary. IR, Raman: CN. HNMR: Two types of aromatic Hs. Mass Spectrometry: C 6 H 4 + NH 2 + CN = C 7 H 6 N 2 ==> 118 Correct Answer: para-aminobenzonitrile Only 2 points deduction for ortho-aminobenzonitrile; the spectra are quite similar (see SDBS). -7-