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12/07/2012 Physical Chemistry Lab Chem343 Lecture 7 (12/07/12) Class Schedule/Grading Final Review Final Review Final Exam & Grading Schedule • Final Exam Schedule Dec 13 (Thr) From 1 PM (2hours) at 130 SES; ~60 % is multiple choice questions ■ Your Your TA will send the grade (Final & Overall) by the end of Dec 13 TA will send the grade (Final & Overall) by the end of Dec 13 by e‐mail. If you need any corrections, please claim it before Dec 14 at 3 pm. ■ We will return your graded notebook on the day of the Final. ■ We will not return the Final or Quiz 4, but let you review them in case that your grade is very close to the border line. ■ All other grades are final. All th d fi l ■ Quiz 4 (Today): All the 6 experiments + lecture 1 12/07/2012 Final Exam • 6 Experiments + Lecture materials • 60‐70 multiple choice questions (60‐70%) • 6 calculation or long questions 2 hours NMR • Review the class materials on NMR from the lectures (Lectures 2, 3) • Review the NMR presentation • Principle of NMR (Spin magnetic moment, Transition energy, Frequency) • 13C signal assignments, 1H signal assignments • DEPT • HETCOR & COSY • The principle of molecular diffusion • Long questions are probably on signal assignments for amino acid(s) or small compounds. id( ) ll d • For Long questions, I may ask you to draw a possible NMR spectrum for a compound. Check out the structures of amino acids and possible chemical shifts. 2 12/07/2012 Zeeman Interaction Spin in a Magnetic Field • When a spin is placed in a magnetic field, the energy is given by Em = ‐ μZB0 = ‐γmħB ħ 0 1 Figure 1. Zeeman energy levels for spins of I =1/2 and 1. Lower energy level attracts more spin population. It induces spin polarization (bulk magnetic moment) 4C ~ H NMR Frequency • The transition energy between the two states is |E| = γħB0. • NMR NMR frequency is easily obtained as f i il bt i d 0 = E/h = B[Q1] γ/2π. 0 1 4C ~ H The frequency is typically in a range of 1‐900 MHz RF (Radio Frequency) 3 12/07/2012 Induction Effects in 1H shifts 1H chemical shifts of CH Cl (ppm) n 4‐n CH4 0 23 0.23 CH3 Cl 3.05 CH2Cl2 5.3 CHCl3 7.27 1H e- CH3 Cl Less e-, Less Shielded shifts of CH3X (ppm) F OH NH2 H Me3Si 4.26 4.26 3.38 2.47 0.23 0.0 TMS Example 13C and 1H NMR spectrum spectra of diethyl ether (CH3CH2)2O (CH (CH33CH CH22))22OO Q. Which is C1H2? Quartet Triplet 4 12/07/2012 Miller plane & index Q. What is the Miller index below? b b a a (1,2) (2,1) Gas Effusion Theory Questions • What is an ideal gas? – Negligible volume compared to gas line – Elastic Collisions = Kinetic Energy remains constant • What are the differences between effusion and diffusion? – Pressure – Mean free path • What is the main factor which affects the mean free path? – Pressure Pressure • Factors that influence average speed / probability density(M‐B Distribution) 5 12/07/2012 Experimental Questions • Why is the diffusion pump important? – Mean free path Mean free path – Back Effusion • What type of gas can be monitored by gas effusion? – Non toxic and non flammable gases (No cold trap on the pump) p p) – Molecule size smaller than pinhole • Constants – Area, Molar Mass, Gas Constant, and Volume Calculation Questions • Calculate the increase/decrease in speed if the t temperature or molar mass t l increases/decreases • Any calculations from the lab – Appropiate Equations will be given Appropiate Equations will be given 6 12/07/2012 CHEM 343_F12_FTIR questions for final_examples Q1: Consider the following analytes and answer which would absorb in IR frequency range (Y/N): A: Phenol B: Water C: CH2Cl2 D: CO E: O2 a.C and E b.Only E c.A, B and D d.None of the above Q2: Consider the following analytes and answer which would show a FINE ROTATIONAL STRUCTURE in its FTIR absorption spectra (assume analyzed molecules are polar): A: Solution of Cholesterol in HCCl3/CH2Cl2 B: Pulverized solid PVC paletted with KBr C: Air sample containing gaseous contaminants D: Aqueous peptide solution E: gaseous pyrolisis products a.A and B b.Only D c.C and E d.All of the above CHEM 343_F12_FTIR questions for final_examples Q3: Consider following statements related to FTIR spectroscopy and choose an answer that applies: A: Heavier the atoms in a diatomic molecule are, smaller the vibrational wavenumber is B: Energy of rotational levels is usually ~ 103 times smaller than that of the corresponding vibrational levels C: Value of rotational constant is dependent on the vibrational energy level D: According to anharmonic oscillator potential energy curve it takes much more energy to move atoms closer together that it takes to move them apart a) A is the only one correct b) All are correct but C c) All are correct Q4: Considering a model of a rigid rotor choose an answer that best describes given symbol or term: A) DJ 2 ( J 1) 2 B) Term for moment of Inertia a) Term for transition energies in P-branch P branch b) Term for vibrational-rotational interaction constant c) Term expressing contribution of centrifugal distortion T T ( v, J ) final T ( v, J ) initial a) b) I=µr2 c) F ( J ) BJ ( J 1) 7 12/07/2012 CHEM 343_F12_FTIR questions for final_examples Q5: FTIR absorption spectrum for DCl with labeled R and P branches with initial state J values is shown below. Which statement(s) is/are correct: A a) In case A: Jinitial is equal 1 b) In case B: Jfinal equals 0 c) In case B peak due to D37Cl is observed d) In case A peak due to D35Cl is observed e) a and b f) c and d g) none of the above B p of 12C16O shows vibrational absorption p band centered at 2170cm-1. At what Q6: The IR spectrum wavenumber would the corresponding peak for 14C16O occur ? Use: Ar(12C)=12; Ar(14C)=14.0032; Ar(16O)=15.995 M1 M 2 M1 M 2 ~0 ,12 CO ~0 ,14 CO 1/ 2 14 CO 12 CO Final Exam Preparation On Nano Diffraction 1. [Theory]: Explain the Bragg equation and deduce the question based on the used model for 2D and 3D dimensions. 2. [Sample]: Lattice system of the crystal in the experiment and parameter comparison of each sample(d or D). 3. [Experiment set up]:Wavelength of the laser; dos and don’ts for better data. 4. [Diffraction pattern]: Difference and reasons for multiple domain and single domain. 5. [Calculation]: How to calculate the d spacing based on the known factors. Establish relationship between D and d based on each structure Establish relationship between D and d based on each structure. 6. [Miller indices]: Simple models. 8 12/07/2012 Examples: Photophysics and Molecular Spectroscopy Review Brian K. Yoo December 7, 2012 9 12/07/2012 Jablonski Diagram http://elchem.kaist.ac.kr/vt/chem‐ed/quantum/graphics/jablon.gif • What is the basis for the observed Stoke’s shift? • Why do we expect to see a mirror images for the Wh d tt i i f th excitation and emission profiles? • Know numerical calculations, basis and meaning of variables, i.e. Beer‐Lambert Law, Henderson‐ Hasselbalch… • What are the differences between fluorescence and UV, vis‐spectroscopy (absorbance)? 10 12/07/2012 Error Propagation Example V RT , T 0.00 0.08 C, P 1.000 0.005 atm P n T(C) T(K) + 273.15K C 0.00 T(K) + 273.15K C T(K) 273.15 273 15 0.08 0 08 K Vm L atm 273.15 K K mol Vm 1.000 atm Vm 22.41 L mol-1 0.08205746 Error Propagation cont. 2 2 2 2 2 V V V V V V2 m R2 m T2 m V2 m T2 m V2 R T ,V T R,V V R ,T T V V T m 2 R V 2 RT 2 V V 2 V2 T2 m V2 m 2 L atm 0.08205746 K mol 2 0.08 K 1.000 atm 2 L atm 273.15 K 0.08205746 2 K mol 0.005 atm 2 1.000 atm V 0.1 L mol-1 m Vm 22.4 0.1 L mol-1 11 12/07/2012 Flash Photolysis of Benzophenone final presentation Chemistry 343 Fall 2012 THEORY Reactive electrones The total electronic spin angular momentum is 2S+1 S for S0 is 0 (1/2-1/2) = singlet Flouroscence X Phosphoroscence: Liquid N2 T RT 12 12/07/2012 REACTION - Isopropanol (take H) - Protonated ketyl radicals Benzoph. Benzoph + Isoprop. - Basic - Deprotonated ketyl radicals - Dimerization Benzopinacol NaOH N OH + H2O Fixed wavelength 13 12/07/2012 CALCULATION • Kobs =slope*el (e:5000 /M.cm, l: 5 cm) • Kobs = k7 k x [H] / k6 • [H] = 10-ph 14