Exp. 13*: CALCULATION, CHROMATOGRAPHIC, AND SPECTRAL APPLICATIONS Objectives: To review common laboratory calculations, chromatographic, and IR spectral techniques. To learn to calculate efficiency of synthetic methods, and determine overall marketability of synthetic products. To learn to use mass spectrometry and NMR spectroscopy for future use in structure elucidation. PROPOSED CHEMICAL EQUATION OH H 2 SO 4 (cat) 2 -m e th yl-2 -p e n ta n o l M W : 1 0 2 .1 7 g /m o l d : 0 .8 3 5 g /m L c o s t: $ 6 7 .2 0 /1 2 m L Am o u n t u s e d : 2 .0 m L REACTANT s u lfu ric a c id c o s t: $ 2 5 .0 0 /5 0 0 m L A m o u n t u s e d : 0 .5 m L CATALYST 2 -m e th yl-1 -p e n te n e M W : 8 4 .1 6 g /m o l d : 0 .6 8 2 g /m L c o s t: $ 1 2 9 .5 0 /2 5 m L P ro d u c t m a s s : 1 .2 0 g PRODUCT Dehydration of 2-methyl-2-pentanol LIMITING REAGENT & THEORETICAL YIELD Mass RCT Moles RCT (using MWrct) Moles RCT Moles PROD (using stoichiometry) Moles PROD Mass PROD (using MWprod) Determine limiting reagent. Theoretical yield is always in the units of GRAMS of PRODUCT! Theoretical yield = # g REACTANT 1 mol of REACTANT #g Amount you started with Molecular weight of starting material 1 mol PRODUCT #g 1 mol REACTANT 1 mol PRODUCT Stoichiometric ratio Molecular weight of product PERCENT YIELD Percent yield = ACTUAL PRODUCT MASS (g) THEORETICAL YIELD (g) X 100 Theoretical yield and percent yield CALCULATIONS Theoretical Yield (g) based on alcohol Show these calculations in your lab notebook! Complete this table electronically and copy/paste into your final lab report! Theoretical Yield (g) Actual Yield (g) Percent Yield Percent Yield GREEN CHEMISTRY CALCULATIONS Green chemistry calculations are used to determine how “environmentally friendly” your choice of reagents, solvents, and conditions were. This includes ATOM ECONOMY, EXPERIMENTAL ATOM ECONOMY, AND “Eproduct”. ATOM ECONOMY Atom economy : based on the efficiency of reactant atoms converted to product atoms. Q: Were ALL of the reactant atoms converted to product atoms? Any atoms of the reactants that did NOT appear in the product structure were converted to side products or waste. Sometimes the side products and waste generated is harmful to the environment. An experiment should be designed to minimize the generation of waste and unnecessary side products. ATOM ECONOMY Atom economy = MW desired product S MW reactants * 100 • Atom economy is based on which reactants were selected to make the product. • It assumes that the reactants were used in equivalent amounts, meaning that no excesses of any reactant were used. • The closer the atom economy is to 100%, the better! EXPERIMENTAL ATOM ECONOMY Experimental atom economy = theoretical yield of product (g) * 100 S mass reactants Q: Did we use ONLY the amount necessary to generate the product? • Sometimes an excess of one reactant is used in order to drive the reaction to completion. For this reason, the experimental atom economy is calculated. • Experimental atom economy is a more precise measure of efficiency than the atom economy—it takes into account the mass of each reactant used. “EPRODUCT “ “Eproduct” = • (% yield X % experimental atom economy) 100 “Eproduct” is the ultimate measure of efficiency, since both the conditions used and the amount of product that resulted under those conditions is taken into account. • “Eproduct” is a number, not a percentage! • The higher “Eproduct” is, the better! IMPROVING EFFICIENCY… An efficient reaction would have 100% Atom Economy and 100% Experimental Atom Economy. One could improve the efficiency of a reaction by adjusting the conditions of a reaction in an effort to improve either of these values, such as: Use different reactants to form the product (AE) Use different amounts of reactants to form the product (EAE). COST ANALYSIS… Cost per synthesis In order to calculate the cost of your synthesis, you must first determine the cost of the amount of each chemical used, including reactants, solvents, and catalysts! Cost of solid ($) = Mass (g) of SOLID “A” used *This calculation is performed for each solid used during course of synthesis! Cost of liquid ($) = Volume (mL) of LIQUID “B” used Cost per synthesis ($) = Cost of “A” + Cost of “B”…etc. *This calculation is performed for each liquid used during course of synthesis! COST ANALYSIS… Cost per gram Now that the cost per synthesis has been determined, based on the amount of product generated… Cost per gram ($/g) = cost per synthesis ($) actual yield (g) COST ANALYSIS… Cost per bottle Now that the cost per gram has been determined, when compared to the manufacturers cost, how marketable is your product? Cost per bottle ($/g) = cost per gram x desired bottle size (*Can also be calculated in mL) Green Chemistry Calculations CALCULATIONS Atom Economy (%) Experimental Atom Economy (%) “E” product Cost per Synthesis ($) Cost per Gram ($/g) Cost per 25 mL bottle Atom Economy (%) Experimental Atom Economy (%) “E” product Cost per Synthesis ($) Cost per Gram ($/g) Cost per 25 mL bottle HPLC and TLC Chromatography Introduced in Experiments 4 and 5. Difference between ANALYTE POLARITY and SOLVENT POLARITY. UV detector is used in both. In order to be detected, compounds must be UV active. Most solvents used in TLC and HPLC are not UV active, therefore do not appear on the TLC plate or in the HPLC chromatogram! GC Chromatography Introduced in Experiment 2. ADJUSTED AREA % must be calculated to eliminate solvent quantity! All chromatograms and spectra are available in folder on course website! IR SPECTROSCOPY Introduced in Experiment 10. Base values are given in correlation tables. Actual values are reported from actual spectrum Don’t ever mention sp3 CH when using IR spectroscopy to differentiate between reactants and products! They are too common! EXAMPLE OF IR SPECTROSCOPY THINGS TO CONSIDER… •What kinds of bonds are present? OH CH 3 • If they appeared in the IR spectrum, where would they be? CH 3 • Now, look at the spectrum. Are they there? Actual spectra are available in folder on course website! IR SPECTROSCOPY BASE VALUES Base values for Absorptions of Bonds (cm-1) O-H 3200-3600 C-O 1000-1300 ***(Esters have two!)*** C-H (sp2) 3000-3100 C-H (sp3) 2800-3000 Aldehyde C-H 2700 & 2800 ***(there are two!)*** C=O 1650-1740 ***(location depends on functional group!)*** C-X 500-700 MELTING POINT ANALYSIS Introduced in Experiment 7. Detects all impurities! Recorded as Ti-Tf range. Pure = matches literature mp EXACTLY! Impure = lower Ti = higher DT! Before coming to the next lab… Go to the website: www.ochem.com From the left menu, select TUTORIALS. From the right column, PRELECTURES, scroll ¾ of the way down the page. Watch the following: MASS SPECTROMETRY SPECTROSCOPY (Part 3 of 4) SPECTROSCOPY (Part 4 of 4) (YOU’LL BE GLAD YOU DID! ) CALCULATING DEGREE OF UNSATURATION CcHhNnOoXx DU = (2c + 2) – (h – n + x) 2 • 1o unsaturation = 1 C=C or 1 ring • 2o unsaturation = 2 C=C, 2 rings, or CΞC, or combination of C=C & rings • 3o unsaturation = combination of double bonds, triple bonds, rings • 4o unsaturation = typically indicates an aromatic ring 13C-NMR SPECTROSCOPY d (ppm) = tells what type of carbon it is. # signals = tells whether or not there is symmetry within the molecule. 13C NMR CHEMICAL SHIFT CORRELATION CHART R R O C O C H R R R 210 O C OR OH R R O C O C Fn NR 2 C sp3 sp3 C o C X C C o C sp3 o 4 --3 --2 --1 C o 0-50d 5 0 -1 1 0 d 1 1 0 -1 6 0 d 1 9 0 -2 2 0 d 220 O C 1 6 0-1 90 d 200 180 160 140 120 p. 118 in lab manual 100 80 60 40 20 0 13C NMR Spectral Analysis 14.68 d 17.67 d 29.20 d 70.98 d 46.46 d 1a OH 4 5 2 4 1a 3 5 2 3 1b C# 1a 1b 3 13.79d 20.91 d 22.34d 40.16 d 109.87 d 145.95 d 2 4 5 d (ppm) C# 1a 1b 2 3 4 5 All chromatograms and spectra are available in folder on course website! d (ppm) 22.34 20.91 1b 1H-NMR SPECTROSCOPY d (ppm) = tells what type of proton it is. # signals = tells whether or not there is symmetry within the molecule. Integration = tells # protons of each type. Multiplicity = tells # neighboring protons, using n + 1 rule. 1H-NMR R O O C C OH 10.0-12.0 d R SPECTROSCOPY H H Fn C C H C H H 9.0-10.0 d 6.5-8.5 d sp3C H C C H 5.0-6.5 d 2.0-4.5 d 0.0-2.0 d (3o > 2o > 1o) 12 11 10 9 8 7 6 5 4 3 2 1 0 1H-NMR Spectral Analysis 1.20 d 6H, s 1.38 d 2H, hex 1.44 d 2H, t 1.71 d 3H, s 4.66 d 1H, s 4.70 d 1H, s 0.93 d 3H, t 1.46 d 2H, pent 2.04 d 1H, s 1.99 d 2H, t 1a OH 4 5 2 4 5 1b H # 1a 1b 2 3 4 5 d (ppm) 2.04 2 1a 3 Int. 1 0.90 d 3H, t Mult. s H# 1a 1b 2 3 4 5 1b 3 d (ppm) 4.66 4.70 X Int. 1 Mult. 1 X s s X All chromatograms and spectra are available in folder on course website! Notice some signals are already assigned for you in the tables! IR Spectral Analysis OH 3616 Base Values (cm-1) OH stretch C-O stretch sp3 CH stretch sp2 CH stretch C=C stretch 3200-3600 1000-1300 2800-3000 1162 2965 3076 1661 2962 Functional Group 2-methyl2-pentanol Frequency (cm-1) 3000-3100 X 1600-1680 X 2-methyl-1pentene Frequency (cm-1) X X MASS SPECTROMETRY— How it works Small amount of sample is vaporized into the ionization source, then bombarded with high energy electrons. When a high energy electron hits the organic molecule, it dislodges a valence electron, to produced a radical cation, called the molecular ion. M + e - M Io n iza tio n m o le cu la r io n (= ra d ic a l ca tio n ) + 2 e - MASS SPECTROMETRY— How it works Electron bombardment transfers so much energy that the bonds in the cation fragments begin to break. Some pieces retain the positive charge, some are neutral. m1 M F ra g m e n ta tio n to : + c a tio n + m2 ra d ic a l (= n e u tra l lo s s ) MASS SPECTROMETRY— How it works Fragments then flow through a strong magnetic field, where the charged fragments are sorted onto a detector based on their mass to charge ratio (m/z). Since the charge number on each ion is usually +1, the value of m/z for each ion simply = mass. The output is a plot of the m/z value of each fragment based on based on its relative abundance. Relative abundance of fragment Mass of fragment MASS SPECTROMETRY— Interpretation The way molecular ions break down can produce characteristic fragments that help in identification Serves as a “fingerprint” for comparison with known materials in analysis (used in forensics) Positive charge goes to fragments that best can stabilize it MASS SPECTROMETRY— Interpretation Positive charge goes to fragments that best can stabilize it! Carbocation stability is discussed in McMurry text, p. 377. H H H H H 3C C C H C H H M eth yl C < P rim ary H C H H 3C C H < H H ~ B en zylic In creasin g carb o catio n stab ility C H 3C C CH 3 H Allylic CH 3 ~ S eco n d ary CH 3 < T ertiary MASS SPECTROMETRY— Alcohols Functional groups cause common patterns of cleavage in their vicinity Alcohols undergo -cleavage (at the bond next to the C-OH) as well as loss of H-OH to give C=C MASS SPECTROMETRY— Alkenes R Important fragment in terminal alkenes is the allyl carbocation at m/z = 41 due to the following cleavage: CH 2 CH CH 2 R CH 2 CH CH 2 H 2C CH CH 2 resonance stabilized allyl carbocation MASS SPECTROMETRY— Carbonyl compounds A C-H that is three atoms away leads to an internal transfer of a proton to the C=O, called the McLafferty rearrangement Carbonyl compounds can also undergo cleavage Mass Spectral Analysis 59 69 84 102 OH m/z 102 (M+) 59 (base) Cation formula C6H14O Structure m/z Molecular Ion 84 (M+) C3H7O Cationic Fragment 69 (base) Cation formula C6H12 Structure Molecular Ion C5H9 Cationic Fragment Mass Spectral Analysis OH m/z 102 (M+) Cation formula C6H14O Structure m/z Molecular Ion 84 (M+) Cation formula C6H12 Structure Molecular Ion C5H9 Cationic Fragment OH 59 (base) C3H7O Cationic Fragment OH 69 (base) Final Lab Report In Lab… Each student will perform all calculations in their own laboratory notebooks and submit yellow copies to instructor for grading. Post Lab… Each lab group will submit ONE copy of a typewritten, paragraph style report addressing all points listed for REACTION #2. All data tables for REACTION #1 and REACTION #2 must be completed and copied into the document. Original copies of tables provided from the course website are UNACCEPTABLE.