Transcript Slide 1
Experiment 56: Synthesis of an Ester from an Alcohol and Carboxylic Acid Structure determination by Infrared Spectroscopy WWU -- Chemistry Infrared Spectroscopy • Read Chapter 25, pp 833 to 867 • Work problems on page 866-867 WWU -- Chemistry Typical Infrared Absorption Regions WWU -- Chemistry O-H stretch • The OH peak is very strong and broad! • It usually appears near 3400 cm-1 WWU -- Chemistry C-H stretch • sp3 C-H stretch comes at 2950 cm-1 • sp2 C-H stretch comes at 3050 cm-1 • sp C-H stretch comes at 3300 cm-1 WWU -- Chemistry C=C stretch • C=C stretch occurs near 1650 cm-1 • It is often weak unless it is conjugated to a C=O WWU -- Chemistry Normal Base Values for C=O Stretching Functional Group Frequency (cm-1) Ester Aldehyde Ketone Carboxylic acid Amide 1735 - 1740 1725 1715 1710 1690 WWU -- Chemistry C-O stretch • The C-O band appears in the range of 1300 to 1000 cm-1 • Look for one or more strong bands appearing in this range! • Ethers, alcohols, esters and carboxylic acids have C-O bands WWU -- Chemistry C-H bendings • Bendings aren’t as important as stretches. • See page 848-850 • CH2 bending: 1450 cm-1 • CH3 bending: 1375 cm-1 WWU -- Chemistry Cyclohexanol O-H stretch sp3 C-H stretch OH bending C-O stretch WWU -- Chemistry Ethyl Butanoate sp3 C-O stretch C-H O C=O stretch C CH3 CH2 CH2 O CH2 CH3 WWU -- Chemistry 4-Methyl-2-pentanone C-H < 3000, C=O @ 1715 cm-1 CH3 C-H stretch C=O stretch O CH3 CH CH2 C CH3 WWU -- Chemistry 4-Methyl-3-penten-2-one C-H stretch O CH3 C CH3 C C H CH3 C=O C=C stretch stretch WWU -- Chemistry Experiment 15 Spearmint and Caraway • • • • Experiment 15, pp124-131 Essay: pp119-123 Technique 25 (Infrared spectroscopy) Technique 22 (Gas Chromatography, especially, Section 22.8 on page 806 and Fig 22.7) • Technique 23 (Polarimetry) WWU -- Chemistry Spearmint and Caraway Oils O O H H (S) + carvone Caraway oil (R) - carvone Spearmint oil Limonene is present In both oils H (S) - Limonene WWU -- Chemistry The experiment • Run the IR spectrum on the two enantiomers • Run a sample of each enantiomer through the gas chromatograph • Determine the optical rotations for each enantiomer • Calculate the specific rotation for each enantiomer WWU -- Chemistry Experiment 21 Nucleophilic Substitution: Competing Nucleophiles WWU -- Chemistry Reading Assignment • • • • • • • pp. 180-190 (Exp 21) and 510-514 (exp 58) Chapter 10 in your lecture textbook Review Techniques 1 through 6 Technique 7 (Sections 7.2, 7.4, 7.5, 7.8) Technique 12 (Sections 12.5, 12.9, 12.11) Technique 22 Technique 21 (omit this quarter) WWU -- Chemistry Changes to Exp 19 laboratory • We will be using 1-pentanol, 2-pentanol, 3-pentanol and 2-methyl-2butanol instead of what is shown in the book. • The procedure stays the same; just change the alcohols. • Start 21A first, then do 21B, and then come back to finish 21A. • Part 21C: gas chromatography only • Signup for 1, 2, and 3-pentanol WWU -- Chemistry The SN2 Mechanism H .. _ O: .. H H C H Br H O H C H H Br .. O .. H H C H H + .. _ : Br : .. WWU -- Chemistry The SN1 Mechanism 1) CH3 CH3 C CH3 CH3 slow CH3 C + : Br: .. CH3 .. _ : Br : .. + carbocation 2) CH3 CH3 C + H CH3 + :O: CH3 fast CH3 C H :O CH3 + H H 3) CH3 CH3 CH3 C :O H CH3 + H fast CH3 C :O .. CH3 + H + H 1935: Hughes & Ingold WWU -- Chemistry Assisted SN2: Mechanism 1) R CH2 O H + H R CH2 O H H 2) slow X + R CH2 O H H X CH2 R + O H H WWU -- Chemistry Assisted SN1: Mechanism 1) CH3 CH3 CH3 C CH2 CH3 + H CH3 C O O H H CH2 CH3 H 2) CH3 CH3 slow CH3 C O 3) CH2 CH3 CH3 C CH2 CH3 H + O H H H CH3 CH3 CH3 C CH2 CH3 + X CH3 C CH2 CH3 X WWU -- Chemistry RBr/RCl ROH H2SO4 NH4Br/NH4Cl H2O organic phase pentane aqueous phase pentane RBr/RCl ROH H2SO4 (trace) H2O (trace) H2O H2SO4 NH4Br/NH4Cl ROH organic phase organic phase pentane RBr/RCl ROH H2SO4 (trace) H2O (trace) H2O aqueous phase pentane NaHCO3 RBr/RCl ROH (trace) H2SO4 (trace) aqueous phase H2O (trace) pentane RBr/RCl ROH (trace) H2O (trace) H2O H2SO4 ROH H2O H2SO4 ROH pentane RBr/RCl ROH (trace) Na2SO4 pentane RBr/RCl ROH (trace) H2O (trace) H2O WWU -- Chemistry Gas Chromatography Results: 1-Chloro pentane and 1-Bromopentane :2WSI R mVolts s:\iln\chemistry\fall2003-summer2004\spring 2004\chem 354\wandler\competingnucs\np1p_8;45;53 pm.run 15.0 5.332 R-Br solvent 12.5 10.0 7.5 5.0 R-Cl 4.579 2.5 0.0 X: 3.4135 Minutes Y: 0.0590 mVolts -1.5 3.0 3.5 4.0 4.5 5.0 5.5 Minutes WWU -- Chemistry Gas Chromatography Results: 1-Chloropentane and 1-Bromopentane from 1-pentanol Ret. Time Width Peak Peak Result Time Offset Area Sep. 1/2 Status No. Name () (min) (min) (counts) Code (sec) Codes ---- ------------ ---------- ------- ------- ---------- ---- ----- -----1 9.9306 4.579 0.000 2113 BB 1.5 2 90.0694 5.332 0.000 19166 BB 1.4 ---- ------------ ========== ------- ======= ========== ---- ----- -----Totals: 100.0000 0.000 21279 Total Identified Counts associated with halides: 21279 counts Round off the values to: 9.9 % 1-chloropentane 90.1 % 1-bromopentane Important! Other components may appear on the printout. If so, be sure to recalculate for only 1-chloro and 1-bromopentane! Make sure that the total equals 100% Assume that all response factors = 1.000 WWU -- Chemistry Do the results of this experiment with 1-pentanol fit with what you expected? WWU -- Chemistry Gas Chromatography Results: 2-Pentanol in the solvent nucleophile mixture :2WSI R + SR 2-bromopentane 3-bromopentane 4.852 mVolts s:\iln\chemistry\fall2003-summer2004\spring 2004\chem 354\wandler\competingnucs\hak2p_9;15;27 pm.run 6 solvent 5 2-chloropentane 3-chloropentane 4.151 4 4.932 3 4.216 2 1 0 X: 3.7785 Minutes Y: 0.0240 mVolts -1 3.0 3.5 4.0 4.5 5.0 Minutes WWU -- Chemistry Gas Chromatography Results: 2-Pentanol in the solvent nucleophile mixture Ret. Time Width Peak Peak Result Time Offset Area Sep. 1/2 Status No. Name () (min) (min) (counts) Code (sec) Codes ---- ------------ ---------- ------- ------- ---------- ---- ----- -----1 21.7171 4.151 0.000 4100 BV 1.4 2 11.6505 4.216 0.000 2200 VB 1.5 3 46.7971 4.852 0.000 8835 BV 1.4 4 19.8353 4.932 0.000 3745 VB 1.5 ---- ------------ ========== ------- ======= ========== ---- ----- -----Totals: 100.0000 0.000 18880 Total Identified Counts associated with halides: 18880 counts Important! Other components may appear on the printout. If so, be sure to recalculate for only the four halides! Make sure that the total equals 100% Round off the values to: 21.7 % 2-chloropentane 11.7 % 3-chloropentane 46.8 % 2-bromopentane 19.8 % 3-bromopentane WWU -- Chemistry Why are we obtaining mixtures of halides in this reaction? Time for chalk!! WWU -- Chemistry Gas Chromatography Results: 2-Methyl-2-butanol in the solvent nucleophile mixture I:2RWS + SR mVolts 2-bromo-2-methylbutane s:\iln\chemistry\fall2003-summer2004\spring 2004\chem 354\wandler\competingnucs\ncdtp_5;28;39 pm.run 2-chloro-2-methylbutane solvent 4.491 5 3.844 4 3 2 1 0 X: 3.1883 Minutes Y: 108 mVolts -0 3.0 3.5 4.0 4.5 WWU -- Chemistry Minutes Gas Chromatography Results: 2-Methyl-2-butanol in the solvent nucleophile mixture Ret. Time Width Peak Peak Result Time Offset Area Sep. 1/2 Status No. Name () (min) (min) (counts) Code (sec) Codes ---- ------------ ---------- ------- ------- ---------- ---- ----- -----1 44.0704 3.844 0.000 5181 BB 1.4 2 55.9296 4.491 0.000 6575 BB 1.5 ---- ------------ ========== ------- ======= ========== ---- ----- -----Totals: 100.0000 0.000 11756 Total Identified Counts for the two halides: 11756 counts Important! Other components may appear on the printout. If so, be sure to recalculate for only the two halides! Make sure that the total equals 100% Round off the values 44.1 % 2-chloro-2-methylbutane 55.9 % 2-bromo-2-methylbutane Assume that all response factors = 1.000 WWU -- Chemistry We expect that the reaction of 2-methyl-2-butanol with the solvent nucleophile mixture to be SN1. Why didn’t it come out as a 50-50 mixture? Life is never straightforward! WWU -- Chemistry Important notice about next week’s lab lecture Friday, May 19th Bond Hall 109 2:00 to 2:50 WWU -- Chemistry Important notice: Final Exam The exam will be held in SL 110 rather than SL 130 on Thursday, June 8th 3:30-5:30 WWU -- Chemistry