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Date Created: 10/28/15
Recrystallization Flow Chart C ZZOliFallZOOS Department of chemistry Villanova University Impure Crystalline Organic Compound X 1 Test solubility of impure x in polarnon polar solvents at roomelewted temperatures For x desire high solubility hotlow solubility co For impurities desire high solubility cold or high insolubility hot 2 Heat to dissolve x in minimum amount ofappropriate organic solvent Three Common S W39W39 v F Durin Recrystallization ofImpure Compounds 2 n of Compound X Hot Solu on of Compound X 195 Insolubles And Impurmes Hot Solution of Compound X And Colored Impurities Insolubles Filter hot thru lter paper or 39te pad to remove insolubles 1 Activated charcoal l Spontaneous crystallization may occur on cooling 2 Filter thru Cellte use ice bath lfnecess or 2 Induce c stallization ifnecess b Hot Solution of Compound X 1 Fania ry y And Impurities Less Insolubles Seeding or scratching Hot Solution of Com ound X less colored impuritiesin solubles Spontaneous crystallization may occur on cooling use ice bath ifnecessary or 2 Induce crystallization ifnecessary by Partially concentrating the solution iftoo much solvent ms use Spontaneous crystallization may occur on cooling Seeding or scratching use ice bath ifnecessary or 2 Induce crystallization ifnecessary by Pure Precipitmd Plartlatlly concegitratlng the solution lftoo much mpwnd X so ven ms use Seeding or scratching 1 Filterto collect crystals 2 Wash crystals with small amount ofcold Solubility Depends on Relative polarity of solvent and solute gtCompounds containing polar groups on NHcoH CON39H etc are usually more soluble in polar or hydruxylic solvents H10RO H gtCompounds ul39 lowpolarity are more soluble in nunrpnlzr solvents hexane Pure Dry toluene Compound X Crystals gt Like dlssnlve himquot I aneigy Lu nigne niei ir higher the lower the solubility solvent 3 Allowto dry TMZB 82008 CHM 2201 Villanova University Organic Chemistry Lab I Fall 2008 Department of Chemistry How to Calculate the quotIndex of Hydrogen Deficiencyquot also known as the quotUnits of Unsaturationquot Given a Molecular Formula Overview Frequently a great deal can be learned about an unknown substance simply from knowledge of its molecular formula This information is based on the following general molecular formulas ac clic alkane C H y n 2mg Difference of2hydrogens cycloalkane or alkene Cann cyclic alkene diene or alkyne CH22 D39fference Of 2 hydrogens for example Notice that each time a ring or a 7 bond is introduced into a molecule the number of hydrogens in the molecular formula is reduced by two For every triple bond two 7 bonds introduced into a molecule the number of hydrogens in the molecular formula is reduced by four When the molecular formula for a compound contains noncarbon or non hydrogen elements the ratio of carbon to hydrogen may change Following are three simple rules that may be used to predict how this ratio will change 1 To convert the formula of an openchain saturated hydrocarbon to a formula containing Group V elements N P As Sb Bi one additional hydrogen must be added to the molecular formula for each such Group V element present In the following examples each formula is correct for a twocarbon acyclic saturated compound C2H6 C2H7N C2H8N2 C2H9N3 2 To convert the formula of an openchain saturated hydrocarbon to a formula containing Group VI elements 0 8 Se Te no change in the number of hydrogens is required In the following examples each formula is correct for a twocarbon acyclic saturated compound C2H6 C2H60 C2H602 C2H603 3 To convert the formula of an openchain saturated hydrocarbon to a formula containing Group VII elements F Cl Br I one hydrogen must be subtracted from the molecular formula for each Group VII element present In the following examples each formula is correct for a twocarbon acyclic saturated compound C2H6 C2H5F C2H4F2 C2H3F3 1 CHM 2201 Villanova University Organic Chemistry Lab Fall 2008 Department of Chemistry The index of hydrogen deficiency sometimes called the unsaturation index is the number of the 7 bonds andor rings a molecule contains It is determined from an examination of the molecular formula on an unknown substance and from a comparison of that formula with a formula for a corresponding acyclic saturated compound The difference in the numbers of hydrogens between these formulas when divided by 2 gives the index of hydrogen deficiency The index of hydrogen deficiency can be very useful in structure determination problems To reiterate A great deal of information can be obtained about a molecule just from the molecular formula For example a compound with an index of one must have one double bond or one ring but it cannot have both structural features A compound with an index of two could have a triple bond or it could have two double bonds or two rings or one of each Benzene contains one ring and three double bonds and thus has an index of hydrogen deficiency of four Any substance with an index of four or more can possibly contain an arene ring a substance with an index of less than four cannot contain such a ring To determine the index of hydrogen deficiency for a unknown compound given its molecular formula apply the following steps 1 Determine the formula for the saturated acyclic hydrocarbon containing the same number of carbon atoms of the unknown substance 2 Correct this formula for the nonhydrocarbon elements present in the unknown one hydrogen atom for each Group V element present ie N and subtract one hydrogen atom for each Group Vll element Le a halogen present 3 Compare this formula with the molecular formula of the unknown Determine the number of hydrogens by which the two formulas differ 4 Divide the difference in the number of hydrogens by two to obtain the index of hydrogen deficiency The equals the sum of the number of 7 bonds andor rings in the structural formula of the unknown substance From Introduction to Spectroscopy by Pavia Lampman and Kriz CHM 2201 Fall 2008 Department of Chemistry Organic Chemistry Lab I Villanova University Nucleophilic Substitution of Alkyl Halides Experimental Procedures amp Notes for Experiments 17 A B and C Chapter 17 in Bell Clark and Taber pgs 188 191 Carry out this experiment in your hood Alkyl halides are toxic avoid breathing vapors and skin contact You will be using warm water baths in this lab A Styrofoam cup placed in a beaker for stability will be used as your water bath but you should immediately start to heat some water in a 400 mL beaker on your hotplate so that you have a supply of hot water ready to add to the Styrofoam cup to adjust the temperature as needed You will also need a timing device of some kind Experiment A Structural Effects on SNl and SNZ Reactivity Series 1 M l SN2 Jquot acetone R X Nal gt R I NaX i Precipi a a X Chlorine bromine 1 Label two groups of ve clean y test tubes with numerals 1 to 5 2 In each group of test tubes add 02 mL use a syringe of the following alkyl halides to the labeled tubes l nhutyl chloride lchlorobutane MCI 2 nhutyl bromide 1 39 39 MBF 3 scobutylchloridc 2chlorobutanc gt CI 4 tenbutylohloridc 397 h 397 r r C Ln crotyl chloride lchloroZbutonc Mel 3 Keep the tubes stoppered with corks or para lm and leave them covered at all times before and after adding reagents Car out all ex eriments in our hood 4 Obtain 15 mL of each of the following solutions a 15 NaI acetone for Series 1 of Experiment A b 1 ethanolic AgNOg for Series 2 of Experiment A 5 Readbecome familiar with steps 69 before continuing 6 With one series of the tubes arranged in order add rapidly and all at once 2 mL of 15 NaI acetone solution to tube 1 and note the time of the addition on your table NOTE Record dataobservations in your notebook in a table like that depicted on page 2 a NOTE after this and subsequent additions carefully watch each of the tubes for the formation this may occur rapidly or slowly of a precipitate look for solids on the bottom andor sides of the test tube39 turbidity or cloudiness is not precipitation which indicates that the reaction has occurred Page 1 of 5 CHM 2201 Organic Chemistry LabI gt1 Fall 2008 Department of Chemistry Villanova University b Record the time in your table if and when precipitation look for solids on the bottom of the test tube begins to occur in each of the test tubes Cloudiness or a milky appearance is not precipitation Remember to keep the tubes stoppered or covered Parafilm before and 0 after adding the NaI time of the addition on your table 9 remaining tubes in the series s 3 4 and 5 0 periodically while the second series is run Series 2 AgNOgethanol SNl conditions AgN03 H20 EtOH gt After 2 to 3 minutes add 2 mL of the NaI acetone solution to tube 2 and note the Continue the process of adding 2 mL portions of the NaIacetone solution to the Allow this series of tubes to stand and observe them for precipitate formation RX x 39 gt Agxi ROH and ROEt N03 1 Arrange the second series of tubes and in the same manner as above add 2 mL portions of the 1 ethanolic AgNOg to each tube at 2 to 3 minute intervals 2 Note the time of each addition and if possible record the times may be rapid or slow when the first annreciable turbiditV 39 J39 forms and then when a definite precipitate occurs 3 If any tubes in the Series 1 NaI series are still clear unstopper the tubes and place them in a 50 C water bath for 10 15 minutes noting any changes that occur 4 When finished with these reactions pour the contents into the organic waste container 5 Explain your results from Series 1 and Series 2 Do your results correlate with what was expected theoretically N aIAcetone AgNO3Ethanol Time of compound Time of Time of Time Time of Time of definite Time addition precipitate Elapsed addition turbidity precipitate elapsed formation appearance formation DO NOT RECORD RESULTS IN THIS TABLE N OTE frlr fig RECORD YOUR RESULTS DIRECTLY IN YOUR BOOK rrui l DO NOT RECORD RESULTS IN THIS TABLE NOTE f i RECORD YOUR RESULTS DIRECTLY IN YOUR BOOK 6133 DO NOT RECORD RESULTS IN THIS TABLE Page 2 Of 5 CHM 2201 Fall 2008 Department of Chemistry Organic Chemistry Lab I Villanova University Experiment B Effects of Solvent on SNl Reactivity Acetonewater I Bu Cl HOH gt t BuOH HCl 1 Label three clean y test tubes with each of the acetonewater solvent mixtures that are available in the hood The solvent mixtures available are a 5545 acetonewater b 60 40 acetone water Solvent systems arranged in order of decreasing polarity c 6535 acetonewater 2 From the three acetonewater solvent mixtures add one 2 mL portion of each mixture to the properly labeled test tube 3 Using a Pasteur disposable pipet add exactly 2 drops of 05 M NaOH and then 23 drops of phenolphthalein solution to each of the above test tubes containing the solvent mixtures 4 Cover the tubes with para lm or corks and place them in a water bath at 35 i 1 C for 3 to 4 minutes to bring the solvent mixtures to the bath temperature Use a Styrofoam cup in a beaker as an insulated container for your bath 5 Using a disposable pipet add exactly 3 drops of tert butyl chloride 2chloro2 methylpropane to each test tube 6 Note the time of the addition record in your notebook in a table like that shown below then brie y swirl the test tubes to mix and replace the tubes in the bath swirling intermittently to insure good mixing 7 Periodically add small amounts of hot water obtained from the hot water in your 400 mL beaker to the bath to maintain the temperature at 35 11 C 8 Record the time for the pink color to disappear in each of the solvent mixtures 9 Explain your results Which solvent mixture causes the fastest reaction Why Also using equations show why the pink phenolphthalein color disappears as the reaction progresses Solvent mixture used Time of addition of ten Time pink color disappeared Time elapsed in seconds 13qu Chloride DO NOT RECORD RESULTS IN THIS TABLE 5545 Acetone Water RECORD YOUR RESULTS DIRECTLY IN YOUR NOTEBOOK DO NOT RECORD RESULTS IN THIS TABLE 6040 Acetone Water RECORD YOUR RESULTS DIRECTLY IN YOUR NOTEBOOK DO NOT RECORD RESULTS IN THIS TABLE 6535 Acetone Water RECORD YOUR RESULTS DIRECTLY IN YOUR NOTEBOOK Experiment C Effect of Temperature on Reaction Rates 1 From your results in Experiment B choose the solvent system for which the neutralization time at 35 C was closest to 5 minutes this usually should be the 5545 acetonewater solvent mixture Add 2 mL of this solvent mixture to a test tube and add exactly 2 drops of the 05 M NaOH and then 23 drops of the phenolphthalein solution Place the test tube in a Styrofoam cup water bath at 25 i 1 C for 4 to 5 minutes to allow the solvent to come to the bath temperature Page 3 of 5 CHM 2201 Organic Chemistry LabI Fall 2008 Department of Chemistry Villanova University 4 Using a disposable pipet add exactly 3 drops of tert butyl chloride to the teSt tube and note the time of the addition in a table like that shown below 5 Swirl the tube to mix place the tube in the water bath and note the time in your notebook table for the pink color to disappear at the 25 1 C temperature 6 Repeat this procedure with the same solvent system at 45 i 1 C and record the times for color disappearance NOTE Prepare a second water bath for this determination since the time required in Step 5 may take 20 7 25 minutes 7 Use the times obtained for the samples at 25 C and 45 C and the time at 35 C from Exp B to make a plot oflog t time in seconds versus lT K 8 From the slope in the above plot calculate the activation energy E for the solvolysis in the solvent used 9 Note that a plot of log tvalues versus 1T K should give a straight line with slope Ea23R R gas constant 199 calmole deg and Ea activation energy See your lab text for this equation Solvent mixture Temperature Time of addition of Time pink color Time Elapsed used Iert Butyl Chloride disappeared In seconds RECORD RESULTS 25 i 10c RECORD RESULTS IN RECORD RESULTS RECORD RESULTS IN NOTEBOOK NOTEBOOK IN NOTEBOOK IN NOTEBOOK RECORD RESULTS 35 i 1 C Previously Previously Previously IN NOTEBOOK determined in determined in determined in Experiment B Egperiment B Egperiment B RECORD RESULTS 45 i 10c RECORD RESULTS IN RECORD RESULTS RECORD RESULTS IN NOTEBOOK NOTEBOOK IN NOTEBOOK IN NOTEBOOK 310 300 290 280 270 26 log t in seconds 250 240 230 220 210 200 Example of plot of log tversus 1T Slope 000314 000325 000336 1T in K Page 4 of 5 a 23R 199 x10393 kcal mol K K C273 CHM 2201 Fall 2008 Department of Chemistry Organic Chemistry Lab I Villanova University Onestep to reactant RI gt RBr gt RC1 gt RF RCHZI gt RCHzBr gt RCHZCI gt RCHZF allyl 3 gt 2 gt 1 gt methyl Methyl allyl gt 1 gt 2 gt 3 3 Alkyl halides undergo only SNl Methyl halides and 1 alkyl halides 1 Alkyl and methyl halides do not undergo only SNZ rate rate reaction reaction if nucleophilic reactants isare TlVJBare 10252008 Page 5 of 5
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