Organic Laboratory Techniques I
Organic Laboratory Techniques I CHM 2211L
University of Central Florida
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This 8 page Class Notes was uploaded by Ellen Braun on Thursday October 22, 2015. The Class Notes belongs to CHM 2211L at University of Central Florida taught by Edward Kluger in Fall. Since its upload, it has received 29 views. For similar materials see /class/227646/chm-2211l-university-of-central-florida in Chemistry at University of Central Florida.
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Date Created: 10/22/15
Aspirin Lab a Acid catalyzed Nucleophilic acyl substitution b Phenol tests i Ferric chloride added color change to purple is positive ii If it stays orange it is negative iii Color intensity is dependent on concentration c Recrystallization i Purpose 1 Solute molecules assimilate into lattice and impurities are excluded 2 There are always losses due to solubility 3 Temperature of solvent is always important 4 The more the crude product the more efficient the process ii Steps 1 Heat solution 2 Filter 3 Allow to cool slowly scratch to induce crystallization 4 Vacuum filter crystals 5 Wash crystals with cold solvent 6 Dry crystals to allow solvent to evaporate d Melting Point i Purpose 1 Purity of your sample when compared against the literature standard ii Incorrect 1 if product is still wet or impure results will be lower broader 2 Higher results if excess solvent Tpentyl chloride a SN1 Unimolecular substitution b E1 c Extraction using sep funnel transferring a solute from one solvent to another d Washing removing impurities through phase transfer e Drying i Water removal from a liquid by means ofa drying agent CaClz f Gravity filtration i Separate heterogeneous mixture using filter paper g Simple distillation i Separation of miscible liquids solution by difference in boiling points ii In the process heating liquid to vapor and cooling condensation of gas to liquid the heat exchanger is your condenser iii Use for separating liquids boiling below 125 at one atm from nonvolatile impurities another miscible liquid boiling at least 25 higher than the first 7 Distillate your liquid product after simple distillation i Theoretical Yield gt Actual yield i Losses due to side reactions competition solubility losses product dissolving in solvent during extraction evaporation losses product vaporizes during isolation and mechanical losses loss during transferring adhering to drying agent or during fraction collection j Percent yield i Actual theoretical X 100 Chromatography a TLC absorbent is spread in a thin layer on plate and a small amount of mixture is spotted on the absorbent The plate is placed vertically in a container with the lower end resting in the solvent The spot must be above the surface of the solvent The developer moves up by capillary action and the components of the mixture are carried with it undergoing separation at varying rates b Plate spotting each distance is measured from the point the mixture is spotted on the adsorbent c Rf value physical property of the substance isolate in terms of Rf the mobility of the substance Value equals the ratio of the distance traveled by substance divided by distance the solvent traveled S3 Silica gel plate stationary phase Whatman paper seen by adding ninhydrin solution 5 Mobile phase developing solvent 4methylcyclohexene a El elimination unimolecular32 b Salting out with NaCl Sometimes the organic product layer is slightly soluble in water when salt is added it dissolves in water which causes your organic layer to be lees soluble in water c Unsaturation alkene tests BrZCCl4 addition of halogens to cyclic olefins from alkene to alkane only anti isomer is formed KMnO4 strong oxidizing agent syn addition occurs for cycloalkenes only the syncis product is isolated forms 12 diol when Oh group adds to C1 and C2 of the olefin brown solid d Salt plates for IR rinsed with chloroform and stored in dessicator e Neutralization with 10 NaCO3 sodium carbonate then check pH ofaqueous layer with pH paper Methyl Orange a Diazotization sodium sulfanilate reacts with sodium nitrate in hydrochloric acid to for an unstable diazonium salt b Coupling step two in which the diazonium ion is used in situ and reacts with NN dimethylaniline to form an acidic azo dye c In situ in test tube d Chromophore Electron withdrawing simple unsaturated group attached to a benzene ring or fused aromatic ring N02 NN CO C E N e Auxochrome electron donating group attached to a benzene ring or fused aromatic ring OH NH2 NHR NR2 VI Eugenol 3 Percent recovery Techniques Simple distillation 7 separation of miscible liquids by differences in boiling point Molecules in the liquid phase enter the gaseous phase depending on temperature size of the molecules and intermolecular attraction Boiling point temperature at which the vapr pressure of a liquid is equal to the con ning pressure atmospheric pressure Specifies that heating causes vaporation cooling causes condensation The heat exchanger is the condenser Used when separating liquids below 1500 Celsius at one atmosphere from nonvolatile impurities high boiler another miscible liquid boiling at least 25 Celsius higher than the first Forerun 7 low boiling liquid before your expected product Boiling range 7 temperature range where liquid distills Fraction 7 one of several liquid portions from your miscible mixture that are distilled at a speci c temperature Receiving ask 7 ask where your liquid fractions are collected Distillate your liquid product collected in the receiving ask Extraction 7 use of a separatory funnel to separate immiscible liquids Transferring a solute dissolved substance from one solvent to another The layer on top will be the one with the lower density Drying agents 7 Water removal from a liquid by means of a drying agent Can use CHzClz MgSO4 or NazSO4 Add the drying agent stir and allow to sit until the mixture is clear DOES NOT MEAN COLOURLESS Gravity ltration 7 Separation of heterogeneous mixtures using filter paper Uses uted filter paper a longstem glass funnel and something to collect the product Neutralization 7 acidbase rxn Second part of forming a soap The carboxylic acid reacts with a base to form the carboxylic acid salt Salting Out 7 keeps the organic out of the aqueous Sometimes the organic layer is slightly soluble in water When salt is added it dissolved in water and causes the organic layer to be less soluble in water Steam Distillation advantages include being able to distill the desired product at a temperature below 1000 Celsius Avoids decomposition The two substances can mix and codistill The desired component is nonmiscible and separates from the water Used in isolating liquids form natural sources eugenol or removing a reaction product from a tarry reaction mixture Uses a roundbottom ask and a re ux condenser with a stopper on top and water continually added Vacuum filtration 7 used to separate solid products from a solvent crystals Used in the recrystallization product Uses a special Erlenmeyer ask connected to vacuum tubing with a rubber piece attached to a funnel and base Filter paper in the base Recrystallization 7 a purifying method Mixture of compound A and impurity B are dissolved in a hot solvent to dissolve the mixture and make a saturated solution As it cools crystals are formed the impurity would remain in solution Multiple solvents can be used the rst one would have compound A and impurity B both soluble in it and then either compound A or impurity B would precipitate in the second solvent Typically followed by vacuum ltration TLC analysis 7 thin layer chromatography Absorbent is spread in a thin layer on a plastic or glass plate Small amount of mixture spotted on the absorbent layer on one end Plate is placed vertically in a container with the lower end resting in the developing solvent the spots must be above the surface of the solvent Spots move up by capillary action with varying rates Includes Rfvalue distance traveled by substance distance traveled by solvent Rotary evaporator 7 used for the ef cient and gentle removal of solvents from samples by evaporation sample was evaporated under reduced pressure Ice water is run through the condenser Used for eugenol Re ux set up Round bottom ask attached to a re ux condenser hooked up to the water Allows the reaction to proceed without burning off the solvent Melting point determination uses the MelTemp apparatus Melting range starts when the rst crystal melts to when the whole sample is melted IR analysis 7tells you what functional groups you have and which ones you don t have A neat sample is an IR sample prepared without any solvent The sample beam is where you place your sample FTIR is the Fourier Transform IR where a single beam instrument uses a computer program and a moving mirror optics Plot of absorption intensity versus wavenumber for a given sample The bands or peaks result when molecules absorb IR energy and speci c bonds stretch or bend Frequencies between 4000650 cm391 and wavelengths between 2515 microns Wavelengths are indirectly proportional to IR energy Percent transmission is the relative measure of speci c band absorption intensities Base trap 7 uses a base bath in a gas trap Basic solution in a beaker in which a longstem funnel connected to gas tubing just barely rests on the surface all connected to a closed off re ux apparatus Iodoform test 7 Tests for methyl ketone and produces a carboxylic acid salt like acetaldehyde forming sodium formate A yellow solid will fonn Benedict s test 7 tests for aliphatic aldehydes A positive is an orangered precipitate General nomenclature Nucleophile 7 a species that donates an electronpair during a chemical reaction Lewis bases All molecules or ions with a free pair of electrons Electrophile 7 a reagent that is attracted to electrons and accepts an electron pair in order to bond to a nucleophile Lewis acids Most are atoms that do not have a full octet or have a positive charge or a partial positive charge Carbocation 7 an ion with a positively charged carbon atom the carbon is usually a sextet Sp2 hybridization with a trigonal planar geometry Carbanion 7 an anion in which the carbon has an unshared pair of electrons and bears a negative charge Usually a conjugate basic of a carbon acid Trigonal pyramid geometry Leaving group 7 a molecular fragment that departs with a pair of electrons in heterolytic bond cleavage Anions or neutral molecules Alpha hydrogens 7 a hydrogen atom directly bonded to an alpha carbon Acidic and easily removed by common bases Enolate an anion derived by the loss of a proton from the alpha carbon of a carbonyl group The anion of an enol Formed as an intermediate in ketoenol tautomerism Generally very basic Aldol 7 betahydroxy ketone or Aldehyde and the product of aldol addition Formed when the enolate of an Aldehyde or a ketone reacts with the alpha carbon with the carbonyl of another molecule under basic or acidic conditions stabilized by resonance serve as nucleophiles in aldol condensation reactions Tautomers 7 isomers of organic compounds that regularly interconvert by a chemical reaction called tautomerization Results in the formal migration of a hydrogen atom or proton accompanied by a switch of a single bond and an adjacent double bond Alpha beta unsaturated ketones and aldehydes occurs as a result of aldol condensation Enones and enals Aldol dehydration Limiting reactant 7 the reagent that runs out rst All of this reagent is gone when the reaction proceeds to completion Theoretical yield 7 how much would be obtained at 100 yield found via stoichiometry Percent yield actually yieldtheoretical yield Actual yield the mass or volume of the product that is actually obtained Percent recovery 7 used for extraction reactions g of what is obtained g of what is put in x 100 Reducing agent the element or compound in a redox reaction that donates an electron to another species It is oxidized Oxidizing agent 7the element or compound in a redox reaction that accepts an electron from another species It is reduced Azeotrope a mixture of two or more liquids in such a ratio that its composition cannot be changed by simple distillation When the azeotrope is boiled the resulting vapor has the same ratio of constituents as the original mixture Distillate 7 a liquid condensed from vapor in distillation normally a puri ed form Filtrate 7 the part that is discarded after ltration Salt plates 7the plates that are placed in an IR that the product is placed on Cannot be touched except around the edges Mobile phase the solvent in thin line or paper chromatography that travels up the silica or paper Developing phase Stationary phase 7 the absorbent that is xed to the silica or paper Rf value 7 distance travelled by substance distance traveled by solvent Used to determine the identity of a substance Plate spotting 7the substances are spotted to make it easier to see how they travel As they travel they will leave a spot that can be measured to identify the substance Soap a carboxylic acid salt RCOO39IMH M is usually Na or K Usually an even number of carbons Hydrophilic 7 water loving Hydrophobic water fearing Micelle 7 the aggregation of soap molecules with dirt and grease particles The hydrophic tails of the soap stick into the grease and the hydrophilic ends stick out into the water Curding 7 a bath tub ring what forms when soap is used in hard water Reacts with Ca Mg or Fe Can be avoided by adding NazC03 or Na3PO4 Biodegradable 7 microorganisms can convert linear soaps into C02 and H20 eliminating soaps from the environment Triglyceride 7 three fatty acids connected to a glycerol molecule Ylide 7 a neutral dipolar molecule containing a negatively charged atom directly attached to a hetero atom with a formal positive charge 1 2 7 dipolar compounds Positive and negative charges are adjacent Zwitterions 7 a positive and negative charge contained within the molecule but they are not adjacent charges
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