Gen Organic Chemistry I
Gen Organic Chemistry I CHEM 3311
University of Memphis
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This 33 page Class Notes was uploaded by Ms. Noemie Klein on Friday October 23, 2015. The Class Notes belongs to CHEM 3311 at University of Memphis taught by Staff in Fall. Since its upload, it has received 29 views. For similar materials see /class/228407/chem-3311-university-of-memphis in Chemistry at University of Memphis.
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Date Created: 10/23/15
Unit I Structure Problems Problem 1 solution Molecular ion 114 indicates need to double the propy1 group Other hydrogehs 2 5 indicated ppm triplet 72 neighbors by ance 1750 cmquot 0 Rabsorb 1 6 ppm multiplet 7 lots ofneighbors lppm triplet e tenninal alkane w2 neighbors Problem 2 Butaclamol is an antipsychotic used in the treatment of schizophrenia How many stereocenters does it have OH N CCH33 00 Problem 2 Solution Namequot 39 e m at room temperature as sp3 and sp2 are close in energy OH N CCH33 coo Problem 3 I Are the structures in the following pairs idemical constitmional isomers enamiomers or diastereomers H cw cw Cl C C C H H CH3 H3CH2CHZOH HCH2CH3 CH3 CHZOH Problem 3 Solution Constitutional Diastereomers H Cl Cl C Cl Cl Cl H Enantiomers H 3 CI H H CH3 CH3CH2CHZOH HCHZCH3 CH3 CHZOH HBC H H CI CHQCHB CH3 Problem 4 Provide systematic IUPAC names for the following structures OH CH2 H3 H30 CHz HCHs Him3 7 H CI Hi Hi CH3 Problem 4 Solution 2R 3 S2chloro3 methylpentane CH2CH3 Z4hexen2ol 9H H30 CHZCHCH3 H H Problem 5 Draw the most stable conformation of 7 Butane 7 Cis12dirnethy1cyclohexane Problem 5 Solution Butane u DR 5 Cis12dimethylcyclohexane Ifyou draw both methyl groups cu equatorial it will be trans so this is the best you can do for this structure Problem 6 2R 2pentanol is a colorless liquid that has a melting point of 50 C and a boiling point of 118 C 7 me its structure An unknown colorless liquid has a melting point of 50 C and a boiling point of 118 C 7 Is the unknown colorless liquid 2R2 pentanol 7 Why or Why not 7 If not What else could it be and how could you 39stinguish the two Acidity and Basicity Quantitative Re ection of Acid Strength Given an acid donating a proton to water 0 II N H 0 C H20 C 3 H3C OH 30 0 HA A39 The extent of that reaction at equilibrium is quantitated by the Ka A 1 H301 HA a Since the products of the reaction are in the numerator larger Ka values are observed for stronger acids Also since pKa log Ka smaller pKa values are observed for stronger acids Quantitative Re ection of Base Strength Given a base accepting a proton from water i I C H20 C OH39 HgC 0 H30 OH B39 HB The extent of that reaction at equilibrium is quantitated by the Kb HB 0H Kb 3 Since the products of the reaction are in the numerator larger Kb values are observed for stronger bases Also since pr log Kb smaller pr values are observed for stronger bases Conjugate AcidBase Pairs Since both Ka and Kb are de ned for reactions involving water their product for conjugate acidbase pairs equals KW 10 0 Since KaKb103914 pKa pr 14 Acid and base strength are therefore conversely related for conjugate acidbase pairs Stronger acids have weaker conjugate bases and VICC VCI SEI KaKb and Free Energy AG Any equilibrium constant can be related to the free energy of the reaction AG 2 RTan OR AG 2 2303RTlogK High Ka values therefore give more negative AG values Determining Relative Acidity from Structure Bronsted acidity depends on Identity of atom donating the proton Relative stability of starting acid and conjugate base produced Charged vs neutral Delocalized charge vs isolated charge Charge delocalization mechanism Resonance vs induction Hybridization of atom donating the proton Atom Identity Problem Given your previous knowledge of acidity rank the following lists of acids from strongest to weakest List 1 H20 HF NH3 CH4 List 2 HCl HBr HF HI Can you relate the order of acidity in your list to trends in the periodic table Relative Stabilities Charged vs Neutral Given the following two acid dissociation reactions which acid do you think is stronger 0 Why H20 Relative Stability Charge Delocalization I Both of the following acid dissociation reactions generate charged products with identical donating atoms o 3 3 H H3C OH H3c o CH3CH20H CH3CH2039 H Are the charges in either product stabilized in any way Which starting material is a stronger acid Relative Stability Charge Delocalization II Both of the following acid dissociation reactions generate charged products with identical donating atoms 0 O H3C OH H3c o o o 3 3 H F3C OH F3c o Are the charges in either product stabilized in any way Which starting material is a stronger acid Atom Hybridization Hybridization in uences acidity because orbitals have differing energy and electrons closer to the nucleus will be more stable and thus less reactive L H H 1 c T gt c c r H H quot H Wthh product H H H H formed in these acidbase reactions H H H 15 most stable and CC gt CC H therefore produced H H H H by the strongest acid Determining Relative Basicity from Structure Bronsted basicity depends on Identity of atom accepting the proton Relative stability of starting base and conjugate acid produced Charged vs neutral Delocalized charge vs isolated charge Chargeelectron delocalization mechanism Resonance vs induction Hybridization of atom accepting the proton Atom Identity Problem Since acid and conjugate base strength are inversely related how can you use the periodic table to predict base strength Come up with a list of three bases in order of increasing strength based on the trends you propose Relative Stability Problem Rank the following bases from most to least basic consider the relative stabilities of the starting materials products and the relative CHANGES in stability from reactants to products NH3 H NH4 o o c H gt c ch NHZ ch NH3 Effect of Solvation on Ionization Charged species are generally not stable Polar solvents can stabilize Charged species HOH O t w Na H Iul4 quot39LH 03 X 0 n Implementing Synthetic Strategies Considerations From last class Construction of carbon skeleton Functional group conversions Regiochernical control Stereochemical control New considerations SolventSolubility Side Reactions Solvent Solubility Many reagents are salts soluble instabilized by polar solvents Many organic molecules are nonpolar and NOT soluble in polar solvents Solution Phase transfer catalysts substances that are able to promote the transfer of salts into organic solvents Phase Transfer Catalysts V 3355 pm New r 2 Q X Q N u n 1 Q N RX 4 Oxgamr RCN RX Oxganir phase r phase CHZCIZ CHZCIZ Here no reaction takes H l the phasertranwfer pl c becausc the catalyst trans arm the nurleuphile N cannut yanide ion as Q 0 39 enter the organic phase mm the organic phase tn mart with RX when the reartiun V H 39N X lakes plate lapxdly Crown Ethers Crown ethers present a hydrophobic outer surface and thus dissolve easily in nonpolar solvents Their internal cavity however is lined with partially negative oxygen atoms which interact strongly with cations of the appropriate size When cations are drawn into fo 5 solution the anions follow 0 539 8390 1 8crown6 Problem What solvent might you choose for the following reactions and which might require a phasetransfer catalyst CN KCN gt OH O H2Cf204 gt z i Side Reactions Desirable organic compounds often have multiple functional groups many of which will react with the same reagents Example the following Grignard reaction does NOT produce 4methyl24heptandiol What is produced instead OH O W CH3MgBr gt Prevention of Side Reactions Protecting Groups Functional groups that might perform undesired reactions can be converted to a different functional group that is inert to the conditions that will be used called a protecting group These protecting groups should be easily removable under other conditions in order to regenerate the initial functional group Protecting Group Example lerIbutyldimethylsilyl chloride TBDMSCI H3C3C CH3 1 OH 0 H3 d 1 HC 0 o 1 39 H 1m1 azoe 3 W C SE C 93 W CH3 CH3MgBr CH CH 0H 0H chgt3cs 3 H3C3C 3 0 OH o O39MgBr H3C H20 H3C lt BU4N F Silyl chlorides react with alcohols to form silyl ethers Silyl ethers can speci cally be converted back to alcohols with uoride ion Problem Which of the following reactions will not produce the listed product due to side reactions and would therefore require the use of at protecting group OH OH Br HBr M OH O O O Polar Reaction Mechanisms Substitutions Substitution Reaction Mechanisms Bimolecular 8N2 Two reactants involved in rate determining step A l p 139 gt C BorCQI quot r Unimolecular 8N1 One reactant involved in rate determining step I p I39 I slow I A Cquot gt gt Bor IIII 8N2 Reaction Energy Diagram Transition state 539X Zts AG Products T AG u l m 4 X YZ Fl eactants errighl 21300 Jnhn Willa nnrl 4115 In
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