Organic Chemistry 2310 Midterm 2 Study Guide
Organic Chemistry 2310 Midterm 2 Study Guide Chem 2310
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This 7 page Study Guide was uploaded by an elite notetaker on Friday October 9, 2015. The Study Guide belongs to Chem 2310 at Ohio State University taught by Dr. Vanden-Eynden in Summer 2015. Since its upload, it has received 127 views. For similar materials see Intro Organic Chem in Chemistry at Ohio State University.
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Date Created: 10/09/15
CHEM 2310 Midterm 2 Study Guide Nomenclature 1 Alcohols 71 Named as alkanols or hydroxyl substituents Hexanol would take precedence over hexane Phenols 73 Phenols are aromatic alcohols named with phenol at the base Example 4cholor3 nitrophenol is a benzene structure with an OH group on carbon 1 a nitrous group on carbon 3 and a chloride on carbon 4 Thiols sulfur is an oddball 717 Thiols are named as alkanethiols They can also be named alkane mercaptan An aromatic ring with an SH group attached is a thiophenol An ethane with an SH group attached can be named ethanethiol or ethyl mercaptan Ethers 81 Named as alkyl alkyl ethers A propyl group attached to an ethyl group by an oxygen would be named an ethyl propyl ether Alphabetical order is important with substituent groups and there are spaces between each It could also be named with the ethyl oxygen as a substituent 1ethoxypropane Epoxides 87 Epoxides are cyclic ethers with 3membered rings named as alkene oxides or as oxiranes An ethyl epoxide could be named ethylene oxide or oxirane When naming as oxirane the oxygen is number first and the carbon branch is named as a substituent An oxirane with a propyl group coming off of carbon 2 with the oxygen being numbered 1 could be named 2propyloxirane Structure Properties 1 Alcohols 72 74 Classified as primary 1 secondary 2 or tertiary 3 based on the of R groups attached to the hydroxyl bearing carbon Hydrogen bonding interaction between a hydrogen and a heteroatom is present This is a stabilizing factor since Hbonds are some of the strongest intermolecular forces makes boiling point much higher than ethers of similar molecular weight Phenom Better acids than alcohols because of resonance Unable to undergo substitution rxns because of sp2 orbitals they form very unstable and structurally unfavorable cations 711 Ortho para directors strong activators 714 Function as antioxidants 716 Thiols Thiolate anions are good nucleophiles Nucs and weak bases pKa 3910 Form disulfide bridges base deprotonates the sulfur which then bonds to another sulfur Very important in amino acids Ethers Low BPs no Hbonds gtgt make good solvents because they can easily be removed gtgt the only forces present are London forces which are relatively weak Polar aprotic solvents Epoxides Produced from alkenes gtgt mCPBA can be a reactant React similar to ethers 3membered rings are strained because the bond angles are not ideal gtgt fast rxns Stereoisomerism Stereoisomers have identical molecular formulas and connectiveties but their arrangements in space are different Think right hand and left hand they are mirror images but cannot be superimposed onto each other 1 Chirality of Carbon Chiral molecules do not have superimposable mirror images 51 Achiral molecules have identical mirror images similar to a tennis ball in the mirror Since single bonds rotate the nonsuperimposable mirror images enantiomers must have four different substituents on carbon CHBrClOH is a chiral molecule Carbon centers with 4 substituents attached are called stereogenic carbon centers 52 There can be multiple chiral centers in a molecule 2 R and S center rules 53 R and S nomenclature defines the configuration of enantiomers Clockwise chiral centers are named R and counterclockwise centers are named S First the group with the lowest priority atomic must be located and then the molecule must be oriented with this lowest priority molecule in the back H is always the lowest priority only thing lower is a lone pair of electrons Priority of molecule is determined by atomic number If there are similar functional groups a tiebreaker may be needed Methyl is always the lowest alkyl subst the longest carbon chain will often have the most priority If the first two carbons of two substituents are the same then move to the next two and rate those and so on until a tiebreaker is reached Pibonds are quotmultiple substituents so it would could as two carbon bonds or two bonds to whatever it was attached to Wedges andor dashes must be present for chirality to be determined if drawing of molecule is 2D then a 5050 or racemic mixture is assumed If the H is a wedge chirality can still be determined because it would be the opposite if H were a dash which is where H should be but this is a shortcut 3 Fischer projections 57 Viewing molecules from underneathabove Looks like a cross with no dashes or wedges but vertical lines mean dashes and horizontal lines would be wedges Therefore the lowest priority should be on the vertical line If lowest priority is not on the vertical line the structure can rotated by rotating 3 of the 4 substituents and leaving one stationary this will give the same molecule but with H in the back IV Multiple stereogenic centers 1 2 chiral centers have varying structures and properties When all centers are inverted the structures are enantiomers If one or more but not all centers are inverted they are diastereomers not mirror images 2 Mesa compounds These are molecules that look like they should be chiral but in fact are not because there is an internal mirror plane making them achiral V Nucleophilic substitution 1 Substitution rxn exchanging one component for another There are strong Nucs which generally are anions and weak Nucs which typically have just a lone pair of electrons Vl Leaving groups are halogens Cl Br I no F Nucs are anionic C N S O I Br or neutral N O S f Nucs are also strong bases side elimination rxns can occur INSERT PHOTO 2 Substitution mechanisms Multiple mechanisms can occur Sn2 or Sn1 63 Sn2 relatively strong Nu 64 a One step mechanism all bonds broken and formed in a single step Backside attack of Nuc 180 approach Nuc R LG gtgt Nuc5 R LG 5 gtgt Nuc R LG b Bimolecular mechanism meaning the rate is dependent on both reactants c Inversion of configuration chiral center inverts since it is a backside attack so R turns to S and S turns to R Sn1 involves poor Nucs carbocation and two steps 65 a First step is slow and is the rate determining step the weak Nuc must wait for the leaving group to just leave on its own before it can attack b Unimolecular mechanism rate relies upon only one component the substrate c Stereochemistry is destroyed there is not net gain and a racemic mixture is often obtained The more stable the cation that is formed the faster the rxn 3 Predicting substitution rxns 66 Better Nuc favors Sn2 weak Nuc favors Sn1 typical weak Nucs are H20 and ROHs Anions gt neutral Elements lower in the group are stronger Nucs and more electronegative elements are worse Nucs Elimination Rxns Usually side rxns to Sn1Sn2 E2 rxn is bimolecular single step 67 Strong bases rather than attacking the carbocation attack the H atom As this happens the leaving group LG typically halogen leaves and the electrons from the C H bond bond to the carbon originally bearing the LG creating a double bond The bond angle between the H and LG mush be 180 otherwise E2 is physically impossible E1 mechanism is unimolecular two steps LG leaves first forming a carbocation and a hydrogen is removed from an adjacent carbon with the electrons from the C H bond bonding with the carbocation This occurs with weak Nucs Side note carbon halogen bonds are very weak because of the high olarity of the bond This is why a weak Nuc can quotwaitquot for the halogen X to break off on its own May not happen at room temperature but is likely under certain conditions Predicting substitution vs elimination a 3 halides do not undergo Sn2 rxns because of steric bulk there is a lot in the way of a backside attack but since they from stable carbocations they will undergo the Sn1 rxn With a weak Nuc look for Sn1 and E1 products with Sn1 typically being major with a strong Nuc the molecule will only undergo E2 b 1 halides do not undergo Sn1E1 because primary carbocations are very unstable and therefore do not easily form A primary cation with a weak Nuc will not react With a strong Nuc it will undergo Sn2 and E2 with Sn2 being major c Large bulky bases will undergo E2 only so something like KOtBu although is a strong Nuc is also a very good base with a lot of steric bulk tbutane and will only undergo E2 reactions d 2 halides gtgt all mechanisms in play Strong basenucleophile E2Sn2 Weak basenucleophile Sn1E1 VII Acidity and basicity 1 BronstedLowry definitions acids are H donors bases are H acceptors 75 Ka acid dissociation constant tells how well an acid will react with a base Strong acids easily give away H weak acids do not pKa is the log of Ka and the lower the pKa the stronger the acid Acid and bases strength is all relative pKa values Mineral acids HX quot39 5 Oxonium ions ROHZ39 quot39 0 Carboxylic acid OR OH quot39 5 Ammonium ion R NH3 quot39 10 WaterAlcohol R OH15 Alkyne quot39 25 Amine R NH2 3935 Alkene 3945 Alkane quot39 55 2 Lewis acidsbases Lewis acids are electron acceptors empty orbitalscarbocationAICI3 Lewis bases are electron donors lone pairs NH3 3 Acidity and basicity factors 76 Stability of conjugate base drives all acid base chemistry More stable conjugate bas means the acid is more acidic Resonance plays a large part in stability if the charge on a conjugate base can be delocalized it will be more stable and therefore its conjugate acid will be stronger There are also inductive effects which have to do with polar covalent bonds If a polar covalent bond creates a partial positive charge on the carbon closest to the negative charge of the base the molecule will be more stable CHFZCHZO39 is more stable than CH3CH2039 Atomic affects more electronegative anion gives a more stable negative charge One atom difference moving across the table makes a significant difference but moving up and down is a bit different Larger size means more stable so although Cl is much more electronegative than I it is not that much more stable because I s size makes it more stable Stable bases are bad bases Conjugate acids of stable bases are good acids 4 Deprotonation of alcohols Strong bases are required to deprotonate alcohols pKa tells us which side will win in a reversible reaction There will be an acid and base on each side of the rxn and which ever side holds the acid with the higher pKa will be the side that the equilibrium shifts to If pKas are the same we will get a 5050 racemic mixture 5 Basicity of alcohols 77 VIII XI In general alcohols are weak bases and strong acids are needed Reactions of Alcohols 1 Dehydration elimination 78 El rxns with strong acids tertiary and secondary alcohols Alcohols are not good leaving groups so they must first be protonated H2504 is generally good for this because HSO439 is not a good Nuc E2 mechanisms primary alcohols avoid carbocation formation First step is always to protonate Most stable alkene mixtures are the major products so if two products are possible the major product will be the product with the most R groups off the double bond Substitution of alcohols with halides HX 79 Sn2 primary and secondary Sn1 tertiary and bulky secondary HBr HCl and HI can turn alcohols into alkyl halides First step is protonation Other preps of RX alkyl halide from ROH PBr3 SOCIZ mechanisms do not need to be known Oxidation of alcohols 712 Reduction addition of H or loss of O Oxidation loss of H or gain of O Alkane oxidizes to alcohol to carbonyl to carboxyl to carbon dioxide Chromates can be used to oxidize alcohols CrOg H2504 HZO NaZCrzO7 H2504 HZO Secondary alcohols are oxidized to ketones primary alcohols are oxidized to aldehydes then carboxylic acids The second reaction cannot be stopped If we wanted a primary alcohol oxidized only to an aldehyde we could use pyridinium chlorochromate or PCC DCM is often used as the solvent Reactions of phenols 1 Phenols do not undergo substitution reactions 711 2 Phenols are orthopara directors 714 3 Oxidation of phenols 715 ph OH goes to phO 4 Phenols are antioxidants 716 Radicals are dangerous and can form tumors phenol radicals are more stable than most so they will react with radicals taking away that lone electron Vitamin E Thiols 1 Good Nucs weak bases pKa quot39 10 Can form disulfide bridges with each other Ethers 1 Use wGrignard reagents 83 alkyl halides react with Mg with ether as solvent to form a carbocation which are strong bases and Nucs 2 Preparation of ethers H cation reaction of alcohols 85 a H cation reaction of alcohols Sn2 rxns of alcohols Alcohols are protonated at 130 C and they will combine to form ethers Mixed ethers are ethers with different R groups on either side Tertiary alcohols can form ethers through Sn1 As long as we have a carbocation we can make an ether b H cation reaction of alkenes H is picked up by one carbon in the double bond and carbocation is formed at other carbon c Williamson ether synthesis alkoxide R X via Sn2 does not work with everything because of steric bulk 3 Cleavage of ethers 86 Ethers don t undergo many other rxns mainly cleavage They are good solvents because they don t do much Can be cleaved with an HX protonation allows for a good leaving group Hydrolysis occurs with addition of water and protonation via Snl since water is a bad Nuc Carbocation is formed XII Epoxides 87 Cyclic ethers React similar to ethers 3membered rings are strained gtgt fast rxns Produced from alkenes with mCPBA May be protonated to form carbocation which is attacked by Nuc or may be attacked by base to form 039 PaulVanden Eynden CHM2310 SubstitutionElimination Guidelines Nucleophile vs Base Predicting Substitution vs Elimination I stronger B G C 6 CH3 9 N CH3HNG Y Y HZNe R CEC G o6 e CH30 G H0 HIR RIH T worse Nuc better Nuc I SN1E1 I 3N2 9 RS9 CN CH3COe R SH F9 R3P poor LG good LG Cle Br 396 0 H20 CH3 weaker B Methods for determining substitution or elimination Remember that there are always exceptions Every case must be evaluated individually 1 Examine the substrate RX where X 1 Br Cl OH2 ORH If CH3X then SN2 only If 1 then SN2 unhindered or E2 branched If 2 then SNl SN2 E1 or E2 If 3 then SNl E1 or E2 2 Examine the nucleophilebase Weak nucleophile weak base favors SNl andor E1 Good nucleophile weak base favors SN2 for 1 and unhindered 2 SNl for hindered 2 and 3 Good base good nucleophile favors SN2 for 1 E2 for hindered 1 SN2 and E2 for 2 E2 for 3 3 SN2 works best with unsolvated nucleophiles polar aprotic solvents while polar protic solvents favor S N1E1 4 Eliminations are favored at higher temperatures and with bulky bases Created by Dr Noel M Paul 2010 Modified by Dr Matthew J Vanden Eynden 2015 Graphical Representation of Data from Pearson R G Sobel H Songstad J J Am Chem Soc 1968 90 319
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