CHM 234| Study Guide for exam 2
CHM 234| Study Guide for exam 2 CHM 234
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Date Created: 02/28/16
CHM 234: Study Guide Exam 2 __________________________________________________________________ Topic: Alcohol & Phenol Ethers & Epoxides Thiols and Sulfides __________________________________________________________________ Alcohol & Phenol: ● Nomenclature a. Find the parent chain which should include the hydroxyl group. b. Find the substituents and name them. c. The hydroxyl group should have the lowest number. (Have the most priority) d. Put the name in alphabetical order e. the suffix ends with “ol” instead of “e”. ● OH have more precedence over the others like double bonds. ● On cyclic alcohols, the OH group is one carbon 1 and it is omitted Type Primary alcohol Secondary alcohol Tertiary alcohol Structure ● When a OH group is on a benzene ring, it is called, phenol. ● Deprotonation of an alcohol compound will produce an alkoxide ion ○ Reagent: NaH ● Solvation Effects ○ Less sterically hindered = more easily solvated ○ More sterically hindered = less easily solvated Primary substrate→S 2→strong nucleophile N Tertiary substrate→S 1→weak nucleophile N (First arrow = requires / second arrow = will be) Addition of OH Acidcatalyzed Reaction (H O, 2cid) Mercurationdemercuration Reaction (Hg(OAc) , H SO with NaBH ) 2 2 4 4 HydroborationOxidation Reaction (BH , THF 3ith H O , NaOH)2 2 Oxidation state Reducing Agent to form OH Catalytic Hydrogenation (H wi2h Pt, Pd, or Ni) Sodium borohydride (NaBH with 4eOH, EtOH, or H O) 2 Lithium aluminum hydride (LAH with H O) 2 LAH is more reactive than NaBH and will react witcarboxylic acid and ester to give alcoh. 4 Diols ● Have two hydroxyl group ● In naming, the “diol” is put in the end of the name. Dihydroxylation Reagent: ● RCO H (Causes transdiols) 3 + ● MCPBA with acid (H )(Causes trans diols) ● OsO with NMO or tert−butyl hydroperoxide(Causes c isdiols) 4 ● KMnO w4th NaOH (Causes c i diols) Grignard reaction to form OH General skeleton: RMgX ● Reagent: Mg with dry ether To form the OH: ● Reagent: Grignard reagent with H O2 Protection of OH For protection: ● Reagent: TMS−Cl with Et N t3 form TMSO To deprotect: + − ● Reagent: H O3, F (TBA−F) Reaction of Alcohols: Substitution and Elimination SN reaction with 3° SN reaction with 1° Reagent for Substitution: ● HBr ● HI ● HCl with ZnCl 2 ● TsCl, Pyridine with halide(goes for SN) ● SOCl with Pyridine (1° and 2°, goes for S2) 2 N ● PBr 3or PCl 3ith Pyridine ○ Carbocation rearrangement is avoided Reagent for Elimination: ● conc. H2SO 4with heat(E1 reaction) ● TsCl, Pyridine with NaOEt(E2 reaction) Note: remember to know how to do ring expansion Oxidation Reagent: ● Strong (to form chromic acid) ○ CrO 3with acetone ○ Na 2r 2 7ith H S2 , 4 O 2 ● Mild ○ PCC with CH Cl2 2 NaCrO / HSO PCC / CH Cl 2 2 7 2 4 2 2 2αH 1° alcohol Acid Ketone 1αH 2° alcohol Ketone Ketone 0αH 3° alcohol None None Phenol still undergo oxidation even though it does not have an alpha hydrogen. Ethers & Epoxides: Nomenclature 1. Name each R group 2. Arrange alphabetically 3. End with “ether” IUPAC names 1. Parent chain: larger R group 2. Name the smaller R group “alkoxy substituent” Structure and Properties of Ethers Bond angle is similar to water and alcohol Hydrogen bond acceptor, not hydrogen bond donator ● Meaning that it can interact with protons like in alcohol, but not with itself. Crown Ether XCrownY ● X Total number of atom in crown ● Y Total number of oxygen atom 12Crown4 The fluorine anion is very reactive because the potassium cation bonded itself to the crown ether. ● Crown ether is called host. ● The metal atom, for example, the K + ion, is called guest. Smaller crown binds to smaller cation. Preparation of Ether Prepared by acidcatalyzed dehydration of ethanol ● Symmetrical ether only Williamson Ether Synthesis ● Can be for nonsymmetrical and symmetrical ether ● Halide goes on less hindered alkyl group ● Alkoxide ion goes on more hindered alkyl group Alkoxymercuration–Demercuration Reagent: Hg(OAc) , Alco2ol with NaBH 4 Reactions of Ether Acid cleavage ● Ether is a poor leaving group ● Only HBr and HI can be used because they are strong acid and good nucleophile When phenyl ether is under cleavage, it will produce a phenol and an alkyl halide. Neither of the two substitution reaction will work because of the sp 2 hybridization If The R group a secondary carbocation, the reaction will be a S N reaction because it is faster. Nomenclature of Epoxides Oxirane Oxetane Oxolane Oxane Oxiranes = Epoxides Nomenclature 1. Oxygen is given the 1position 2. Naming similar to alkane, but an “epoxy” is placed into the name for the carbon bonded to the oxygen. Epoxides are not substituents, thus it does not get the same rule as other substituents like methyls and ethyls. So when writing the prefix “epoxy”, the word goes before the parent chain’s name. Preparation of Epoxides Reagent: ● RCO H 3 ● MCPBA Preparation from Halohydrins Reagent: ● Br2 with H2O(To form Halohydrin) ● Br with H O, then NaOH (To form Epoxide) 2 2 Enantioselective Epoxidation Select one of the two enantiomers. Reagent: ● Ti[OCH(CH 324with (±)DEM (Sharpless catalyst) ○ +: above plane ○ : below plane ● tbutyl hydroperoxide Only with allylic alcohol The orientation when drawing the Sharpless asymmetric epoxidation, the hydroxyl group is at the upper right corner. RingOpening Reactions of Epoxides Epoxides are more reactive than ethers because of the stress in the threemember ring in a nucleophilic substitution reaction. The ring will open up as a result of reacting. nucleophile will attack the l ess substituted position. AcidCatalyzed Ring Opening nucleophile will attack the m ore substituted position . Will attack Dominant factor 1° vs. 2° 1° steric effect 2° vs. 3° 3° electronic effect 1° vs 3° 3° electronic effect Thiols and Sulfides Thiol = SH When naming, the compound ends with “thiol” instead of “ol” Thiols are also known as mercaptans “mercapto” is used when thiols are a substituent Preparation of Thiol Reagent ● NaSH Thiols can be prepared with a S 2 reaction with sodium hydrosulfide (NaSH) and alkyl halide. N Sulfides Similar structure to ether with oxygen, ether structure with sulfur are called sulfides or thioethers. diethyl ether diethyl sulfide Prepared by nucleophilic attack of a thiolate on an alkyl halide SAM SAdenosylmethionine (SAM) is a good biological methylating agent Same effect can happen with methyl iodine. Methylation is the process of substituting methyl group into the molecule, replacing the hydrogen atom.
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