CHM 234| Epoxides and thiols
CHM 234| Epoxides and thiols CHM 234
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This 6 page Class Notes was uploaded by Alvin Notetaker on Saturday February 27, 2016. The Class Notes belongs to CHM 234 at Arizona State University taught by Pillai in Fall 2015. Since its upload, it has received 38 views. For similar materials see General Organic Chemistry II in Chemistry at Arizona State University.
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Date Created: 02/27/16
Epoxides (On the last note when naming the epoxides, those names were wrong.) 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 Reagents: ● MCPBA ● Peroxyacetic acid Preparation from Halohydrins Reagent: halides with water Reagent: strong base ● To make epoxide Mechanism:  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 Chiral catalyst can lower the activation energy for formation of one enantiomers is more effective than formation of both enantiomers. 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. When the epoxides is unsymmetrical, the nucleophile will attack the less substituted position. This will cause an inversion: AcidCatalyzed Ring Opening Acid protonate the oxygen atom When the epoxides is unsymmetrical, the nucleophile will attack the more substituted position. This attack is an S N2 reaction 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” 3methyl1butanol 3methyl1butanethiol Thiols are also known as mercaptans 3mercapto3methyl1butanol “mercapto” is used when thiols are a substituent. Thiols can be prepared with a S N reaction with sodium hydrosulfide (NaSH) and alkyl halide. 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. Synthesis problem
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