2ABSTRACT: An experiment that compares product distribution obtainedby either substitution or elimination utilizing alkyl bromides and methoxide,ethoxide, or t-butoxide as the base (or nucleophile) is described. The changein product distribution caused by steric effects of the base and substrate arereadily apparent. Prior work on this experiment focused on only the olefinproducts using a method without internal standards. The experiment examinesall ether and olefin products as well as starting material and illustrates keyprinciples of S2-SNl and E2-E1 reactions. For this experiment, a gas chro-matographic method was developed that allows for complete product analysis.The new method examines the product distributions as a function of primary,secondary, and tertiary alkylbromide and base structure and can be expanded toinclude the interpretation of gas chromatographic data. Relative response factorswere developed for the ether versus olefin products. If desired, the data in thesupporting information can be utilized for in-dass problems pertaining to substitution and elimination reactions.KEYWORDS: Second-Year Undergraduate, Analytical Chemistry, Laboratory Instruction, Organic Chemistry, Hands-On Learning/Manipulatives, Inquiry-Based/Discovery Leaming, Elimination Reactions, Gas Chromatography, Nucleophilic Substitutionpart of any organic curriculum; however, the concepts areoften difficult for students to grasp. The variables that affect theproduct outcomes include nucleophiles, solvent, and substrate.An experiment studying simple variations reinforces students'comprehension of key principles that control product distribu-tion. The use of a gas chromatographic for product analysisillustrates the utilization of this technique as practiced in theorganic laboratory. The experiment utilizes primary, secondary,and tertiary alkyl halides with three different bases, sodiumJournal of Chemical EducationScheme 1. Overall ReactionsH₂CH₂C-H₂C BrTable 1. ReagentsH₂C CH₂R-Me, Et. -Butyl1-Bromopentane2-Bromopentane2-Bromo-2-methylBr+ MR-O-butaneNa Methoxide/ 1.5methanolNa Ethoxide/ethanolCH₂1.51.5Reagent Molarity/M Molar Mass/(g/mol) Volume/mL05 (10 drops)~0.5 (10 drops)~0.5 (10 drops)+MR-O -K1-Butoxide/-butyl alcoholNot RelevantMTBESaturated NHC Not Relevant+MR-OM-K for RH-ButylM- Na for R-Me. Et151.04151.04151.04Not Relevant 10Not Relevant 2 x 10The basic experiment can be completed in a 3-h lab with subsequentanalysis of products by gas chromatography taking only 15-20 minper sample. If desired, the experiment can be expanded to include amore interactive approach to gas chromatogram interpretation.E40Response150-dichlorides from a starting diol, which utilized a variety of analysistechniques. Nucleophilic substitution utilizing a phase-transfercatalysis provided a safer process for undergraduate lab instruction in Horowitz's paper. A solvolysis experiment utilizingtriphenyl bromide and several alcohols illustrated S,I reactionsand provided an isolatable product in high yields."Latimer studied only the elimination reactions of 1- and2-bromopentane and focused only on the yield of the olefins andratio of olefin isomers. The experiment can lead to erroneous datagiven the variation in the conversion that is inherent in student runrimante and the fame an anke the alahin endure Without the100-olefinether50-1-0 2-82-91 1-8MeO MO810MO16 10129 20BO 1800 180 180LABORATORY EXPERIMENTRetention Time/minFigure 1. GC of the products of the reaction between 2-bromopentaneand sodium ethoxide in ethanol.Jeremy3.5 40 45 50 55 60 65 70 75 80Retention Time/minFigure 2. GC of the products of the reaction between 1-bromopentaneand sodium ethoxide in ethanol. 1. Name and draw structures of the alkyl halides and nucleophiles/bases used below.

Question

2ABSTRACT: An experiment that compares product distribution obtainedby either substitution or elimination utilizing alkyl bromides and methoxide,ethoxide, or t-butoxide as the base (or nucleophile) is described. The changein product distribution caused by steric effects of the base and substrate arereadily apparent. Prior work on this experiment focused on only the olefinproducts using a method without internal standards. The experiment examinesall ether and olefin products as well as starting material and illustrates keyprinciples of S2-SNl and E2-E1 reactions. For this experiment, a gas chro-matographic method was developed that allows for complete product analysis.The new method examines the product distributions as a function of primary,secondary, and tertiary alkylbromide and base structure and can be expanded toinclude the interpretation of gas chromatographic data. Relative response factorswere developed for the ether versus olefin products. If desired, the data in thesupporting information can be utilized for in-dass problems pertaining to substitution and elimination reactions.KEYWORDS: Second-Year Undergraduate, Analytical Chemistry, Laboratory Instruction, Organic Chemistry, Hands-On Learning/Manipulatives, Inquiry-Based/Discovery Leaming, Elimination Reactions, Gas Chromatography, Nucleophilic Substitutionpart of any organic curriculum; however, the concepts areoften difficult for students to grasp. The variables that affect theproduct outcomes include nucleophiles, solvent, and substrate.An experiment studying simple variations reinforces students'comprehension of key principles that control product distribu-tion. The use of a gas chromatographic for product analysisillustrates the utilization of this technique as practiced in theorganic laboratory. The experiment utilizes primary, secondary,and tertiary alkyl halides with three different bases, sodiumJournal of Chemical EducationScheme 1. Overall ReactionsH₂CH₂C-H₂C BrTable 1. ReagentsH₂C CH₂R-Me, Et. -Butyl1-Bromopentane2-Bromopentane2-Bromo-2-methylBr+ MR-O->butaneNa Methoxide/ 1.5methanolNa Ethoxide/ethanolCH₂1.51.5Reagent Molarity/M Molar Mass/(g/mol) Volume/mL05 (10 drops)~0.5 (10 drops)~0.5 (10 drops)+MR-O -K1-Butoxide/-butyl alcoholNot RelevantMTBESaturated NHC Not Relevant+MR-OM-K for RH-ButylM- Na for R-Me. Et151.04151.04151.04Not Relevant 10Not Relevant 2 x 10The basic experiment can be completed in a 3-h lab with subsequentanalysis of products by gas chromatography taking only 15-20 minper sample. If desired, the experiment can be expanded to include amore interactive approach to gas chromatogram interpretation.E40Response150-dichlorides from a starting diol, which utilized a variety of analysistechniques. Nucleophilic substitution utilizing a phase-transfercatalysis provided a safer process for undergraduate lab instruction in Horowitz's paper. A solvolysis experiment utilizingtriphenyl bromide and several alcohols illustrated S,I reactionsand provided an isolatable product in high yields.&#34;Latimer studied only the elimination reactions of 1- and2-bromopentane and focused only on the yield of the olefins andratio of olefin isomers. The experiment can lead to erroneous datagiven the variation in the conversion that is inherent in student runrimante and the fame an anke the alahin endure Without the100-olefinether50-1-0 2-82-91 1-8MeO MO810MO16 10129 20BO 1800 180 180LABORATORY EXPERIMENTRetention Time/minFigure 1. GC of the products of the reaction between 2-bromopentaneand sodium ethoxide in ethanol.Jeremy3.5 40 45 50 55 60 65 70 75 80Retention Time/minFigure 2. GC of the products of the reaction between 1-bromopentaneand sodium ethoxide in ethanol. 1. Name and draw structures of the alkyl halides and nucleophiles/bases used below.

Accepted Answer

A nucleophile and a base are electron-rich compounds. The difference lies in the fact that where…

H₂C H₂C- H₂C Br CH₂ Br CH₂ R-Me, Et. -Butyl H₂C Br+ MR-O +MR-O +MR-O M-K for RHButyl. M-Na for R-Me. Et