Transcription of Substitution and Elimination Reactions Comparative Chart
1 Substitution and Elimination Reactions Comparative Chart Reaction Structure of RX Reactivity of Nu: Conc. Of Nu: Solvent StereochemistrySN21>2>3 Only this reaction andE2 will most likelyreact with a primaryRXStrong nucleophilefavors reactionHigh concentration ofnucleophile favorsreactionAprotic polar solvent favorsa SN2 reaction if either ofthe reactants is chargedex: DMF DMSO Acetoneinversion of configurationE23>2>1 Major product is moresubstituted alkeneunless*the base is large*the alkyl halide is analkyl flouride*the alkyl halidecontains one or moredouble bondsStrong Base favorsreactionHigh concentration ofbase favors reactionAprotic polar solvent favorsa E2 reaction if either ofthe reactants is chargedex.
2 DMF DMSO AcetoneIf the reactant has 2 H bondedto the carbon from which a H isto be removed, both E and conformers that has thebulkiest groups on oppositesides will be the major and syn Elimination if itis cyclohexane, it has to beaxial (anti)SN13>2>1 Forms a carbocationNot effected by strengthof nucleophile but aweak nucleophile favorsit by not favoring aSN2 reactionNot effected but lowconcentration disfavors aSN2 reactionProtic polar favors a SN1reaction if the reactant is : H2O, CH3OH, (with someinversion because of ionpairing)E13>2>1 Forms a carbocationWeak base favors E1reaction by disfavoringE2 reactionNot effected but a lowconcentration of basefavors E1 by disfavoring aE2 reactionProtic polar favors a E1reaction if the reactant is : H2O, CH3OH, groups on oppositesidesSN Versus E Methyl halide Primary halideSecondary halideTertiary halideSN2 reaction mostfavoredNo Eliminationreactions!
3 SN2 when the mainreaction is with goodnucleophiles/weakbases such as I- andCH3CO2-E2 if you use strongbulky bases such as t-butoxide steric effectsSN2 if the main reaction is with weak base or Nu: where Pka ofconjugate acid is 11 or less ex: I- or Ch3CO2-E2 if the main reaction is with a strong base or Nu: where Pka ofconjugate acid is 11 or greater- , high temperatures and bulkybases increas eliminationSN1/E1 are common in Reactions with weak Nu: in polar protic solventslike water, high temps favor E1 E2 if Main reaction is with strong baseslike OH- and RO-SN1/E1 if main reaction is with a poorNu: High temperatures favor E1 out of thetwo.
