everything about unimolecular substitution and pathways of elimination
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each of the black spaces below before clicking
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| solvolysis | when a substrate undergoes substitution by a solvent molecule. when water is the solvent, its called HYDROLYSIS |
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| SN1 reaction (unimolecular reaction) | rate determining step is decided by the starting haloalkane and nothing else, rate does not depend on concentration of nucleophile | but nucleophile strength dtermines the major product, stronger nucleophile = major product |
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| Steps of an sn1 reaction | 1.RATE DETERMINING STEP, halide disassociates w haloalkane, making carbocation and halogen 2. the carbocation is SUPER electrophilic so it is jumped by solvent and creates a new ion 3. deprotenation occurs, one H+ is lost | all steps of an sn1 reaction are reversible depending on the conditions |
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| stereochemical consequences of sn1 reactions | carbocation assumes trigonal planar geometry, generally produces a racemic mixture |
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| elimination 1 | multiple steps, start w a branched haloalkane, remove the HX and create a double bond. the RDS in E1 is the same as SN1 reactions, dissociation to a carbocation |
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| elimination 2 | single step 1. deprotenation of the base 2. departure of leaving group 3. rehybridization of carbon center from sp3 to sp2 |
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| competition between substitution and elimination | weak basic nucleophile = substitution, primary and secondary halides will be sn2, tertiary substrates will be sn1 strong basic nucleophiles = elimination | 3 things to look at when predicting e vs s 1. base strength of nucleophile, weak base = substitution, strong base = elimination. 2.sterics of nucleophile:unhindered = substitution, hindered = elimination | 3.sterics around carbon in R-X: unhindered = substitution, hindered = elimination
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| difference between stereochemistry of sn1 and sn2 reactions | sn1: racemic mix of products, equal probability of attack from top or bottom | sn2, attack from back, inverts the molecule, switches r to s and vice versa |
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| sn1 reactions need | great leaving groups, weak nucleophiles, polar protic solvents, the solvent is often the nucleophile | teritiary substrate better for sn1 reactiosn |
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| absolutes | never ever ever do a sn1 or e1 reaction w a methyl or primary, carbocation is too unstable | never do sn2 or e2 reaction w tertiary bc of steric hindrance |
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| most good leaving groups ae larger than carbon, anything that forms a bond w carbon is a bad leaving group |
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| properties of sn1 reactions | rate of reaction increases as solvent polarity increases, sn1 works faster w protic solvents, sn2 react faster w aprotic solvents | better leaving group = faster sn1 reaction. strength of nucleophile doesn't effect reaction rate but does affect product distribution, SN1 reaction works best on tertiary and least well on primary because tertiary carbo cations are more stable | as steric hindrance increases, strongly basic nucleophiles will support elimination vs substitution, sterically hindered bases generally support elimination
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