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SN2 reactions
everything on SN2 reactions
| Question | Answer | Answer Cont. | answer. cont |
|---|---|---|---|
| SN2 | also called biomolecular nucleophilic reaction, one step process, nucelophile attacks haloalkane as leaving group is forced out, both things occur at same time so it is called a CONCERTED reaction | SN2 reactions are STEREOSPECIFIC, produce a specific stereoisomer, SN2 is always backside attack and switches the (R) (S) config of a molecule. if it was R before, it's now S and vice versa | |
| Leaving group: ability to accomodate negative charge | strength of a leaving group increases going down the column of halogens, fluorine so weak of a leaving group that it doesnt even have an sn2 reaction | leaving group ability inversely related to base strength. weak bases accomodate negative charge better, therefore are better leaving groups, weak bases are conjugates of strong acids, therefore good leaving groups are conjugate bases of strong acids | |
| substrates with more than one stereocenter? | inversion only happens at one stereocenter, unless its with a mesocompound | ||
| nucleophile trends | the more negative charge a nucleophile has, the stronger it is. also, between a bas and its conjugate acid, the more basic substance is more nucleophilic. basicity decreases left to right on a PT, so nucleophilicty decreases as well | nucleophilicity increases moving down a periodic table | sterically hindered nucleophiles make poor reagents |
| what kinds of molecules have sn2 reactions | methyl and primary, secondary and tertiary don't have sn2 reactions bc of steric hindrance | ||
| what kind of nucleophile do you need | nucleophile: one of the molecules involved in the transition state of an sn2 reaction | you need a nucleophile with a negative charge, ie. strong | |
| what kind of substrate do you need> | substrates are one of the other molecules involved in an sn2 reaction | methyl is the best, after that 1 >2 >3 | |
| leaving group | stable, carrying a negative charge, should not have a halogen | ||
| nucleophilic substitution | when a reagent attacks a haloalkane and replaces the halide nucleophile can approach from front, FRONTSIDE DISPLACEMENT, approaching in the same direction as halide | or from back, BACKSIDE DISPLACEMENT,approaching from opposite side as halide when approaching from backside, the negative charge of the nucleophile will push the rest of the molecule to switch | in substrates with more than one stereocenter, inversion of R andS only occurs at carbons undergoing reaction w nucleophil |
Created by:
hsinha93
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