ochem ch 6 alkyl halides part 3
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for a substitution reaction, nucleophilic strength ____ as you go down thje periodic table
increases, because of size and polarizability increase
for an Sn2 reaction, bulky molecules are _____ nucleophiles
polar protic solvents
- reduce the strength of the nucleophile (which
- makes it more favorable for Sn1 and less favorable for Sn2). The hydrogen bonds
- between the solvent and the nucleophile must be broken before the nucleophile
- can attack the carbon
polar aprotic solvents
- do not form hydrogen bonds with the nucleophile.
- Favors Sn2 reactions and disfavors sn1 reactions
Does Sn2 (walden inversion) always result in a change in the configuration of the chiral carbon? (ex. if the original molecule was in (S) configuration but changed to (R)
after the halogenation)
- inversion doesn't always result in a change i
- nthe configuration of the chiral carbon, but 99% of the time it does.
Does racemization occur in an sn1 reaction?
what is the rate law for an Sn1 reaction?
rate = k[R-X]
- so, concentration of nucleophile doesn't play a role in the rate, only the
- concentration of the alkyl halide does.
what is the order of reactivity for an Sn1 reaction?
does sn1 reaction prefer weak or strong nucleophile?
How does the Sn1 mechanism work?
unimolecular (meaning only one molecule is involved in the transition stat eof the rate limiting step) nucleophilic substitution. it is a multi-step reaction (2-3 steps) that involves a carbocation intermediate.
- Step 1 formation of carbocation (slow step)
- Step 2 nucleophilic attack
- Step 3 Loss of Hydrogen ion (H+) if needed
what is a unimolecular reaction?
there is only one molecule involved in the transition state of the rate-limiting step
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