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Level 200

SN1 & SN2 Reactions


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SN2
?:CN
Sn1
Both mechanisms are sensitive to the nature of the leaving group but the _______ mechanism is more sensitive
increases, increases
Leaving ability _______ from left to right and _______ down a column of periodic table
Decreases
nucleophilicity _______ across a row on the periodic table
increases
pull down, spring force _______, producing a net force upward
stabilize
Electron donating groups (like R groups) _______ a positive charge
Hammond Postulate
in an endothermic reaction, the more stable product is formed faster, in an exothermic reaction this is not necessarily true
Both Sides
planar, sp2 hybridized atoms react with which side(s) of the plane
vinyl halide
A derivative of an alkene in which one (or more) of the hydrogen atoms on the double-bonded carbon atoms has been replaced by a halogen.
aryl halide
An aromatic compound (benzene derivative) in which a halogen is bonded to one of the carbon atoms of the aromatic ring.
allylic halide
Halides that have X bonded to the Carbon atom adjacent to a C=C bond.
benzylic halide
Halides that have X bonded to the Carbon atom adjacent to a benzene ring.
H2O, alcohols, acetic acid
examples of polar protic solvents
examples of polar aprotic solvents
acetone, DMSO, DMF, HMPA, THF, acetonitrile
negatively charged nucleophiles
-OH, -OR, CH3COO-, N3-, -CN, Cl -, HS-, RS-
neutral nucleophiles
H2O, ROH, NH3, NH3, RNH2, H2S, RSH
SN1 order of stability
Favors 2 and 3 degree alkyl halids whereas SN2 favors 1 degree or methyl and aprotic.
Substrate
SN1 rate limiting step
1 degree, 3 degree.
If LG is xxx degree, it's SN2, if LG is xxx degree, it's SN1.
Sn2 Reaction
Bimolecular (Second order) Kinetics - rate dependent on electrophile + nucleophile
Sn1 best solvent
polar, because the solvation stabilizes the carbocation intermediate.
Aprotic polar
Sn2 best solvent
Sn1 best substrate
tertiary, allylic, and benzylic halides (because the most stable carobocations are formed)
Sn2 best substrate
methyl or primary substrates, a few secondary substrates (because of steric hindrance with secondary or tertiary substrates)
Sn2 transition state
involves partial bond formation between the nucleophile and the substrate
Carbocation intermediate
In the stepwise mechanism the leaving group leaves, generating a _______
Sn2 results
inversion of chiral center (change in configuration - 100% R or S, if started with S or R respectively)
Sn1 results
racemic (50-50 mixture) of two enantiomers
No Reaction
1° Carbon (Poor Nucleophile)
SN2/E2
?OH
E2
1° Carbon (Strong Base, Hindered)
SN1/E1
2° Carbon (Poor Nucleophile)
E2 (nonzaitsev)
secondary alkylhalide, strong nucleophile, strong, bulky base
no reaction (or very slow SN2)
tertiary alkylhalide, strong nucleophile, weak base