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Level 206

E1 & E2 Reactions


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acid catalyzed dehydration
removes H-OH from molecule, creating a double bond and eliminating an alcohol group
[H2SO4], H2O, heat
acid catalyzed dehydration of an alcohol
Zaitsev's Rule
The more substituted double bond will form in larger proportions (and trans(E))
[H3PO4], H2O, heat
eliminates water to form a double bond, with zaitsev's rule giving the major product
NaOEt (or KO+But)
used when there is a tertiary alcohol where all R groups are equal, O is a good leaving group, but not SN2. E2 reaction
oxidation
addition of oxygen or loss of electrons
primary alcohols
oxidize to form a carboxylic acid
secondary alcohols
oxidize to form a ketone
tertiary alcohols
NO REACTION
oxidizing agents
H2CrO4, Na2Cr2O7, CrO3, K2Cr2O7
PCC, CH2Cl2
oxidizes a 1* alcohol just to an aldehyde, leaves double bonds untouched, but will still take a 2* alcohol to a ketone
HIO4
cleaves the bond that goes in between a 1, 2 diol HO\_x_/OH leaves c=o like in oxidative cleavage. Needs to be a cis diol!!!
Unimolecular
A reactions involving a single species. A unimolecular reaction occurs when a molecule rearranges itself to produce one or more products.
E1 reaction
1-Heterolysis of c-x bond to form carbocation
E2 reaction
Leaving group comes off as proton is removed. 1 step
Characteristics of e1 reaction
1-rate of e1 increases as # of R groups on carbon w/leaving group increases
Difference between sn1 & e1
Sn1-nu attacks carbocation, forming substitution product
Less b/c e1 occur with competing sn1
E1 reactions are more or less useful than e2.
Syn periplanar
E2 reaction transition state of 4 atoms w/H and X on same side
Anti periplanar
E2 reaction transition state of 4 atoms w/H and X on opposite sides
Staggered
Anti periplanar has what confirmation?
Eclipsed
_______ conformations are at energy maxima
What requirement must chair conformation meet for e2 reaction to occur?
H and Cl must be axial (less stable conformation) which is called trans diaxial geometry
Axial. Duh..
In cis isomer of a chair conformation, what configuration must Cl be in?
With double bond connected to tertiary b/c hyperconjugation.
The major product from e2 reaction contains more stable double bond in chair conformation.
Sigma to nascent pi star hyperconjugation
Why is transition state stabilized in e2?
Stereo selectivity
E 2butene vs Z 2butene
Stereo selectivity, stable product
E 2-butene b/c steric repulsion. (Starting molecule's most stable configuration is methyl groups being anti to each other)