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SN2 reactions
- Second-order rate reactions
- biomolecular
- happens in concetrated step
- attacks come from the back side by Nu
- Nu attack then loss of LG
- methly and primary react quickly wiith Nu attack
- secondary react more slowly
- tertiary dont react
- May require proton transfer to start reaction and at end
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SN1 reactions
- Step wise process
- Loss of LG, forms carbocation, and then Nu attack
- Unimolecular
- based on first order reaction
- tertiary reactions quickly
- primary and methyl barely react
- Some require proton transfer whenever Nu is not neutral
- may require proton transfer to start reaction
- OH is bad LG
- Rearrangement may occur
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How to Determine if Reaction will occur Via SN1 or SN2?
- the substrate-methyl ,primary favor Sn2 tertiary favor SN1
- the LG -must have good leaving good
- the Nu -SN2( strong Nu) SN1(weak Nu)
- The solvent -polar protic(SN1) or polar aprotic(SN2)
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polar protic solvents
- solvents that contain at least one hydrogen atoms connected directly to an electronegative atom.
- Used for SN1 reactions
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polar aprotic solvent
- contains no hydrogen atoms that are connected directlyto an electronegative atom.
- used for SN2 reactions
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Solvolysis
when the solvent functions as a Nu
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alkenes
are compounds with double bond carbons
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E2 reactions
- tertiary halides react better
- One concerted step
- regiochemistry is important
- the more substituted alkene is the Zaitsev product/ major product
- when both the substrate abd vase are sterically hindered the less substituted the Hoffan product is the major product
- trans disubstitued
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Anti-coplanar
- staggered
- on the sameplane
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syn-coplanar
- elclipsed
- on the same plane
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E1 reactions
- first order rate reactions
- tertiary halides react most readily while primary halides are nonreactive
- a carboncation rearrangement occurs if it will produce a more stable carboncation intermediate
- occurs same as SN1 stepwise
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E&Z (sterodescriptors)
- Used when alkenes possesses nonsimilar groups
- E describes priority groups on different sides
- Z describes priority groups on the same side
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Predicting if and reaction will proceed vis E1 or E2?
- E1-
- base strenght not important
- needs ionizing solvent
- first order rate
- rearrangement are common
- E2-
- Strong base required
- polarity of solvent not important
- second rate
- rearrangement not possible
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Addition reactions
- are characterized by the addition of two groups across a double bond
- favorable at low temps
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hydrhalogenation
- reactions are characterized by the addition of H and X across a pi bond
- X= Br, Cl
- regioselective
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Markovnikov addition
halogens are placed at the more substituted position
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anti-Markovnikov addition
- less substituted area
- Addidtion of HBr proceeds vis this process
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hydration
addition of (H and OH) across a double bond
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Acid - Catalyzed hydration
- addition of water in the presence of an acid
- which generally proceeds via a markovnikov
- carboncation intermediate which is attacked by water to produce an oxonium ion followed by deprotonation
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Oxymercuration-demercuration
- achieves hydration of an alkene without carbocation.
- The reaction proceeds via a bridged intermiate called mercurinium ion (AcOHg)
- when the mercury is removed it use demercuration
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catalyic hydrogenation
- involves the addition of molecular hydrogen (H2) across a double bond in the presence of a metal catalyst.
- reduces an alkene to a alkane
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heterogeneous catalyst
- do not dissolve in the reaction medium
- ex. Pt,pd,Ni
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homogeneous catalysts
- are soluble in the reaction medium
- most common are called Wilkinson' catalyst
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Halogenation
involves the addition of Br2 or Cl2 across an alkene
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anti addition
Places two halogens atoms on opposite sides of the pi bond
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Halohydrion Formation
- when bromaination occurs in a non- nucleophilic solvent
- the product of Br and Oh across an alkene is called bromohydrin
- Oh is placed in the more substituted position
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dihydroxylation
the addition of OH and OH across an alkene
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Poisoned catalyst
- will catalyze the conversion of an alkyne into a cis alkene.
- P-2
- Lindlar catalyst
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geminal dihalide
both halogens are connected to the same carbon atom
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vicinal
two halogens are connected to the adjacent carbon atom
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tautomers
constututional isomer that rapidly interconvert via the migration of a proton
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keto-enol tautomerization
the interconversion between an enol and a ketones
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