Chapter 9 Notes Flashcards
nucleophilic substitution
any reaction in which an electron rich nucleophile replaces a leaving group
leaving group
the group that is displaced in a substitution reaction or the Lewis base that is lost in an elimination reaction
acid base reaction
this is often not classified as one of the five types of organic reactions, but it is an incredibly common transformation that occurs within them and can eb classified with nucleophiles and electrophiles
addition reaction
two atoms or groups of atoms react with one double bond to form a compound with two new atoms bonded to the carbons of the original double bond
substitution reaction
one atom or group of atoms is substituted by another atom or group of atoms
elimination reaction
two atoms are removed from a molecule to form one new double bond
oxidation-reduction reaction
transfer of electrons between two species
radical reaction
any reaction involving radicals
SN2 Mechanism
-a bimolecular (two species involved) nucleophilic substitution reaction
SN1 mechanism
a unimolecular (one species in rate determining step) nucleophilic substitution reaction
-solvolysis: a nucleophilic substitution in which the solvent is also the nucleophile
step 1: break a bond
step 2: make a bond
step 3: remove a proton
kinetics of SN2
reactions are bimolecular and the rate of reaction is affected by concentration of both the electrophile and nucleophile
kinetics of Sn1
reaction is unimolecular the rate of reaction is only affected by the concentration of the electrophile
stereochemistry of SN2
SN2 leads to complete inversion of the chiral center due to “backside attack” this can be monitored with isotopic labeling
stereochemistry of SN1
SN1 goes through an achiral carbocation intermediate that can be attacked from either side, leading to partial or complete racemization of stereochemistry
SN2 structure
- governed by mainly steric factors
- steric hindrance: the ability of groups because of their size to hinder access to a reaction site with a molecule
- SN2 can occur with primary and secondary haloalkanes but not tertiary
- steric hindrance also occurs from beta branches slowing the rate of SN2 reactions
SN1 structure
- governed mainly be electronic factors
- resonance stabilizes carbocations, thus increases likelihood of SN1 over SN2
leaving group
more stable an anion is on a Lv the better the Lv
the solvent
- the solution the reaction is run in influences
- nonpolar solvents aree bad at screening charges
- polar solvents are good at screening changes
- aprotic solvents cannot serve as a hydrogen donor
effect of solvent on SN1 reactions
-polar protic solvents “solvate” the intermediate Staes increasing the reaction rate
effect of solvent on SN2 reaction
-polar protic solvents “solvate” the nucleophiles, decreasing its reactivity/reaction rate
B-elimination
all nucleophiles are also bases; competing reactions depend n nucleophilicity vs basicity
dehydrohalogenation
type of B elimination where -H and -X are removed from adjacent carbons to form an alkene
Zaitsev’s rule
predicts that the more substituted (more stable) C=C double bond product from a B elimination reaction is favored
E1 Mechanism
E1 reaction: unimolecular B-elimination reaction
step 1: break a bond
step 2: take a proton away
E2 mechanism
E2 reaction: bimolecular B-elimination
E1 Kinetics
- unimolecular
- rate of reaction is only affected by the concentration of the electrophile
E2 Kinetics
- bimolecular
- rate of reaction is affected by the concentration of both the electrophile and nucleophile
E1 Regioselectivity
the major product is the more stable alkene by going through the more stable carbocation intermediate
E2 regioselectivity
the major product is the more stable alkene by going through the lower energy transition sate
E2 stereoselectivity
-the Lowest energy transition Tate is when -Lv and -H are oriented anti and coplanar to each other
