Quiz 6 Flashcards
Tertiary sulfonates will undergo — in strongly basic reagants and — — in polar protic solvents
E2 and unimolecular reactions
when forming a sulfonate is there inversion of the carbon attatched to the oxygen?
no, there is no inversion of the carbon because the sulfonate group is “strapped” to the oxygen not the carbon
What is the beginning step in any conversion of OH into a better leaving group?
a proton transfer so the OH can be converted into H2O which is a good leaving group
When converting alcohols into better leaving groups what kind of reagant will produce a substitution reaction?
An HX regant
X= a halogen
What kind of alcohols will undergo an E1 reaction
tertiary alchols treated with Heat and H2SO4
what kind of alcohols will undergo an SN1 reaction?
primary or secondary alcohols
dont forget about carbocation rearrangements
What are the three steps to retrosynthesis?
- identify a bond that can be broken or formed
- select suitable reagants and substrated to break or make that identifed bond
- draw the forward reaction
dont forget to count your carbons
Addition Reactions
Two things are added to either side of a pi bond and pi bond is protonted to form a singma bond
can be seen as a reverse elimination reaction (X added, pi bond broken)
Addition reactions are made possible because?
pi bonds can act as weak bases or weak nucleophiles
True or false?
addition and elimination reactions are favored at low temperatures?
False, addition is favored at low temperatures and elimination is favored at high temperatures
bc/ G needs to be negative for a spontaneous process
Hydrohalogenation
addition of a halide and proton to an alkene
does hydrohalogenation follow markovnikovs rule?
yes
what are the mechanistic steps of hydrohalogenation?
- pi bond is protonated to form a carbocation intermediate
- nucleophilic attack by halide
What is the rate determining step for hydrohalogenation?
the formation of the carbocation intermediate
True or false?
Hydrohalogentation is unlike SN1 if a re-arrangment is possible there will be no mixture formed
false, if a rearrangment is possible for a hydrohalogenation reaction then the products will be a mixture of with and without the rearrangement
Markovnikovs rule
the proton will be placed on the less substitued end of the alkene (place with more H already present)
X will go on more substituted end (or whatever other group it is)
Explain the stereochem of hydrohalogenation
if the addition of a group produces a chiral center a racemic mixture of both R and S is formed
Acid catalyzed hydration
one of three possible hydration reactions
the addition of OH and H across an alkene in the presence of an acid
the rate of a acid catalyzed hydration reaction depends on —–
the substitution of the alkene, the more substitued the better
What are the mechanistic steps of Acid catalyzed hydration?
- protonation of the pi bond by the acid
- addition of H2O
- Proton transfer to get rid of any charges
— acid will favor products in an acid catalyzed hydration
dilute acid
— acid will favor reactants in acid catalyzed hydration
concentrated acid
Stereochem of Acid cataylzed Hydration
similar to hydrohalogenation, if a chiral center is formed by the addition of a group then a racemic mixture will be formed
Hydroboration Oxidation
third of three hydration reactions
- anti markovnikov addition of water using BH3 to stabilize any charges that would form
OH is added to less substituted side and H on more substitued side
What are the two mechanistic steps to hydroboration oxidation?
- hydroboration attatches to less substitued side of alkene, triggering simultaneous hydride shift
- Boron group is replaced with oxygen group
explain the eletronic and steric reasons why anti markovinikov addition is seen in hydroboration oxidation
- electronic reasons: positive charges form on more substitued positions so as a partial charge is forming BH3 must attatch to the less substitued positon
- Steric reasons: BH3 is larger than just H so it attaches to the less substitued positon to reduce steric interactions
Explain the stereochem of hydroboration oxidation
- syn addition: OH and H groups are added on same side as each other
- anti markovnikov
If one chiral center is formed for hydroboration oxidation?
an enantiomer is observed
If two chiral centers are formed in hydroboration oxidation?
syn addition is a requriement and they are added on the same side (only the both wedged and both dashed stereoisomers are seen)
Oxymercuration Demercuration
two of three hydration reactions
markovnikov addition of water across an alkene using a mercurium atom to stabilize charges
What are the mechanistic steps of oxymercuration demercuration
- mercuric acetate dissociates in mercurium cation and attatches to the less substitued side of alkene to form cylic intermediate
- nucleophilic attack on more substitued side of alkene
- dermercuration: mercurium cation is removed and replaced with H
sterochem of oxymercuration demercuration
- anti addition: H and O group added to opposite sides of each other
- if a chiral center is formed racemic mixtures are observed
racemic mixtures are also seen in acid catalysed and hydrohalogenation
catalytic hydrogenation
addition of two H with the use of a metal catalyst
What is the stereochem of catalytic hydrogenation
syn addition is observed when two chiral centers are formed
look out for meso compounds
— alkenes will produce meso compounds
symmetrical
what does the metal cataylst do to aid in the addition of hydrogens across the alkene?
it coordinates the molecule and adsorbds the hydrogens
Halogenation
addition of two halogens across an alkene
only addition of Cl or Br
stereochem of halogenation
anti addition bc of cylic intermediate
how does the cylic intermediate create anti addition in halogenation
it triangle ring occupies either the top or the bottom of the molecule so the nucleophile in the second step must attack opposite to the triangle ring
mechanistic steps of halogenation
- pi bond attacks Cl2 or Br2 (nucleophilic attack + llg)
- solo halogen created in step one attacks molecule from opposite side
Halohydrination
X + OR group added across an alkene
mechanistic steps of halodhydrin
- pi bond attacks Cl2 or Br2 + llg
- OR group attakcs opposite side of molecule
- proton transfer to create neutral product
stereochem of halohydrin
anti bc of cylic intermediate
regiochem of halohydrin
OR group attacks more substitued carbon where an electrophilic carbocation would have been likely to form
Dihydroxylation
addition of two OH groups across an alkene
syn dihydroxylation
OH groups are added to the same side
concerted rxn
anti dihydroxylation
OH groups are added to the opposite sides bc of cylic intermediate
What reagant promotes anti dihydroxylation?
peroxy acids, MCPBA
what reagant promotes syn dihydroxylation?
cold potassium permanganate or a osmate esther group
ozonolysis
C=C bond is split by O3 (ozone) to form C=O bonds
what is the only reaction we know to make ketones and aldehydes?
ozonolysis
