Organic Chemistry Exam 2

How do you choose where to draw double bond after an elimination reaction?
Stability based on number of substituents on the alkene
Where does Nu- attack epoxide in acidic conditions?
More substituted carbon because of partial positive stability
Where does Nu- attack epoxide in basic conditions?
Less substituted because there is less steric hindrance.
Rank these LG from fastest to slowest: Cl, OMe, I, Br, OTf.
OTf > I > Br > Cl > Ome
When drawing cyclic compounds to undergo epoxide synthesis, you must do a backside attack, so you need to place the largest molecules…
In the equatorial positions and the two groups involved in substitution must be 180 degrees apart.
What must happen first in SN1 and E1?
LG must leave
Markovnikov addition
X adds to the C w/ more substituents
oxymercuration reduction:
Markovnikov selective
hydroboration oxidation:
anti-Markovnikov
What reagent do you use to form an epoxide?
mCPBA, Markovnikov
SN2 reacts best w/
primary alkyl halides
Polar protic solvent favors
E2
Heat favors
elimination reactions
Primary alkyl halides will undergo SN2 unless there is a bulky base in which case they will undergo
E2
Polar aprotic is good for
SN2 because giving off protons would hinder Nu- from pulling off LG
Stereochemistry inverted in
SN2
Can tertiary alcohols undergo SN2?
No
Which is a better nucleophile: PhS- or Pho-?
PhS-
Are DMSO and DMF and acetone protic or aprotic?
aprotic
How does resonance affect a nucleophile?
Makes it less nucleophilic because the charge is stabilized
How does cyclic propane affect nuclephilicity?
Makes it less nucleophilic because the transition state of SN2 is trigonal planar and wants 120 degrees geometry
Is E2 an anti or syn elimination?
anti elimination
E2 needs 180 degrees between the two things it’s eliminating (one is a H). True or false
True, this means they need to be up and down in the axial positions of a chair conformation on a cyclohexane.
Which is weaker C-H or C-D?
C-H because D is heavier than the single proton, meaning it will vibrate more slowly, and it has less energy… it is more stable (C-D)
What does MeOH as a reagent cause with an alkyl halide?
SN1 and E1
NaOH, NaCN, NaOCH3, NaN3, NaSPh, and KI are examples of
strong nucleophiles
H2O, ROH, H2S, and RSH are examples of
weak nucleophiles
NaH is a
strong base
Strong bases favor
E2
The more electronegative an atom, the ____ nucleophilic.
less
Resonance ______ nucleophilicity
decreases
Electron withdrawing groups will _______ nucleophilicity.
decrease
How does SN1 affect stereochemistry?
It produces a racemic mixture.
What lacks a full octet but is highly reactive because it has two bonding e- in one orbital?
Carbene
What produces a carbene?
HCCl3 in KOtBu
What is the difference between a carbene and a carbenoid?
Carbene is attached to two additional Cl, and carbenoid is only the cyclic propane.
What produces a carbenoid?
CH2I2 with Zn/Cu
For a secondary alcohol, what do you look at to determine whether it was a SN2 or SN1 rxn?
Stereochemistry of the products
What does PBr3 do to an alcohol?
Replace the leaving group (OH) with Br, which is a better LG
What does PCl5 do to an alcohol?
Replace the leaving group (OH) with Cl, which is a better LG
What does the anhydrous oxidative reagent do to a primary alcohol? (CrO3, pyridine)
Only one oxidation, forms a double bond to the oxygen
What does the oxidative reagent (H2CrO4, Na2CrO4 w/ H2SO4, Na2Cr2O7 w/ H2SO4) do to a primary alcohol?
Forms a double bond to the oxygen and adds a hydroxide to that C.
Epoxide formation is a _______ mechanism.
concerted
secondary alkyl halide and large Nu- favor
elimination
What matters more: the stability of the double bond or the stability of the C+?
Stability of the double bond
I- is the _____ likely to take electrons and leave in comparison with other halogens
most (meaning it’s the best leaving group)
IS carboxylic acid very acidic?
Yes because of resonance
Oxidation ______ the number of electron-withdrawing substituents.
increases
PCC stops at a ______ when oxidizing a primary alcohol.
aldehyde
What solvent should we use with a Grignard reagent?
THF
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