Lecture Quiz 5 - Lectures 21-27 Flashcards
When can carbocation rearrangement happen?
whenever we have a carbocation intermediate (Sn1/E1)
List the order from best carbocation to worst
methyl, 1, 2, 3*
3* - better C+, lower E
2*
1*
methyl
When you do SN1/E1 mech with a carbocation, the result is 2 SN1 products and 4 E1 products. How do you determine which product is the major/minor one?
Major = rearranged
When does a hydride shift typically happen?
2C C+ next to a 3 –> will rearrange
How many carbons are moved during a hydride shift?
Typically don’t more more than 1 carbon.
When there is no available H, is it possible to move an alkyl group?
Yes - aka alkyl shift
Is it possible to move an alkyl group at the same time as a leaving group?
Yes = aka concerted rearrangement
Gives 3 examples of sp3 oxygens
H2O water, ROH alcohol, and ROR’ ether
H2O has a (low/high) boiling point.
high
Alcohol ROH (can/can’t) H-bond, has a ? DP, is (nonpolar/polar), and (is/isn’t) H2O soluble. It is miscible up to (0/1/2/3) carbons
ROH:
-can H-bond
-polar
-miscible up to 3C
sp3 Oxygens (can/can’t) get protonated. (H2O/ROH/ether) tends to be nucleophilic.
sp3 oxygens can get protonated
H2O + ROH tend to be nucleophilic
If there are 2 alcohol groups on a molecule, how would you name it?
nonane-di-ol
hexane-tri-ol
T/F Alcohols are able to act as both acids and bases.
True
For alcohols, steric hindrance affects>
solvation of ion
For alcohols, induction….
removes/adds electrons to ion
What is the pKa range for alcohols that act as acids?
What does ROH turn into?
pka 15~18
ROH–> RO-
deprotonated, H leaves, O is (-)
For alcohols acting as an acid, larger alkyl groups are typically (better/worser) acids
larger alkyl group = worser acid
List the following alkyl groups from best acid to worst if bonded to an alcohol.
methyl, 3, 2, 1*
methyl-O- oxygen has more space for solvation, easier to make ion or keep the (-) charge
1-O-
2-O-
3*-O- minimal solvation. alkyl groups are sterically hindered, charge is unsupported, harder to form weaker conjugate acid, better conjugate base
Alcohols range from pka 15-18. Where would 1* and methyl typically fall on this spectrum? What about 2* and 3*?
pka15 = 1* and methyl // better acid
pka18 = 2* and 3* // worser acid
For alcohols acting as a base, what is the pka range?
pka -2~-4
Would a tertiary alcohol be a better acid than a primary alcohol? What about base?
primary alcohol would be a better acid AND base. tertiary alcohols have minimal solvation and there’s steric hindrance so it’s harder for them to form ions.
pka is affected by ?
solvation
1*ROH/ROH2+ has a
(low/mod/high) pka, and (poor/mod/good) solvation
mod pka (15 + -2)
good solvation
3*ROH/ROH2+ has a
(low/mod/high) pka, and (poor/mod/good) solvation
extreme pka, poor solvation b/c of hindrance
(18 + -4)
induction has a (subtle/extreme/no) effect on pka
subtle effect
More EN neighbors, larger # of EN atoms, and closer EN atoms would have more effect
T/F Alcohols are generally not very water soluble and have moderate to low boiling points due to low mass.
False
T/F The variance in pka between primary and tertiary alcohols is due to solvation of the resulting alkoxide or alkyloxonium ions.
True
T/F Alcohols can form hydrogen bonds with more of themselves
True
T/F Industrial reactions tend to make large volumes of complex molecules.
False because they make SIMPLE molecules
T/F Laboratory synthesis works generally the same for a functional group regardless of the alkane backbone of the molecule.
True
T Industrial reactions tend to use gaseous reagents and recycleable metal surface catalysts.
True - they tend to use gas phase and solid phase catalysts
T/F Laboratory synthesis is able to work with molecules with multiple functional groups and/or stereochemistry.
True
Between industrial and laboratory scale, which one avoids purification?
Industrial = avoid purification
Lab = puridication, distillation, chromatography, crystallyization
What substance phase do laboratories usually deal with?
solution phase
To form a primary alcohol from an RX, what nucleophiles would be used? This is via?
NaOH, H2O
SN2 - minimal E2 contamination, only 1 regioisomer
To form a tertiary alcohol from a R-X, what nucleophile would be used? This is via?
H2O
Sn1/E1, lose steroeochem at reacting C - going to have E1 product, and can possibly do C+ rearrangement (possible though unlikely)
To form a secondary alcohol from a R-X, what nucleophiles would be used? Via?
1) CH3COONa
2) NaOH, H2O
Redox is the (transfer/exchange) of electrons
exchange of e-
Oxidation is the (loss/gain) of e-
(loss/gain) of EN atoms
or
(loss/gain) of H bonds
Ox = loss of e-, gain of EN bonds, loss of H bonds
Reduction is the (loss/gain) of e-
(loss/gain) of EN atoms
or
(loss/gain) of H bonds
Red = gain of e-, loss of EN atoms or gain of H bonds
What is the most reduced redox molecule? (Easy/hard) to be selective, leads to?
CH4 - alkane
hard to be selective
What is the most oxidized redox molecule?
C=O=C
List order from most reduced to most oxidized
alcohol, carboxylic acid, carbonyl (aldehyde/ketone), alkane, and carbon dioxide
alkane
alcohol
carbonyl
carboxylic acid
carbon dioxide
oxidizing agent causes something else to be (reduced/oxidized) and itself gets (reduced/oxidized).
oxidizing reagent causes something to be oxidized and itself gets reduced
reducing agent causes something else to be (reduced/oxidized) and itself gets (reduced/oxidized).
reducing agent causes something else to be oxidized and itself gets reduced
we can create alcohols from carbonyls via?
hydride reagents
(ex: LiAlH4 or NaBH4)
LiAlH4 is (less/more) aggressive and a (weaker/stronger) reducing agent than NaBH4
LiAlH4 = more aggressive, stronger red agent
NaBH4 = more moderate red agent
To convert a 1*ROH to an aldehyde, you need to (oxidize/reduce)/
oxidize 1*ROH to aldehyde
To convert 2*ROH to ketone, you need to (oxidize/reduce)
oxidize 2*ROH to ketone
When you oxidize a tertiary alcohol, is there a reaction?
NO REACTION
can’t remove any C-H bonds to form another CO, can’t remove H2
To reduce aldehyde to a primary alcohol, you can use 1) LiAlH4 and 2) H3O+. Which molecule donates the H-? What about the H+?
LiAlH4 donates the H-
H3O+ donates the H+
LiAlH4 is a _______ ______ donor
covalent hydride donor
Describe the first and second step of reducing an aldehyde to a 1*ROH
1st step = hydride adds, irreversible
2nd step = protonate
T/F NaBH4 is mellower so it can exist with ROH, not H3O+. and it gets a transition state.
True
How many steps is LiAlH4? What about NaBH4?
LiAlH4 = 2 step process
NaBH4 = 1 step process
The transition state of NaBH4 is similar to the reverse of (Sn1/SN2/E1/E2) and has a _______ bond formation
reverse of E2
concerted bond formation
When oxidize a 2*ROH to a ketone, we stop at ketone because we run out of
C-H
To convert a primary alcohol to carboxylic acid, we can use
Jones Reagent to oxidize 1*ROH
True/False When we convert 1*ROH to carboxylic acid, we get an aldehyde transition state.
True
T/F Oxidation of a primary alcohol gives a ketone.
False
will get an aldehyde instead of ketone
2*ROH gets ketone
T/F Many organic reactions involve oxidizing an alkane to an alcohol directly
False
True/False Primary, secondary, and tertiary alcohols can all be formed by reduction of C=O with LiAlH4.
False - Can use NaBH4 to reduce C=O to get tertiary
T/F Reducing agents are difficult to handle since many of them react violently with the oxygen and water in the air.
True
What reagent would we use to oxidize a 1*ROH to an aldehyde?
PCC, CH2Cl
PCC pyridinium chlorochromate in CH2Cl solvent
Why would we use PCC as opposed to Jones Reagent?
PCC has no H2O present so if our goal is to get aldehyde from 1ROH or a ketone from a 2ROH, we need to use PCC.
We would only use Jones reagent when carboxylic acid is our goal. H2O is present in it so we go from OH to COOH
T/F PCC can oxidize 1ROH to aldehyde and 2ROH to keton
True
Is PCC a better reagent than Jones Reagent?
No, it just doesn’t have H2O present. Plus, it’s gentler and easier to work with
What are the 2 extreme agents?
Oxidizing agent = H2CrO4(aq) chromic acid
Reducing agent = LiAlH4
We can form carbanions via ??? reagents
organometallic reagents
T/F PCC can oxidize primary, secondary, and tertiary alcohols to C=O.
False
sp3 carbanion is a (weak/strong) base so we need to add a (acid/base)
C- is strong base
must add base
What is RMgBr?
A Grignard reagent (RMgX)
aka organomagnesium
What organometallic reagents can we use to get a carbanion?
RMgBr and RLi
and we can also se R-Cl, R=Br, or R-I
Why doe need to be very careful about Li?
It catches on fire
Organometallic reagents are formed by reacting a ??? with Li or Mg
haloalkane R-X
RMgX or RLiX
Reacting a ketone with a Grignard reagent will give a (primar/secondary/tertiary) alcohol
ketone
+ 1) RMgX, 2) H3O+
=3*alcohol
aldehyde
+ 1) RLiX, 2) H3O+
=2*alcohol
We prefer (linear/convergent) synthesis and which has (fewer/more) steps in a sequence
convergent synthesis preferred due to fewer steps and higher yield
T/F Analysis of the target compound when a starting material is not given is called retrosynthetic analysis
True
Williamson ether synthesis makes (linear/cyclic/both) ethers.
both linear and cyclic
If we’re making a linear molecule it will (never/sometimes/always) be symmetrical and (never/sometimes/always) use unhindered primary alcohols.
sometimes be symmetrical
always use unhindered 1*ROH
T/F Alkoxide are good Nu-
True – do SN2 with 1*RX
If we have a hindered 1, 2, or 3* ROH, we use what mech?
E2
If we want 100% completion or a higher yield, we must use a (weak/mod/strong) base to get an alkoxide ion.
STRONG BASE
When ROH act as weak bases, they get
protonated by strong acids
Nucleophilic acids have a conjugate (acid/base) as a Nu-
conjugate base is Nu-
T/F HBr and Hi are better nucleophilic acids than HCl
True
For non-nucleophilic acids, its conjugate base is?
a Nu-
When we use a nucleophilic acid (ex: HCl, HBr, HI) with an ROH, what mech will we do?
1ROH, 2ROH, 3*OH
Nucleophilic acid
1ROH = SN2
2/3*ROH = SN1
Why is there no E2 product when we react a 2/3ROh with a nucleophilic acid?
There will be an electrophilic addition so e get a reverse alkene formation. Basically, the alkene is a good Nu- and will pick up the H again, which reverses the rxn. So we can do E 1 but the rxn doesn’t last long
When we use a NON-nucleophilic acid (ex: H2SO4,H3PO4,PTsOH,TFA) with an ROH, what mech will we do?
1ROH, 2ROH, 3*OH
NON-nucleophilic acid
1ROH = E2, especially at high Temp, S favored b/c disorder increases (1 starting particle to 2 ending particles)
2/3*ROH = E1, perfers more stable alkene
When we react a NON-nucleophilic acid with an ROH via E1 mechanism, what rxn happens
dehydration rxn, loss of H2O to form C=C
What is the problem with carbocations?
Irritating, lose stereochemistry, can get side rxns (SN1/E1), , can rearrange
How do we avoid carbocations?
change SN1 to Sn2
1*ROH react with ??? via ??? mechanisms to form haloalkanes
HBr or HI via SN2
form haloalkane with nucleophilic acid + 1*ROH via Sn2
3*ROH react with ??? via ??? mechanisms to form alkenes.
H2SO4 via E1
Form an alkene by E1 mech with nonnucl acid+ 3*Roh
2*ROH react with ??? via ??? mechanisms to form haloalkanes.
This reaction (does not/does) also give alkenes as a product because ??
HBr or HI via SN1
does not give alkene product b/c this mechanism can for alkenes but they react with the acid reagent
T/F Carbocation rearrangements will always start with the formation of a carbocation
False
1*ROH react with ??? via ??? mech to form alkenes
H2SO4 via E2 to form alkene
One advantage of SOCl2 is it (does not/does) undergo carbocation rearrangements
does not undergo carbocation rearr
When we want to form a haloalkene from a 2/3ROH, what can we do to avoid the carbocation rearrangement?
IF Sn1 = carbocation rearrangement :(
IF Sn2 = avoids C+ rearr
Must change from Sn1 to SN2 and use SoCl2, Pcl5, PBr3, or PI3 which convert the ROH to a good leaving group.
T/F PCl5, SOCl2, and HCl are all interchangeable and will give the same products
False
Ethers generally are water (insoluble/soluble). Ethers generally have (low/mod/high) boiling points for their size.
Ethers = H2O insoluble and low BP
A cyclic ether which forms a 4 member ring will have the IUPAC name
oxacyclobutane
Rank for IUPAC priority:
ROH, R-X, ether, alkane
ROH – highest priority
alkane, R-X, and ether
T/F Formation of ethers via acid catalysis prefers very high temperatures (e.g. 180 degrees C)
False
T/F Formation of ethers with acid catalysis tends to form symmetrical ethers.
True
T/F Williamson ether synthesis is commonly used to form secondary and tertiary linear ethers.
False
T/F The major factor between formation of ethers vs alkenes from alcohols with acid catalyst is enthalpy.
False
Enthalpy prefers (minimal/maximal) ring strain so a (smaller/larger) ring is preferred.
Enthalpy = minimal ring strain preferred
Larger/med ring preferred
Entropy prefers if the ends are (closer/further apart) so a (smaller/larger) ring is preferred.
Entropy = wants closer ends
Smaller rings preferred
Entropy is a bigger factor at (lower/higher) temperatures
Higher
When temp is 180*C, there is (less/more) energy and entropy is (less/more) of a factor. We would use (substitution/elimination) mech.
180*C = more E, Entropy more significant
1ROH = E2
2ROH/3*ROH = E1
When temp is 135*C, there is (less/more) energy and entropy is (less/more) of a factor. We would use (substitution/elimination) mech.
135*C = less E, Entropy less significant
1ROH = Sn2
2ROH/3*ROH = Sn1
Linear ethers generally do not react with ??? and do react with ???. This means they make (poor/good) solvents for most reactions.
NR w/ base, Nu-, ox agent, red agent (harder to protonate)
R w/ strong acids, O2
good solvents
Which ether breaks faster? 1ether or 2 ether. Which one prefers to do SN2 mechanisms in the presence of HX.
1*ether breaks faster
Sn2
Which ether breaks faster? 3ether or 2 ether. Which one prefers to do SN2 mechanisms in the presence of HX.
3*ether breaks faster
Sn1
For ether rxns, we get mixes when we have
1/1, 2/2, or 3/3 because it means the nucleophile can come in on both sides
When the sides of the ethers aren’t equally substituted:
3* –> ___ mech @ which side
Sn1 at 3* side
For an ether rxn, when there is no 3, is CH3 faster or slower than 1?
Ch3 faster - via Sn2
When we have only 2* for ether rxns, we do ??? mech and we get a mix of products.
SN1 rxn
Rings generally react like linear versions of the same function group. What is the exception?
lots of ring strain
