Chapter 11 Ethers and Alcohols Flashcards
(87 cards)
1
Q
What is the boiling point of an ether comparable to?
A
Hydrocarbons with the same number of carbons
2
Q
What has a higher boiling point ethers or alcohols and why?
A
Alcohols because they have hydrogen bonds
3
Q
What are the relative solubilities of hydrocarbons, ethers, and alcohols in water?
A
Ethers and alcohols have high solubility relative to hydrocarbons because they can hydrogen bond with water
4
Q
What happens to the relative solubility of alcohols in water and why?
A
As alcohols get longer hydrocarbon chains they become more alkane like and therefore their solubility decreases
5
Q
What is a way to make alcohols from alkenes?
List the steps and reagents
A
Acid-catalyzed Hydration of Alkenes
- (Acid/Water) The double bond takes the Hydrogen from the acid and becomes a carbocation with one H and one positive carbon
- (Water in eq) Water attacks the carbocation and bonds
- (Water in eq) Another water molecule deprotonates the H2O+
6
Q
What are some alcohols that are infinitely soluble in water?
A
Methanol, Ethanol etc.
7
Q
What are some features of acid-catalyzed hydration of alkenes into alcohols?
A
- Markovnikov Regioselective ie. Adds to most substituted carbon
- Possible carbocation rearrangement
- Syn addition (To same side)
8
Q
What is a way to make alcohols from alkenes?
List the steps and reagents
A
Oxymercuration-Demercuration
- (Hg(OAc)2/H20, THF) OH is added to one carbon and Hg(OAc) is added to the other carbon (Anti addition)
- (NaBH4 or Strong base/ NaOH) This removes the Hg(OAc) and adds a Hydrogen where it ones
9
Q
What are the 3 ways to make alcohols from alkenes and what selectivity are they?
A
- Acid-catalyzed hydration- Markovnikov
- Oxymercuration-demercuration-Markovnikov
- Hydroboration-Oxidation-Anti Markovinikov
10
Q
What are some features of Oxymercuration-demercuration?
A
- Markovnikov Regioselective ie. Adds OH to most substituted carbon
- Anti Stereoselective ie. Added to carbons on opposite sides
- No possibility of carbocation rearrangement
11
Q
What is a way to make alcohols from alkenes?
List the steps and reagents
A
Hydroboration-Oxidation
- (BH3, THF) H and BH2 are added to adjacent carbons
- (NaOH,H2O2) OH- attacks and knocks off the BH2 molecule
via. SN2
12
Q
What are the features of Hydroboration-Oxidation
A
- Antimarkovnikov regioselective
- Syn stereoselective
- No possibility of carbocation rearrangement
13
Q
What type of mechanism should you NOT use to create an alcohol from an alkene when there is a T-butyl of isopropyl group and why?
A
Don’t use acid-catalyzed hydration because it will rearrange
14
Q
What are the 3 main points to remember when reacting alcohols?
A
- Reactions happen because the -OH group is nucleophilic and weakly basic
- The H atom of the -OH is weakly acidic
- -OH group can be converted to a good leaving group
15
Q
What is a good way to turn an -OH group into a good LG?
A
Pronate it with a strong acid
16
Q
What should any nucleophile in acidic solution be?
A
A weak base
17
Q
What do alcohols have acidities similar to?
A
Water
18
Q
Rank the acidities and basicities of:
NH3 Terminal alkyne H20 ROH H2 RH
A
Most Acidic to least:
H20 ROH Terminal alkyne H2 NH3 RH
Most Basic to least:
R- NH2- H- Deprotonated terminal alkyne RO- OH-
19
Q
What was the general trend of the last slide?
A
H2O and ROH (alcohol) were stronger acids and weaker bases
20
Q
What are 3 ways to convert alcohols to alkyl halides?
A
- H-X (Hydrogen halide)
- PBR3
- SOCL2
21
Q
What might be a purpose of changing an alcohol to an alkyl halide?
A
We might do this to protect the alcohol if it is in acidic solution because otherwise, it will H-bond
22
Q
What is the reactivity of alcohols ranked?
What is the order of reactivity of hydrogen halides?
A
Alcohols: 3>2>1>Meth
Hydrogen Halides: HI>HBr>HCl HF doesn’t react
23
Q
Will and Alcohol react with Na-X, why or why not?
What can you do to change this?
A
No, because the OH- is a bad leaving group
We can acid catalyze it to turn the OH into a good leaving group
24
Q
What conditions are used to turn an alcohol into an alkyl halide and why?
A
Acidic, need to make the OH- into a good leaving group
25
How do meth and 1 alcohols to form alkyl halides?
| List steps reactants and conditions
These reactions occur in Acid when it is not H-X
Meth/1- (Use Na or H with a halide AND the alcohol) SN2
Step 1. The Halogen splits and turns into a halide either by pronating the OH or losing the Na in which case it must be acid catalyzed
Step 2. If needed the acid pronates the OH group
Step 3. The halide attacks via SN2 and backside attacks knocking off the OH LG
26
How do 2,3, benzylic, and allylic alcohols to form alkyl halides?
List steps reactants and conditions
These reactions occur in Acid when it is not H-X
2,3, Benzylic, allylic (Halide and Alcohol) SN1
A carbocation intermediate is formed in this reaction
Step 1. The OH group is pronated-(Fast)
Step 2. The OH group leaves-(Slow)
Step 3. The halide attacks (Fast)
27
What do we make when we react PBr3 with 3 counts of alcohol?
Alkyl halides and H3PO3
28
What are the steps in PBr3 reacting with an alcohol? and what do we need?
We need PBr3 and 1 or 2 alcohol
Step 1: O attacks the electropositive Phosphorous knocking off a Br
Step 2: The Br- attacks and knocks off the +HOPBr2
29
What are characteristics of PBr3 reacting with alcohol?
1. Happens with 1 and 2 alcohols
2. No carbocation rearrangement, especially if below 0 degrees Celsius
3. Adds a bromine
30
What are the steps in the reaction of SOCL2 and alcohol? and what do we need?
We need SOCl2, Pyridine, and a 1 or 2 alcohol
Don't need to know mechanism, also we use pyridine to pick up extra Hydrogens
31
What are characteristics of SOCl2 reacting with alcohol
1. 1 or 2 alcohol
2. No carbocation rearrangement especially if below 0 degrees Celsius
3. Use pyridine as a Hydrogen grabber
4. Adds a chlorine
32
What are 3 good Leaving groups?
1. Tosylate
2. Mesylate
3. Trifates
33
What is a problem with reacting a primary alcohol via SN2?
OH is a bad leaving group so we can convert it to a good one
34
What is the reaction to convert a primary alcohol into a good leaving group and what do we need?
We add Tosyl, mesyl, or trifyl chloride and use pyridine as a reactant to add these to make OTs, OMs, or OTf.
This will allow a nucleophile to attack via SN2
35
What happens to stereochemistry when we convert OH to a good LG with Ms, Ts etc.
Stereochem is retained, but when the nucleophile come in via SN2 and inverts the stereochemistry
36
How do you show the inversion of stereochemistry at a given carbon at on a ring system?
Switch at the same carbon from the axial or equatorial to the corresponding axial or equatorial
37
What are the ways to make ethers?
1. Intermolecular dehydration of alcohols-Alcohol and Acid
2. Williamson ether synthesis-Alcohol and Base
3. Alkoxy-Demercuration-Alkyne with mercury, alcohol, and base
38
Explain the steps and what is needed for dehydration of an alcohol to make an ether?
What is this synthesis good for making?
We need an alcohol, an acid, the exact alcohol as before, and heat
Step 1. The acid pronates the alcohol
Step 2. The alcohol attacks and the water leaves
Step 3. Water removes the H from the pronated ether
ONLY GOOD FOR SYMMETRICAL ETHERS
39
How do we make 3 different ethers with one reaction?
React 2 different primary alcohols with acid. This gives you a combination of all 3 R-O-R', R-O-R, R'-O-R'
40
What is a good way to make an ether with an ether connected to 1 carbon on one side and 3 carbons on the other side?
What are the steps?
Add a primary and tertiary alcohol in catalytic acid (H2SO4)
Step 1: The acid makes the 3 alcohol into a good LG and a carbocation forms
Step 2: The primary ether attacks and joins
41
What are some characteristics reactants of the Williamson ether synthesis?
1. It occurs via SN2 so the nucleophile (R-X) must be primary
2. The substrate is R'OH
3. R'OH can be 1, 2, or 3
42
What are the steps of the Williamson ether synthesis? and what is needed
A primary Alkyl halide, a 1,2,or3 alcohol, and A BASE
Step 1. The base removes the H from the alcohol
Step 2. The alkoxide attacks the primary alkyl halide via SN2
43
What bond must break in retrosynthesis of Williamson ether?
Break the bond that gives us a primary or methyl group for the R-X
44
What can happen when there are an alcohol and halide on opposite ends of a chain?
If it reacts with a base the alkoxide end will attach and knock of the halide creating a ring
45
What happens when you react a ring with adjacent halide and OH group with a strong base if they are trans and cis?
Why does this happen?
Trans-An epoxide forms
Cis-No reaction occurs
46
What is an easy way to form an epoxide?
Use cyclohexane with adjacent trans halide and OH- then react with strong base
47
What do ethers do to the solubility of a molecule in water?
Adding an ether makes a molecule more soluble in water
48
What are the steps of alkoxy-demercuration?
| What is needed?
An alkene, (Mercury and alcohol), (Strongbase/NaOH)
Step 1: Hg(OCCF3)2 and R'OH add via Markovnikov
Step 2: The base removes the Hg group
49
What are the characteristics of alkoxy-demercuration?
1. Markovnikov regioselective ie.OR gets added to ore substituted
2. The is no possibility of a rearrangement
50
What are 2 kinds of protecting groups that must often be added to form ethers?
1. Tert-Butyl protecting group
| 2. Silyl protecting group
51
Why are protecting groups used?
To protect a hydroxyl group
52
What reactants do you need to add a t-butyl group to an alcohol to form a protecting group?
A primary alcohol, and (Acid/2-methyl-prop-1-en)
53
What can be used to remove a t-butyl group?
Dilute aqueous acid (H+/H2O)
54
What is a Grignard reagent?
R-Mg-X
55
Why must a primary alcohol be protected when a Grignard reagent is being used?
Because the MGX is positive and the double bond is negative meaning it will react with the alcohol otherwise
56
What does BrMg of Grignard reagents do?
It leaves and creates a - charged R group
57
What is a silyl ether protecting group?
It is a useful protecting group for primary alcohols
58
How do we add a silyl ether protecting group and what do we need?
We need TBSCL and a primary alcohol, we react these with (imidazole/aprotic solvent)
59
How do we remove a silyl protecting group?
Bu4NF/THF or HF (aq)/THF
60
What are the steps with a protecting group?
1. Add the group
2. Add the reagent
3. Remove the group
61
What is the only thing dialkyl ethers react with and what does this do to the ether?
They only react with acids which pronate the O and creates a salt
62
How do you cleave ethers?
Heat dialkyl ethers with strong acid which breaks the C-O bonds and gives us water
63
What would ether cleavage of diethyl ether reacting with 2H-Br lead to?
H20 and 2 Bromoethane
64
What are the steps of ether cleavage and what is needed?
Use 2 counts of acid and the ether
Step 1. The ether takes an H off the acid
Step 2. The X of the acid attacks one side of the alkyl group and the oxygen takes up the nearest bond
Step 3. Oxygen removes another proton from the acid
Step 4. The X of the acid attacks the remaining alkyl group and the O is protonated while the bond breaks
65
What is an epoxide?
A 3 membered ring with a central oxygen
66
What are the ways to make epoxides?
1. Electrophilic Epoxidation-React an alkene with a peroxy acid aka peracid
67
What do you need for electrophilic epoxidation?
An alkene and a (peracid/acid)
68
What are common types of peracids and what is the structure of a peracid?
They are carboxylic acids with an extra O between the C and the OH
1. MCPBA
2. Peracetic acid
69
What are the reactants and products of electrophilic epoxidation
Alkene + Peracid ---------------> Epoxide + Carboxylic Acid
70
What stereochemistry happens during electrophilic epoxidation?
The stereochemistry is retained meaning if it is a trans of cis double bond the carbons will stay like that
It is syn (cis) addition
71
What bond will form an epoxide if there are 2 double bonds?
The more electron dense ie. more substituted because alkyl groups push electron density into the double bond
72
What about epoxides structure make them reactive compared to other ethers?
The highly strained ring means they are more reactive towards nucleophilic substitution
73
What are the 2 ways to open an epoxide?
1. Acid catalyzed-More substituted
| 2. Base catalyzed-Less substituted
74
What are the steps of acid-catalyzed epoxide opening, what do you need, and what does it add?
An acid and an epoxide are needed
Step 1. Acid pronates epoxide
Step 2. Same water molecule that was an acid attack Carbon and the oxygen takes up a bond opening the ring
Step 3. Water removes proton from water on carbon
This adds an alcohol and the acid without an H
75
What are the steps of base-catalyzed epoxide opening, what do you need, and what does it add?
A base and an epoxide are needed
Step 1. A base R-O- attacks one carbon and opens the ring
Step 2. The negative oxygen grabs a hydrogen off the base
This adds an alcohol and the base without an H
76
What is a diol?
2 OH groups in a compound
77
If an epoxide is unsymmetrical what does a base and an acid attack respectively?
Base-Goes to less substituted (Antimarkovnikov)
Acid-Goes to more substituted (Markovnikov)
78
What happens if you add an acid to a protonated epoxide (ie. + on the O)
You get a R-O-H and the O is positive
79
What is anti-dihydroxylation, and what is needed?
It is a 2 step procedure where 2 OH groups are added to create a diol via the ring opening of epoxides. An alkene ring, MCBPA and (acid/water) are needed
80
What are the steps in Anti-Dihydroxylation?
Step 1. MCBPA creates an epoxide from the double bond
Step 2. Acid protonates the Oxygen
Step 3. Water joins the ring
Step 4. Water is deprotonated
2 OH groups are added anti
81
How do you make cis-diols and trans-diols from a cyclohexene?
```
Cis-
Cold KMNO4 and OH-
or
1. OsO4
2. NaHSO3 (Strong base)
```
Trans-
1. MCPBA
2. H+/H20
82
What are 3 ways to make primary alcohols?
1. OH- attacking an alkyl halide via SN2
2. Girdans reactant: 1 Epoxide 2. Water
3. Hydroboration of a terminal alkene
1. (BH3/THF)
2. (H2O2/NaOH)
83
What are 3 ways to make a secondary alcohol?
1. Terminal alkene (Acid/Water)
2. Hydroboration of a middle alkene
1. (BH3/THF)
2. (H2O2/NaOH)
3. Oxymercuration-demercuration of middle or side alkene
1. Hg(OAc)2, H20
2. NaBH4
84
What are 3 ways to make a tertiary alcohol?
1. Tertiary alkyl halide with acid and water
2. 2-propene with acid and water
3. Oxymercuration-demercuration of 2-propene
85
What are 5 primary alcohol reactions?
1. TSCl and pyridine=Terminal OTS
2. Acid and heat=Termnal Alkene
3. SoCl2=Terminal alkyl halide
4. PBr3=Temrinal alkyl halide
5. 1. Base 2. R-X=Ether
86
What are the 2 ways to make ethers?
1. Williamson
| 2. Acid catalyzed with heat
87
How do you cleave ethers?
Add acid, protonate and then attack with base
