Exam 3 Flashcards
(171 cards)
0
Q
what is a carboxylic acid?
A
HO-C=O
R
1
Q
what is a carbonyl group?
A
C=O
2
Q
what is an acid chloride?
A
Cl-C=O
R
3
Q
what is an ester?
A
R-C=O
OR’
4
Q
what is an amide?
A
R-C=O
N(bonded to 2 more things)
5
Q
what is an acyl group?
A
RCO-
6
Q
what is the geometry of a carbonyl carbon?
A
sp2 hybridized, trigonal planar, 120° angles
7
Q
What kind of bond does the carbonyl group have?
A
polarized - O is electronegative, so C is electron deficient
8
Q
what do carbonyl compounds react with and why?
A
nucleophiles, because the electronegative oxygen makes the carbonyl carbon electrophilic, it is uncrowded because it is trigonal planar, and it has a pi bond which is easily broken
9
Q
what is an aryl group?
A
a substituent formed by removing one H from an aromatic ring
10
Q
what are the general reactions of carbonyl compounds?
A
aldehydes and ketones undergo nucleophilic addition
carbonyl compounds that contain leaving groups undergo nucleophilic substitution
11
Q
what is the mechanism for nucleophilic addition on an aldehyde or a ketone?
A
1) nucleophile (:Nu-) attacks electrophilic carbonyl. As the new bond to nucleophile forms, the pi bond is broken, moving an electron pair out on the O atom forming an sp3 hybridized intermediate
2) protonation of the negatively charged O atom by H2O (or another proton source) forms the addition product
- -> elements of H and Nu are added across the pi bond
12
Q
what is more reactive towards nucleophilic attack, ketones or aldehydes?
A
aldehydes are more reactive than ketones because aldehydes are less crowded (steric reasons) and they are less stable (electronic reasons) because there is only one R group stabilizing the positive charge on the carbonyl (rather than 2 R groups on a ketone)
R groups are electron donors
13
Q
what is the mechanism of nucleophilic substitution of RCOZ where Z = leaving group?
A
1) nucleophile (:Nu-) attacks the electrophilic carbonyl forming sp3 hybridized intermediate (the same as nucleophilic addition)
2) intermediate contains electronegative atom Z, Z can act as a leaving group. electron pair on O re-form pi bond, Z leaves with the electron pair in the C-Z bond.
Nu replaces Z
14
Q
how can you tell if a leaving group is good?
A
the weaker the base, the better the leaving group
in other words, the stronger the conjugate acid, the better the leaving group (the lower the pKa of the conjugate acid, the better the leaving group)
if the conjugate acid is weak, it’s not a good leaving group
15
Q
how does leaving group identity affect reactivity of RCOZ?
A
the better the leaving group Z, the more reactive RCOZ is in nucleophilic acyl substitution.
16
Q
Order leaving group ability from least to most leaving group ability
A
- NH2, -OH, -OR’, Cl- (-OH and -OR’ are similar in leaving group ability)
- –> Cl is best leaving group, NH2 is weakest
17
Q
Which kind of carbonyl is the most reactive? Which is the least? What’s in the middle?
A
acid chlorides (RCOCl) are most reactive
Carboxylic acids & esters (RCOOH and RCOOR’) fall in the middle (leaving groups are similar basicity)
amides are the least reactive (RCONH2)
18
Q
Why don’t aldehydes and ketones undergo substitution?
A
they have no leaving group bonded to the intermediate sp3 hybridized carbon - it would form H:- - very strong base, so poor leaving group
19
Q
what is the difference between oxidation and reduction reactions?
A
oxidation reactions reduce the number of C-H bonds
reduction reactions increase the number of C-H bonds
20
Q
alcohols, aldehydes and ketones, carboxylic acids or one of it’s derivatives - what kinds of reactions can these undergo: reduction or oxidation?
A
aldehydes and ketones can be reduced (to alcohols)
aldehydes can be oxidized (to carboxylic acids)
carboxylic acids & their derivatives (RCOZ) are already highly oxidized, so they can only be reduced (to aldehydes or primary alcohols usually)
21
Q
what are aldehydes and ketones reduced to?
A
aldehydes are reduced to 1° alcohols
ketones are reduced to 2° alcohols
22
Q
what are aldehydes oxidized to?
A
carboxylic acids
23
Q
what can you use to reduce aldehydes and ketones?
A
metal hydride (polar metal-hydrogen bond) followed by water or other proton source
sodium borohydride (NaBH4) and lithium aluminum hydride (LiAlH4) are most common
both are a source of nucleophile hydride: H:-
LiAlH4 is stronger reducing agent than NaBH4 because Al-H is more polar than B-H bond
24
What is usually the solvent with NaBH4 and with LiAlH4?
NaBH4 is usually with CH3OH
| LiAlH4 is usually with H2O
25
why would you pick one hydride over another?
NaBH4 selectively reduces aldehydes & ketones in the presence of most other functional groups
LiAlH4 reduces aldehydes, ketones & many other functional groups as well
26
What is the mechanism of hydride reduction?
1) nucleophile (AlH4-) donates H:- to carbonyl group, leaving pi bond & moving electron pair onto O. This forms new C-H bond
2) alkoxide is protonated by H2O (or CH3OH) to form alcohol reduction product. This acid-base reaction forms a new O-H bond.
- --> addition of the elements of H2 to carbonyl pi bond
27
What is catalytic hydrogenation of aldehydes and ketones
H2 and Pd (or another metal catalyst) reduces aldehydes & ketones to 1° and 2° alcohols
28
if a compound contains both C=O and a C=C, how can you selectively reduce the bond of choice?
C=C is reduced faster than C=O with H2 (Pd-C), so if you say, 1 equivalent of H2, it will reduce the C=C bond and not the C=O bond
C=O is reduced with NaBH4 and LiAlH4, but C=C is inert
29
what is the stereochemistry of hydride reduction of an achiral ketone?
reduction of achiral ketone with LiAlH4 or NaBH4 gives a racemic mixture of 2 alcohols when a new stereogenic center is formed (they will be enantiomers - non-superimposable mirror images)
30
What are reducing agents that can be used to reduce carboxylic acid derivatives?
LiAlH4 (strong reducing agent)
DIBAL-H (diisobutylaluminum hydride [(CH3)2CHCH2]2AlH - less reactive than LiAlH4 b/c 2 bulky isobutyl groups - H:- atom is donated in hydride reactions
Lithium tri-tert-butoxyaluminum hydride {LiAlH[OC(CH3)3]3} - less nucleophilic than LiAlH4
31
what is acid chloride + LiAlH4 2)H2O =
1° alcohol (with strong reducing agent)
32
what is acid chloride + LiAlH[OC(CH3)3]3 2)H2O =
aldehyde
| mild reducing agent
33
How do you make an alcohol from an acid chloride?
use a strong reducing agent
| LiAlH4 and H2O
34
How do you make an aldehyde from an acid chloride?
use a mild reducing agent
| LiAlH[OC(CH3)3]3 and H2O or DIBAL-H and H2O
35
How do you make an alcohol from an ester?
strong reducing agent
| LiAlH4 and H2O
36
What is ester + LiAlH4 and H2O =
1 ° alcohol
37
How do you make an aldehyde from an ester?
mild reducing agent
| DIBAL-H and H2O
38
what is an ester + DIBAL-H and H2O =
aldehyde
39
what is an ester?
RCOOR'
40
what is the leaving group in a reduction of acid chloride?
Cl-
41
What is the leaving group in a reduction of an ester?
CH3O-
| then it's protonated by H2O to form CH3OH
42
What is the mechanism of reduction of acid chlorides and esters with a metal hydride reagent?
Nucleophilic substitution forms aldehyde:
1) nucleophilic attack of H:- (from LiAlH4) --> forms tetrahedral intermediate with leaving group Z
2) pi bond re-formed & Z- comes off. Results in addition of H:- and elimination of Z- (substitution of H for Z)
Nucleophilic addition forms 1° alcohol
3) nucleophilic attack of H:- (from LiAlH4) forms alkoxide
4) protonation of alkoxide by H2O resulting in overall addition of H2
43
What is carboxylic acid + LiAlH4?
1° alcohol
44
Can you use mild reducing agents with carboxylic acid?
No, they are not strong enough to initiate reaction
45
Can you oxidize ketones?
no - they don't have an H on the carbonyl C (to oxidize you have to lose a C-H bond)
46
How can you oxidize aldehydes?
CrO3, Na2Cr2O7, K2Cr2O7
in the presence of other functional groups, you can oxidize aldehydes selectively with silver (I) oxide in aqueous ammonium hydroxide (Tollens reagent) Ag2O in NH4OH
47
what is an organometallic reagent?
C bonded to a metal
R-M
M= metal
most common M = Li, Mg, Cu
48
what is distinctive about organometallic reagents?
metals are more electropositive than C, so they donate electron density toward C, C bears partial negative charge
the more polar the C-M bond, the more reactive the organometallic reagent
49
what is an Grignard reagent?
R-Mg-X
| very reactive
50
what is an organocopper reagent?
organocuprate
R2CuLi
less polar C-M bond than organomagnesium (Grignard) so less reactive
51
How to organometallic reagents act in reactions?
as bases and nucleophiles
| reacts as carbanion (with M+) on the side
52
How do you prepare a Grignard reagent?
Mg inserts into R-X bond
R-X + Mg ---> R-Mg-X
(i.e. CH3-Br + Mg ---> CH3-Mg-Br) prepared in diethyl ether (CH3CH2)2O
53
How can you make an acetylide anion?
R-CtriplebondC-H + Na+-NH2 (or + Na+-H) ---> R-CtriplebondC:- Na+ + NH3
54
How do organometallic reagents act as bases?
strong bases that readily attract a proton from water to form hydrocarbons
CH3-Li + H-:O:H ---> CH3-H + Li+OH-
55
How do you convert an alkyl halide into an alkane?
R-X + M ---> R-M + H2O----> R-H
56
what is R-M + aldehyde and ketones =
alcohol
| R'-M + H2O and aldehyde or ketone = alcohol-R' (double bonded O turns to alcohol, and new R group is added to carbonyl C
57
How can you make an alcohol and a new R group from a ketone or an aldehyde?
add R-M then 2) H2O
58
what is carboxylic acid or carbonyl-Z + R'-M and 2) H2O
ketone or alcohol
depending on R'-M and leaving group Z, the doubled bonded O becomes OH and R' is added twice OR double bonded O stays and R' is added to replace Z (ketone)
59
What is R-M + CO2 and 2) H2O?
carboxylic acid
60
How do you make a carboxylic acid from R-M?
add 1) CO2 and 2) H2O
61
what is R-M + epoxide?
alcohol
62
how do you make an alcohol from an R-M?
add 1) epoxide and 2) H2O
63
What is the mechanism of addition of R"MgX (or other organolithium reagents) to RCHO and R2C=O?
1) nucleophile (R")- attacks carbonyl carbon and pi bond cleaves, forming alkoxide (forms a new C-C bond)
2) protonation of alkoxide by H2O forms alcohol (acid-base reaction forms the O-H bond)
overall addition of R"- from R"MgX and H+ from H2O to carbonyl group
64
How do you make a 1° alcohol from R'MgX?
add it to formaldehyde (CH2=O)
65
How do you make a 2 ° alcohol from R"MgX?
add it to an aldehyde
66
How do you make a 3 ° alcohol from R"MgX?
add it to a ketone
67
When can you add a new alkyl group with an organometallic reagent?
only under anhydrous conditions, otherwise the organometallic will react with the water and reduce yield.
water is added AFTER addition to protonate the alkoxide
68
How can you determine what carbonyl and Grignard components are needed to prepare a given compound?
1) find C-OH in the product
2) break the molecule into 2 components: one alkyl group bonded to the C bonded to the OH comes from the organometallic reagent, the rest comes from the carbonyl component
69
When do organometallic reagents NOT undergo nucleophilic addition reactions?
when they react with a compound that also has an O-H bond. Then they undergo acid-base with the O-H (transfer the H from the O-H to the R group of the R-M turning it into RH + M+
70
What is ester or acid chloride + (2)grignard or organolithium reagent?
3° alcohol
| adds 2 R" and turns double bonded O into OH
71
What is the mechanism of R"MgX (or R"Li) with RCOCl and RCOOR'
Nucleophilic substitution forms a ketone
1)nucleophilic attack of (R")- (from R"MgX) forms tetrahedral intermediate with leaving group Z (Z=Cl, OR')
2) Pi bond reformed & Z- comes off. addition of (R")- & elimination of Z- is substitution of R" for Z
now you have a ketone - can react with second equivalent of R"MgX to form alcohol by:
nucleophilic addition
3) nucleophilic attack of (R")- (from R"MgX) to form alkoxide
4) protonation of alkoxide by H2O gets 3° alcohol
72
How can you figure out what ester & Grignard reagent are needed to prepare a 3° alcohol?
must have 2 identical R groups, and those R groups have to come from RMgX. Remainder of the molecule comes from the ester
73
How can you form a ketone from an acid chloride?
use R'2CuLi
| need a less reactive organometallic reagent that won't react with the ketone to turn it into an alcohol
74
Can you make a ketone from an ester using an organometallic reagent?
No. Their leaving group OR- is too poor to react with R'2CuLi, and RMgX or RLi are too strong to leave the reaction at a ketone - they will continue & add on a second R, making a tertiary alcohol.
75
What is ester or acid chloride + (2)grignard or organolithium reagent?
3° alcohol
| adds 2 R" and turns double bonded O into OH
76
What is the mechanism of R"MgX (or R"Li) with RCOCl and RCOOR'
Nucleophilic substitution forms a ketone
1)nucleophilic attack of (R")- (from R"MgX) forms tetrahedral intermediate with leaving group Z (Z=Cl, OR')
2) Pi bond reformed & Z- comes off. addition of (R")- & elimination of Z- is substitution of R" for Z
now you have a ketone - can react with second equivalent of R"MgX to form alcohol by:
nucleophilic addition
3) nucleophilic attack of (R")- (from R"MgX) to form alkoxide
4) protonation of alkoxide by H2O gets 3° alcohol
77
How can you figure out what ester & Grignard reagent are needed to prepare a 3° alcohol?
must have 2 identical R groups, and those R groups have to come from RMgX. Remainder of the molecule comes from the ester
78
How can you form a ketone from an acid chloride?
use R'2CuLi
| need a less reactive organometallic reagent that won't react with the ketone to turn it into an alcohol
79
Can you make a ketone from an ester using an organometallic reagent?
No. Their leaving group OR- is too poor to react with R'2CuLi, and RMgX or RLi are too strong to leave the reaction at a ketone - they will continue & add on a second R, making a tertiary alcohol.
80
What are the general steps of reactions of organometallic reagents?
1) organometallic reagents R-M attack electrophilic carbon atoms - especially carbonyl carbons
2) after organometallic reagent adds to carbonyl group, fate of intermediate depends on presence or absence of leaving group
-with leaving group, it is nucleophilic substitution
-without leaving group, it is nucleophilic addition
3) polarity of R-M bond determines reactivity of reagents
RLi and RMgX are very reactive
R2CuLi is much less reactive
81
What is ester or acid chloride + (2)grignard or organolithium reagent?
3° alcohol
| adds 2 R" and turns double bonded O into OH
82
What is the mechanism of R"MgX (or R"Li) with RCOCl and RCOOR'
Nucleophilic substitution forms a ketone
1)nucleophilic attack of (R")- (from R"MgX) forms tetrahedral intermediate with leaving group Z (Z=Cl, OR')
2) Pi bond reformed & Z- comes off. addition of (R")- & elimination of Z- is substitution of R" for Z
now you have a ketone - can react with second equivalent of R"MgX to form alcohol by:
nucleophilic addition
3) nucleophilic attack of (R")- (from R"MgX) to form alkoxide
4) protonation of alkoxide by H2O gets 3° alcohol
83
How can you figure out what ester & Grignard reagent are needed to prepare a 3° alcohol?
must have 2 identical R groups, and those R groups have to come from RMgX. Remainder of the molecule comes from the ester
84
How can you form a ketone from an acid chloride?
use R'2CuLi
| need a less reactive organometallic reagent that won't react with the ketone to turn it into an alcohol
85
Can you make a ketone from an ester using an organometallic reagent?
No. Their leaving group OR- is too poor to react with R'2CuLi, and RMgX or RLi are too strong to leave the reaction at a ketone - they will continue & add on a second R, making a tertiary alcohol.
86
What are the general steps of reactions of organometallic reagents?
1) organometallic reagents R-M attack electrophilic carbon atoms - especially carbonyl carbons
2) after organometallic reagent adds to carbonyl group, fate of intermediate depends on presence or absence of leaving group
-with leaving group, it is nucleophilic substitution
-without leaving group, it is nucleophilic addition
3) polarity of R-M bond determines reactivity of reagents
RLi and RMgX are very reactive
R2CuLi is much less reactive
87
what is R2CuLi + R'-X =
R-R' (and by products of RCu + LiX)
88
How can you synthesize a hydrocarbon R-R'?
R-X + (2)Li ---> R-Li + CuI ---> R2CuLi + R'-X ---> R'-R
89
How do you make an organolithium reagent?
R-X + 2Li ---> R-Li (and LiX)
90
How can you make a Grignard reagent?
R-X + Mg --->(with (CH3CH2)2O) ---> R-Mg-X
91
How can you make an organocuprate reagent?
R-X + 2Li ---> R-Li + LiX
| 2R-Li + CuI ---> R2Cu-Li+ + LiI
92
How do you make a lithium acetylide?
R-CtriplebondC-H + R'-Li ---> R-CtriplebondC-Li + R'-H
93
How do you make a sodium acetylide?
R-CtriplebondC-H + Na+-NH2---> R-CtriplebondC- Na+ + NH3
94
how does reactivity of a carbonyl compound change with number of R groups?
as number of R groups around carbonyl carbon increases, reactivity of carbonyl compound decreases
95
How do you name an aldehyde using IUPAC?
1) if CHO is on a chain, find longest chain with CHO. change -e ending of parent alkane to -al.
if CHO is bonded to a ring, name the ring & add -carbaldehyde
2) number chain or ring with CHO as 1st C - don't include the number 1 in name
96
what is the common name for methanal?
formaldehyde
| 2 H's bonded to carbonyl C
97
what is formaldehyde?
2 H's bonded to carbonyl carbon
98
what is the common name of ethanal
acetaldehyde
99
what is acetaldehyde?
CH3 and H bonded to carbonyl group
100
what is the common name for benzenecarbaldehyde?
benzaldehyde
| aromatic ring and H bonded to carbonyl group
101
what is benzaldehyde?
benzene ring and H bonded to carbonyl group
102
How do you name an aldehyde using the common system?
take the common parent name & add suffix -aldehyde
use greek letters to name the substituents
alpha, beta gamma delta
103
what are the common parent names?
```
form- (carbonyl + H)
acet- (carbonyl + CH3)
Propion- (carbonyl + CH3CH2)
butyr- (carbonyl + CH3CH2CH2)
valer- (Carbonyl + CH3CH2CH2CH2)
```
104
How do you name a ketone using IUPAC?
1) find longest chain with carbonyl group. change -e ending of parent alkane to -one
2) number chain to give carbonyl carbon the lowest number
105
How do you name an alcohol substituent?
hydroxy
106
How do you name ketones using common names?
name both alkyl groups on the carbonyl carbon & arrange them alphabetically. add the word ketone
107
what is acetone?
propanone
| 2CH3 groups bonded to carbonyl
108
what is the common name for propanone?
acetone
109
what is acetophenone?
benzyl ring and CH3 bonded to carbonyl
110
what is the common name for benzyl ring bonded and CH3 bonded to carbonyl group?
acetophenone
111
what is the common name for 2 benzyl rings bonded to a carbonyl group?
benzophenone
112
what is benzophenone?
2 aromatic rings bonded to the same carbonyl group
113
how do you name a ketone or an aldehyde as a branch?
oxo
114
how do you name a carboxylic acid as a branch?
carboxy
115
what is the IUPAC name for benzophenone?
diphenyl ketone
116
what is an acyl group?
RCO-
117
how do you name an acyl group as a substituent?
take either IUPAC or common parent name and add suffix -yl or -oyl
118
what is a formyl group?
carbonyl + H bonded to something else
119
what is an acetyl group?
carbonyl bonded to CH3 bonded to the bigger group
120
what is a benzoyl group?
carbonyl bonded to aromatic ring bonded to something bigger
121
what is a benzyl group?
aromatic ring bonded to CH2 which is bonded to the bigger group
122
what kind of intermolecular forces do ketones and aldehydes have?
dipole-dipole, so they are not capable of intermolecular hydrogen bonding (no O-H bonds).
less polar than alcohols or carboxylic acids
123
rank alkanes, alcohols & ketones/aldehydes in order of increasing boiling points
alkanes lowest, then ketones & aldehydes, then alcohols have the highest boiling points
124
what is the solubility of ketones & acetones?
both soluble in organic solvents no matter what size
| with less than 5 C's, they are soluble in H2O because they can hydrogen bond with H2O
125
how can you make an aldehyde from an alkyne?
hydroboration 1)BH3
| 2) H2O2, -OH
126
what is alkyne + BH3 and H2O2 and -OH?
| R-CtriplebondC-R
RCH2-C=O
I
H
127
how can you make an aldehyde from an ester?
R-C=O
I
OR'
reduction reaction
1) DIBAL-H
2) H2O
R-C=O
I
H
128
what is R-C=O + 1) DIBAL-H
I 2) H2O
OR'
aldehyde
R-C=O
I
H
129
how do you make an aldehyde from an acid chloride?
R-C=O
I
Cl
```
reduction reaction
1)LiAlH[OC(CH3)3]3
2) H2O
R-C=O
I
H
```
130
What do you get when you react acid chloride with 1)LiAlH[OC(CH3)3]3
2)H2O
aldehyde
131
How do you get an aldehyde from an alcohol?
```
oxidation reaction
it has to be 1° alcohol
add PCC
RCH2-OH + PCC ---> R-C=O
I
H
```
132
what do you get with a 1° alcohol + PCC?
aldehyde
133
how do you make a ketone from an alcohol?
```
has to be 2° alcohol
oxidation reaction w/Cr6+ reagent
CrO3 or NaCr2O7 or K2Cr2O7 or PCC
R-C-R'
I
OH + PCC ---> R-C=O
I
R'
```
134
what do you get with 2° alcohol + CrO3 or Na2Cr2O7 or K2Cr2O7 or PCC?
ketone
135
how do you make a ketone from acid chloride?
organocuprate
R-C=O + 1)R'2CuLi 2) H2O ---> R-C=O
I I
Cl R'
136
what do you get with acid chloride + R'2CuLi and H2O?
ketone
137
How do you make a ketone from a benzyl ring?
```
Friedel-Crafts acylation
ring + (acid chloride) + AlCl3 ---> ring-C=O
R-C=O I
I R
Cl
```
138
what do you get with a benzyl ring + acid chloride + AlCl3?
ketone on a ring ring-C=O
I
R
139
how do you make a ketone from an alkyne?
```
hydration
H2O, H2SO4 and HgSO4
R-CtriplebondC-H ---> R-C=O
I
CH3
```
140
what do you get with alkyne + H2O + H2SO4 + HgSO4?
ketone
141
what happens at the alpha carbon on a carbonyl group?
the C-H bond is more acidic because reaction with a base forms a resonance-stabilized enolate anion
142
what are enolates?
nucleophile, and so they react with electrophiles to form a new bond on the alpha carbon
when an H is removed from the alpha carbon of a carbonyl group
R-C=:O:
I + :B ---> R-C=:O: R-C=CH2 + H-B+
CH2-H I I
:-CH2 ::O-:
+ E+ (an electrophile) ---> R-C=:O:
I
CH2-E (new bond on the alpha carbon)
143
when does nucleophilic attack precede protonation on an aldehyde or ketone?
with a strong neutral or negatively charged nucleophile
144
when does protonation precede nucleophilic attack with ketones and aldehydes?
when the nucleophile is weak - not strong enough to attack carbonyl C unless it has a positive charge
145
what is the general mechanism for an acid-catalyzed nucleophilic addition?
1) protonation of the carbonyl group: protonation of carbonyl O forms resonance-stabilized cation that bears full positive charge
R-C=:O: + H-A ---> R-C=:O+H R-C+-:O:H + A:-
I I I
H (R') H (R') H(R')
Nucleophilic attack & deprotonation
2) nucleophile attacks
3) deprotonation forms neutral addition product resulting in addition of H and Nu to carbonyl group
R-C+-OH + H-Nu: ---> R-C-OH (and another H or R on top of C)
I I
H(R') +Nu-H + A:- ---> H-A with Nu attached to remaining group
146
Which nucleophiles are good in substitution reactions at sp3 hybridized carbons, but not in addition?
Cl-, Br-, I-
because it would cleave the C-O pi bond to form an alkoxide, forming stronger base than the Cl-, equilibrium would favor the reactants, not the addition products
147
what happens when you add H2O in presence of acid or base to a carbonyl?
adds H and OH across C=O, forming gem-diol (hydrate)
148
how do you make a gem-diol from a carbonyl compound?
add H2O with acid or base catalyst
149
what kinds of carbonyl compounds can give good yields of gemdiols?
unhindered aldehydes like formaldehyde and aldehydes with nearby electron withdrawing groups like chloral Cl3C-C=O
I
H
150
how does the stability of carbonyl affect yield of gem-diol?
the more stable the carbonyl, the more equilibrium will favor the carbonyl and the smaller the yield of gem-diol will be
increasing R groups on carbonyl carbon decreases amount of gem-diol (hydrate)
formaldehyde (smallest carbonyl) yields most product, then acetaldehyde, then acetone - hardly any 2%
151
what else affects yield of gem-diols from carbonyl compounds?
```
electron withdrawing groups destabilize carbonyl, so more product
electron donating (like R groups) stabilize, so less product
```
152
what is the mechanism of base-catalyzed addition of H2O to a carbonyl group?
1) nucleophile (OH-) attacks carbonyl group, cleaving pi bond & moving electron pair onto O
2) protonation of negatively charged O atom by H2O forms the gem-diol
153
what is the mechanism of acid-catalyzed addition of H2O to a carbonyl group?
1) protonation of carbonyl oxygen forms resonance-stabilized cation that bears full positive charge
2) nucleophile (H2O) attacks + C (entire water molecule attaches, now it has a positive charge)
3) deprotonation forms neutral addition product
overall result is addition of H and OH to carbonyl group & regeneration of acid catalyst
154
how does acid increase the reaction rate of H2O addition to carbonyl compounds?
it protonates the carbonyl group, making it more electrophilic towards nucleophile attacks
155
how does base increase the reaction rate of H2O addition to carbonyl compounds?
converts the H2O into -OH, a stronger nucleophile
156
do acid or base catalysts in hydration reactions with carbonyl compounds affect equilibrium constant?
No - just increases the rate
157
how can you convert a gem-diol to an aldehyde or ketone?
catalyzed by acid and base - reverse mechanism of hydration
158
what is an acetal?
any compound derived from an aldehyde or a ketone having 2 OR groups bonded to a single carbon
159
How can you form an acetal?
aldehyde or ketone + 2 equivalents of alcohol in presence of acid (often TsOH)
160
how can you form a cyclic acetal?
use a diol in place of 2 equivalents of ROH.
| both O's in the cyclic acetal will come from the diol
161
how are gem-diol and acetal formation similar?
they are both equilibrium reactions, so they are both reversible
162
how can you drive acetal formation to the products?
remove water as it is formed (it is a byproduct)
163
what is the mechanism of acetal formation?
Part 1: formation of hemiacetal
1) protonation of carbonyl O forms resonance-stabilized cation that bears full positive charge
2) nucleophile (ROH) attacks the carbocation
3) deprotonation of attached nucleophile forms neutral addition product
result is addition of H and OR to carbonyl group
Part 2: formation of acetal
4) protonation of OH group in hemiacetal forms a good leaving group (H2O)
5) Loss of H2O forms resonance-stabilized cation
6) nucleophilic attack on the cation by ROH
7) deprotonation of attached ROH forms acetal
resulting in addition of a second OR group to the carbonyl group
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what is a hemiacetal?
a C bonded to one OH group and one OR group
165
how can you form an aldehyde or ketone from an acetal?
H+ and large excess of H2O
166
How do you go from an alcohol to a ketone?
PCC (from 2° alcohol)
167
how do you go from an alcohol to an aldehyde?
PCC (weak oxidizing agent) from 1° alcohol
168
What are the general steps of reactions of organometallic reagents?
1) organometallic reagents R-M attack electrophilic carbon atoms - especially carbonyl carbons
2) after organometallic reagent adds to carbonyl group, fate of intermediate depends on presence or absence of leaving group
-with leaving group, it is nucleophilic substitution
-without leaving group, it is nucleophilic addition
3) polarity of R-M bond determines reactivity of reagents
RLi and RMgX are very reactive
R2CuLi is much less reactive
169
what is amide + LiAlH4 and H2O?
RCH2-NR2
C=O replaced with CH2 to make an amine
amide is C=O bonded to NR2
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what won't PCC work with?
oxidizing an aldehyde to a carboxylic acid
only a Cr6+ or Tollens reagent (Ag2O + NH4OH)
CrO3, K2Cr2O7, Na2Cr2O7, KMnO4 work
