12.1 One method for assigning an oxidation state to a carbon atom of an organic compound is to
base that assignment on the groups attached to the carbon; a bond to hydrogen for (anything less
electronegative than carbon) make it –1, a bond to oxygen, nitrogen, or halogen (or to anything
more electronegative than carbon) make it +1, and a bond to another carbon makers it to 0. Thus
the carbon of methane is assigned an oxidation state of –4, and that of carbon dioxide, +4. (a) Use
this method to assign oxidation states to the carbon atoms of methanol, formic acid, and
formaldehyde. (b) Arrange the compounds methane, carbon dioxide, methanol, formic acid, and
formaldehyde in order of increasing oxidation states. (c) What change in oxidation state
accompanies the reaction, methanol → formaldehyde? (d) Is this an oxidation or a reduction? (e)
When H2CrO4 acts an oxidizing agent in this reaction, the chromium of H2CrO4 becomes Cr3+.
What change in oxidation state does chromium undergo?
(a) Oxidation states to the carbon atoms of methanol –2, formic acid +2, formaldehyde 0.
(b) Methane, methanol, formaldehyde, formic acid, and carbon dioxide.
(c) Oxidation states to the carbon atoms from methanol –2 to formaldehyde.
(d) An oxidation.
(e) Oxidation state of chromium form +6 to +3.
12.2 (a) Use the method described in the preceding to assign oxidation states to each carbon of
ethanol and to each carbon of acetaldehyde. (b) What do these numbers reveal about the site of
oxidation when ethanol is oxidized to acetaldehyde? (c) Repeat this proceduce for the oxidation of
acetaldehyde to acetic acid.
(a) H3C
H2
C
-3
0;
OH
O
H3C
C
H
-3
+1;
(b) It reveals that the carbon of methyl has no oxidation state changed, but the carbon of
CH2OH has been oxidized.
O
(c) H3C
-3
C
H
+1;
O
H3C
C
OH
-3
+3;
It reveals that the carbon of methyl has no oxidation state changed, but the carbon of
O
C
OHhas been oxidized.
12.3 (a) Although we have described the hydrogenation of an alkene as an addition reaction,
organic chemists often refer to it as a “reduction.” Refer to the method described in Problem 12.1
and explain. (b) Make similar comments about this reaction:
O
+ H
H3C
C
Ni
H
CH3CH2OH
H
Answer:
During the addition reaction, the oxidation state of the carbonyl carbon changes from +1 to –1, it
means that this carbon is reduced.
12.4 Which reducing agent, LiAlH4 or NaBH4, would you use to carry out the following
transformations?
(a)
H3C
H3C
O
C
OH
C
H2
OH
(b)
OH
O
CH
H3C
H3C
O
C
OH
C
H2
OH
(c)
OH
O
CH
H
H
O
O
C
(a) LiAlH4
OCH3
(b) LiAlH4
12.5 Show how
each
C
OCH3
(c) NaBH4
of
the
following
transformations
could be accomplished.
PCC
(a)
CH2 OH
CHO
CH2Cl2
(b)
(c)
KMnO4
CH2OH
COOH
H 3O
OH
PBr3
Br
1, Mg
2, CO2
3. H3O+
COOH
O
1. O3
(d)
O
HCCH2CH2CH2CH
2. Zn / H2O
12.6 Write equations similar to the above for the reaction that take place when phenyl-lithium is
threated with (a) water and (b) ethanol. Designate the stronger and weaker acids and strong and
weaker bases.
(a)
Li
H
OH
+
water
(Stronger
acid)
phenyl-lithium
(stronger base)
HO
+
Li
Hydroxide ion
(weaker base)
benzene
(weaker
acid)
(b)
Li
H
O
ethanol
(Stronger
acid)
phenyl-lithium
(stronger base)
+
C2H5
O
C2H5
+
alkoxide ion
(weaker base)
benzene
(weaker
acid)
12.7 Assuming you have bromobenzene (C6H5Br), magnesium, dry ether, and deuterium oxide
(D2O) available, show how you might synthesize the following Deuterium-labeled compound.
D
Answer:
Step 1:
Mg
MgBr
Br
Et2O
Step 2:
MgBr
+
D
OD
D
Li
12.8 Phenylmagnesium bromide reacts with benzoyl chloride C6H5COCl, to form
triphenylmethanol , (C6H5)3COH. This reaction is typical of the reaction of Grignard reagents
with acyl chlorides, and the mechanism is similar to that for the reaction of a Grignard reagent
with an ester just shown. Show the steps that lead to the formation of triphenylmethanol
Answer:
O
BrMgO
O
Cl
MgBr
Cl
MgBr
O
NH4 Cl
OH
H2O
12.9 Show how Grignard reactions could be used to synthesize each of the following compounds.
(You must start with an organic halide and you may use any other compounds you need.)
(a)
2-Methyl-2-butanol (three ways)
(b)
3-Methyl-3-pentanol (three ways)
(c)
3-Ethyl-2-pentanol (two ways)
(d)
2-Phenyl-2-pentanol (three ways)
(e)
Triphenylmethanol (two ways)
Answer:
(a)
1)
O
Mg
Br
MgBr
1)
2) NH4 Cl
Et2 O
2)
O
2 CH3MgBr
O
OH
3)
CH3
O
(b)
1)
CH3MgBr
OH
OH
O
Mg
Br
1)
MgBr
OH
O
Et2O
2) NH4Cl
2)
O
OH
Mg
Br
1)
MgBr
Et2O
2) NH4Cl
3)
CH3
CH3MgBr
O
OH
(c)
1)
OH
O
Br
MgBr
Mg
1) H3C
Et2O
H
2) NH4 Cl
2)
O
OH
H
1)
CH3MgBr
2) NH4Cl
(d)
1)
OH
O
Br
Mg
H3C
MgBr
1)
Et2 O
2) NH4Cl
2)
OH
O
Mg
1)
Br
3)
Et2O
MgBr
2) NH4Cl
OH
O
1)
CH3MgBr
2) NH4Cl
(e)
1)
O
Mg
1)
Br
Et2O
MgBr
2) NH4Cl
OH
2)
O
O
Mg
1)
Br
Et2O
2) NH4Cl
MgBr
OH
12.10 Outline a synthesis of each of the following. Permitted starting materials are
phenylmagnesium bromide, oxirane, formaldehyde, and alcohols or esters of four carbon atoms or
fewer. You may use any inorganic reagents and oxidizing agents such as pyridinium
chlorochromate (PCC).
(a) C6H5CH(OH)CH2CH3
(c) (C6H5)2C(OH)CH2CH3
(b) C6H5CHO
(d) C6H5CH(OH)CH(CH3)2
Solution:
(a)
OH
PCC,CH 2Cl2
CHO
OH
MgBr
1) Et2O
+
CHO
2) H+
(b)
O
MgBr
1) Et2O
+
H
H
2)
CHO
PCC, CH 2 Cl2
(c)
H+
OH
MgBr
O
1) Et2O
+
2) NH4Cl,H2O
O
OH
(d)
OH
MgBr
1) Et2O
+
CHO
2) H+
12.11 What product (or products) would be formed from the reaction of isobutyl bromide,
(CH3)2CHCH2Br, with each of the following reagents?
(a) OH-, H2O
(b) CN-, ethanol
(c) (CH3)3CO-, (CH3)3COH
(d) CH3O-, CH3OH
(e) Li, Et2O, then CH3COCH3, then NH4Cl, H2O
(f) Mg, Et2O, then CH3COCH3, then H2O
(g) Mg, Et2O, then CH3COOCH3, then NH4Cl, H2O
O
(h) Mg, Et2O, then
, then H2O
(i) Mg, Et2O, then HCOH, then NH4Cl, H2O
(j) Li, Et2O, then CH3OH
(k) Li, Et2O, then CH3CCH
Answer:
(a) (CH3)2CHCH2OH
(b) (CH3)2CHCH2CN
(c) (CH3)2C=CH2
(d) (CH3)2CHCH2OCH3
(e)
OH
(f)
OH
(g)
(h)
OH
OH
(i)
OH
(j)
(l)
(CH3)2CHCH3
CH3CCLi (CH3)2CHCH3
12.12 What products would you expect from the reaction of ethylmagnesium bromide
(CH3CH2MgBr) with each of the following reagents?
(a) H2O
(e) C6H5COOCH3, then NH4Cl, H2O
(b) D2O
(f) C6H5COCH3, then NH4Cl, H2O
+
(c) C6H5CHO, then H3O
(g) CH3CH2CCH, thenCH3CHO, then H3O+
(d) C6H5COC6H5 then NH4Cl, H2O
(h) Cyclopentadiene
Answer:
(a) CH3CH3
(e) (C2H5)2CC6H5OH and CH3OH
OH
OH
and
C6H5
CH3
C2H5
(b) CH3CH2D
(f)
OH
OH
(c)
C2H5
OH
OH
and
and
C2H5
C6H5
H3C
C6H5
H
C6H5
H
C2H5
H
(g)
CH3
H3C
C
CCH2CH3
H3CH2CC
H
C
MgBr
(d) C2H5C(C6H5)2OH
(h)
12.13 What products would you expect from the reaction of propyllithium (CH3CH2CH2Li) with
each of the following reagents?
(a) (CH3)2CHCHO, then H3O+
OH
H3C
Products:
H
C
C
H
H2
C
CH3
(b) (CH3)2CHCOCH3, then NH4Cl, H2O
Products:
H2
C
CH3
OH
H3C
H
C
C
CH3
CH3
H2
C
H2
C
CH3
(c) 1-Pentyne, then CH2COCH3, then NH4Cl, H2O
Products: CH3CH2CH3
OH
H3C
C
C
H2
C
C
H2
C
CH3
CH3
(d) Ethanol
Products: CH3CH2CH3, CH3CH2Oli
(e) CuI, then CH2=CHCH2Br
Products: CH2=CHCH2CH2CH2CH3
(f) CuI, then cyclopentyl bromide
Products:
CH2CH2 CH3
(g) CuI, then (Z)-iodopropene
Products:
H3CH2CH2C
H
CH3
H
(h) CuI, then CH3I
Products: Butane
(i)
CH3CO2D
Products: CH3CH2CH2D, CH3COOLi
12.14 Which oxidizing or reducing agent would you use to carry out the following
transformations?
(a) CH3COCH2 CH2CO2CH3
CH3 CHOHCH2CH2CH2OH + CH3OH
(b) CH3COCH2CH2CO2CH3
CH3 CHOHCH2CH2CO2CH3
(c) HO2CCH2 CH2 CH2CO2H
HOCH2CH2 CH2 CH2CH2OH
(d) HOCH2CH2CH2CH2CH2 OH
HO2CCH2CH2CH2CO2H
(e) HOCH2 CH2CH2CH2CH2OH
OHCCH2CH2CH2CHO
Answer: (a) LiAlH4/Et2O (Lithium aluminum hydride)
(b) NaBH4/H2O
(Sodium borohydride)
(c) LiAlH4/Et2O
(Lithium aluminum hydride)
(d) KMnO4 (potassium permanganate)
(e) pcc (pyridinium chlorochromate)
12.15 Outline all steps in the synthesis that would transform isopropyl alcohol, CH3CH(OH)CH3,
into each of the following:
(a) (CH3)2CHCH(OH)CH3
CH3CHCH3
PBr3
OH
CH3CHO
Mg
CH3 CHBrCH3
(CH3 )2CHMgBr
Et2 O
(CH3)2 CHCHCH3
OH
(b) (CH3)2CHCH2OH
CH3CHCH3
PBr3
OH
CH2O
Mg
CH3 CHBrCH3
Et2 O
(CH3 )2CHMgBr
(CH3 )2CHCH2OH
(c) (CH3)2CHCH2CH2Cl
CH3CHCH3
PBr3
OH
O
Mg
CH3 CHBrCH3
(CH3 )2CHCH2CH2OH
Et2 O
PCl3
(CH3 )2CHMgBr
(CH3 )2CHCH2CH2Cl
(d) (CH3)2CHCH(OH)CH(CH3)2
CH3CHCH3
OH
HCOOC2H5
PBr3
CH3 CHBrCH3
Mg
Et2 O
(CH3 )2CHMgBr
(CH3)2 CHCHCH(CH3)2
OH
(e) CH3CHDCH3
CH3CHCH3
OH
PBr3
CH3CHBrCH3
Mg
Et2 O
(CH3)2CHMgBr
D 2O
CH3CHCH3
D
(f)
CH3
CH
CH3
CH3CHCH3
PBr3
OH
CH3 CHBrCH3
Li
CH3CHLiCH3
Br
Cu
CH3
H 3C
CH
H3 C
CuLi
2
CH
CH3
12.16 What organic products would you expect from each of the following reactions?
(a) Methyllithium +1-butyne
(b) Product of (a) + cyclohexanone, then NH4Cl, H2O
(c) Product of (b) +Ni2B (P-2) and H2
(d) Product of (b) +NaH, then CH3CH2OSO2CH3
(e) CH3CH2OCH3 +NaBH4
base
(f) Product of (e) +mesyl chloride
(g) Product of (f) +CH3CO2Na
(h) Product of (g) +LiAlH4, then H2O
(a)
Li
(b)
OH
(c)
HO
(d)
O
(e)
OH
(f)
OSO2Me
(g)
OCOCH3
(h)
OH
12.17 Show how 1-pentanol could be transformed into each of the following compounds. (You
may use any needed inorganic reagents and you need not show the synthesis of a particular
compound more than once.)
(a) 1-Bromopentane
HO(CH2)4CH3
Br2
Br(CH2 )4CH3
(b) 1-Pentene
HO(CH2)4CH3
conc H2 SO4
H2C CH(CH2)2CH3
(c) 2-Pentanol
H2C CH(CH2)2CH3
H2 O/H2 SO4
H3CCHOH(CH2)2CH3
(d) Pentane
H2C CH(CH2)2 CH3
H2 /Pt
H3C(CH2)3 CH3
(e) 2-Bromopentane
H2C CH(CH2)2CH3
HBr
H3CCHBr(CH2)2CH3
(f) 1-Hexanol
Br(CH2 )4CH3
(g) 1-Heptanol
KOH
HO(CH2 )5CH3
HO(CH2 )5CH3
Br2
Br(CH2 )5CH3
Mg/Et2O
MgBr(CH2)5CH3
HCHO
HO(CH2 )6CH3
(h) Pentanal (CH3CH2CH2CH2CHO)
HO(CH2)4CH3
PCC/CHCl2
H3C(CH2)3CHO
(i) 2-Pentanone (H3CCO(CH2)2CH3)
H2CrO4/H3O
H3CCHOH(CH2)2CH3
H3CCO(CH2 )2CH3
(j) Pentatonic acid (CH3CH2CH2CH2CO2H)
HO(CH2)4 CH3
KMnO4/H3 O
H3C(CH2)3COOH
(k) Dipentyl ether (two ways)
conc H2SO4
H3C(CH2)4O(CH2 )4CH3
140℃
HO(CH2 )4CH3
CH(CH2)2CH3
H C(CH2 )4O(CH2)4 CH3
(OAC)2Hg/ H3O 3
HO(CH2)4 CH3
H2C
(l) 1-Pentyne
H2C
Br2/CCl4
CH(CH2)2CH3
BrH2CCH2Br(CH2)2CH3
KOH
HC
C(CH2)2CH3
(m) 2-Bromo-1-pentene
HC
C(CH2) 2CH3
HBr
H2C
CHBr(CH2) 2CH3
(n) Pentyllithium
Br(CH2)4CH3
Li/Et2O
-10℃
Li(CH2)4CH3
(o) Decane
Li(CH2)4 CH3
CuI
[(CH2)4 CH3 ]2 CuLi
Br(CH2)4CH3
H3C(CH2)8 CH3
(p) 4-Methyl-4-nonanol
1
CH3 CH2 CH2CH2CH2Mg
H3 CCO(CH2)2CH3
2 H3O+
H3 C(CH2 )4COH(CH3)(CH2)2CH3
12.18 Show how each of the following transformations could be carried out.
(a) Phenylethyne
(b) C6H5COCH3
(c) Phenylethyne
(d) Phenylethene
(e) 2-phenylethanol
(f) 2-phenylethanol
Answer:
(a)
C6H5C
CC(OH)(CH3)2
1-phenylethanol
Phenylethene
2-phenylethanol
4-phenylbutanol
1-methoxy-2-phenylethane
CMgX
O
RMgX
+
CC(CH3)2
H2O
C6H5C
CC(OH)(CH3)2
OMgX
(b)
OH
O
NaBH4
H2 O
(c)
H2
BaSO4
(d)
OH
1. BH3
2. H2 O2, OH-
(e)
OH
Br
MgBr
O
Mg
HBr
(Et)2O
OMgX
OH
H2O
(f)
OH
OCH3
CH3OH
H2SO4
12.19 Assuming that you have available only alcohols or esters containing no more than four
carbon atoms show how you might synthesize each of the following compounds. You must use a
Grignard reagent at one step in the synthesis. If needed you may use oxirane and you may use
bromobenzene, but you must show the synthesis of any other required organic compounds.
Assume you have available any solvents, and inorganic compounds, including oxidizing and
reducing agents, that you require.
(a) (CH3)2CHCOC6H5
(b) 4-Ethyl-4-heptanol (c) 1-Cyclobutyl-2-methyl-1-propanol
(d) C6H5CH2CHO
(e) (CH3)2CHCH2CH2CO2H (f) 1-Propylcyclobutanol
(g) CH3CH2CH2COCH2CH(CH3)2
(h) 3-Bromo-3-phenylpentane
Answer:
(a)
PCC
CHO
CH2 Cl2
OH
Br
Mg
MgBr
Et2 O
OH
Et2O
MgBr
CHO
+
H3 O
OH
O
H2CrO4
CH2 Cl2
(b) CH3 CH2CH2OH
CH3 CH2 CH2MgBr
+
CH3CH2CH2Br
PBr3
Et2O
Br
PBr3
Et2O
NH4Cl
O
OH
CH3CH2CH2 MgBr
OH
+
O
(c)
Mg
H2O
Mg
MgBr
Et2O
PCC
OH
CH2Cl2
CHO
Et2O
MgBr
+
H 3O
CHO
OH
(d)
Br
Mg
MgBr
Et2O
H 3O
PCC
CH2Cl2
oxirane
CHO
CH2OH
(e)
PBr3
Mg
Br
MgBr
OH
Et2 O
KMnO4
OH
oxirane
H3O
COOH
PBr3
OH
(f)
Br
Mg
MgBr
Et2O
OH
O
PCC
CH2 Cl2
HO
O
Et2 O
+
MgBr
H 3O
OH
(h)
PCC
CHO
CH2Cl2
CH3CH2CHO
Mg
PBr3
MgBr
OH
Br
Et2O
H 3O
MgBr
PCC
CH2Cl2
O
OH
H2SO4
Et2O NH4Cl
H2O
HBr
170℃
HO
C6 H5
C6H5
Br
C6H5
12.20 Compound X(C5H10O) shows a strong IR absorption bar near 1710 cm-1, The broadband
proton-decoupled 13C NMR spectrum of X is in shown in page 569. Propose a structure for X.
Answer:
O
12.21 Show how a Grignard reagent might be used in the following synthesis.
OH
O
H3C
OH
O
H3C
Solution:
O
CH3
O
+
H3C
MgBr
BrMgO
+ H3C
MgBr
O
CH3
CH3
H2 O
BrMgO
HO
CH3
(T.M.)
CH3
BrMgO
OH
12.22 Starting with compounds of four carbon atoms or fewer, outline a synthesis of racemic
Meparfynol, a mild hypnotic (sleep-inducing compound).
CH3
H3C
H2
C
C
C
CH
OH
Answer:
O
HC
CH
NaNH2
HC
(1)
CNa
(2)NH4Cl,H2O
CH3
H3 C
H2
C
C
C
CH
OH
12.23 Although oxirane (oxacyclopropane) and oxetane (oxacyclobutane) react with Grignard
reagents and organolithiums to form alcohols, tetrahydrofuran (oxacyclopentane) is so unreactive
that is can be used as the solvent in which these organometallic compounds are prepared. Explain
the difference in reactivity of these oxygen heterocycles.
Answer: The 5 members ring has no ring strain at all. Moreover, the oxygen serves as Lewis base
stabilizing the Grignard reagent.
12.24 Predict the products that would result from the reaction of a Grignard reagent with the
following:
O
(a) Diethyl carbonate,
C2H5
O
C
O
(b) Ethyl formate, H
Answer:
(a)
C
O
C2H5
O
C2 H5
O
C2 H5
O
O
C
R
C2H5
C2H5
O
O
C
MgBr
O
O
O
C2H5
C2 H5
O
C
R
R
R
R
R
R
R
MgBr
C
R
R
R
R
R
R
O
OH
O
O
C2H5
R
MgBr
(b)
O
O
H
C
R
H
C2 H5
O
C
MgBr
O
O
C2H5
H
C
R
R
R
OH
O
H
MgBr
R
H
12.25 Use a Grignard synthesis to prepare the following
1-bromo-4-hydroxymethylcyclohexane and any other reagents necessary.
R
R
R
compound
from
OH
HO
Answer:
MgBr
Br
Br
O
Mg
CH2OH
O
1
O
OH
O
H3C
O
O
H
H3C
2 H3+O
HO
12.26 Explain how 1H NMR, 13C NMR, and IR spectroscopy could be used to differentiate
2-phenylethanol, 1,2-diphenylethanol, 1,1-diphenylethanol
[(C6H5)2CHCO2H] and benzyl
2-phenylethanoate (C6H5CH2CO2CH2C6H5).
Answer:
From 1HNMR, If there is a single methyl group, that should be 1,1-diphenylethanol. If the
splitting pattern is triplet and triplet around the aliphatic region, it should be 2-phenylethanol. If
the splitting pattern is triplet and doublet around the aliphatic region, it should be
1,2-diphenylethanol. If there are two singlet matched with benzylic protons, this would be benzyl
2-phenylethanoate. The left one is the 2,2-diphenylethanoic acid. Beyond the chemical shift,
integration of the peak area will give you the ratio of the equivalent protons in one molecule.
From 13C NMR, 2-phenylethanol shows six peaks, 1,2-diphenylethanol shows 10 peaks,
1,1-diphenylethanol shows six peaks, 2,2-diphenylethanoic acid shows six peaks too, but one
should be carbonyl carbon. 2-phenylethanoate shows eleven peaks, one of them should be
carbonyl carbon.
12.27 When sucrose (common table sugar) is treated with aqueous acids it is cleaved and yields
simpler sugars of these types:
HC
CH2OH
O
R
and H
C
O
OH
R
For reasons to be studied later, in the use of this procedure for the identification of the sugars
incorporated in a saccharide like sucrose, the product mixtures are often treated with sodium
borohydride before analysis. What limitation(s) does this put on identification of the sugar
building blocks of the starting saccharide?
Answer:
The limitation is that when the product mixtures are treated with sodium borohydride, we get the
same product, HOCH2CH(OH)R.
12.28 An unknown X shows a broad absorption band in the infrared at 3200 to 3550 cm-1 but none
in the 1620-1780 region. It contains only C, H, and O.
A 166-mg sample was treated with an excess of methylmagnesium bromide, producing 48.7 ml
methane gas collected over mercury at 20℃ and 750 mmHg.
The mass spectrum of X has its heaviest peak (barely detectable) at 116 m/z and a fragment
peak at 98.
What does this information tell you about the structure of X?
Answer:
The IR indicates the presence of OH and absence of C=C and C=O. The MS indicates a
molecaular weight of 116 amu and confirm the presence of hydroxyl. The reaction data indicate X
contains 2 protons per molecule that are acidic enought to reac with a Grignar reagent, meaning
two hydroxyl groups per molecule.(This analytical procedure, the Zerewitinoff determination, was
routunely done before the advent of NMR.)
Thus X has apartial structure like:
C6H10(OH)2 with one ring, or C5H6O(OH)2 with two rings, or (less likely)
C4H2O2(OH)2 with three rings.