Chemistry
10th Edition
ISBN:9781305957404
Author:Steven S. Zumdahl, Susan A. Zumdahl, Donald J. DeCoste
Publisher:Steven S. Zumdahl, Susan A. Zumdahl, Donald J. DeCoste
Chapter1: Chemical Foundations
Section: Chapter Questions
Problem 1RQ: Define and explain the differences between the following terms. a. law and theory b. theory and...
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Can you explain the mechanism? Can you provide a shortcut?
Transcribed Image Text:II. Addition of ROH: Synthesis of hemiacetals and acetals: (acid-catalyzed)
A.
R"-OH
R
'R'
R/R' = H, it is an aldehyde (one mole)
R/R' = alkyl, it is a ketone
B.
O
R
O=
R₁
+
+
2R"-OH
(two moles)
H3O+
H₂O
R
R
ОН
OR"
R
OR"
LOR"
R'
hemiacetal
+ H₂O acetal
Transcribed Image Text:Mechanism for hemiacetal:
R
R
R
Ö:
HO
II
0:
H
CHO
H 2 OH
3
R'
-H
H- -OH
-OH
R'
4
5
H*
(acid)
O:
R Hemiacetal
R H
Mechanism for acetal formation: For this you need 2 moles of alcohol if you start with
RAH
R-Ö:
aldehyde/ketone
HÖH
:OH
H*
(acid)
R
+
R
R
-0
H
HO
R'
6CH2OH
D-Glucose; an aldohexose
Fischer Projection
6
R'
*5
ОН
*
OH 3
-H₂O
-OH
R
ОН
O
Do this for deoxyribose, an aldo
pentose sugar in DNA!
H
R'
FO
R-OH
(weak nucleophile)
RR
R
+
Intramolecular hemiacetal formation: Five and six membered rings are especially stable
(carbohydrates)
HO
ROH
(2nd alcohol)
Ht transfer from one
oxygen to another
HO
6
5
ОН
OH 3
OH
R
R R'
О. ОН
НО ОН
R R₁
0:
H₂O
H₂O:
carboH
OAnomeric carbon HO
new chiral HO
a
3
R
R
R
OH
R₁
O: Acetal
HO
16
2
R'
5
OH
+ H3O*
+ H3O*
HO
ОН
a-D-glucose (blood glucose; Haworth formula and
chair conformation)
B-D-ribose, pentose sugar in RNA
O
Vnew chiral
carbon
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