Carbohydrates I - ChemConnections

Photosynthesis
Energy Capture → Carbohydrates
n CO2(g) + n H2O(g) + energy →
CARBOHYDRATES
Carbohydrates
Carbohydrates / Saccharides / Sugars
Water, carbon dioxide, light and chlorophyll in green
plants:
n CO2 + n H2O
Cn(H2O)n + n O2
Empirical formula = CH2O
Classification of Carbohydrates
C5 : pentoses - ribose, arabinose
C6 : hexoses - fructose, glucose
Can be either an aldose (aldehyde + alcohols) or
ketose (ketone + alcohols)
Classification of Carbohydrates
monosaccharide
disaccharide
oligosaccharide
polysaccharide
Monosaccharide
is a fundamental unit and is not cleaved to a simpler
carbohydrate on hydrolysis
glucose, for example, is a monosaccharide
C6H12O6
Disaccharide
Disaccharide
is cleaved to two monosaccharides on hydrolysis
these two monosaccharides may be the
same or different
is cleaved to two monosaccharides on hydrolysis
these two monosaccharides may be the
same or different
C12H22O11 + H2O
C12H22O11 + H2O
sucrose
(a disaccharide)
sucrose
(a disaccharide)
Higher Saccharides
glucose
(a monosaccharide)
fructose
(a monosaccharide)
Classes of Carbohydrates
oligosaccharide:
No. of carbons
gives three or more monosaccharide units on
hydrolysis
polysaccharide:
yields more than 10 monosaccharide units
Aldose !
C6H12O6 + C6H12O6
Aldose
Ketose
4
Aldotetrose
Ketotetrose
5
Aldopentose
Ketopentose
6
Aldohexose
Ketohexose
7
Aldoheptose
Ketoheptose
8
Aldooctose
Ketooctose
Aldose or Ketose? ! Aldose or Ketose? !
Ketose !
Aldose !
C ! Ketose !
Fischer Projections and D-L Notation
Fischer Projections
Fischer Projections
Fischer Projections of Enantiomers
Fischer Projections of Enantiomers
4
1
2
S- = L-
R- = D-
3
Question
Enantiomers of Glyceraldehyde
Which one of the following is D-glyceraldehyde?
A)
C)
B)
D)
CH
H
D
O
OH
CH2OH
(+)-Glyceraldehyde
CH
HO
L
O
H
CH2OH
(–)-Glyceraldehyde
An Aldotetrose
1
H
The Aldotetroses
H
CH
2
OH
3
4
O
OH
CH2OH
stereochemistry assigned on basis of whether
configuration of highest-numbered stereogenic center
is analogous to D or L-glyceraldehyde
An Aldotetrose
An Aldotetrose
1
H
H
D
CH
2
3
4
O
1
OH
H
OH
H
CH
O
OH
OH
CH2OH
D-Erythrose
The Four Aldotetroses
O
3
4
CH2OH
stereochemistry assigned on basis of whether
configuration of highest-numbered stereogenic center
is analogous to D or L-glyceraldehyde
CH
CH
2
The Four Aldotetroses
O
CH
O
CH
H
OH
HO
H
D-Erythrose and
L-erythrose are
H
OH
HO
H
OH
HO
H
enantiomers
H
OH
H
CH2OH
CH2OH
CH2OH
D-Erythrose
L-Erythrose
D-Erythrose
O
H
OH
CH2OH
D-Threose
D-Erythrose and
D-threose are
diastereomers
The Four Aldotetroses
CH
HO
O
CH
H
HO
H
O
H
OH
CH2OH
CH
L-Erythrose and
D-threose are
H
HO
The Four Aldotetroses
D-Threose and
L-threose are
diastereomers
enantiomers
CH2OH
L-Erythrose
D-Threose
O
CH
O
OH HO
H
HO
H
OH HO
H
H
CH2OH
D-Erythrose
CH2OH
L-Erythrose
OH
D-Threose
H
O
H
CH
H
OHHO
CH2OH
D-Threose
O
OH
H
CH2OH
H
HO
CH2OH
L-Threose
How many stereoisomers are possible for an
aldopentose?
A) 3
B) 4
C) 8
D) 9
L-Threose
The Aldopentoses
There are 8 aldopentoses.
Aldopentoses and Aldohexoses
O
OH
Question
CH
H
H
H
CH2OH
The Four Aldotetroses
CH
HO
CH
O
Four belong to the D-series; four belong to
the L-series.
Their names are ribose, arabinose, xylose,
and lyxose.
The Four D-Aldopentoses
CH
O
OH
H
CH
D-Ribose
OH
H
CH2OH
O
CH
CH2OH
D-Arabinose
O
OH
H
The Four D-Aldopentoses
CH
D-Xylose
OH
H
CH2OH
O
CH
O
CH
O
CH
OH HO
H
H
OH
H
OH HO
H
H
OH
H
OH
OH
CH2OH
D-Ribose
CH2OH
D-Arabinose
H
H
CH
O
OH
H
OH HO
H
OH
H
OH
OH
CH2OH
D-Ribose
H
CH2OH
D-Arabinose
HO
D-Xylose
O
H
OH
H
CH2OH
CH2OH
D-Lyxose
CH
O
CH
O
CH
O
CH
O
OH HO
H
H
OH HO
H
HO
H
H
OH
H
OH HO
H
H
OH
H
OH
OH
OH
H
CH2OH
D-Xylose
CH
The Four D-Aldopentoses
O
H
O
H
The Four D-Aldopentoses
CH
CH
H
CH2OH
D-Lyxose
O
CH2OH
D-Lyxose
CH2OH
D-Ribose
H
CH2OH
D-Arabinose
Aldohexoses
There are 16 aldopentoses.
H
CH
OH HO
H
HO
H
CH2OH
D-Xylose
OH
H
CH2OH
D-Lyxose
Question
Which of the following carbohydrates belong to the L
series?
8 belong to the D-series; 8 belong to the Lseries.
Their names and configurations are best
remembered with the aid of a mnemonic.
A) 2 only
C) 1 and 4
O
B) 3 only
D) 2 and 3
The Eight D-Aldohexoses
All
Allose
Altruists
Altrose
Gladly
Glucose
Make
Mannose
Gum
Gulose
In
Idose
Gallon
Galactose
Tanks
Talose
CH
H
L-Aldohexoses
O
OH
CH2OH
Question
The carbohydrate shown at the right is classified
as a(n)
A) D aldotriose
B) D aldotetrose
C) L aldotriose
D) L aldotetrose
E) D aldopentose
There are 8
aldohexoses of the
L-series.
H
They have the
HO
same name as
H
their mirror image
except the prefix is H
L- rather than D-.
CH
O
OH
H
CH
HO
H
O
H
OH
OH
HO
H
OH
HO
H
CH2OH
D-(+)-Glucose
CH2OH
L-(–)-Glucose