Chemistry Reference
In-Depth Information
Figure 1.1
Illustration of the two types of pro-
jection formulas and the chair-like conforma-
tion of
D
- glucose. The open - chain (Fischer) (a)
and hexopyranose (Haworth) projection formu-
las (b) as well as the
4
C
1
low - energy chair - like
pyranose conformation (c) are presented.
Structural variability at the anomeric center (
information on assignment of anomeric posi-
tions and contributions of pyranose and open-
chain forms to the equilibrium, please see
Figure 1.2 and its legend. Epimer formation
from
D
- glucose (c) to
D
- galactose (d) leads to
the axial positioning of the 4-hydroxy group in
D
-galactose and changes in the topological sig-
nature of hydroxy and polarized C
α
or
) is symbolized by a wavy line. For further
H groups.
β
−
Figure 1.2
Illustration of the equilibrium includ-
ing the two anomeric forms of
D
- glucose. The
percentages of presence of the two anomeric
hexopyranose and the open-chain forms in
equilibrium are given in the bottom line.
As early as 1883, B. Tollens demonstrated that monosaccharides fail to react in
common tests for free aldehydes. This observation intimates an intramolecular
reaction. Its product is depicted in the Haworth projection in Figure 1.1b. This
structure, in chemical terms a semialdehyde, is a derivative of the heterocyclus
pyran, which explains the term ' pyranose ' . Therefore, a monosaccharide symbol
can be accompanied by an italic '
p
'. However, it is often omitted, since most of
the physiologically important hexoses occur as pyranoses. Like cyclohexane, the
