Study Set Content:
when written as a Fischer projection has the –OH group on its penultimate carbon to the right
D-Monosaccharide
when written as a Fischer projection has the –OH group on its penultimate carbon to the left
L-Monosaccharide
• When aldehydes and ketones react with alcohol, they form
hemiacetal and hemiketal respectively.
This happens when their carbonyl group (C=O) reacts with a hydroxyl group (-OH). This interaction produces a
ring
Monosaccharides have hydroxyl and carbonyl groups in the
same molecule
Monosaccharides have hydroxyl and carbonyl groups in the same molecule. As a result, they exist almost exclusively as
five- and six-membered rings
Cyclic hemiacetal
Cyclic hemiketal
a common way of representing the cyclic structure of monosaccharides
Haworth Projections:
In a Haworth projection, a five- or six-membered ring is represented as a
planar pentagon or hexagon, respectively
Groups bonded to the carbons of the ring lie either
above or below the plane of the ring.
The new carbon stereocenter created in forming the cyclic structure is called
anomeric carbon
– Stereoisomers that differ in configuration only at the anomeric carbon are called
anomers
The anomeric carbon of an aldose is
carbon 1
anomeric carbon of a ketose is
carbon 2
In the terminology of carbohydrate chemistry, the designation α means that the
OH group on the anomeric carbon lies on the side opposite to the terminal
CH2OH.
onversely, the designation β means that the
–OH group on the anomeric carbon lies on the same side as the terminal –CH2OH.
A six-membered hemiacetal ring is indicated by
–pyran
and a five-membered hemiacetal ring is indicated by
–furan.
Because the α and β forms of glucose are six-membered cyclic hemiacetals, they are named as indicated above. The designations –furan and –pyran are not always used. thus, glucopyranose is named simply as
α-D-glucose and β-D-glucose
