In: Chemistry
1) Glucose has molecular formula C6H12O6.
a) Draw the three distinct forms of glucose that exist in equilibrium in solution.
b) What is the term used to describe the inter-conversion of the three forms of glucose?
This is one question asked on my tutorial with no pictures etc. I'm at an absolute loss if you can help. Thank you!
1.The molecular formula of glucose is C6H12O6
Empirical formula is a representation of a molecular formula in
which the combining elements are written in the simple whole number
ratio.
so,the empirical formula of glucose is CH2O.
The Configuration of Glucose
The four chiral centers in glucose indicate there may be as many as
sixteen (24) stereoisomers having this constitution.
These would exist as eight diastereomeric pairs of enantiomers, and
the initial challenge was to determine which of the eight
corresponded to glucose. This challenge was accepted and met in
1891 by the German chemist Emil Fischer. His successful negotiation
of the stereochemical maze presented by the aldohexoses was a
logical tour de force, and it is fitting that he received the 1902
Nobel Prize for chemistry for this accomplishment. One of the first
tasks faced by Fischer was to devise a method of representing the
configuration of each chiral center in an unambiguous manner. To
this end, he invented a simple technique for drawing chains of
chiral centers, that we now call theFischer projection formula.
Click on this link for a review.
At the time Fischer undertook the glucose project it was not
possible to establish the absolute configuration
of an enantiomer. Consequently, Fischer made an arbitrary choice
for (+)-glucose and established a network of related aldose
configurations that he called the D-family. The
mirror images of these configurations were then designated the
L-family of aldoses. To illustrate using present
day knowledge, Fischer projection formulas and names for the
D-aldose family (three to six-carbon atoms) are shown below, with
the asymmetric carbon atoms (chiral centers) colored red. The last
chiral center in an aldose chain (farthest from the aldehyde group)
was chosen by Fischer as the D / L designator site. If the hydroxyl
group in the projection formula pointed to the right, it was
defined as a member of the D-family. A left directed hydroxyl group
(the mirror image) then represented the L-family. Fischer's initial
assignment of the D-configuration had a 50:50 chance of being
right, but all his subsequent conclusions concerning the relative
configurations of various aldoses were soundly based. In 1951 x-ray
fluorescence studies of (+)-tartaric acid, carried out in the
Netherlands by Johannes Martin Bijvoet (pronounced "buy foot"),
proved that Fischer's choice was correct.
It is important to recognize that the sign of a compound's specific
rotation (an experimental number) does not correlate with its
configuration (D or L). It is a simple matter to measure an optical
rotation with a polarimeter. Determining an absolute configuration
usually requires chemical interconversion with known compounds by
stereospecific reaction paths.