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Encyclopedia Britannica

C6H12O6

This article appears in Volume V25, Page 892 of the Encyclopedia Britannica.

Encyclopedia Britannica - Main :: BUN-CAL

C6H12O6 =2C2H60+2CO2.
These enzymes have an extremely specific action, producing, for instance, the

change

CHANGE (derived through the Fr. from the Late Lat. cambium, cambiare, to barter; the ultimate derivation is probably from the root which appears in the Gr. 冠 urmu', to bend)

ordinary

ORDINARY (med. Lat. ordinarius, Fr. ordinaire)

natural

glucose

GLUCOSE (from Gr. - twais, sweet)

, but not at all in its artificial antipode, and so they are often valuable means of isolating an antipode from the inactive mixtures or racemic compounds; this method has indeed been used for the isolation of the

glucose

GLUCOSE (from Gr. - twais, sweet)

-antipode from the artificial racemic form. The fundamental fact here is due once more to Pasteur, but Emil Fischer added that sugars are acted upon by zymase in an analogous way if their configuration shows a certain amount of identity. For example yeast acts on
d-Glucose d-Mannose d-Fructose
HCO HCO H2COH
HCOH HOCIIH CO
HOH HOH HOCH
HCOH HCOH HOH
HCOH HCOH HCOH
H2OH H2COH I-I2COH,
and we observe that the three formulae agree indeed in the lower four-carbon chain. This particular behaviour led Fischer to the expression that the enzyme-action on given substances needs a corresponding feature as " lock and key." There are indications that in the synthesis by enzymes, of which examples have been realized in fats, sugars, glucosides and albuminoids, an analogous behaviour prevails.
6. Mutual Transformation of

Antipodes

ANTIPODES (Gr. avri, opposed to, and 7r6 es, feet)

.Thus far we have
supposed the molecule to be stable with atoms in fixed places, as may be the case at absolute zero; in reality, at

ordinary

ORDINARY (med. Lat. ordinarius, Fr. ordinaire)

temperatures, atoms probably are endowed with

movement

MOVEMENT

, and this may be supposed to take place along the fixed places just mentioned as centres, which

movement

MOVEMENT

can go so far as to lead to total trans-formation, the one stereo-isomer changing over into the other. These cases may be considered now.
As a general

rule

RULE

the liquid, gaseous or dissolved antipode is it itself unstable, tending to be transformed into inactive complexes Temperature may accelerate this, and, as a

rule

RULE

, sufficient heat will. produce the loss of optical activity, half of the

original

ORIGINAL

compound: having changed over into its optical antipode. This transformation has been often used for preparing the latter, as was first done by Le Bel with the optically active amyl alcohol, HC(CH3)(

C2H6

C2H6

)(CH2OH), rendering it inactive by sufficient

heating

HEATING

, and separating from the obtained complex the stereo-isomer. Walden found that in some cases analogous transformations take place at ordinary temperature, as for instance with d-phenylbromacetic acid, which within three years totally lost its considerable rotative power; this transformation has been termed " autoracemization." It explains that till now the most simple compounds with asymmetric carbon have not yet been obtained in

antipodes

ANTIPODES (Gr. avri, opposed to, and 7r6 es, feet)

; active CHCIBrF might be obtained by treating chlorobromofiuoracetic acid with potash, but autoracemization, which especially shows itself when halogens are linked to the asymmetric carbon, might, without

special

SPECIAL

precautions, lead to an inactive mixture of antipodes.
When two asymmetric carbons are present, four stereo-isomers are possible, which may be represented by:
(i) A-I-B, (2) (A+B), (3) AB, (4) (AB),
(I) and (2), as well as (3) and (4), being antipodes. The stable form will be in this case also the inactive mixture, corresponding in the solid state either to (I), (2) or (3), (4). In the last case, suppose the primitive compound is (I), the first step towards stability may be the production of (3), so that practically
one stereo-isomer changes over into another Ito of a different type. Such has, for instance, been proved by Bechmann for 1-menthol,
HCC3H7

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