Dare

See also: Ose (homonymy)

The ose S (or monosaccharides) are the Monomère S of the Glucide S. They are not hydrolysables. Just like the Disaccharide S, they have a capacity sweetening, and are water soluble. One distinguishes them by the length from their chain from carbon, as follows:

Physical properties

Some have a sweetened pleasant savor. However it is false to generalize this property: the starch for example, does not have any sweetening capacity. Contrary, others made up not being oses, the such Glycine or the Aspartic acid (whose drift the Aspartame, well-known of the people supervising their line) for example, have a sweetened savor. The oses are in addition of color blanchâtre and easily crystallizable.

Structure

Empirical formula

Cn (H2O) n where N is an integer representing the number of carbons (from 3 to 7 for the natural oses) FOR MANY OSES. This property should not be generalized! For example, the acetic Acid , which is not to in no case an ose has the empirical formula CH3COOH is C2 (H2O) 2. In addition, of derived from ose, as the Glucosamine (which has other atoms that the Carbone, the Hydrogène and the Oxygène; in fact, the Azote) do not present stated property Ci above valid for many oses.

Acyclic structure

An ose with N carbons is composed of a not ramified carbonaceous chain, from 3 to 7 carbons, comprising only simple connections. All carbons carry a function alcohol (OH) except one which carries a function Carbonyle.

That thus determines two categories of oses:

  • if the function carbonyl is a function Aldéhyde, it is on the first carbon and it is about an aldose (for example glucose).
  • if the function carbonyl is a function Cétone, it is on the second carbon, and it is about a ketose (for example fructose).

All the oses have a rotatory Pouvoir because of presence of at least a asymmetrical Carbone: the oses are known as chiral.

Two enantiomer S (antipodes optical) only have same the properties except for one: their optical Activity opposite. Figure 1 accounts for both enantiomer S of the Glucose, the form D-glucose is the natural form.

  • In the form D , the grouping alcohol (- OH) carried by carbon n-1 is with right (of representation of Fischer);
  • In the form L , the grouping alcohol (- OH) carried by carbon n-1 is with left (of representation of Fischer).

Cyclic structure

The representation of Haworth is often used for their cyclic forms.

There is hemiacetalisation between the function carbonyl and a OH, since they are distant of at least 3 carbons. (Ex: between carbon 1 and 5 of glucose or between carbon 2 and 5 of the fructose, or between carbon 1 and 4 of ribose). The OH born of cyclization is called OH Anomérique or Anomère. It gives place to a new asymmetrical carbon (carbon carrying the function carbonyl: n°1 in the case of an aldose or n°2 in the case of a ketose) and according to whether it is placed under or on the plan of the cycle it gives rise to two isomers alpha (α) or beta (β) (alpha meaning with the lower part; and beta with the top).

Once the folded up carbonaceous chain, the proximity of the double connection of the function aldehyde (or ketone if it were acts of a ketose) allows, because of its brittleness, the rupture of the connection  and connection OH of the function alcohol (here of C n°5), allowing the establishment of a new connection C n°1 and O of the old function alcohol of C n°5, thus closing a cycle.

Cycle in furan form

The oses cyclisant itself in furan form (Furan) are:

(in the following image, the anomeries are: on the left is the form α fructofuranose and on the right is the form β fructofuranose)

Cycle in pyranic form

The oses cyclisant itself in pyranic form (Pyran) are:

Nomenclature

They can be presented in crystalline form. Monosaccharides are of two types:

  • If the function carbonyl of monosaccharide is a Aldéhyde it is a Aldose.

  • If this function is a Cétone, it is a Cétose (or cétulose).

Derivatives of oses

Polyalcohols

They are obtained by reduction of the function aldehyde out of alcohol, it is the case for example Glycérol.

Osamines

The function alcohol (- OH) in C2 is replaced by - NH2. One can also add a grouping acétyl to him

The désoxyoses or bone

They are created by hydrogen substitution to replace the Groupement hydroxyl, one can note the example of the Désoxyribose.

See too

  • Glucid S
  • Chiralité (chemistry)

External bonds

  • Nomenclature of sugars

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