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Pentose

 

 
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Pentose
 
 
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A pentose is a monosaccharide
Monosaccharide

Monosaccharides are the most basic unit of carbohydrates. They are the simplest form of sugar and are usually colorless, water-soluble, crystal solids....
 with five carbon
Carbon

Carbon is a chemical element with chemical symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalence?making four electrons available to form covalent bond chemical bonds....
 atom
Atom

|-! bgcolor=gray | Properties|-||}The atom is a basic unit of matter consisting of a dense, central atomic nucleus surrounded by a electron cloud of electric charge electrons....
s.

They either have an aldehyde
Aldehyde

An aldehyde is an organic compound containing a terminal carbonyl group. This functional group, which consists of a carbon atom bonded to a hydrogen atom and double bond to an oxygen atom , is called the aldehyde group....
 functional group
Functional group

In organic chemistry, functional groups are specific groups of atoms within molecules that are responsible for the characteristic chemical reactions of those molecules....
 in position 1 (aldopentoses), or a ketone
Ketone

In organic chemistry, a ketone is a type of organic compound which contains a carbonyl group bonded to two other carbon atoms in the form:Neither of the substituents R1 and R2 may be equal to hydrogen ....
  functional group in position 2 (ketopentoses).

The aldopentoses have three chiral centres ("asymmetric carbon atoms") and so 8 different stereoisomers are possible.

The 4 D-aldopentoses are:

CH=OCH=O CH=O CH=O | | | | HC-OH HO-CH HC-OH HO-CH | | | | HC-OH HC-OH HO-CHHO-CH | | | | HC-OH HC-OH HC-OHHC-OH | | | | CH2OH CH2OH CH2OHCH2OH D-Ribose
Ribose

Ribose, primarily occurring as D-ribose, is an organic compound that occurs widely in nature. It is an aldopentose, that is a monosaccharide containing five carbon atoms that, in its acyclic form, has an aldehyde functional group at one end....
  D-Arabinose
Arabinose

Arabinose is an aldopentose — a monosaccharide containing five carbon atoms, and including an aldehyde functional group. It has chemical formula Carbon5Hydrogen10Oxygen5 and a molar mass of 150.13 g/mol....
  D-Xylose
Xylose

Xylose, or wood sugar, is an aldopentose — a monosaccharide containing five carbon atoms and including an aldehyde functional group. It has chemical formula 5105....
  D-Lyxose
Lyxose

Lyxose is an aldopentose — a monosaccharide containing five carbon atoms, and including an aldehyde functional group. It has chemical formula 5105....


The ketopentoses have 2 chiral centres and therefore 4 possible stereoisomers — ribulose
Ribulose

Ribulose is a ketopentose — a monosaccharide containing five carbon atoms, and including a ketone functional group. It has chemical formula 5105....
 (L- and D-form) and xylulose
Xylulose

Xylulose is a ketopentose, a monosaccharide containing five carbon atoms, and including a ketone functional group. It has the chemical formula 5105....
 (L- and D-form).

The D-isomers of both are known to occur naturally as is the L-isomer of xylulose
Xylulose

Xylulose is a ketopentose, a monosaccharide containing five carbon atoms, and including a ketone functional group. It has the chemical formula 5105....
: CH2OHCH2OH | | C=O C=O | | HC-OH HO-CH | | HC-OHHC-OH | | CH2OHCH2OH D-Ribulose
Ribulose

Ribulose is a ketopentose — a monosaccharide containing five carbon atoms, and including a ketone functional group. It has chemical formula 5105....
  D-Xylulose
Xylulose

Xylulose is a ketopentose, a monosaccharide containing five carbon atoms, and including a ketone functional group. It has the chemical formula 5105....


The aldehyde and ketone functional groups in these carbohydrates react with neighbouring hydroxyl
Hydroxyl

Hydroxyl in chemistry stands for a molecule consisting of an oxygen atom and a hydrogen atom connected by a covalent bond. The neutral form is a hydroxyl Radical and the hydroxyl anion is called a hydroxide....
 functional groups to form intramolecular
Intramolecular

Intramolecular in chemistry describes a process or characteristic limited within the structure of a single molecule; a property or phenomenon limited to the extent of a single molecule....
 hemiacetal
Hemiacetal

Hemiacetals and hemiketals are compounds of the general formula R1R'1COR2, where R2 is not hydrogen....
s or hemiketals, respectively.






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Encyclopedia


A pentose is a monosaccharide
Monosaccharide

Monosaccharides are the most basic unit of carbohydrates. They are the simplest form of sugar and are usually colorless, water-soluble, crystal solids....
 with five carbon
Carbon

Carbon is a chemical element with chemical symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalence?making four electrons available to form covalent bond chemical bonds....
 atom
Atom

|-! bgcolor=gray | Properties|-||}The atom is a basic unit of matter consisting of a dense, central atomic nucleus surrounded by a electron cloud of electric charge electrons....
s.

They either have an aldehyde
Aldehyde

An aldehyde is an organic compound containing a terminal carbonyl group. This functional group, which consists of a carbon atom bonded to a hydrogen atom and double bond to an oxygen atom , is called the aldehyde group....
 functional group
Functional group

In organic chemistry, functional groups are specific groups of atoms within molecules that are responsible for the characteristic chemical reactions of those molecules....
 in position 1 (aldopentoses), or a ketone
Ketone

In organic chemistry, a ketone is a type of organic compound which contains a carbonyl group bonded to two other carbon atoms in the form:Neither of the substituents R1 and R2 may be equal to hydrogen ....
  functional group in position 2 (ketopentoses).

The aldopentoses have three chiral centres ("asymmetric carbon atoms") and so 8 different stereoisomers are possible.

The 4 D-aldopentoses are:

CH=OCH=O CH=O CH=O | | | | HC-OH HO-CH HC-OH HO-CH | | | | HC-OH HC-OH HO-CHHO-CH | | | | HC-OH HC-OH HC-OHHC-OH | | | | CH2OH CH2OH CH2OHCH2OH D-Ribose
Ribose

Ribose, primarily occurring as D-ribose, is an organic compound that occurs widely in nature. It is an aldopentose, that is a monosaccharide containing five carbon atoms that, in its acyclic form, has an aldehyde functional group at one end....
  D-Arabinose
Arabinose

Arabinose is an aldopentose — a monosaccharide containing five carbon atoms, and including an aldehyde functional group. It has chemical formula Carbon5Hydrogen10Oxygen5 and a molar mass of 150.13 g/mol....
  D-Xylose
Xylose

Xylose, or wood sugar, is an aldopentose — a monosaccharide containing five carbon atoms and including an aldehyde functional group. It has chemical formula 5105....
  D-Lyxose
Lyxose

Lyxose is an aldopentose — a monosaccharide containing five carbon atoms, and including an aldehyde functional group. It has chemical formula 5105....


The ketopentoses have 2 chiral centres and therefore 4 possible stereoisomers — ribulose
Ribulose

Ribulose is a ketopentose — a monosaccharide containing five carbon atoms, and including a ketone functional group. It has chemical formula 5105....
 (L- and D-form) and xylulose
Xylulose

Xylulose is a ketopentose, a monosaccharide containing five carbon atoms, and including a ketone functional group. It has the chemical formula 5105....
 (L- and D-form).

The D-isomers of both are known to occur naturally as is the L-isomer of xylulose
Xylulose

Xylulose is a ketopentose, a monosaccharide containing five carbon atoms, and including a ketone functional group. It has the chemical formula 5105....
: CH2OHCH2OH | | C=O C=O | | HC-OH HO-CH | | HC-OHHC-OH | | CH2OHCH2OH D-Ribulose
Ribulose

Ribulose is a ketopentose — a monosaccharide containing five carbon atoms, and including a ketone functional group. It has chemical formula 5105....
  D-Xylulose
Xylulose

Xylulose is a ketopentose, a monosaccharide containing five carbon atoms, and including a ketone functional group. It has the chemical formula 5105....


The aldehyde and ketone functional groups in these carbohydrates react with neighbouring hydroxyl
Hydroxyl

Hydroxyl in chemistry stands for a molecule consisting of an oxygen atom and a hydrogen atom connected by a covalent bond. The neutral form is a hydroxyl Radical and the hydroxyl anion is called a hydroxide....
 functional groups to form intramolecular
Intramolecular

Intramolecular in chemistry describes a process or characteristic limited within the structure of a single molecule; a property or phenomenon limited to the extent of a single molecule....
 hemiacetal
Hemiacetal

Hemiacetals and hemiketals are compounds of the general formula R1R'1COR2, where R2 is not hydrogen....
s or hemiketals, respectively. The resulting ring structure is related to furan
Furan

Furan, also known as furane and furfuran, is a Heterocyclic compound organic compound. It is typically derived by the thermal decomposition of pentose-containing materials, cellulosic solids especially pine-wood....
, and is termed a furanose
Furanose

A furanose is a simple sugar that contains a five-membered furan-based ring structure and is a sub-terminal ketone which gives it reducing power....
. The ring spontaneously opens and closes, allowing rotation to occur about the bond between the carbonyl group and the neighbouring carbon atom — yielding two distinct configurations (α and β). This process is termed mutarotation
Mutarotation

'Mutarotation is the term given to the change in the specific rotation of a cyclic monosaccharide as it reaches an equilibrium between its α and β anomeric forms....
.

Ribose
Ribose

Ribose, primarily occurring as D-ribose, is an organic compound that occurs widely in nature. It is an aldopentose, that is a monosaccharide containing five carbon atoms that, in its acyclic form, has an aldehyde functional group at one end....
 is a constituent of RNA
RNA

Ribonucleic acid is a type of molecule that consists of a long chain of nucleotide units. Each nucleotide consists of a nucleobase, a ribose sugar, and a phosphate....
, and the related deoxyribose
Deoxyribose

Deoxyribose, also known as D-Deoxyribose and 2-deoxyribose, is an aldopentose — a monosaccharide containing five carbon atoms, and including an aldehyde functional group in its linear structure....
 of DNA
DNA

Deoxyribonucleic acid is a nucleic acid that contains the genetics instructions used in the development and functioning of all known living organisms and some viruses....
.

A polymer
Polymer

A polymer is a large molecule composed of repeating structural units typically connected by covalent chemical bonds. While polymer in popular usage suggests plastic, the term actually refers to a large class of natural and synthetic materials with a variety of properties....
 composed of pentose sugars is called a pentosan.

See also


  • Triose
    Triose

    A triose is a monosaccharide containing three carbon atoms. There are only two trioses, an aldotriose and a ketotriose . Trioses are important in Cellular respiration....
  • Tetrose
    Tetrose

    A tetrose is a monosaccharide with 4 carbon atoms. They either have an aldehyde functional group in position 1 or a ketone functional group in position 2 ....
  • Hexose
    Hexose

    In organic chemistry, a hexose is a monosaccharide with six carbon atoms, having the chemical formula C6H12O6. Hexoses are classified by functional group, with aldohexoses having an aldehyde at position 1, and ketohexoses having a ketone at position 2....
  • Heptose
    Heptose

    A heptose is a monosaccharide with seven carbon atoms.They either have an aldehyde functional group in position 1 , or a ketone functional group in position 2 ....
  • Pentose phosphate pathway
    Pentose phosphate pathway

    The pentose phosphate pathway is a process that serves to generate NADPH and the synthesis of pentose sugars. There are two distinct phases in the pathway....
  • The aniline acetate test
    Aniline acetate test

    The aniline acetate test is a chemical test to identify the presence of certain carbohydrates. These carbohydrates may be converted to furfural, which reacts with aniline acetate to produce a bright pink color....
     for distinguishing pentoses from other carbohydrates