Polyhydroxy ketone

Carbohydrates may be divided into monosaccharides, disaccharides and polysaccharides. The monosaccharides under certain conditions react as polyhydroxy-aldehydes or polyhydroxy-ketones two important representatives are glucose CjHjjO (an aldose) and fructose (laevulose) CgHuO, (a ketose). Upon hydrolysis di- and polysaccharides 3deld ultimately monosaccharides. Common disaccharides are sucrose, lactose and maltose (all of molecular formula C,2H2. 0,), whilst starch, dextrin and cellulose, (CjHjoOj), in which n > 4, are typical polysaccharides. 

Historically carbohydrates were once considered to be hydrates of carbon because their molecular formulas m many (but not all) cases correspond to C (H20) j It IS more realistic to define a carbohydrate as a polyhydroxy aldehyde or polyhydroxy ketone a point of view closer to structural reality and more suggestive of chemical reactivity... 

Over 200 different monosaccharides are known They can be grouped according to the number of carbon atoms they contain and whether they are polyhydroxy aide hydes or polyhydroxy ketones Monosaccharides that are polyhydroxy aldehydes are called aldoses, those that are polyhydroxy ketones are ketoses Aldoses and ketoses are further classified according to the number of carbon atoms m the mam chain Table 25 1 lists the terms applied to monosaccharides having four to eight carbon atoms... 

From the organochemical point of view, carbohydrates/polysaccharides are more or less substituted polyhydroxy aldehydes (e.g., glucose—>glucans) or polyhydroxy ketons (e.g., fructose-n fructans). From the physicochemical point of view, an enormous heterogeneity also exists in... 

Parent monosaccharides are polyhydroxy aldehydes H-[CHOH] -CHO or polyhydroxy ketones H-[CHOH]n-CO-[CHOH]m-H with three or more carbon atoms. 

Carbohydrates are the most abundant organic component of plants. Structurally, carbohydrates are usually polyhydroxy aldehydes or polyhydroxy ketones (or compounds that hydrolyze to yield polyhydroxy aldehydes and ketones). Since carbohydrates contain carbonyl groups and hydroxyl groups, they exist primarily as acetals or hemiacetals. 

A simple reaction that was studied by Wilhelmy, and since then by various investigators, is the transformation (hydrolysis) of sucrose in water solution into glucose (CsHiyO. a polyhvdroxy aldehyde) plus fructose (C(,H,cO,. a polyhydroxy ketone), which proceeds at a measurable, steady rate in the presence of acid (hydrogen ion). The rate of reaction at any instant is found to be proportional to the amount of sucrose present at that instant. 

The basic carbohydrate molecules are simple sugars, or monosaccharides, which are polyhydroxy aldehyde, polyhydroxy ketone, and their derivatives. All simple monosaccharides have the general empirical formula, (CH20)n, where n is the whole number ranging 3 to 8. 

The simplest carbohydrates are the monosaccharides which under specified conditions are structurally characterised as polyhydroxy aldehydes or polyhydroxy ketones these are termed aldoses and ketoses respectively. Aldoses and ketoses are sub-classified, according to the number of carbons present in each molecule, into aldotetroses, aldopentoses, aldohexoses, etc., or ketotetroses, ketopentoses, etc. 

Carbohydrates are polyhydroxy aldehydes or polyhydroxy ketones, or substances that give such compounds on hydrolysis. They are classified as monosaccharides, oligosaccharides, and polysaccharides. 

Monosaccharides, or simple sugars, are carbohydrates that cannot be hydrolyzed to simpler compounds. Figure 23-1 shows Fischer projections of the monosaccharides glucose and fructose. Glucose is a polyhydroxyaldehyde, and fructose is a polyhydroxy ketone. Polyhydroxyaldehydes are called aldoses (aid- is for aldehyde and -ose is the suffix for a sugar), and polyhydroxyketones are called ketoses (ket- for ketone, and -ose for sugar). 

Most important carbohydrates, such as starch and cellulose, are polymers composed of monomers called monosaccharides, or simple sugars. The monosaccharides are polyhydroxy ketones and aldehydes. The most important contain five carbon atoms (pentoses) or six carbon atoms (hexoses). One important hexose is fructose, a sugar found in honey and fruit. Its structure is... 

Monoprotic acid an acid with one acidic proton. (7.2) Monosaccharide (simple sugar) a polyhydroxy ketone or aldehyde containing from three to nine carbon atoms. (22.6) Myoglobin an oxygen-storing biomolecule consisting of a heme complex and a protein. (20.8)... 

Ketose (Section 27.2) A monosaccharide comprised of a polyhydroxy ketone. 

Historically, carbohydrates were thought to be hydrates of carbon on the basis of their molecular formulas Cn(H20)m- More realistically, carbohydrates are now considered polyhydroxy aldehydes, polyhydroxy ketones, or substances that yield such compounds on acid hydrolysis. 

The term carbohydrate refers to a class of polyhydroxy aldehydes and polyhydroxy ketones with the general formula (CH O),. The name derives from the composition of the formula unit, that is, carbon plus water. All carbohydrates are composed of basic units called monosaccharides. Polymers containing two to six monosaccharides are called oligosaccharides those with more are called polysaccharides. Starch, cellulose, and glycogen are examples of polysaccharides. Monosaccharides and oligosaccharides are also called sugars. 

Carbohydrates are polyhydroxy aldehydes, polyhydroxy ketones, or compounds that can be hydrolyzed to them. A carbohydrate that cannot be hydrolyzed to simpler compounds is called a monosaccharide. A carbohydrate that can be hydrolyzed to two monosaccharide molecules is called a disaccharide. A carbohydrate that can be hydrolyzed to many monosaccharide molecules is called a polysaccharide. 

Historically, carbohydrates were defined as substances with the empirical formula Cn(H20)ni. The common sugars such as glucose and fructose (n = m = 6), or sucrose (n=12, m=ll) fit this formula, but nowadays the convention is to regard as a carbohydrate a polyhydroxyaldehyde or polyhydroxy ketone with the classical formula, a molecule closely related to it, or oligomers or polymers of such molecules. Their study evolved as a separate sub-discipline within organic chemistry for practical reasons - they are water-soluble and difficult to crystallise - so that their manipulation demanded different sets of skills from classical natural products such as terpenes, steroids, alkaloids, etc. 

Carbohydrates Polyhydroxyaldehydes or polyhydroxy ketones or substances that yield these by hydrolysis. They are obtained from plants or animals. 

Early chemists noted that carbohydrates have molecular formulas that make them appear to be hydrates of carbon, C (H20) —whence the name. Eater structural studies revealed that these compounds were not hydrates because they did not contain intact water molecules, but the term carbohydrate persists. Carbohydrates are polyhydroxy aldehydes such as o-glucose, polyhydroxy ketones such as o-fmctose, and compounds such as sucrose that can be hydrolyzed to polyhydroxy aldehydes or... 

A monosaccharide can be a polyhydroxy aldehyde such as D-glucose or a polyhydroxy ketone such as o-liructose. Polyhydroxy aldehydes are called aldoses ( aid is for aldehyde ose is the suffix for a sugar), whereas polyhydroxy ketones are called ketoses. Monosaccharides are also classified according to the number of carbons they contain Monosaccharides with three carbons are trioses, those with four carbons are tetroses, those with five carbons are pentoses, and those with six and seven carbons are hexoses and heptoses, respectively. A six-carbon polyhydroxy aldehyde such as o-glucose is an aldo-hexose, whereas a six-carbon polyhydroxy ketone such as o-fructose is a ketohexose. 

Monosaccharides are most commonly five-carbon and six-carbon polyhydroxy ketones and aldehydes... 

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