Disaccharides the Monosaccharides Are Linked by Glycosidic Bonds

Aldehydes can add H20 to form hydrates or can add alcohols to form hemiacetals and acetals. 

Different forms of glucose that result from dissolving glucose in water. At 25°C in water, glucose reaches an equilibrium containing about 0.02% free aldehyde, 38% a-pyranose form ([ce] D= 113), 62% /3-pyranose form ([ajD=9), and less than 0.5% of the furanose forms. The anomeric carbon is shown in color. 

Comparison of the Fischer (a) and Haworth (b) projections for a- and /3-D-glucose. The Haworth projection is a step closer to reality. Chair configurations for the two anomers of D-glucose are the most accurate depiction (c) but they are not always used because of the difficulty in drawing. Note that the largest substituent, —CH2OH, is in an equatorial location in both structures. The differences between the two anomers are shown in color. 

Formation of methyl glucosides. Glucosides (or glycosides) are quite stable in alkali, but they hydrolyze readily in dilute acid. 

Four commonly occurring disaccharides. The configuration about the hemiacetal group has not been specified for lactose, maltose, or cellobiose because both anomers exist in equilibrium. 

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