Monosaccharides containg an aldehyde group are called aldoses while those containing a keto group are called ketoses. The aldehyde group is usually present at C_1 while the keto group is usually present at C_2. All monosaccharides containing five ans six carbon atoms have cyclic structures , furanose (five membered) and pyranose (six membered). During ring formation. C_1 in aldoses and C_2 in ketoses becomes chiral and hence all these monosaccharides exist in two steroismeric forms called the alpha-anomer and the beta-anomer while C_1 and C_2 are called glycosidic or anomeric carbon atoms. In contrast, steroisomers , which differ in configuration at any other chiral carbon other than the glycosidic carbon are called epimers. Two molecules of the same or different monosaccharides combine together through glycosidic linkage to form dissacharides. All monosaccharides (aldoses and ketoses) and disacchardies expect sucrose reduce Tollens' reagent and Fehling's solution , undergo mutarotation and form osazones. Two forms of D-glucopyranose are called