{"id":1815,"date":"2018-03-21T15:57:01","date_gmt":"2018-03-21T15:57:01","guid":{"rendered":"https:\/\/courses.lumenlearning.com\/suny-orgbiochemistry\/chapter\/properties-of-monosaccharides\/"},"modified":"2018-11-15T21:05:21","modified_gmt":"2018-11-15T21:05:21","slug":"properties-of-monosaccharides","status":"publish","type":"chapter","link":"https:\/\/courses.lumenlearning.com\/suny-monroecc-orgbiochemistry\/chapter\/properties-of-monosaccharides\/","title":{"raw":"16.5 Properties of Monosaccharides","rendered":"16.5 Properties of Monosaccharides"},"content":{"raw":"
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Learning Objectives<\/h3>\r\n
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  1. Identify the physical and chemical properties of monosaccharides.<\/li>\r\n<\/ol>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n
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    Monosaccharides such as glucose and fructose are crystalline solids at room temperature, but they are quite soluble in water, each molecule having several OH groups that readily engage in hydrogen bonding. The chemical behavior of these monosaccharides is likewise determined by their functional groups.<\/p>\r\n

    An important reaction of monosaccharides is the oxidation of the aldehyde group, one of the most easily oxidized organic functional groups. Aldehyde oxidation can be accomplished with any mild oxidizing agent, such as Tollens\u2019 reagent or Benedict\u2019s reagent. (For more information about aldehyde oxidation, see Chapter 14 \"Organic Compounds of Oxygen\"<\/a>, Section 14.5 \"Reactions of Alcohols\"<\/a>.) With the latter, complexed copper(II) ions are reduced to copper(I) ions that form a brick-red precipitate [copper(I) oxide; Figure 16.7 \"Benedict\u2019s Test\"<\/a>].\u00a0 (<\/p>\r\n

    Note that the equations below are not balanced because the actual Tollens' and Benedict's reagents and reactions are more complex than shown.<\/p>\r\n\r\n

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    Any carbohydrate capable of reducing either Tollens\u2019 or Benedict\u2019s reagents without first undergoing hydrolysis is said to be a reducing sugar<\/span><\/strong><\/span>. Because both the Tollens\u2019 and Benedict\u2019s reagents are basic solutions, ketoses (such as fructose) also give positive tests due to an equilibrium that exists between ketoses and aldoses in a reaction known as tautomerism<\/em>.<\/p>\r\n\r\n

    \r\n\r\n[caption id=\"\" align=\"aligncenter\" width=\"448\"]\"image\" Figure 16.7 Benedict\u2019s Test. <\/em>Benedict\u2019s test was performed on three carbohydrates, depicted from left to right: fructose, glucose, and sucrose. The solution containing sucrose remains blue because sucrose is a nonreducing sugar.[\/caption]\r\n\r\n<\/div>\r\n

    These reactions have been used as simple and rapid diagnostic tests for the presence of glucose in blood or urine. For example, Clinitest tablets, which are used to test for sugar in the urine, contain copper(II) ions and are based on Benedict\u2019s test. A green color indicates very little sugar, whereas a brick-red color indicates sugar in excess of 2 g\/100 mL of urine.<\/p>\r\n\r\n

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    Concept Review Exercises<\/h3>\r\n
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      Why are monosaccharides soluble in water?<\/p>\r\n\r\n<\/div><\/li>\r\n \t

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      What is a reducing sugar?<\/p>\r\n\r\n<\/div><\/li>\r\n<\/ol>\r\n<\/div>\r\n

      \r\n\r\n[reveal-answer q=\"902843\"]Show Answer[\/reveal-answer]\r\n[hidden-answer a=\"902843\"]\r\n\r\n1. Monosaccharides are quite soluble in water because of the numerous OH groups that readily engage in hydrogen bonding with water.\r\n\r\n2. any carbohydrate capable of reducing a mild oxidizing agent, such as Tollens\u2019 or Benedict\u2019s reagents, without first undergoing hydrolysis[\/hidden-answer]\r\n
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      Key Takeaways<\/h3>\r\n