《有机化学》课件第18章 碳水化合物[精品].pptVIP

* 蔗糖的水解 D-葡萄糖 [?]D=+52.6o D-果糖[?]D= –92o 蔗糖[?]D=+66.5o(转化糖) C12H22O11 + H2O C6H12O6 C6H12O6 + H+ 转化反应 (1:1混合物[?]D= –22o) Sucrose, or ordinary table sugar, is probably the most abundant pure organic chemical in the world. Whether from sugar cane (20% by weight) or from sugar beets (15% by weight), and whether raw or refined, all table sugar is sucrsoe. Fundamentals of Organic Chemistry John McMurry * Sucrose—John McMurry Sucrose is a disaccharide that yields 1 equivalent of glucose and 1 equivalent of fructose on hydrolysis. This 1:1 mixture of glucose and fructose is often referred to as invert sugar because the sign of optical rotation changes (inverts) during the hydrolysis from sucrose, [?]D=+66.5o, to a glucose/fructose mixture, [?]D=?22o. Insects such as honeybees have enzymes called invertases that catalyze the hydrolysis of sucrose to glucose + fructose. Honey, in fact, is primarily a mixture of glucose, fructose, and sucrose. Fundamentals of Organic Chemistry John McMurry * 二糖－麦芽糖(Maltose) 4-O-(?-D-吡喃葡萄糖基)-?-D-吡喃葡萄糖苷 C12H22O11 还原糖 有变旋光现象 能生成脎 分子中有苷羟基 苷羟基 * 二糖－纤维二糖(Cellobiose) 还原糖 有变旋光现象 能生成脎 分子中有苷羟基 4-O-(?-D-吡喃葡萄糖基)-?-D-吡喃葡萄糖苷 苷羟基 * 多糖－直链淀粉(Amylose) 1,4-O-(?-D-glucopyranoside)polymer 直链淀粉约占淀粉总含量的20％ 1,4-苷键 1,4-苷键 1 4 * 支链淀粉约占淀粉总含量的80％。平均每25个葡萄糖基就有一个支链 ?-1,4-苷键 ?-1,6-苷键 多糖－支链淀粉(Amylopectin) * Starch—John McMurry Nature uses starch as the medium by which plants store energy for later use; potatoes, corn, and cereal grains all contain large amounts of starch. When eaten, starch is digested in the mouth and stomach by enzymes called glycosidases(消化酶), which catalyze the hydrolysis of glycoside bonds and release individual molecules of glucose. Like most enzymes, glycosidases are highly selective in their action. They hydrolyze only the ?-glycoside links in starch and leave the ?-glycoside links in cellulose untouched. Thus, humans can eat potatoes and grains but not grass. Fundamentals of Organic Chemistry John McMurry * 多糖－糖原(Glycogen) Glycogen is a p