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1、TextACarbohydratesManycarbohydrates(碳水化合物)canbeexpressedintheform[Cx(H20)y],butthisisnotanaccuratedescriptionoftheirstructure.Carbohydratesareinfactpolyhydroxy(多疑棊)aldehydes(醛)orketones(酮)andthetermalsoincludesanycompoundsthatcanbehydrolyzedtoformcarbohydrates.Thesimplestcarbohydratesarecalled
2、sugars(ormonosaccharides(单糖))andthesemaylinktogethertoformmorecomplexcarbohydrates,starches(orpolysaccharides(多糊))・Thediversityofdietarycarbohydratesnecessitatesdiscussionofseveralclassesofthesemolecules,rangingfromsimplesugarstohuge,branchedpolymers.1.MonosaccharidesMonosaccharidesorsimplesug
3、arsareeitherhexoses(6-carbon)(六碳糖)likeglucose(葡萄糖),galactose(半乳糖)andfructose(果糖),orpentoses(5-carbon)(五碳糖)likeribose(核糖)・Thesearethebreakdownproductsofmorecomplexcarbohydratesandcanbeefficientlyabsorbedacrossthewallofthedigestivetube(消彳匕道)andtransportedintoblood・Simplesugarsaremonosaccharides.
4、Thesearecharacterisedbyhydroxyl(疑基),aldehydeandketonegroups(功能团).Monosaccharidesareeitheraldoses(醛糖)orketoses(酮糖).Thealdo-andketo-prefix(前缀)identifiesthenatureofthecarbonyl(碳棊,碳酰)group,andthe-osesuffix(后缀)designatesacarbohydrate・InFischerprojections(费歇尔投影式),ifthehydroxylgroupattheloweststereog
5、eniccentre(手相中心),C5inthiscase,pointstotheright,itmaybelabelledaD-sugar,ifitpointstotheleft,itisanL-sugar.Thenumberofcarbonatomsisalsoindicated,soforexample,aldohexoseisthesix-carbonaldehydesugar,moreconunonlyreferredtoasglucose・Intramolecular(分子内),nucleophilicaddition(亲核加成)cantakeplacebetweena
6、hydroxylandacarbonylgroupofthesamemolecule,resultinginthefc)nnationofacyclichemiacetal(半写g醛)•Simplemonosaccharidesconsistofaldehydeorketonegroupsandbothprimaryandsecondaryhydroxylgroups,allofwhichareavailableforreaction.Analkaline(碱的,强碱的)solutionofcopper(铜)(Fehling'ssolution(斐林试剂))oxidises(氧化)
7、analdosetoanaldonate(醛糖蛊h),andisitselfreducedtocopper,precipitating(沉淀)asredCu2O.Hydrogenation(红化作用)offructose,andcarbohydratesingeneral,involvesadditionofhydrogen(氢)tothedoublebond(双键)ofthecarbonylgroup.Theresultingproductshavean-itols