不同葡萄糖的結(jié)構(gòu)式及特性的解答
來源：http://la-lin.cn 日期：2019-06-04 發(fā)布人：admin
結(jié)晶葡萄糖有兩種，一種是從乙醇中結(jié)晶出來的，熔點146℃。它的新配溶液的[α]D為+112°，此溶液在放置過程中，比旋光度逐步降落，到達+52.17°以后維持不變；另一種是從吡啶中結(jié)晶出來的，熔點150℃，新配溶液的[α]D為+18.7°，此溶液在放置過程中，比旋光度逐步上升，也到達+52.7°以后維持不變。糖在溶液中，比旋光度自行轉(zhuǎn)變?yōu)槎ㄖ档默F(xiàn)象稱為變旋現(xiàn)象。顯然葡萄糖的開鏈構(gòu)造不能解釋此現(xiàn)象。
There are two kinds of crystalline glucose, one is crystallized from ethanol, the melting point is 146 C. The [alpha] D of its new solution is + 112 degrees. The specific rotation of this solution decreases gradually in the process of placement and remains unchanged after reaching + 52.17 degrees. The other is crystallized from pyridine, the melting point is 150 degrees, and the [alpha] D of the new solution is + 18.7 degrees. During placement, the specific rotation of this solution increases gradually and remains unchanged after reaching + 52.7 degrees. The phenomenon that the specific rotation of sugar changes itself into a fixed value in solution is called the rotation phenomenon. Obviously, the open-chain structure of glucose can not explain this phenomenon.
從葡萄糖的開鏈構(gòu)造可見，它既具有醛基，也有醇羥基，因而在分子內(nèi)部能夠構(gòu)成環(huán)狀的半縮醛。
From the open-chain structure of glucose, we can see that it has both aldehyde group and alcohol hydroxyl group, so it can form a cyclic semiacetal inside the molecule.
成環(huán)時，葡萄糖的羰基與C-5上的羥基經(jīng)加成反響構(gòu)成穩(wěn)定的六元環(huán)。葡萄糖分子固然具有醛基，但在反響性能上與普通的醛有許多差別，例如對NaHSO3的加成十分遲緩，其緣由是在溶液中，葡萄糖簡直以環(huán)狀的半縮醛構(gòu)造存在的緣故。
The carbonyl group of glucose and the hydroxyl group of C-5 react by addition to form a stable six-membered ring. Glucose molecule has aldehyde group, but there are many differences in reactivity with ordinary aldehydes. For example, the addition of NaHSO3 is very slow. The reason is that in solution, glucose exists almost in the form of cyclic semiacetals.
成環(huán)后，使原來的羰基碳原子（C-1）變成了手性碳原子，C-1上新構(gòu)成的半縮醛羥基在空間的排布方式有兩種可能。半縮醛羥基與決議單糖構(gòu)型的羥基（C-5上的羥基）在碳鏈同側(cè)的叫做α型，在異側(cè)的稱為β型。α型和β型是非對映異構(gòu)體。它們的不同點是C-1上的構(gòu)型，因而又稱為異頭物（端基異構(gòu)體）。它們的熔點和比旋光度都不同。
After cyclization, the original carbonyl carbon atom (C-1) is transformed into chiral carbon atom. There are two possibilities for the spatial arrangement of the newly formed semi-acetal hydroxyl groups on C-1. The hydroxyl groups of hemiacetal and monosaccharide (the hydroxyl groups on C-5) are called alpha on the same side of the carbon chain and beta on the opposite side. Types alpha and beta are non-enantiomers. The difference between them is the configuration of C-1, so they are also called heteropoly (terminal isomer). Their melting point and specific rotation are different.
葡萄糖的變旋現(xiàn)象，就是由于開鏈構(gòu)造與環(huán)狀構(gòu)造構(gòu)成均衡體系過程中的比旋光度變化所惹起的。在溶液中α-D-葡萄糖可轉(zhuǎn)變?yōu)殚_鏈式構(gòu)造，再由開鏈構(gòu)造轉(zhuǎn)變?yōu)?beta;-D-葡萄糖；同樣β-D-葡萄糖也變轉(zhuǎn)變?yōu)殚_鏈式構(gòu)造，再轉(zhuǎn)變?yōu)?alpha;-D-葡萄糖。經(jīng)過一段時間后，三種異構(gòu)體到達均衡，構(gòu)成一個互變異構(gòu)均衡體系，其比旋光度亦不再改動。
The variation of specific rotation of glucose is caused by the change of specific rotation in the equilibrium system formed by open-chain structure and ring structure. In solution, alpha-D-glucose can be converted to open-chain structure, and then from open-chain structure to beta-D-glucose. Similarly, beta-D-glucose can also be converted to open-chain structure and then to alpha-D-glucose. After a period of time, the three isomers reach equilibrium, forming a tautomeric equilibrium system, and the specific rotation does not change.
不只葡萄有變旋現(xiàn)象，凡能構(gòu)成環(huán)狀構(gòu)造的單糖，都會產(chǎn)生變旋現(xiàn)象。
It is not only the grape that has the phenomenon of rotation, but also the monosaccharide that can form the ring structure.