同分异构2.doc

第三章 有机化合物的构造、构型和构象构造、构型和构象的概念及关系描述分子的结构(structure)是指分子中各原子间是如何相互结合的，即包括分子中原子相互连接的顺序和方式，又指分子中各原子和基团在空间的相对位子即几何形象。分子的几何形象对于分子的化学及物理性质的影响，有时是非常惊人的，如碳原子本身，可以彼此结合形成不同的同素异形体，如无定型碳、石墨、金刚石和近来发现的足球烯，由于具有不同的几何形象，因此具有完全不同的性质，外观分别为黑色粉末至块状、暗灰色片状、无色透明和黄色的晶体。有机化合物分子中只有少数简单的分子具有二维形象，而大多数有机分子都具有三维形象，如饱和碳SP3杂化为正四面体结构。分子几何形象的细微差别对自然界及生命现象都起着难以估计的影响。绝大多数的生命及生理化学过程，是受分子几何形象控制的，因此它不仅是有机化学而且是许多其它相关科学的研究对象。有机化合物的构型和构象就是描述分子的形象的，是指分子中各原子和基团在空间的相对位置。因此描述分子的结构通常分为三个层次：构造(constitution)、构型(configuration)和构象(conformation)。Constitution-构成和构造Configuration-构造、外形和轮廓Conformation-构造和形态 构造异构同分异构 顺反异构（几何异构） 构型异构 立体异构 光学异构构象异构构造是分子中原子相互连接的顺序和方式。构造异构是指分子式相同，分子中原子相互连接的顺序和方式不同。构型和构象是分子中各原子和基团在空间的相对位子，是分子结构体现的一种表现现象，即分子的形象。构型和构象异构统称为立体异构。是分子的构型相同，而分子中各原子和基团在空间的相对位子不同。一个分子由于单键的旋转而使分子呈现的立体形象称为构象。一个分子，只要它有可自由旋转的单键，就有无数个不同的构象存在。由于单键旋转需要的能量很低，构象异构体很难分离。构型是指各原子在空间的排列次序。构型异构体包括顺反异构和光学异构。 构造、构型和构象的关系单键旋转，使分子的构象改变了，但是原子间的排列次序并没有改变，所以构型没有改变。构型和构象异构体写成平面式，都是构造相同一、构造异构1 构造异构体分四种情况：碳链异构，官能团异构， 官能团位置异构，互变异构。官能团异构如：环烷烃和烯烃；炔烃和二烯烃、环烯烃；醇和醚；醛和酮及烯醇；羧酸和酯。互变异构是指在室温下，不同官能团异构体处于动态平衡之中，能很快的相互转变，是一种特殊的官能团异构。如酮与烯醇：又如对亚硝基苯酚与对苯：2书写构造异构体的方法：按主链碳原子数减少的顺序先写碳架异构；再写官能团位子不同的异构体；再写不同官能团的异构体。举例1：分子式为C6H12己烯的同分异构体（只写出带有双键的异构体）按主链碳原子数减少的顺序先写碳架异构： 再加进C=C双键官能团的位置异构：举例2：写出分子式C4H8O2羧酸的同分异构体二、顺反异构1顺反异构产生条件（1）分子中存在不能自由旋转的键或环平面；（2）双键两个碳原子上必须是不同的原子或基团，环上必须有两个或两个以上带有不同取代基或原子的碳。2顺反异构体的标记方法（1）顺反标记法如果两个相同的原子或基团在双键平面或环平面的同侧称为顺式，在不同侧为反式。如：顺-2-戊烯 反-2-戊烯（2）Z/E标记法按照原子或基团的大小次序规则，优先的两个原子或基团位于双键或环面同侧者为Z式，反之为E式。如： E-4-甲基-3-庚烯 E-4-甲基环己基甲酸PheromonesInsects emit compounds called pheromones to transmit messages to each other. These compounds are remarkably species-specific; that is, each insect is sensitive only to the pheromones of its own species. one of the main uses for these compounds is as sex attractants. Normally, the female emits the pheromone and the male is attracted by its scent. Only a very small quantity is necessary, in some cases as little as 10-12g.Pheromones are often very simple compounds, though usually with long chains. Two examples are 9-tricosene,the sex attractant of the common housefly, and bombykol, secreted by the female silkworm month:The 9-tricosene secreted by the female housefly is the cis isomer. The trans isomer does not attract male houseflies and is not secreted by the female. Similarly, the bombykol of the silkworm moth is the trans-cis compound, and none of the three other stereo isomers work, (this is a general rule in nature: in most cases where more than one stereo isomer is possible, nature uses only one.The discovery of pheromones has given us a possible way to control harmful insects without polluting the environment(as happens with chlorinated insecticides) a small quantity of a synthetic pheromone can be used to lure male insects into a trap, where they can be killed. Without males, the females cannot propagate. Some of this has already been done-for example, with Japanese beetles-and it is likely that its use will increase.Cis-Trans Isomerism in VisionThe retina, the light-detector layer in the back of our eyes, contains colored compounds called visual pigments. They are insoluble in water and can be extracted from the retina with aqueous detergents. in the dark these pigments are reddish, but the color fades upon exposure to light.The rhodopsin molecules contain a protein called opsin plus a derivative of vitamin. A called 11-cis retinal:11-cis retinal all-trans-retinalIn the dark, 11-cis-retinal is stable and fits nicely into the folds of the surrounding opsin. When light hits the rhodopsin, the 11-cis-retinal becomes all-trans-retinal and no longer fits into the cavity of opsin. The opsin and the all-trans-retinal separate. The change in rhodopsin conformation is eventually transmitted to the nerve cells and then the brain. The stereo isomerism of retinal is thus an important part of the vision process.Note that only one of the five double bonds is affected in this transformation, but when this one changes from cis to trans, the sha