同分異構(gòu)2.doc

第三章 有機(jī)化合物的構(gòu)造、構(gòu)型和構(gòu)象構(gòu)造、構(gòu)型和構(gòu)象的概念及關(guān)系描述分子的結(jié)構(gòu)(structure)是指分子中各原子間是如何相互結(jié)合的，即包括分子中原子相互連接的順序和方式，又指分子中各原子和基團(tuán)在空間的相對(duì)位子即幾何形象。分子的幾何形象對(duì)于分子的化學(xué)及物理性質(zhì)的影響，有時(shí)是非常驚人的，如碳原子本身，可以彼此結(jié)合形成不同的同素異形體，如無(wú)定型碳、石墨、金剛石和近來(lái)發(fā)現(xiàn)的足球烯，由于具有不同的幾何形象，因此具有完全不同的性質(zhì)，外觀分別為黑色粉末至塊狀、暗灰色片狀、無(wú)色透明和黃色的晶體。有機(jī)化合物分子中只有少數(shù)簡(jiǎn)單的分子具有二維形象，而大多數(shù)有機(jī)分子都具有三維形象，如飽和碳SP3雜化為正四面體結(jié)構(gòu)。分子幾何形象的細(xì)微差別對(duì)自然界及生命現(xiàn)象都起著難以估計(jì)的影響。絕大多數(shù)的生命及生理化學(xué)過(guò)程，是受分子幾何形象控制的，因此它不僅是有機(jī)化學(xué)而且是許多其它相關(guān)科學(xué)的研究對(duì)象。有機(jī)化合物的構(gòu)型和構(gòu)象就是描述分子的形象的，是指分子中各原子和基團(tuán)在空間的相對(duì)位置。因此描述分子的結(jié)構(gòu)通常分為三個(gè)層次：構(gòu)造(constitution)、構(gòu)型(configuration)和構(gòu)象(conformation)。Constitution-構(gòu)成和構(gòu)造Configuration-構(gòu)造、外形和輪廓Conformation-構(gòu)造和形態(tài) 構(gòu)造異構(gòu)同分異構(gòu) 順?lè)串悩?gòu)（幾何異構(gòu)） 構(gòu)型異構(gòu) 立體異構(gòu) 光學(xué)異構(gòu)構(gòu)象異構(gòu)構(gòu)造是分子中原子相互連接的順序和方式。構(gòu)造異構(gòu)是指分子式相同，分子中原子相互連接的順序和方式不同。構(gòu)型和構(gòu)象是分子中各原子和基團(tuán)在空間的相對(duì)位子，是分子結(jié)構(gòu)體現(xiàn)的一種表現(xiàn)現(xiàn)象，即分子的形象。構(gòu)型和構(gòu)象異構(gòu)統(tǒng)稱(chēng)為立體異構(gòu)。是分子的構(gòu)型相同，而分子中各原子和基團(tuán)在空間的相對(duì)位子不同。一個(gè)分子由于單鍵的旋轉(zhuǎn)而使分子呈現(xiàn)的立體形象稱(chēng)為構(gòu)象。一個(gè)分子，只要它有可自由旋轉(zhuǎn)的單鍵，就有無(wú)數(shù)個(gè)不同的構(gòu)象存在。由于單鍵旋轉(zhuǎn)需要的能量很低，構(gòu)象異構(gòu)體很難分離。構(gòu)型是指各原子在空間的排列次序。構(gòu)型異構(gòu)體包括順?lè)串悩?gòu)和光學(xué)異構(gòu)。 構(gòu)造、構(gòu)型和構(gòu)象的關(guān)系單鍵旋轉(zhuǎn)，使分子的構(gòu)象改變了，但是原子間的排列次序并沒(méi)有改變，所以構(gòu)型沒(méi)有改變。構(gòu)型和構(gòu)象異構(gòu)體寫(xiě)成平面式，都是構(gòu)造相同一、構(gòu)造異構(gòu)1 構(gòu)造異構(gòu)體分四種情況：碳鏈異構(gòu)，官能團(tuán)異構(gòu)， 官能團(tuán)位置異構(gòu)，互變異構(gòu)。官能團(tuán)異構(gòu)如：環(huán)烷烴和烯烴；炔烴和二烯烴、環(huán)烯烴；醇和醚；醛和酮及烯醇；羧酸和酯?；プ儺悩?gòu)是指在室溫下，不同官能團(tuán)異構(gòu)體處于動(dòng)態(tài)平衡之中，能很快的相互轉(zhuǎn)變，是一種特殊的官能團(tuán)異構(gòu)。如酮與烯醇：又如對(duì)亞硝基苯酚與對(duì)苯：2書(shū)寫(xiě)構(gòu)造異構(gòu)體的方法：按主鏈碳原子數(shù)減少的順序先寫(xiě)碳架異構(gòu)；再寫(xiě)官能團(tuán)位子不同的異構(gòu)體；再寫(xiě)不同官能團(tuán)的異構(gòu)體。舉例1：分子式為C6H12己烯的同分異構(gòu)體（只寫(xiě)出帶有雙鍵的異構(gòu)體）按主鏈碳原子數(shù)減少的順序先寫(xiě)碳架異構(gòu)： 再加進(jìn)C=C雙鍵官能團(tuán)的位置異構(gòu)：舉例2：寫(xiě)出分子式C4H8O2羧酸的同分異構(gòu)體二、順?lè)串悩?gòu)1順?lè)串悩?gòu)產(chǎn)生條件（1）分子中存在不能自由旋轉(zhuǎn)的鍵或環(huán)平面；（2）雙鍵兩個(gè)碳原子上必須是不同的原子或基團(tuán)，環(huán)上必須有兩個(gè)或兩個(gè)以上帶有不同取代基或原子的碳。2順?lè)串悩?gòu)體的標(biāo)記方法（1）順?lè)礃?biāo)記法如果兩個(gè)相同的原子或基團(tuán)在雙鍵平面或環(huán)平面的同側(cè)稱(chēng)為順式，在不同側(cè)為反式。如：順-2-戊烯 反-2-戊烯（2）Z/E標(biāo)記法按照原子或基團(tuán)的大小次序規(guī)則，優(yōu)先的兩個(gè)原子或基團(tuán)位于雙鍵或環(huán)面同側(cè)者為Z式，反之為E式。如： E-4-甲基-3-庚烯 E-4-甲基環(huán)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