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巧解高中化学有机同分异构体
发布时间:2021-06-15 12:53  来源:未知  点击量:

  High school chemistry,Often involves the concept of isomers of organic matter,More difficult to master.Here,Tell everyone the only technique for judging isomers.

  1. Reasons for the variety of organic matter

  There are many types and quantities of organic compounds.the reason is:

  1.1 magical carbon atom

  A C atom can form four chemical bonds,Both can be atoms of other elements,C atoms can also be combined with each other,Form a relatively stable chemical bond.

  1.2 magical carbon skeleton

  Carbon atoms in organic matter,There are a variety of three-dimensional spatial arrangements,Most of them exist in the form of regular tetrahedrons,It can also exist in a flat triangular or linear structure.

  There are currently more than 30 million compounds in the world,The number of organic matter exceeds 20 million.

  (3) Five types of bonds between carbon atoms

  Carbon atoms can form four covalent bonds,You can do it yourself: ①single bond, ②double bond, ③triple bond, ④chain, ⑤ring, etc. (Single bond, double bond and ring are the main ones in middle school),All easily confused vision.

  2. How to judge the structure and quantity of isomers

  Judge the isomers of organic matter,the most important is:

  According to the chemical formula,Judge how many double bonds, triple bonds, and rings there are?

  2.1 Unsaturation

  Introduce a concept of unsaturation,

  1) C=C double bond

  The degree of unsaturation of a C=C double bond is 1;

  2) Ring

  The degree of unsaturation of a ring is 1;

  3) Carbon-carbon triple bond

  The degree of unsaturation of the carbon-carbon triple bond is 2.

  The concept of unsaturation,You will learn it in college.

  We already know some general structural formulas of hydrocarbons:

  2.2 General formula of organic matter

  1) Alkanes: general formula CnH2n+2.(Satisfying this general formula,The degree of unsaturation is 0.)

  Contains only C-C single bond,Does not contain double bonds, triple bonds and rings;

  2) Olefins: general formula CnH2n.(Compared with alkanes,For every 2 H atoms missing,Is an unsaturation)

  The degree of unsaturation of this general formula is 1,and so,May contain a C=C double bond,Or contain a ring,Does not contain three keys;

  3) Alkynes: general formula CnH2n-2.

  The degree of unsaturation of this general formula is 2.

  May contain a carbon-carbon triple bond,Or other situations (double bond, ring unsaturation are all 1,Combination of the two,Three situations);

  The above knowledge,Everyone knows it.

  4) Heteroatom problem

  In practical applications,Heteroatoms other than C and H often appear,How to judge the degree of unsaturation?

  The trick is here:

  For every additional heteroatom,Then in terms of the number of H atoms,"Plus 2,Subtract the valence of this heteroatom."

  It's that simple!

  3. Examples of judging isomers

  Example 1: If the chemical formula of an organic substance contains halogens (F, Cl, Br, I),它们的化合价都是1,每含有一个卤素原子,则加上2,再减去它们的化合价1(+2-1=1),结果还是1。

  结论1:化学式中含卤素原子,通常可以认为是氢原子,计算到化学式的通式中。

  例2:如果化学式中含有氧,化合价是2,计算H原子个数时候,加2、减2,等于零。

  结论2:化学式中含O原子,计算氢原子时候,可以忽略不计O原子的存在。

  例3:含有其它杂原子,例如N,就需要按照几种情形分别处理。

  (1)只含有N、不含O,这个N按照三价计算;

  (2)含N、也含O,就需要将N分别按照3价,5价两种情况计算。不过,这个时候的过渡中一定有提示,告诉我们这个N是怎么存在的。

  知道了有机物的化学式,因此知道了它的不饱和度,它的同分异构体问题就迎刃而解了。

  这里就不一一阐明了。

  口诀是:

  双键为一环为二,

  不饱和度先分清。

  卤素象H氧为零,

  加2减化合价即可行。

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