What is an isomer? Take out an organic matter, how to write its similarities and differences

Chemistry books say that compounds have the same molecular formula, but compounds with different structures are called isomers with each other.

To write isomers, these elements are arranged according to different structures.

For example, if you write an isomer of an alkane, you can first discharge C with a different structure, and then discharge hydrogen.

Isomerism, that is, the chemical formula of the writing is the same, but the structure is different, that is, the two are not the same thing. There are also allotropes and so many more, and it is best to write their structural formulas

In the general examination, if you do not test the isomer of a certain organic matter, it is useless to know it, and the college entrance examination does not test this knowledge. You will only see this in multiple-choice questions, just know that isomers are: the molecules are the same, the structure is different.

That is, the molecular formula is the same, but the structure is different.

For example, butane has two isomers, namely n-butane without branched chain and 2-methylpropane, also known as isobutane, which has a methyl branched chain.

It's really a matter of mathematical possibility, writing all the cases.

Isomers are commonly referred to as having the same chemical formula but different structures of molecules. First write about the carbon chain, first write the straight chain structure, and then write the molecule with the branch chain structure, specifically, it is best to do two such topics under the guidance of the teacher in person, it is easy to understand, and it will be ,...... quickly

Isomers have the same molecular formula and different structures! ...That is, the branch chain changes!

Isomers are those with the same molecular formula but different structural formulas. Isomers can be written according to different carbon chains.

The molecular formula is the same, but the structure is different.

The molecular formula is the same, but the structure is different...

For example, let's write a 5 C acid, and first write a straight chain of C-C-C-C-COOH, right?

Then start writing the branching case.

1.Write c-c(c)-c-cooh and c-c-c(c)-cooh as a branch

2.Then write two c, one branched chain, c-c(c-c)-cooh, but note here that after this is written, it is actually the same as the second case of a c as a branched chain... If there is a repetition, don't write anymore.

3.Write two C's for two branches, which is C-C(C)(C)-COOH, right?

The (c) I wrote is even on the carbon without () in front of it This is actually typing and can't explain it clearly Or learn more by yourself Ask the teacher more I wish you a smooth college entrance examination!

Carbon straight chain, string of strings.

Pick from the beginning and hang in the middle;

Row to the side, not to the end.

The main chain goes from long to short.

The branch chain is from whole to scattered.

The location is from the heart to the edge.

(1) Carbon chain isomerism: refers to the isomerism phenomenon caused by different carbon skeletons in the molecule. For example, all alkane isomers belong to carbon chain isomerism.

2) Positional isomerism: refers to the isomerism phenomenon caused by the different positions of functional groups in the molecule. Such as l-butene and 2-butene, l-propanol and 2-propanol, o-xylene and m-xylene and paraxylene.

3) Functional group isomerism: refers to the phenomenon of isomers with the same molecular formula but different functional groups of organic matter.

4) C-trans isomerism: the isomerism caused by the different arrangement of atoms or clusters in the molecule in space due to the fact that the carbon-carbon double bond cannot be rotated. The arrangement of two identical atoms or clusters of atoms on the same side of a double bond is called cis structure; The arrangement of two identical atoms or clusters of atoms on either side of a double bond is called a trans structure.

Writing techniques for isomers.

The types of isomers include carbon chain isomerism, functional group type isomerism, functional group position isomerism, etc.

For the isomerization of the carbon chain, the shortened carbon chain method can be adopted: first write the longest carbon chain as the main chain (omit the hydrogen atom), and then, reduce the carbon atoms one by one, connect the reduced carbon atoms to the main chain as substituents, change the position, and obtain various different structures, and finally, supplement the hydrogen atoms according to the tetravalent.

When writing, it is often easy to omit writing. In order to prevent omission, attention should be paid to selecting the longest carbon chain as the parent chain, and finding the center of symmetry or axis of symmetry, and writing according to the following rules:

The main chain is from long to short, and the branch chain is from whole to scattered;

The position is from the heart to the edge, and the arrangement is similar to different (from neighbor to between).

Example] Write out the isomer of C7H16.

1) All the carbon atoms in the molecule are connected into a straight chain as the parent chain.

c-c-c-c-c-c-c

2) Truncate one carbon atom from one end of the parent chain and connect it to each C atom on one side of the central symmetry line of the remaining parent chain in turn. Care should be taken to prevent the branch chain from becoming the longest main chain again.

c-c-c-c-c-c

cc-c-c-c-c-c

c(3) Cut off two carbon atoms from one end of the parent chain, and first connect the two carbon atoms as a whole (ethyl group) to each C atom (including the central carbon atom) on one side of the central symmetry line of the remaining parent chain according to the principle of branching from whole to scattered.

c-c-c-c-ccc

Then the two carbon atoms are dispersed into two carbon atoms (two methyl groups), which are connected to each C atom on one side of the central symmetry line of the remaining parent chain in turn, and the position is changed in order from the same carbon to the different carbon, from the adjacent carbon to the carbon spaced between the phases, and from the less interval to the more spaced.

cc-c-c-c-c

c cc-c-c-c-c

c c-c-c-c-c

c cc-c-c-c-c

c c4) then cut off three carbon atoms from one end of the parent chain, respectively as one branch (propyl), two branches (one methyl group and one ethyl) or three branched chains (three methyl groups), and write them as in the previous step. Care should be taken to prevent the branch chain from becoming the longest main chain again.

c cc-c-c-c

c(5) The number of carbon atoms intercepted from the parent chain shall generally not be more than the remaining part of the parent chain.

If it is an alkane, gradually shorten the length of the main chain and change the position of the branch chain, but pay attention to the repetition;

Alkanes and alkenes, first change the position of the double (or triple bond) and then change the backbone length, while changing the position of the double bond and triple bond.

The basis of isomers is the isomer of alkanes, and it is necessary to be proficient in writing basic substances, and then expand to the derivatives of hydrocarbons, from carbon chain isomerism, position isomerism and functional group isomerism to write, all three cases together are that there are several structural formulas of an organic matter.

Regarding whether the substitution of different structures will be affected or not, the substitution depends on the equivalent hydrogen atoms of different isomers are different, and the substitution products are also different. For example, n-butane C-C-C-C, there are two hydrogen atoms, there are two kinds of monochlorine substitutes, and there are two hydrogen atoms in isobutane C-C(CH3)-C, and there are two hydrogen atoms (H on the three methyl groups and H on the middle 2C), and there are also two kinds of monochlorinated substances, so there are 4 kinds of monochlorinated substances in C4H10, and the structure of these four substances is different, so the properties are also different.

The addition is simpler, for example, c=c-c-c and c-c=c-c are isomers, which are different from bromine water addition products.

Don't worry, organic chemistry is very regular, not scattered like inorganic chemistry. Instead of "how many structural formulas does an organism have", give you a molecular formula, ask you how many isomers it has (these isomers are called isomers of this molecular formula), and ask you about the corresponding properties of these isomers, which usually have the following types:1

This is mainly the position of the double or triple bond, and the different positions will also affect the structure; 3.Species isomerism: For example, ketones and aldehydes are isomers, and acids and esters are isomers.

That's probably all there is to it.

C3H8 is a saturated hydrocarbon, and the C value is less than 4, so there is only one.

C4H8 is an unsaturated hydrocarbon, respectively

CH3-CH = CH-CH3 (2-butene) CH2 = CH-CH2-CH3 (1-butene).

ch2-ch2丨丨.

CH2-CH2 (cyclobutane).

There is no shortcut to finding isomers, and generally speaking, it is best to list them all, without duplication or omission.

Hello classmates, according to your question, my answer is as follows. First, we take any vertex of the cubeane and replace it with chlorine (see the blue dot in the figure), and then we use this vertex to see its orientation. There are three vertices at the nearest distance to the remaining vertices, and if you take any of these three vertices, the effect is the same, so this is the first case.

Similarly, see the second and third scenarios in the diagram. In the second case, the effect is the same regardless of which red dot is chosen to replace it. In summary, the number of isomers is 3.