How can you distinguish between homologs or isomers in organic compounds?

We refer to compounds with similar structures and molecular composition differing by one or more CH2 clusters as homologues.

Methane, ethane, butane, etc. in alkanes, they differ by n CH2 and are homologues of each other;

Another example (assuming it exists, just to illustrate) CH2O, C2H4O2, C3H6O3, they are n CH2O apart, and they are also homologues of each other;

For example, methane (CH4), ethane (C2H6), propane (C3H8), butane (C4H10), etc. are homologues, which can be expressed by the general formula CNH2N+2. Among them, methane and n-butane are homologues of each other, and methane and isobutane are also homologues of each other.

An isomer is a compound with the same chemical formula, the same chemical bonds, and different atomic arrangements. To put it simply, the phenomenon that compounds have the same molecular formula but have different structures is called isomerism; Compounds with the same molecular formula but different structures are isomers of each other. Such as ethanol and methyl ether [C2H6O].

Homologues have the same functional group and the molecular formula differs by n CH2

Isomers are those with the same molecular formula but different structural formulas. One is the different way the carbon atoms are attached, and the other is the isomerization of functional groups (such as the isomerization of aldehydes and ketones, the isomerization of alcohol ethers).

Isomers.. It's just that the molecular formula is the same.

There are several more CH2s between the congeners

Note: NH3 is not a homolog to N2H6.

The molecular formula of the congeners is not necessarily the same; The isomer molecular formula must be the same.

Isomers must have the same molecular formula and different structures.

The molecular formula of the congeners is not the same, the structure is similar, and the molecular formula differs by a multiple of CH2 or CH2. Note that the structure must be similar and belong to the same class of compounds. For example.

CH3CH2CH2COOH(C4H8O) and CH3CH2COOH(C3H6O) are homologs of each other;

CH3CH2CH2COOH (C4H8O) is isomeric of CH3Cooch2CH3 (C4H8O).

CH3CH2CH2COOH (C4H8O) and CH3COOCH3 (C3H6O) are not homogeneous, one is a carboxylic acid and the other is an ester, and they are neither homologues nor isomers.

C5H12 is pentane and has three isomers.

1. There are 9 kinds of dichloride of n-pentane.

2. There are 11 kinds of dichloride of isopentane.

3. There are 2 kinds of dichloride of neopentane.

So there are 22 kinds of dichlorides.

There are 8 monochlorinated compounds in C5H12, 16 in dichlorogenated compounds, 17 in C6H14, and 34 in dichlorogenated C5

Monochlorolate of H12: 3 n-pentanes, 4 isopentanes, and 1 neopentane.

Monochlorinated substitutes, also known as monochlorine substitutes, generally refer to organic compounds, which refer to the substitution of one of the organic substances by chlorine. Chlorine-containing inorganic substances are called chlorides, and in organic matter, they are called monochlorine substitutes.

For example, there is chloromethane, monochloroethane. In multi-carbon organic compounds, according to the position of hydrogen, the substitution position of chlorine atoms is also different, and there are substitutions for carbon atoms. There are also differences in the location of hydrogen in aromatic groups, with pro-, meta-and para-nic distinctions.

Method:

The method can be "fixed one to move two" (one chlorine atom is fixed and the second chlorine atom is moved).

According to the order in which isomers are written, they are generally functional group isomerism, carbon chain isomerism, and positional isomerism.

Because the functional group in this question has been fixed to 2 chlorine atoms, we should first write the three carbon chain isomers of the possible symbol C5H12, i.e., n-, iso, and neopentane (writing the carbon skeleton is a fuel loss), and then use "fixed one shift two" to write the position isomerism.

1. In terms of definition chemistry, we refer to compounds with similar structures and differing in composition by one or several atomic clusters as homologues. In chemistry, we refer to compounds with similar structure, chemical properties, and general formulas, and with one or more CH2 clusters (system differences) in composition and the same functional groups, and we refer to compounds with similar structures and one or more different atomic groups in composition as homologues. It is mostly used for organic compounds.

2. Judge the law.

Homologue. Judgment law: 1. Difference: The molecular composition is different by several certain atomic clusters, that is, the relative molecular mass difference is consistent, just like the tolerance in the equal difference series.

Together: Same as the same type. Similar: similar in structure.

College Entrance Examination Center] 3. Characteristics.

Characteristics of homologues:

1.The homologues must conform to the same general formula; However, it is not necessarily the homolog that conforms to the same general formula.

2.Congeners must be of the same class.

3.The chemical formula of the congeners must be different.

4.The constituent elements of the homologues are the same.

5.Homologues are structurally similar and not necessarily identical.

6.There are several clusters of CH2 atoms between the congeners. 4. Homologues.

For example, methane (CH4), ethane (C2H6), propane (C3H8), butane (C4H10), etc., in which methane and n-butane are homologues to each other, and methane and isobutane are also homologues to each other. Ethylene, propylene, butylene, etc. are homologues of each other. Another example (assuming it exists, just to illustrate) CH2O, C2H4O2, C3H6O3, they are n CH2O apart, and they are also homologues of each other;

There are isomers not only between organic and inorganic substances, but also between inorganic and organic substances. For example, urea CO(NH2)2 and ammonium cyanate NH4CNO are very typical examples.

Two or more compounds with the same chemical formula, but different structures and properties, are called isomers of each other, and this phenomenon is called "isomerism".

Not necessarily, it does not specify whether it is an organic compound or not. It's just that it's more common in organic matter. You can take a look at the following:

How isomers are written:

When writing isomers, the key is the order and regularity of the writing.

Example 1: Write the simple formula for the structure of all organic matter with the formula C7H16.

Analysis] It was judged that C7H16 was an alkane.

The first step is to write the longest carbon chain:

In the second step, one carbon atom in the longest carbon chain is removed as a branch, and the remaining carbon atoms are used as the main chain, and the possible position of the branch chain in the main chain is found in turn (similar below).

In the third step, the two carbon atoms in the longest carbon chain are removed, as two branched chains (two methyl groups).

They are attached to two different carbon atoms.

Each is attached to the same carbon atom.

as a branched chain (ethyl).

In the fourth step, the three carbon atoms in the longest carbon chain are removed as three branched chains (three methyl groups).

As two branched chains (one methyl and one ethyl): no new isomers can be generated.

Finally, the four valence bonds of the carbon atom are complemented with hydrogen atoms.

Example 2: Write an isomer with the formula C5H10.

Analysis] When writing isomers containing functional groups, it can usually be written in the order of functional group position isomerism, carbon chain isomerism, functional group heterogeneity, or other order, but no matter which order is written, attention should be paid to orderly thinking to prevent omission or rewriting.

Heterogeneous writing by functional group position:

ch2=ch-ch2-ch2-ch3 ②：ch3-ch=ch-ch2-ch3

Written by carbon chain isomerism:

Then write according to heterogeneous heterogeneity:

into a straight chain, a string of strings", "pick from the beginning, hang in the middle", "row to the side, not to the end".

Taking C5H12 as an example, various isomerisms of C5H12 are written.

1) "Into a straight chain, a string": ch3 - ch2 - ch2 - ch2 - ch3

2) "Pick from the beginning and hang in the middle":

3) "Row to the side, not to the end": repeat the above two formulas and repeat (2) and (3) steps, you can write another isomer of C5H12, so there are three isomers of C5H12.

2.The correct way to write isomers of various types of organic matter.

It is written in the order of functional group isomerism, carbon chain isomerism, and position isomerism.

Method for determining the number of isomers of hydrocarbons.

1. Equivalent hydrogen method.

The determination of the number of primary substituents of hydrocarbons is essentially based on the number of hydrogen atoms in different positions. It can be judged by the "equivalent hydrogen method". The three principles for judging "hydrogen equivalent" are:

Hydrogen atoms on the same carbon atom are equivalent; For example, 4 hydrogen atoms in methane are equal.

Methyl groups attached to the same carbon atom are equivalent; For example, the 12 hydrogen atoms on the 4 methyl groups in neopentane are equivalent.

The hydrogen atoms in the symmetrical position are equivalent; For example, the 6 hydrogen atoms in ethane are equivalent to 2,2,3,3-tetramethylbutane.

The 24 hydrogen atoms on the are equal and the 6 hydrogen atoms on the benzene ring are equal.

Before determining the isomers, it is necessary to find the symmetry plane and determine the equivalent hydrogen, so as to determine the number of isomers.

Example 2: In alkanes containing 10 or less carbon atoms, one of the halogenated alkanes does not have isomers in the alkanes (

a.2 b3 types c4 d5 kinds.

2. Axis movement method.

For fused cyclic aromatic hydrocarbons with multiple benzene rings together, to determine whether they are isomers, an axis can be drawn, and then translated or flipped to determine whether they are isomers of each other.

Example 3: The structural formula of the naphthalene molecule can be expressed as , and the two are equivalent. Benzo[a]pyrene is a strong carcinogen (found in chimney ash, coal tar, smoke from burning tobacco and exhaust fumes from internal combustion engines).

Its molecule is formed by the merger of five benzene rings, and its structural formula can be expressed as ( ) or ( ), both of which are also equivalent. Existing structural formula (a) (d), where.

1) The structural formula equivalent to ( ) is

2) It is isomeric with ( ).

3. Determine the method of one shift and two moves.

For the determination of isomers of binary substituents, one substituent position can be fixed and the other substituent position can be moved to determine the number of isomers.

Example 4: If two hydrogen atoms in a naphthalene molecule are replaced by bromine atoms, the number of compounds formed is (

b. 7 c. 8 d. 10

Fourth, permutation and combination method.

Example 5: If two hydrogen atoms in the naphthalene molecule are replaced by bromine atoms, the number of compounds formed is ( d ).

a. 5 b. 7 c. 8 d. 10

Example 6: There are three different groups, which are x, y, and z, and if the three hydrogen atoms on the benzene ring are replaced at the same time, the number of isomers that can be formed is.

a. 10 b. 8 c. 6 d. 4

1: Carbon skeleton isomerism--- carbon skeleton simulation method (note the ring) 2: Chiral isomerism --- chiral carbon atom method.

3: Differential head isomerism--- differential carbon atom method.

Basically, the specific operation is more troublesome and needs to be very careful, if you urgently need an answer, you may wish to check the chemistry ** or database.

1.Step Category: Overall Introduction Required Tools Raw Materials Methods Steps Precautions.

2.General Knowledge: Direct questions give specific reasons in detail Reason introduction.

Of course, I drew them one by one.