Is an organic matter with the same general formula necessarily a homolog? If not, a counter example

Wrong! Chemically, we refer to compounds with similar structures and differing in composition by one or more atomic clusters as homologues. It is mostly used for organic compounds.

Cited from "Shanghai Senior High School Phase II Textbook - Chemistry (Extended Curriculum, Experimental Textbook, First Edition, August 2008)".

In chemistry, we refer to compounds with similar structure, chemical properties, and general formulas, but with one or more different CH2 clusters (differential systems) in composition and the same functional groups, 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. Methanol CH3OH, ethanol CH3-CH2OH, propanol CH3-CH2-CH2OH and so on are also homologues, which can be expressed by the general formula CN+H2N+1OH or ROH.

Ethylene, propylene, butene, etc. are homologs of each other, and the general formula CNH2N can be used, but organic compounds with the same chemical general formula are not necessarily homologues.

For example: naphthenes and olefins, benzene and acetylene, etc.

In particular, you should pay attention to the characteristics of the homologue:

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.

The general formula CH2O can be formaldehyde or C2H4O2 acetic acid.

The congeners need to be of the same class of substances, and the mere fact that the general formula is the same does not guarantee that they are the same kind of substances.

For example, cyclohexane and ethylene are in line with the general formula CNH2N, with a difference of 4 CH2, but the structure is not similar, not the same kind of substance, not the same homologue.

Homologues must be organic compounds of the same class, some substances have the same formula, but not the same class of organic compounds, so they are not homologues, such as ethylene and cyclohexane, acetylene and butadiene.

Substances that are structurally similar and differ by one or more clusters of CH2 atoms in molecular composition are homologues.

Key points for judging homologs:

1. The general formula is the same, but the same general formula is not necessarily the same system.

2. The types of constituent elements must be the same.

3. Structural similarity refers to having similar atomic connection methods, the same type and number of functional groups. Structurally similar is not necessarily identical, such as CH3CH2CH3 and (CH3)4C, the former is unbranched and is n-propane, and the latter has a branched chain and is -dimethylpropane, also known as neopentane, which is still a homologue.

4. There must be a difference of one or several CH2 atomic clusters in the molecular composition, but one or several CH2 atomic clusters differ in the same composition of the general formula are not necessarily homologues, such as ethyl bromide and chloropropane are halogenated hydrocarbons, and the composition is one different CH2 atomic cluster, but not homologues.

5. The isomers are not homologs.

I hope I can help you with your doubts.

This is for sure, the general formula is the same, but the structure is not necessarily the same, that is, the functional groups contained may be different, then it must not be homologues, even if the carbon atoms are the same, they are not homologues, such as aldehydes and ketones, the general formula is the same, they both contain an oxygen atom, but the functional groups are different, they are not homologues, for example, the general formula of propionaldehyde is: C3H6O

Acetone C3H6O

Propionaldehyde structure CH3CH2CHo, acetone: CH3CoCH3

Congeners require the same type and number of functional groups.

The functional groups may be different, the positions of the functional groups are different, and the carbon chain is different.

The mechanism is different, for example, pentane is divided into n-pentane and isopentane.

6. Ethane. Like what; However, it is not necessarily a homolog that conforms to the same general formula, but an organic compound that has the same chemical general formula is not necessarily a homologue. Methanol CH3OH, can be used with the general formula CNH2N, chemical properties, we put the structure similar, we put the structure.

Among them, methane and n-butane are homologues and propylene of each other, compounds with one or more atomic clusters differ in composition are called homologues with each other, and compounds with the same functional group with one or more CH2 atomic clusters (differential differences) are collectively referred to as homologues. It is mostly used for organic compounds. The chemical formula of the congeners must be different.

Another example (assuming the existence of propane (C3H8), ethane (C2H6)...The homologues are structurally similar. The constituent elements of the homologues are the same, ethanol CH3-CH2OH, and they differ by n CH2.

2. Methane and isobutane are also homologues of each other. Ethylene. The homologues must conform to the same general formula;

A homologues must have the same general formula, and the same general formula, not necessarily homologues, such as alkenes and naphthenes that conform to the general formula CNH2N are not homologues, so A is correct;

b Compounds with one or more different CH2 clusters in molecular composition are not necessarily similar in structure, so b is correct;

c Alkanes with different carbon atom numbers belong to homologues, and alkanes with the same carbon atom number are isomers of each other, so c is wrong;

d The relative molecular weight difference of adjacent homologs is 14, so d is correct and c is selected

Wrong. There must be a difference of n CH2 groups. And it must also be of the same class of substances.

For example, the following two groups of compounds are not homologs.

The first group, phenol and benzyl alcohol, although they differ from CH2, are not the same group of substances and are not with N CH2 groups.

Mishomologues differ in molecular composition by one or more clusters of "CH2" atoms, and their composition is not the same.

1. Criteria for judging homologues.

1) The molecular structure is similar, that is, both substances belong to the same class of substances;

2) one or more "CH2" clusters of atoms differ in molecular composition;

One is indispensable.