Hydrocarbon (“carbon”, “hydrogen” consecutive reading) is a kind of organic compound. This compound consists of only two elements, carbon and hydrogen, including cyclic hydrocarbons, alkanes, alkynes, alkenes, and aromatic hydrocarbons. It is the matrix of many other organic compounds.

classification of hydrocarbons

Hydrocarbons can be divided into:

(1) open-chain hydrocarbons (hydrocarbon molecules of carbon atoms in the open-chain binding) saturated hydrocarbons (alkanes), unsaturated hydrocarbons [olefins and polyenes (including carbon-carbon double bond, unstable), alkynes and polyalkenes (Carbon-containing carbon triple bond, more unstable)]

(2) Alicyclic hydrocarbons [cycloalkanes (cyclopropane), cycloalkenes, cycloalkynes]

(3) Aromatic hydrocarbons [monocyclic aromatic hydrocarbons (benzene and its homologues), fused ring aromatic hydrocarbons (naphthalene, anthracene and other fused ring aromatic hydrocarbons and their homologues), polycyclic aromatic hydrocarbons (polycyclic aromatic hydrocarbons and their homologues)].

Molecular formula

Alkanes general formula: CnH2n+2 (n is greater than or equal to 1)

Alkene (Olefin) general formula: CnH2n (n is greater than or equal to 2)

Diene general formula: CnH2n-2 (n is greater than or equal to 3)

The general formula of cycloalkane: CnH2n (n is equal to or greater than 3)

The general formula of alkyne: CnH2n-2 (n is greater than or equal to 2)

The general formula of aromatic hydrocarbon: CnH2n6 (n is greater than or equal to 6)

Benzene and its homologues: CnH2n-6 (n is greater than or equal to 6).

Hydrocarbons in Petroleum

Hydrocarbon is the abbreviation of hydrocarbon, which is a combination of “fire” in “carbon” and “li” in “hydrogen”. Hydrocarbons are divided into saturated hydrocarbons and unsaturated hydrocarbons.

Most hydrocarbons in petroleum are saturated hydrocarbons, but unsaturated hydrocarbons such as ethylene and acetylene are generally available only during petroleum processing. There are three types of hydrocarbons in petroleum:

(1) Alkanes

It is a chain hydrocarbon compound connected by a single bond between carbon atoms. Due to the difference in the number of carbon and hydrogen atoms that make up hydrocarbons, the result is that petroleum contains hydrocarbon molecules with large and small differences.

Alkanes are named according to the number and number of carbon atoms contained in the molecule. If the number of carbon atoms is less than 10, use A, B, C, D, P, H, H, G, S, N, dec Alkanes are used, and those with more than 11 carbon atoms are represented by numbers. Alkanes in petroleum include normal and isoparaffins. Normal paraffin is high in paraffin-based petroleum, isoparaffins are high in asphalt-based petroleum.

Alkanes are also called paraffinic hydrocarbons. The general formula of the molecular formula of alkanes is CnH2n+2, where n represents the number of carbon atoms in the molecule.

2n + 2 represents the number of hydrogen atoms. Under normal temperature and pressure, C1-C4 alkane is in a gaseous state and exists in natural gas, C5-C16 alkane is liquid and is the main component of petroleum, C16 and above are solid.

(2) Naphthenes

As the name suggests, it is a ring structure. The most common is a ring composed of five carbon atoms or six carbon atoms, the former is called cyclopentane, and the latter is called cyclohexane. The general formula of the cycloalkane molecular formula is CnH2n. Naphthenes are also called naphthenic hydrocarbons.

(3) Aromatic hydrocarbons

Also known as aromatic hydrocarbons. Generally, it consists of one or more six-membered rings (benzene rings) with a special structure. The simplest aromatic hydrocarbons are benzene, toluene, and xylene. They can be obtained from the production of platinum reformers during petroleum refining. The general formula of the molecular formula of the aromatic hydrocarbon is CnH2n-6.


1. Select the main chain (the carbon chain with more carbon atoms is used as the main chain, and the chain containing the functional group should be selected as the main chain if there are functional groups)

2. Main chain number (to follow “near”, “simplified” and “small”)

3. Representation of substituents

4. Representation of the name

5. “Equal length” principle

6. Numbering principle of “equal proximity”

Common nomenclature

1. The alkane is generally called “a certain alkane”, and a certain refers to the number of carbon atoms in the alkane. It is represented by one to ten with A, B, C, D, E, G, G, Xin, Ren, and G, and it is represented by Chinese characters since ten.

For example:

(1) CH4 is called methane, CH3CH3 is called ethane, and CH3CH2CH3 is called propane;

(2) C15H32 is called pentadecane.

2. To distinguish between isomers, use “positive”, “iso” and “new”.

Common nomenclature is simple and convenient. But it can only be used for alkanes with relatively simple structures. Systematic nomenclature must be used for alkanes with a more complex structure.

Systematic nomenclature

In systematic nomenclature, branched-chain alkanes are considered as derivatives of alkyl substituents for linear alkanes.

The remaining part of a hydrocarbon molecule losing a hydrogen atom is called a hydrocarbon group, the remaining part of an alkane molecule losing a hydrogen atom

Partly called alkyl. General formula: CnH2n+1 (n≥1), usually expressed by “R-“.

Common alkyl groups:

CH3 — methyl, CH3 — CH 2 — ethyl

CH3 — CH2 — CH2 — n-propyl, CH3 — (CH3) CH — isopropyl.

The nomenclature for branched-chain alkanes can be carried out according to the following steps:

(1) Set the main chain, called “a certain alkane”.

The longest carbon chain in the selected molecule is the main chain, and it is called “a certain alkane” according to the number of carbon atoms in the main chain. (The carbon number of 1 ~ 10 is named after A, B, C, D, E, H, G, Xin, NU, DEC.)

Example 1: CH3 — CH (CH3) — CH2 — CH2 — CH2 — CH3

The carbon chain in the middle line of the above formula is the longest. As the parent, it contains six carbon atoms, so it is called hexane. Methyl is used as a substituent.

(2) Write the number and fix the location of the branch chain.

① After the main chain is selected, the main chain’s order number is to be determined, that is, the position of the substituent is determined. The main chain is numbered from one end to the other end, and the number is represented by 1, 2, 3┉, etc. 1, 2, 3, etc.

②Simple alkanes are numbered from the end closest to the branch chain, and the position and the noun of the substituent should be connected by a “-” half-word line. When there are several numbering possibilities, the position of the substituent should be selected to be the smallest.

Example 2: ①CH3 —②CH2 — ③CH (CH3) — ④CH2 — ⑤CH2 — ⑥CH3

(3) Write the name, the same group is written together, and the different substituents are from small to capital.

① If there are several identical substituents, combine them, the number of substituents is expressed by one, two, three, etc., written in front of the substituents, if there are several different substituents, put The name of the small substituent is written in the front, and the big is written in the back ( the order of the alkyl is: methyl, ethyl, propyl, butyl, pentyl, hexyl, isopentyl, isobutyl, isopropyl) ), The order of which must be indicated one by one, and the numbers of the order must be separated by “,”.

Example 3:

CH3 -C(CH3)2 -CH(CH2CH3)-CH-CH2 -CH3

Naming: 2,2-dimethyl-3-ethylhexane.

②When chains with the same length can be used as the main chain, select the carbon chain with the largest number of branches (or the simplest branch).

Example 4:

CH3 — CH(CH3) — CH(CH3) — CH(CH2CH2CH3) — CHCH3 — CH3 — CH3

Naming: 2,3,5-trimethyl-4-propylheptane.

The principle for determining the rank of the main chain is:

①The longest principle: select the longest carbon chain as the main chain

② Simplest principle: when two identical main chain carbon atoms, selected from branched-chain the easiest one for the backbone.

③The nearest principle: the starting point is closest to the branch chain

④Minimum principle: when the branch chains are at the same distance from both ends, the smallest sum of the values ​​of the positions of the substituents is correct.