What Is an Alkane?
A paraffin (wán tng) is an open-chain saturated group. The carbon atoms in the molecule are connected by a single bond, and the remaining valence bonds are combined with hydrogen. [1] The general formula is C n H 2n + 2 , which is the simplest organic compound. The main sources of alkanes are oil and natural gas, which are important chemical raw materials and energy materials.
Alkanes
- A compound consisting of only two elements, hydrocarbons, is called a hydrocarbon, or simply
- 1. When the number of carbon atoms is less than or equal to 4, the alkanes are gaseous at normal temperature, and other alkanes are solid or liquid at normal temperature (nepentane is gaseous at normal temperature).
- 2. Not soluble in water, easily soluble in organic solvents.
- 3. As the number of carbon atoms increases, the boiling point gradually increases.
- 4. As the number of carbon atoms increases, the relative density gradually increases. The density of alkanes is generally less than the density of water.
- Because the alkane contains only CC single bond and CH single bond, the strength of these two types of bonds is very large, and the electronegativity between carbon and hydrogen is very small. Therefore, the polarity of CH bond is very small and belongs to weakly polar bond. Compared to other organic substances, alkane ion reagents have considerable chemical stability. In general, alkanes do not react with most reagents such as strong acids, strong bases, and strong oxidants. However, under certain conditions, such as at high temperatures or in the presence of a catalyst, alkanes can also interact with some reagents. [1]
- The main sources of hydrocarbons are natural gas and petroleum. Although the natural gas composition varies from place to place, almost all of them contain 75% methane, 15% ethane, and 5% propane, and the rest are higher-level alkanes. The most alkane-containing types are petroleum. Petroleum contains chain alkane and some cyclic alkanes with 1 to 50 carbon atoms. Cyclopentane, cyclohexane and their derivatives are the main types of petroleum. Contains aromatic hydrocarbons. The petroleum produced in different parts of China has different compositions, but they can be fractionated into different fractions and applied as required. Alkanes are not only an important source of fuel, but also a feedstock for the modern chemical industry. In addition, alkanes can also be used as food for some bacteria. After the alkanes are consumed by the bacteria, many useful compounds are secreted, that is, the alkanes can become more useful compounds after being "processed" by the bacteria.
- The above situation shows that the development of the petroleum industry is very important for the development of the national economy and organic chemistry.
- Although petroleum is rich in various alkanes, this is a complex mixture. Except for C1 to C6 alkanes, it is difficult to completely separate them into extremely pure alkanes due to the small molecular weight differences between the components and similar boiling points. Although gas chromatography can be used for effective separation, it is only suitable for research and cannot be used for mass production. Therefore, in use, only petroleum is separated into several fractions for application. Sometimes pure alkane is used as a reference in petroleum analysis, which can be prepared by synthetic methods.
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- Gasoline (petrol) burns in an internal combustion engine and deflagrates or knocks, which reduces the power of the engine and damages the engine. The tendency of fuel to cause knocking is expressed as an octane value. The octane number of 2,2,4-trimethylpentane is set to 100 in the gasoline combustion range. The higher the octane number, the stronger the ability to prevent knocking. The linear alkane with more than six carbons has a low octane number, and branched, unsaturated alicyclic rings, especially aromatic rings, are the most ideal, some more than 100. Most modern equipment requires an octane number between 90 and 100. Naphtha, atmospheric residue, and sometimes gas oil can be processed to increase the octane number to about 95, and then mixed into gasoline for use. One of the processing methods is catalytic reforming, which mainly aromatizes more than C6 components in naphtha, that is, becomes aromatic hydrocarbons. In addition to increasing the octane number of naphtha, this method is mainly used in the chemical industry to produce aromatic hydrocarbons. The second method is catalytic cracking. In addition to increasing the octane number, this method is mainly used in the chemical industry to produce propylene and butadiene. Ene. [3]
- There are three commonly used nomenclatures of alkanes, which are described below (only in China):
Common Nomenclature of Alkanes
- Ordinary nomenclature, also known as customary nomenclature, is applicable to simpler alkanes. Alkanes with a carbon number of less than 10 are represented by the number of carbon atoms using the names of A, B, C, D, P, P, H, G, S, N, and dec. For example: CH 4 is called methane, and C 2 H 6 It is called ethane, C 3 H 8 is called propane, and the rest can be deduced by analogy; when the number of carbon atoms is 10 or more, it is represented by Chinese numerals. For example, C 11 H 24 is called undecane, and C 18 H 38 is called octadecane.
- In order to distinguish isomers, it can be expressed by prefixes such as "positive", "different", "new", and the like. E.g:
- N-hexane
- CH 3 CH 2 CH 2 CH 2 CH 2 CH 3
- Isohexane
- CH 3 CHCH 2 CH 2 CH 3
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CH 3
- Neohexane
- CH 3
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CH 3 CHCHCH 3
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CH 3
- 2,2-dimethylbutane
- CH 3
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- CH 3 CCH 2 CH 3
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- CH 3
- Derivative nomenclature [6]
- Derivative nomenclature uses methane as the parent and treats other alkanes as alkyl derivatives of methane. When naming, choose the carbon atom with the most alkyl groups. The alkyl groups are arranged in order of size, with the smaller ones in front. E.g:
- CH 3 CH CH 2 CH 3
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CH 3
Dimethyl ethyl methane
- Dimethyl ethyl isopropyl methane
- Although this nomenclature can reflect the molecular structure of alkanes, it is still not suitable for the construction of more complex alkanes.
Alkanes system nomenclature
- This is a systematic nomenclature formulated by adopting the universal IUPAC naming principles and combining the characteristics of Chinese characters. The naming of straight-chain alkanes is basically the same as that of ordinary nomenclature, except that the word "normal" is omitted; and branched-chain alkanes are regarded as alkyl derivatives of straight-chain alkanes, and are named according to the following rules:
- (1) The longest carbon chain in the molecule is selected as the main chain, and the branched alkyl group is regarded as a substituent on the main chain. According to the number of carbon atoms contained in the main chain, it is called an alkane.
- (2) Starting from the end closest to the branch chain, the carbon atoms of the main chain are numbered with Arabic numerals, and the position of the branch chain is indicated by the number of the carbon atom to which it is connected.
- (3) Write the name of the substituent in front of the name of the alkane. If the main chain contains several different substituents, they are arranged in ascending order; if they contain several identical substituents, they can be listed in the substituents. The name is indicated by two, three, four ...
- If the position of the first substituent is the same from either end of the carbon chain, the sum of the numbers representing the positions of all substituents is required to be the smallest number.