1. Idioms

(1) How many carbon atoms in the molecular composition are called alkanes: alkanes with four carbon atoms in the composition are called butane; Alkanes containing eighteen carbon atoms are called octadecane.

(2) normal, different and new distinguished isomers are added before alkanes. Unbranched is called "positive"; The methyl branch on the second carbon atom is called a "heterocyclic ring"; Two methyl branches on the second carbon are called "new". There are three kinds of pentane: n-pentane, isopentane and neopentane.

CH3-CH2-CH2-CH2-CH3

These three pentanes have the same composition, different structures and different physical properties. In alkanes with the same molecular formula, the more branches, the lower the boiling point.

2. Systematic nomenclature

(1) Select the main chain and determine the matrix.

That is, the chain with the largest number of carbon atoms is the main chain, and the main chain with several carbon atoms is called an alkane.

In the molecular structure, the two main chains have the same number of carbon atoms, but different main chains will have different number of branches. In order to solve this problem, a supplementary principle is added to the principle of selecting the main chain. When the number of carbon atoms is the same, the branched chain is the main chain.

(2) Select the starting point and fix the supporting position;

That is, choose the end of the main chain near the branch as the starting point and number it according to 1, 2,3 ... to determine the location of the branch.

(3) The bases are the same and should be merged; Different bases, Jane first:

Example 1. Named as: 2,2,3,4-tetramethylpentane.

Example 2. Named as: 4- methyl -3- ethyl heptane.

note:

1. Arabic numerals are separated by commas, and Chinese characters are separated by short lines.

2. When the distance between the two ends of the branch chain and the main chain is equal, the number of substituents and the small end are required as the starting point. For example, the name of example 1 is not 2,3,4,4-tetramethylpentane.

3. The system naming method should be applied correctly. No methyl group (-CH3) was found at the 1 position, no ethyl group (-CH2-CH3) 3 at the 2-position and no propyl group (-CH2-CH2-CH3) at the 3-position.

Named by systematic nomenclature, the law is (taking alkanes as an example):

1, select the main chain and call an alkane (note the longest principle and the most branched principle)

2. Select the starting point (nearest principle: closest to the branch) and the number (minimum principle: second to the branch, smallest) to determine the branch (simplest principle: the branch is the simplest).

3. Writing rules: Before the branch name, the main name and the branch name are the same. If the branch names are different, simplify them first.

The leftmost and topmost here should be regarded as a chain, the longest principle in 1.

The other link is on the fourth carbon in the lower left corner.

Name: 4- methyldodecane 4- methyldodecane

Choose the longest chain as the main chain. If there are other groups, select the group that has it. The c of the nearest branch begins to be numbered. How many C's in the branch are bases? The next one is

5,6-methyl, decane alkane is a saturated hydrocarbon, a chain hydrocarbon with only carbon-carbon single bond and the simplest organic compound. Among alkanes, the number of hydrogen atoms reaches the maximum, and its general formula is CnH2n+2. Every carbon atom in the molecule is sp3 hybrid. The simplest alkane is methane.

In alkanes, each carbon atom is tetravalent, and a strong σ bond is formed with four carbon atoms or hydrogen atoms around it by using sp3 hybrid orbitals. Carbon atoms with 1, 2, 3 and 4 carbons are called primary carbon, secondary carbon, tertiary carbon and quaternary carbon respectively. Hydrogen atoms on primary, secondary and tertiary carbon are called primary, secondary and tertiary hydrogen respectively.

In order to minimize the repulsive force of bonds, four atoms connected to the same carbon form a tetrahedron. Methane is a standard regular tetrahedron with a bond angle of109 28' (exact value: arccos(- 1/3)).

Theoretically, all alkanes can exist stably because of their stable structure. However, alkanes in nature do not exceed 50 carbons at most, and methane is the most abundant alkane.

Because the carbon atoms in alkanes can be arranged randomly according to the law, the structure of alkanes can be written in countless ways. Linear alkanes are the most basic structure, and theoretically this chain can be extended indefinitely. It is possible to produce branched chains on straight chains, which undoubtedly increases the types of alkanes. Therefore, starting from alkanes with four carbons, the molecular formula of the same alkane can represent multiple structures, which is called isomerization. With the increase of carbon number, the number of isomers will increase rapidly.

Alkanes may also undergo optical isomerization. When the four groups attached to a carbon atom are different, the carbon is called chiral carbon, which has optical activity.

Alkane loses a hydrogen atom, and the rest is called alkyl, which is generally expressed by R-. Therefore, alkanes can also be represented by the general formula RH.

Alkanes were originally named by customary nomenclature. However, this nomenclature is difficult to be used for alkanes containing more carbon and isomers. So some people put forward the nomenclature of derivatives, and regarded all alkanes as derivatives of methane. For example, isobutane is called 2- dimethylpropane.

At present, the naming method adopts IUPAC naming method, and the systematic naming rules of alkanes are as follows:

Find the longest carbon chain as the main chain and name the main chain according to its carbon number. The first ten carbon chains are composed of celestial poles (A, B, C ...), and when the carbon number is greater than ten, they are named after chinese numerals, such as undecane.

From the nearest number of substituent positions: 1, 2, 3 ... (The smaller the number of substituent positions, the better). Numbers represent the positions of substituents. Use-between numbers and chinese numerals.

When there are multiple substituents, the carbon chain with the smallest and longest number of substituents is the main chain, and all substituents are listed in the order of methyl, ethyl and propyl.

When two or more substituents are the same, chinese numerals is added before the substituents: I, II and III, such as dimethyl, and the substituents are juxtaposed separately.

The structural formula of isooctane (2,2,4-trimethylpentane). Isooctane is a standard of gasoline antiknock, and the octane number is 100. For some simple or commonly used alkanes, common names are often used. For example, it is customary to add the word "positive" before the name of straight-chain alkanes, but this word is not in the system name. Those with a methyl group in the 2-position of the main chain are called "hetero" and those with two methyl groups in the 2-position are called "new". Although this only applies to butane and pentane with few isomers, it has been preserved out of habit, and even 2,2,4-trimethylpentane, which should not be called "iso", has been named "isooctane".

physical features

Are alkanes denser than water? 2 Hey? Thank you? What's wrong with this medicine? Hey? International? Resist ????? 1? International? ∮? % (methane to butane) is gaseous, 5- 17 (pentane to heptadecane) is liquid, and more than 18 of carbon (octadecane) is solid.

chemical property

The properties of alkanes are very stable, because C-H bond and C-C double bond are relatively stable and not easy to break. Except for the following three reactions, alkanes can hardly undergo other reactions.

oxidizing reaction

R + O2 → CO2 + H2O

All alkanes can burn, and the reaction releases a lot of heat. Complete combustion of alkanes produces carbon dioxide and H2O. If the amount of O2 is insufficient, it will produce toxic gas carbon monoxide (CO) and even carbon black (C).

Take methane as an example:

CH4 + 2 O2 → CO2 + 2 H2O

When the oxygen supply is insufficient, the reaction is as follows:

CH4 + 3/2 O2 → CO + 2 H2O

CH4 + O2 → C + 2 H2O

High molecular weight alkanes often cannot be completely burned. When they burn, they produce black smoke, that is, black smoke. The same is true of black smoke in automobile exhaust.

halogenate

R + X2 → RX + HX

Because the structure of alkanes is too strong, ordinary organic reactions can't be carried out. Halogenation of alkanes is a radical substitution reaction, and the initial reaction requires light energy to generate free radicals.

The following are the steps of methane halogenation. This highly exothermic reaction will lead to an explosion.

Chain initiation stage: two Cl free radicals are formed under the catalysis of ultraviolet rays.

Cl2 → Cl* / *Cl

Chain growth stage: separating an H atom from methane; CH3Cl began to form.

CH4+Cl* → CH3++HCl (slow)

CH3+ + Cl2 → CH3Cl + Cl*

Chain termination stage: two free radicals recombine.

Cl* and Cl*, or

R* and Cl* or

CH3* and CH3*.

Cracking reaction

Cracking reaction is the process of cracking macromolecules into small molecules at high temperature, high pressure or in the presence of catalysts. Cracking reaction belongs to elimination reaction, so alkane cracking will always produce olefins. For example, hexadecane (C 16H34) can be cracked to give octane and octene (C8H 18).

Because each bond is in a different environment, the probability of fracture is also different. Let's take the cracking of butane as an example to discuss this point:

CH3-CH2-CH2-CH3 → CH4 + CH2=CH-CH3

In this process, the CH3-CH2 bond is broken with a probability of 48%.

CH3-CH2-CH2-CH3→CH3-CH3+CH2 = CH2

In this process, the possibility of CH2-CH2 bond breaking is 38%.

CH3-CH2-CH2-CH3→CH2 = CH-CH2-CH3+H2

The probability of C-H bond breaking in the process is 14%.

In the cracking reaction, different conditions can trigger different mechanisms, but the reaction process is similar. Carbon radicals are generated during thermal decomposition, and carbon cations and hydrogen anions are generated during catalytic cracking. These extremely unstable intermediates form stable small molecular hydrocarbons through rearrangement, bond breaking and hydrogen transfer.

In industry, deep cracking is called cracking, and the products of cracking are all gases, called cracking gas.

Because of the high preparation cost of alkanes (olefins are usually used for catalytic hydrogenation), alkanes are not prepared in industry, but extracted directly from petroleum? S sent a message? Chasing ash [5]? From γ? What do you mean by staring at the string? Hey? せ? Pony? Thin?

The main function of alkanes is to make fuel. Natural gas and biogas (mainly methane) are widely used clean energy sources in recent years. Various fractions obtained by petroleum fractionation are suitable for various engines:

C1~ C4 (fraction below 40℃) is liquefied petroleum gas, which can be used as fuel;

C5 ~ c 1 1(40 ~ 200℃ fraction) is gasoline, which can be used as fuel and chemical raw materials.

C9 ~ c 18( 150 ~ 250℃ fraction) is kerosene, which can be used as fuel;

C 14 ~ C20(200 ~ 350℃ fraction) is diesel oil, which can be used as fuel;

Fractions above C20 are heavy oil, and lubricating oil, asphalt and other substances can be obtained after vacuum distillation.

In addition, in recent years, the reaction of cracking alkanes to olefins has become an important method to produce ethylene.

pbwfvwgkx 2009- 12- 12 0 1: 19:46 123. 15.232。 *

gynostemma pentaphyllum

cucurbitaceae

The Chinese name Hedysarum hedysari, also known as Hedysarum hedysari, is called South Ginseng, Ganman Tea and Gospel Grass in Japan, and is called Beauty God and Curator of All Diseases in Singapore and Malaysia. It is a perennial herb vine. 100% sweet pure-leaf Gynostemma pentaphyllum raw materials are superior in quality, high in effective components, economical and practical, and suitable for consumers who need to drink in large doses.

Gynostemma pentaphyllum is a plant of Gynostemma in Cucurbitaceae. There are 13 species in the world and 1 1 species in China. Gynostemma pentaphyllum and Prunus mume (Vitaceae) grown in the wild are very similar in plant morphology. Fresh Gynostemma pentaphyllum is a perennial herb vine, with slender stems, 1-3m, pentagonal or polygonal cross section, tendrils born in leaf axils, dark green leaves, compound leaves, 5-7 oval leaflets with petioles, shriveled leaves, easy to break, serrated edges, panicles, 8-20cm long, fruit-like florets with a diameter of 5-20cm. In folk, Gynostemma pentaphyllum is used to treat cough, expectoration and asthma, chronic bronchitis, infectious hepatitis and other diseases. Since 1974, Japanese scholars have isolated more than 50 kinds of saponins from this plant, of which 4 kinds have the same structure as ginsenoside, and 1 1 species is similar. From 65438 to 0984, China began to investigate and develop the distribution and resources of Gynostemma pentaphyllum. Studies at home and abroad have consistently shown that Gynostemma pentaphyllum has pharmacological effects such as inhibiting tumor cell proliferation, relieving fatigue, protecting liver, resisting gastric ulcer and regulating lipid metabolism. The harvest period is from May to August every year. After cutting the stems and leaves together, if there is soil, it should be washed and dried, then cut into 5cm sections with a straw cutter, processed according to the method of baking green tea, fixed, twisted, deblocked, dried or fried to make the primary product of Gynostemma pentaphyllum tea, refined and molded, and packaged into teabags. Some twisted blue teas are mixed with about 20% jasmine tea to make their fragrance more harmonious and soft. Its stems and leaves may not contain polyphenol oxidase, so it is not easy to make black tea-type Gynostemma pentaphyllum tea after fermentation. Green tea-type Gynostemma pentaphyllum tea is fragrant, light and bitter in taste, sweet in aftertaste and light yellow and clear in soup color. Known as "Southern Ginseng", there is a product named "Southern Ginseng Tea". According to relevant data, Gynostemma pentaphyllum does have the function of nourishing and calming the nerves, and has an auxiliary effect on some chronic diseases. It has no side effects, is not addictive if taken frequently, and is a healthy drink worthy of recommendation.

Also known as Hedysarum, Xiaokuyao and Gongluo Pot Bottom.

It comes from Gynostemma pentaphyllum. Makino, a plant of Gynostemma in Cucurbitaceae, whose rhizome is used as medicine. Harvesting in autumn, cleaning, drying and pulverizing.

Bitter and cold in nature.

Function: clearing away heat and toxic materials, relieving cough and resolving phlegm. Can be used for treating chronic bronchitis, infectious hepatitis, nephritis and gastroenteritis.

Usage and dosage: 0.75 ~ 1g (powder)

Excerpted from the National Collection of Chinese Herbal Medicine

Gynostemma pentaphyllum (thumb. ) Mu Ye. As a cucurbitaceae plant, the whole herb is used as medicine to relieve cough and asthma, and is mainly used for treating cough. Chronic tracheitis. It contains chemical components similar to ginsenoside, and has many functions such as anti-cancer and health care. It is distributed in provinces south of the Yangtze River basin and southwestern Shaanxi, and is an industrial raw material medicine. It is also planted in the south, Shaanxi, Shandong and Beijing. In addition, it belongs to several plants with high saponin content, such as Gynostemma pentaphyllum. Gynostemma pentaphyllum, Gynostemma pentaphyllum and compressed Gynostemma pentaphyllum

Plant characteristics:

Gynostemma pentaphyllum is a perennial herb vine with a length of 100 ~ 150 cm. Rhizomes are slender and transverse, with a length of 50 ~ 100 cm and a diameter of 1 cm. They are branched or unbranched, with fibrous roots on the nodes. The stems are slender, with sparse hairs on the nodes. Leaves alternate, usually 5 leaves form a bird's toe compound leaf, sparse 3 or 7 leaves. Leaflets are ovoid or ovoid, with petioles, blunt or short tips, wedge-shaped bases, short hairs on the lower veins, and leaflets on both sides are paired and planted on the same petiole. Summer flowers are yellow-green, axillary panicles, loose, 9 ~ 15 cm long; Flowers unisexual, dioecious, calyx small, corolla lobes lanceolate, apex caudate, about 2 mm long. Berries are round, dark green, and the seeds are oval and wrinkled.

Growth characteristics:

Wild Gynostemma pentaphyllum grows in mountains, ditches and wet places in valleys. Shady environment, the upper coverage is about 50%-80%, ventilated and light-permeable, and the sand, sandy loam or gravel are rich in humus loam. Neutral slightly acidic soil or slightly alkaline soil can grow.

It germinates from late March to early April, grows vigorously from April to August, and blooms from July to September. 1late October to1late October, 10 ~165438+early February, withered after frost, and the underground part remained dormant.

Gynostemma pentaphyllum, which is propagated by seeds and rhizomes, grows slowly in the early stage, has less dry matter accumulation, and is moist and cool in autumn and grows vigorously. Harvest at one time in late autumn and early winter, with about 3750 kilograms of stems and leaves per hectare. Rootstocks overwinter in the field and grow rapidly in the second year. At the beginning of June, the aboveground stems were harvested, and more than 65,438+0,500 kilograms of dry stems and leaves were harvested per hectare. Strengthen field management in autumn to promote the rapid growth of Gynostemma pentaphyllum, and harvest more than 3000 kilograms of dry stems and leaves in early winter.