Organic Chemistry Saturated Aliphatic Hydrocarbons

Organic Chemistry Saturated Aliphatic Hydrocarbons: Organic compounds containing only CH elements are hydrocarbon knowledge, including the general formula and isomerism of alkanes, naming, structure of alkanes, physical and chemical properties of alkanes, etc.

Edited at 2022-10-12 00:17:14

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Organic Chemistry Saturated Aliphatic Hydrocarbons

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Outline

Saturated aliphatic hydrocarbons: Organic compounds containing only two elements CH are hydrocarbons

General formula and isomerism of alkanes

CnH2n 2

Alkanes above C4 exhibit isomerism

name

Primary, secondary, tertiary, and quaternary carbon atoms and primary, secondary, and tertiary hydrogen atoms

Linear alkanes: The number of carbon atoms from one to ten is represented by the name of the heavenly stem: A, B, C, D, E, Ji, Geng, Xin, Ren, Gui The number of carbon atoms is greater than ten, so it is called by number: Eleven, twelve, twenty-three, etc.

Isomers, prefix: positive, different, new

alkyl

Alkanes remove one hydrogen atom and the remaining group is: R— Usually less than 5 carbons

Backbone selection and substituent position numbering

The longest chain is the main chain Minimum number of substituents The chain with the most substituents is the main chain Small groups come first (English is arranged in alphabetical order) When different groups have the same number, make the small substituent number the smallest. The combination of the same substituents is represented by uppercase numbers. Numbers are separated by "," "Lowest Series" compares the different rankings of each series one by one, encountering the series with the lowest ranking first.

Alkane structure

Methane ethane molecular structure: carbon atomic orbitals SP3 hybridization Ingredients: 1/4 S, 3/4 P Angle of symmetry axis: 109.5°

Atomic orbitals cross each other along the bond axis (head to head), forming a cylindrical axis-symmetric orbit, called a σ orbital, and the covalent bond formed by the orbit is called a σ bond Taking the key axis as the axis of symmetry, the orbits intersect greatly when forming a bond, and the bond is strong. Two atoms connected by a σ bond can rotate relative to each other without affecting the distribution of the electron cloud.

Ethane and its series of conformations: Chiasma conformation - the most stable extreme conformation, with the farthest distance between atoms and low internal energy Twisted conformations – countless Overlapping conformation - the most unstable extreme conformation, van der Waals repulsion, high internal energy

Butane conformation: cross (most stable Partially overlapping (less stable Ortho-crossed type (more stable Full overlap type (the most unstable

Physical and chemical properties of alkanes

Physical properties: Insoluble in water, soluble in non-polar organic solvents

boiling point ①Number of carbon atoms↑, boiling point↑ ②The number of carbon atoms is the same: branched chain ↑, boiling point ↓ ③The number of branches is the same: symmetry ↑, boiling point ↑

melting point ① Number of carbon atoms: number ↑, melting point ↑ (odd number, even number) ② The number of carbon atoms is the same: branch chain ↑, melting point ↓ ③ The number of branches is the same: symmetry ↑, melting point ↑ ④ Highly symmetrical isomers>Linear chain isomers

Density (the density of hydrocarbons is less than that of water, and the relative density is less than 1) ① Number of carbon atoms: number ↑, density ↑ ② The number of carbon atoms is the same: branch chain ↑, density ↓

Chemical properties: Great chemical stability, often used as solvents and lubricants. It does not interact with strong acids, strong bases, strong oxidants, and strong reducing agents at room temperature. The bond has low polarity and is not easy to break. The chemical properties of homologues are basically similar, but the reaction rates are very different.

1. Substitution reaction (mainly halogenation reaction) Hydrogens in alkanes are replaced by other atoms or groups ①The reaction requires light or heating ② Absorbing one photon during illumination can produce thousands of methyl chloride

Free radical reaction, three steps 1. Chain initiation: chlorine molecules absorb energy and decompose into two active chlorine free radicals 2. Chain growth: repeatable. The H atoms in the chlorine radicals deal with the alkane molecules to generate methyl radicals, which then interact with the chlorine molecules to generate methyl chloride and new chlorine radicals. 3. Termination of the chain: free radicals combine with each other

2. Oxidation reaction Complete oxidation: Alkanes burn in the air and are completely oxidized to generate CO2 and water, while releasing a large amount of heat. Controlled oxidation: alcohols, aldehydes, ketones, carboxylic acids, etc. are obtained, and the products are mostly mixtures

3. Cracking and pyrolysis Thermal decomposition reaction of alkanes under high temperature and anaerobic conditions

Relative stability of free radicals: 3o > 2o > 1o Different halogens have different reactivity F2>Cl2>Br2>I2 F2 is highly exothermic and difficult to control. Cl2 mainly replaces tertiary-secondary hydrogen, Br2 mainly replaces tertiary-secondary hydrogen, and I2 is difficult to react. As halogen activity decreases, selectivity increases

write

Single bonds can be omitted, but double bonds and triple bonds cannot. The aldehyde group and carboxyl group can be abbreviated as "-CHO" or "-COOH".

Keyline type: Generally represents organic matter with more than 2 carbon atoms Only C-H bonds are ignored, and the remaining chemical bonds cannot be ignored. C=C, C≡C bonds and other functional groups must be represented.