Homogeneous and isomeric
Same series: A series of compounds that have the same general formula, similar structures, and similar chemical properties. The physical properties change regularly with the increase in the number of carbon atoms.
Homologues: Compounds in the same series are homologues of each other
Isomers: Compounds with the same molecular formula but different structures and properties are called isomers, or isomers for short.
Primary, secondary, tertiary, and quaternary carbon atoms (Bozhongshuji)
name
common nomenclature
Straight-chain alkanes (without branches) are called "n-alkanes"
A, B, C, Ding, Wu, Ji, Geng, Xin, Rengui, after 10, use capital letters, eleven, twelve...
Alkanes containing branched chains: simple isomers can be distinguished by the prefix n.
Different: There is a methyl group on the second carbon atom at the end of the carbon chain and no other branches.
New: There are two methyl groups on the second carbon atom at the end of the carbon chain and no other branches.
Nomenclature of alkyl groups
When an H is removed from an alkane, the remaining atomic group is called an alkyl group R- (according to the common nomenclature)
systematic nomenclature
The naming of straight-chain alkanes is the same as the ordinary nomenclature, and there is no need for the word "normal" in front of it.
The naming of branched alkanes is divided into three steps:
Choose the main chain: The longest carbon chain is the main chain, and the other side chains are used as substituents, which is called an alkane.
If the main chains are the same length, choose the one with the most straight links as the main chain.
Numbering: Number the carbon atoms in the main chain sequentially from the end closest to the branch chain.
substituent
Listed after the better groups
For the atom where the free valence of the substituent is located, the one with the larger atomic number is given priority. When the atomic numbers are the same, the mass number of the isotope is used. The one with the larger mass number is given priority.
For polyatomic substituents, when the atom where the free valence is located is the same, the second atom connected to the atom is compared in sequence. If the second atom is the same, the third atom is compared, and so on.
For substituents containing double and triple bonds, they can be viewed as having 2 or 3 single bonds connected to the same atom.
In the English name, the substituents are written in alphabetical order.
Alkane structure
hybrid orbital theory
In the process of forming a polyatomic molecule, the central atom can become an excited state, and several different types of atomic orbitals with similar energies are linearly combined to redistribute energy and determine the spatial direction to form an equal number of new atomic orbitals. This The process is called hybridization, and the new orbital formed is called a hybrid orbital.
Hybrid orbital characteristics
advantage
The electron cloud distribution is more concentrated
Stronger directionality and enhanced bonding ability of atoms
Hybridization expands the angle between orbitals and increases the bond angle, which is conducive to the formation of strong bonds and stable molecules.
spatial arrangement
Each orbit is as dispersed as possible and distributed symmetrically
Conformations of ethane and butane
Conformation: A molecule with a certain structure presents different three-dimensional images due to the rotation of a single bond changing the relative position of its atoms or atomic groups in space.
The most stable conformation of ethane is the cross
The order of butane conformational stability is: para-cross (ap) > ortho-cross (sc) > partial overlap (ac) > full overlap (ap)
Conformational isomers: Isomers with the same molecular composition and the same structural formula, but resulting from different relative positions of atoms or groups of atoms in space (there are countless conformational isomers of molecules)
physical properties
Relative density: The relative density of alkanes increases with the increase in relative molecular mass, but is always less than 1
Polarity: A molecule has no polarity or only very weak polarity
Solubility: Easily soluble in weakly polar and non-polar solvents
Material state: Alkanes at room temperature and normal pressure: 1C~4C (g), 5C~16C (l), 17C~ (s)
Boiling point: Straight-chain alkanes: The boiling points of alkanes gradually increase with the increase of molecular weight; as the relative mass of the molecule increases, the boiling point increase decreases quickly with each additional CH2; Branched-chain alkanes: For alkanes of the same molecular weight, the more branched chains they have. , the lower the boiling point
chemical properties
Chlorination: Alkanes react with chlorine, resulting in the replacement of hydrogen atoms in the alkanes with chlorine (reaction conditions: heating or light)
Oxidation and combustion: In organic reactions, adding oxygen and removing hydrogen is oxidation, and adding hydrogen and removing oxygen is reduction.
Stability: At room temperature, strong acids, strong bases, strong oxidants, etc. cannot react with alkanes, or the reaction is very slow.
Free radical mechanism: The reaction is repeated, the old free radicals disappear, and new free radicals are generated. The reaction with chain initiation, chain growth, and chain termination is called a free radical reaction in chemistry. Activity: 3°H>2°H> 1°H, relative stability of free radicals: 3°C>2°C>1°H
The boiling point of a liquid depends on the size of the intermolecular attraction. There is only very weak dispersion force between alkane molecules, and the dispersion force is related to the contact area of the molecules.
The conformation with the lowest energy is the most stable, and the most stable conformation is the dominant conformation. The dominant conformation is not the only conformation of the molecule, but the most common conformation
The more S components, the shorter the orbit, the greater the binding force of the atomic nucleus to the electrons, and the greater the electronegativity; the more P components, the longer the hybrid orbit, and the smaller the electronegativity.
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