stayOrganic compoundIn the molecule, C-CSingle bondrotateResulting fromatomorGroupNumerous specific images arranged in space are called conformations.Refers to a molecule that does not changecovalent bondStructure, only the spatial arrangement generated by the placement of atoms around the single bond.Different conformations can transform each other. In various conformational forms,potential energyThe lowest and most stable conformation is the dominant conformation.When one conformation is changed to another, the covalent bond is not required to be broken and re formed.Conformational changes do not change the moleculesOptical activity。[1]
Conformational isomer
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The isomers formed by the rotation of C-C single bond around σ bond are called conformational isomers, and the isomers formed are called conformational isomersIsomerbe calledRotational isomerorConformational isomer。
When the C-C single bond rotates, there can be countless conformational isomers, and the limiting conformations areCascading、Clockwise and wrongly、Reverse errorandInversionEtc.stayCongruent conformationMedium, connected on two carbonschlorineThe atom is closest to the chlorine atom, producing strongRepulsion, with the highest internal energy, belongs to the most unstable conformation of the molecule;stayReverse conformationIn, the chlorine atom is the most distant from the chlorine atom, with the smallest mutual repulsion force and the lowest internal energy, which is the most stable conformation of the molecule.Cis dislocation conformationandReverse dislocation conformationThe stability of is between the two conformations, and their stability order is: inverted>clockwise>inverted>clockwise.
conformation
Various conformational isomers of molecules are not evenly distributed, and their most stable conformations are always the main form of existence at room temperature, that isDominant conformationIf it deviates from the dominant conformation, torsional tension will occur.On adjacent carbon atomsBetter groupAngular scale between (or atoms)Torsional angle(Torsion angle, also known asDihedral angle)。variousConformational isomerThe energy generated by torsional tension must be overcome for mutual transformation between them, generally between 12 and 20 kJ · mol-1.At room temperature, molecular collision can produce 84kJ · mol-1 energy, so it is difficult to separate these conformational isomers at room temperature.[2-3]
Isomer
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linear alkane conformation
Linear alkane conformation has staggered, eclipsed and gauche.Ethane is the simplest compound containing C-C single bond. If one carbon atom in ethane molecule is stationary and another carbon atom rotates around the C-C bond, three hydrogen atoms on one carbon atom can be arranged in countless ways relative to three hydrogen atoms on the other carbon atom. Among them, overlapping formula and cross formula are classical conformations.[1]
If the carbon atoms in the cyclohexane molecule are on the same plane, the C-C bond angle is 120 degrees, and there is a large angular tension.In fact, molecules automatically bend to form a non planar conformation. In the dynamic balance of a series of conformations, chair conformation and boat conformation are two typical conformations.At room temperature, because the thermal movement of molecules can make the boat and chair conformation transform each other, it is impossible to separate a certain conformational isomer of cyclohexane in the boat or chair conformation.[1]
Cyclohexane conformation
Other examples of conformational isomers are molecular folding, which makes certain shapes more stable and has certain functions.BesidesEnantiomerism(attrisoler), etc.[1]
Effect of Conformation on Physicochemical Properties of Molecules
Molecular conformation not only affects the physical and chemical properties of compounds, but also affects some biological macromolecules (such asprotein, enzyme, nucleic acid).Conformational isomerism of many drug molecules and drugsbiological activityIt is closely related. Generally, the drug receptor is only combined with one of a variety of drug conformations, which is called the pharmacodynamic conformation.The non effective conformational isomers of drugs are difficult to bind to drug receptors, and usually have low or no effect.For example, the pharmacodynamic conformation of dopamine, an anti polio drug, acting on the receptor is in the para crossed form.[1]
