How to quickly judge chiral carbon atoms, and what is the method of judging chiral carbon atoms?

Judgment method. 1. Chiral carbon atoms must be saturated carbon atoms;

2. The four groups connected by chiral carbon atoms should be different.

Definition. People refer to carbon atoms with four different groups as chiral carbon atoms (chiral carbon atoms are often labeled with *).

Example. Chiral carbon atoms are found in many organic compounds, especially those related to life phenomena. For example: glucose, fructose, lactic acid, etc.

Chiral carbon atom is also called asymmetric carbon atom, which is now defined in college organic chemistry textbooks as follows: a carbon atom has four different atoms or groups, and this carbon atom is called asymmetric carbon atom. The asymmetric carbon atoms containing hydrogen and hydroxide are d-type, and the rest are l-type.

To determine whether a carbon atom is chiral carbon, the first condition to be met is that the carbon atom must be saturated carbon, that is, there are 4 groups connected; Secondly, if a carbon atom is a chiral carbon atom, then the four groups attached to the carbon atom must be different;

If you want to judge the configuration of a chiral carbon atom, you need to arrange the four groups on the carbon atom in a regular order. The smallest group is placed at the farthest point from the eye, and the other three groups rotate in the direction from large to small, the direction of rotation is clockwise, and the chiral carbon is in the r configuration;

If the direction of rotation is counterclockwise, chiral carbon is of the S configuration (the Latin sinister initial).

Chemical properties. All compounds containing one chiral carbon atom have a pair of enantiomers. Compounds containing two distinct chiral carbon atoms have 4 optical isomers (two enantiomers).

With the further increase of the number of different chiral carbon atoms contained in the molecule, the number of optical isomers will also increase, and the number of optical isomers in molecules containing n different chiral carbon atoms is theoretically 2n and 2n-1 pairs.

If two chiral carbon atoms contain the same atom or group, it is customary to place the two identical atoms or groups on the same side of the Fischer projection, which is called red type; On the opposite side it is called the Su type. Therefore, the four isomers can also be named after the red and Soviet types.

1. To judge whether a carbon atom is chiral carbon, the first condition to be met is that the carbon atom must be saturated carbon, that is, there are 4 groups connected; Quietly.

2. Secondly, if a carbon atom is a chiral carbon atom, then the four groups connected to the carbon atom must be different;

3. If you want to judge the configuration of a chiral carbon atom, you need to arrange the size of the four groups on the carbon atom according to the order rules;

4. Place the smallest group at the farthest point from the eye, and the other three groups rotate in the direction from large to small, the rotation direction is clockwise, and the chiral carbon is the r configuration;

5. If the direction of rotation is counterclockwise, the chiral carbon is of the S configuration (the prefix of the Latin sinister).

6. Chiral carbon atoms must be saturated carbon atoms;

7. The four groups connected by chiral carbon atoms should be different.

4.A method for judging chiral carbon atoms.

1) Saturated chain molecules: The four groups connected by carbon atoms do not contain double-bonded carbon atoms or rings. Generally, only the group structure, that is, the way the atoms are connected, does not need to consider the spatial configuration.

2) Molecules with carbon-carbon double bonds in the groups connected to carbon atoms: In the case of the same group structure, the cis-trans isomerism of double-bonded carbons needs to be considered. If the double-bonded carbons in the group are cis-cis-ci and trans-trans, then the central atom is not a chiral carbon atom. If the two double-bonded carbons are cis-trans, then the central carbon atom is a chiral carbon atom.

The method of quickly judging chiral carbon atoms is: chiral carbon atoms must be saturated carbon atoms; The four groups to which the chiral carbon atom is attached should be different.

Chiral carbon atom refers to the carbon atom with four different groups connected to it as chiral carbon atom, and the chiral carbon atom is often marked with *. This atom is present in living compounds.

Judging method:1Chiral carbon atoms must be saturated carbon atoms;

2.The four groups to which the chiral carbon atom is attached should be different.

1. Compounds containing two different chiral carbon atoms.

In this type of compound, the four groups attached to the two chiral carbon atoms are not identical. A compound containing one chiral carbon atom has one pair of enantiomers, so how many enantiomers does a compound containing two chiral carbon atoms have? If a and b represent two different chiral carbon atoms, since each chiral carbon can have two opposite configurations, a+, a-, b+, b-.

In this way, according to the permutations and combinations, the configuration of the whole molecule can be as follows.

That is, a compound containing two chiral carbon atoms can theoretically have four enantiomers. where is a mirror image of , is a mirror image of , so they are two pairs of enantiomers and , or and , although some of them are mirrored, but the other part is the same, so they are not enantiomers, but diastereomers. Diastereomers and enantiomers are different in that their properties, both physical and chemical, are different.

But since they belong to the same kind of compounds, the chemical properties are somewhat similar.

The other is the carbon atom that has only one methyl group attached.

Why is this picture in your book so slippery? It's easy to misunderstand that the correct diagram would look like this:

In the figure, the red circles of the three letters show three chiral carbons.

The green box is the place where your book is easy to cause misunderstanding, and it should be disconnected, otherwise it is easy for people to think that there is a crossover there.

For general chiral molecules, we can judge chiral carbon atoms by the following steps:

Determine if the carbon atom in the molecule has four different substituents, if not, it is not a chiral carbon atom.

For carbon atoms with four different substituents, the substituents are numbered in order of priority from high to low, and the numbering principle is as follows: the atom with higher atomic number has the higher priority, and if the priority is the same, the atom in the next substituent group is compared.

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The numbered subsituents are arranged from high priority to low, and if they are arranged in a clockwise direction, they are r-type chiral carbon atoms; If they are arranged in a counterclockwise direction, they are s-type chiral carbon atoms.

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It should be noted that for molecules with symmetry, such as cyclic molecules and symmetrical stereoisomers, the symmetry of chiral carbon atoms needs to be considered. At the same time, the properties of chiral carbon atoms are of great significance for medicinal chemistry, biochemistry and other fields, so chiral orange chemistry is one of the important branches in chemistry.

Chiral carbon is judged as follows:

The simplest is to have a chiral center, that is to say to have chiral carbon. Generally, as long as the four groups on the carbon are not the same, then the carbon is chiral.

Chemical properties of chiral carbon atoms:

1. People refer to the carbon atom with four different groups as a chiral carbon atom, and the optical rotation and the chemical structure of the molecule determine whether it is chiral or not. Among organic compounds, most of the chiral molecules contain chiral carbon atoms.

2. So, in general, it is possible to determine whether a molecule is chiral by judging whether it has chiral carbon atoms. A molecule containing a chiral carbon atom must be a chiral molecule. A chiral carbon atom can have two configurations, so, contains a chiral carbonogen.

3. There are two molecules with different configurations, and they form a pair of enantiomers, one makes the polarized light right-handed, and the other makes the polarized light left-handed. Optical isomers are present due to the presence of chiral carbon atoms. <>

Methods for judging chiral carbon atoms include determining the binding mode of carbon atoms, drawing the three-dimensional structure, applying the cahn-ingold-prelog rule, assigning priority to each band segment group of carbon atoms, observing the spatial arrangement, and judging the chiral properties.

1.Determine how the carbon atoms are combined.

It is necessary to determine whether the carbon atom is attached to four different groups or not. It is possible for a carbon atom to be chiral only if it has four different groups attached. If there are two or more identical groups in the group to which the carbon atom is attached, then the carbon atom is not a chiral carbon atom.

2.Draw a three-dimensional structure.

When drawing the three-dimensional structure of organic molecules, a spatial model or a wedge-shaped cone projection can be used to represent the spatial arrangement of carbon atoms and other groups in the molecule. This helps to better visualize the three-dimensional structure of the molecule and thus determine the chiral carbon atom.

3.Apply the cahn-ingold-prelog rule.

The Cahn-Ingold-Preserve (CIP) rule is a method used to determine the ranking and naming of chiral carbon atoms. According to this rule, the four groups to which the carbon atom is attached are assigned priority, which is usually determined by comparing the atomic number of atoms in the group. Groups with higher atomic numbers have a higher priority.

4.Priority is assigned to each group of the carbon atom.

According to the CIP rule, a priority is assigned to each group to which the carbon atom is attached. In general, the higher the atomic number, the higher the priority. If the atoms in both groups are the same, then the atoms that connect these groups need to be compared until a higher priority group is found.

5.Observe the spatial arrangement.

Observe the spatial arrangement of the four groups connected by the carbon atoms. If the spatial arrangement of the group is asymmetrical and cannot be coincident with its mirror image by rotation or translation, then the carbon atom is chiral.

If the four groups of a carbonogen or file are arranged in a plane, then it is not a chiral carbon atom; If the four groups of a carbon atom are arranged in space and cannot be coincident with its mirror image by rotation or translation, then it is a chiral carbon atom.

6.Determine the nature of chirality.

Based on the chiral nature of the carbon atom, the chirality of the molecule can be judged. If there is a chiral carbon atom, then the molecule is chiral. If all carbon atoms are achiral carbon atoms, then the molecule is achiral.