stereoisomers

Question 1

Define structural (constitutional) isomers.

Answer 1

Structural isomers are molecules with the same molecular formula but a different attachment of atoms.

Question 2

Define stereoisomers.

Answer 2

Stereoisomers are molecules with the same molecular formula and the same attachment of items - but they differ in structure because of a different arrangment in space. This can arise as E/Z stereoisomers (diastereomers), as stereoisomers with two or more chiral carbons but not mirror images (diastereomers) or nonsuperimposable mirror images enantiomers.

Question 3

Define diastereomers.

Answer 3

Diastereomers are stereoisomers which are not enantiomers. They arise as E/Z isomers - that is, different spacial arrangement due to a double bond, or when there are two or more chiral carbons but the molecules are not mirror images.

Question 4

Define enantiomers.

Answer 4

Enantiomers are stereoisomers which result due to the fact they are non-superimposable mirror images. We can recognize a molecule as a potential enantiomer if it has a chiral center or if the molecule does not have a plane of symmetry.

Question 5

Define chiral center.

Answer 5

Chiral center is an atom (usually carbon) with four different groups attached.

Question 6

In checking for potential stereoisomer, why is it important to consider whether there is a plane of symmetry?

Answer 6

If a molecule DOES NOT have a plane of symmetry, then this molecule must be chiral. For the CHEM 212/222 courses this can only happen if there is at least one chiral center.

Question 7

Define meso compound.

Answer 7

A meso compound is one with two or more chiral carbons, but which also has a plane of symmetry. Therefore, although there are chiral carbons, the compound is NOT chiral.

Question 8

Does this molecule have E, Z, or no stereochemistry?​

Answer 8

This molecule has no stereochemistry because carbon 3 has identical groups attached (and therefore it is not possible to prioritize).

Question 9

Does this molecule have E, Z, or no stereochemistry?

Answer 9

This molecule has Z stereochemistry because (as shown in the diagram) the higher priority groups on each of the stereocarbons are on the same side.

Question 10

Does this molecule have R, S, or no stereochemistry?

Answer 10

As drawn this molecule has no stereochemistry. Although it does has a chiral carbon, the three-dimensional wedge/dash perspective is not shown.

Question 11

Does this molecule have R, S or no stereochemistry?

Answer 11

This molecule has S stereochemistry.

Question 12

What is the relationship of the molecules represented by these structures?

Answer 12

These molecules are enantiomers - that is non-superimposable mirror images. Notice that the methyl group and hydrogen are switched.

Question 13

What is the relationship of the molecules represented by these structures?

Answer 13

These molecules are enantiomers - that is non-superimposable mirror images. Notice that the methyl group and fluorine are switched.

Question 14

What is the relationship of the molecules represented by these structures?

Answer 14

These molecules are constitutional (or structural) isomers - that is they have a different attachment of atoms.

Question 15

What is the relationship of the molecules represented by these structures?

Answer 15

These molecules are E/Z-type stereoisomers (diastereomers). The molecule on the left is Z and the molecule on the right is E.

Question 16

What is the relationship of the molecules represented by these structures?

Answer 16

Although these molecules have double bonds, they have a different attachment of atoms, therefore they are constitutional (structural) isomers.

Question 17

Molecules with the same molecular formula but a different attachment of atoms.

Answer 17

Structural (constitutional) isomers.

Question 18

Molecules with the same molecular formula and the same attachment of items - but they differ in structure because of a different arrangment in space. This can arise as E/Z stereoisomers (diastereomers), as stereoisomers with two or more chiral carbons but not mirror images (diastereomers) or nonsuperimposable mirror images enantiomers.

Answer 18

Stereoisomers.

Question 19

Stereoisomers which are not enantiomers. They arise as E/Z isomers - that is, different spacial arrangement due to a double bond, or when there are two or more chiral carbons but the molecules are not mirror images.

Answer 19

Diastereomers.

Question 20

Stereoisomers which result due to the fact they are non-superimposable mirror images.

Answer 20

Enantiomers.

Question 21

A carbon with four different groups attached.

Answer 21

Chiral carbon

Question 22

A compound with two or more chiral carbons, but which also has a plane of symmetry. Therefore, although there are chiral carbons, the compound is NOT chiral.

Answer 22

Meso compound.