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Stereoisomerism - The Organic Chemistry Tutor

2-chlorobutane

  • Butane has four carbons with a chlorine atom on carbon two.

  • The chlorine atom can be in the front or the back.

  • Two stereoisomers can be drawn for two-chlorobutane. These are enantiomers because they have opposite configurations at their chiral centers and no internal plane of symmetry.

2-bromo-3-chloropentane

  • Pentane with a bromine atom on carbon two and a chlorine atom on carbon three.

  • Potentially up to four stereoisomers because there are two chiral centers (2n2^n$$2^n$$ or 22=42^2 = 4$$2^2 = 4$$, where nn$$n$$ is the number of chiral centers).

Stereoisomer 1

  • Bromine atom on a wedge and chlorine atom on a dash.

Stereoisomer 2

  • Change the stereochemistry of the first stereoisomer.

  • Compounds 1 and 2 are diastereomers because only one chiral center changed.

Stereoisomer 3

  • Change the chiral center with the bromine atom, putting the chlorine atom back on the wedge.

  • Compounds 1 and 3 are diastereomers because only one chiral center has changed.

  • Compounds 2 and 3 are enantiomers because both chiral centers have changed their configuration.

Stereoisomer 4

  • Put the bromine atom in the back and the chlorine atom in the back.

  • One and four are enantiomers (all chiral centers changed, no internal plane of symmetry).

  • Two and four are diastereomers (differ by only one chiral center).

  • Three and four are diastereomers.

1,2-dibromocyclohexane

  • Drawing all stereoisomers for this molecule, designating carbons one and two.

Stereoisomer 1

  • First stereoisomer.

Stereoisomer 2

  • Changing one of the chiral centers.

  • Compounds 1 and 2 are diastereomers.

Stereoisomer 3

  • Changing both chiral centers.

  • Compounds 2 and 3 are diastereomers.

  • Compounds 1 and 3 are meso compounds with an internal plane of symmetry, thus they are identical.

Stereoisomer 4

  • Last Stereoisomer

  • Compounds 2 and 4 are enantiomers because all chiral centers have changed and there's no internal plane of symmetry.

  • Compounds 1 and 3 are meso compounds (identical).

  • Compounds 1 and 2 are diastereomers.

  • Compounds 3 and 4 are also diastereomers.

  • Total of three stereoisomers (1, 2, and the meso compound).


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Stereoisomerism - The Organic Chemistry Tutor

2-chlorobutane

  • Butane has four carbons with a chlorine atom on carbon two.

  • The chlorine atom can be in the front or the back.

  • Two stereoisomers can be drawn for two-chlorobutane. These are enantiomers because they have opposite configurations at their chiral centers and no internal plane of symmetry.

2-bromo-3-chloropentane

  • Pentane with a bromine atom on carbon two and a chlorine atom on carbon three.

  • Potentially up to four stereoisomers because there are two chiral centers (2n2^n or 22=42^2 = 4, where nn is the number of chiral centers).

Stereoisomer 1

  • Bromine atom on a wedge and chlorine atom on a dash.

Stereoisomer 2

  • Change the stereochemistry of the first stereoisomer.

  • Compounds 1 and 2 are diastereomers because only one chiral center changed.

Stereoisomer 3

  • Change the chiral center with the bromine atom, putting the chlorine atom back on the wedge.

  • Compounds 1 and 3 are diastereomers because only one chiral center has changed.

  • Compounds 2 and 3 are enantiomers because both chiral centers have changed their configuration.

Stereoisomer 4

  • Put the bromine atom in the back and the chlorine atom in the back.

  • One and four are enantiomers (all chiral centers changed, no internal plane of symmetry).

  • Two and four are diastereomers (differ by only one chiral center).

  • Three and four are diastereomers.

1,2-dibromocyclohexane

  • Drawing all stereoisomers for this molecule, designating carbons one and two.

Stereoisomer 1

  • First stereoisomer.

Stereoisomer 2

  • Changing one of the chiral centers.

  • Compounds 1 and 2 are diastereomers.

Stereoisomer 3

  • Changing both chiral centers.

  • Compounds 2 and 3 are diastereomers.

  • Compounds 1 and 3 are meso compounds with an internal plane of symmetry, thus they are identical.

Stereoisomer 4

  • Last Stereoisomer

  • Compounds 2 and 4 are enantiomers because all chiral centers have changed and there's no internal plane of symmetry.

  • Compounds 1 and 3 are meso compounds (identical).

  • Compounds 1 and 2 are diastereomers.

  • Compounds 3 and 4 are also diastereomers.

  • Total of three stereoisomers (1, 2, and the meso compound).