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Chemistry · Grades 11–12

Chirality and geometric isomerism

Recognize when spatial labels require enough structural information.

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Chiral

A chiral object is not superimposable on its mirror image.

Center

A tetrahedral carbon bonded to four different substituents is a common source of chirality.

Alkenes

Geometric isomerism around C=C requires each alkene carbon to have two different substituents.

Labels

R/S and E/Z require priority rules and adequate spatial information; a name cannot be guessed from formula alone.

Worked examples

Which tetrahedral carbon is a candidate stereogenic center in a simple example?

Four distinguishable substituents can create two nonsuperimposable arrangements.

One bonded to four different groups.

Can CH₂=CH₂ have E/Z isomerism?

Each double-bond carbon must have two different substituents.

No; each carbon has two identical hydrogen substituents.

Check your understanding

  1. Two nonsuperimposable mirror-image molecules are called what?

    1. Isotopes.
    2. Conformers in every case.
    3. Enantiomers.

  2. A tetrahedral carbon is bonded to H, OH, CH₃ and CH₂CH₃. How many different attached groups are listed?

  3. Why cannot R or S usually be assigned from a plain molecular formula?

Answers and marking notes

Answers and marking notes
  1. Enantiomers.

    This is the defining mirror-image relationship.

  2. 4

    Each listed group differs from the others.

  3. Connectivity, priorities and three-dimensional orientation are needed.

    A formula only provides atom counts.

Further reading and review references

These are reference links, not copied exercises, institutional endorsement or proof of independent review.

Independent educational review required. Grade bands are approximate; these are not officially aligned curricula.