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Introduction to Organic Chemistry

E-Z Stereoisomerism and CIP Priority Rules

  • 3 things to know
  • Papers 2 and 3

Overview

Why restricted rotation causes E-Z isomerism, and assigning priority by the CIP rules.

What you need to know

Answer each one before you reveal it.

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Key term

What structural feature is required for E-Z stereoisomerism to occur in alkenes?

Key term

Why does restricted rotation around a carbon-carbon double bond lead to stereoisomerism?

Key term

What does the CIP priority system stand for?

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    What structural feature is required for E-Z stereoisomerism to occur in alkenes?

    Model answer

    Each carbon of the carbon-carbon double bond must have two different groups attached to it.

  2. 2

    Why does restricted rotation around a carbon-carbon double bond lead to stereoisomerism?

    Model answer

    The pi bond prevents rotation around the double bond, so groups attached to the double bond carbons are fixed in position relative to each other.

  3. 3

    What does the CIP priority system stand for?

    Model answer

    Cahn-Ingold-Prelog priority rules.

  4. 4

    How are priorities assigned to atoms directly attached to a double bond carbon in the CIP system?

    Model answer

    By atomic number, with higher atomic number giving higher priority.

  5. 5

    If two atoms directly attached to a double bond carbon are identical, how is priority determined?

    Model answer

    By examining the atoms attached to those identical atoms, continuing outward until a difference is found.

  6. 6

    What defines the E isomer in E-Z nomenclature?

    Model answer

    The higher priority groups on each carbon of the double bond are on opposite sides (E from German 'entgegen' meaning opposite).

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