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Ch. 7 - The Reactions of Alkynes • An Introduction to Multistep Synthesis
Bruice - Organic Chemistry 8th Edition
Bruice8th EditionOrganic ChemistryISBN: 9780135213711Non è quello che usi tu?Cambia libro di testo
Capitolo 7, Problema 58

α-Farnesene is a dodecatetraene found in the waxy coating of apple skins. What is its systematic name? Include E and Z where necessary to indicate the configuration of the double bonds.

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Step 1: Analyze the structure of α-Farnesene provided in the image. It is a hydrocarbon with four double bonds, making it a tetraene. The molecule is composed of 12 carbon atoms, indicating it is a dodecatetraene.
Step 2: Identify the longest continuous carbon chain in the structure. The chain contains 12 carbons, and the double bonds are located at specific positions along the chain.
Step 3: Assign the locants (positions) for the double bonds. Number the carbon chain starting from the end closest to the first double bond to ensure the lowest possible locants for the double bonds.
Step 4: Determine the stereochemistry (E/Z configuration) of each double bond. Analyze the substituents on either side of each double bond to decide whether the configuration is E (opposite sides) or Z (same side).
Step 5: Combine the locants, stereochemistry, and the base name (dodecatetraene) to write the systematic name of α-Farnesene. Include the E/Z designations for each double bond in the name.

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Dodecatetraene Structure

A dodecatetraene is a hydrocarbon with a chain of twelve carbon atoms and four double bonds. Understanding its structure is crucial for determining the systematic name, as the position and configuration of the double bonds influence the naming convention. The presence of multiple double bonds also affects the compound's reactivity and physical properties.
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Drawing Resonance Structures

E/Z Configuration

The E/Z nomenclature is used to describe the geometric configuration of double bonds in alkenes. 'E' (from the German 'entgegen') indicates that the highest priority substituents on either side of the double bond are on opposite sides, while 'Z' (from 'zusammen') indicates they are on the same side. Correctly identifying these configurations is essential for accurately naming compounds with multiple double bonds.
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E/Z Diastereoisomerism

IUPAC Nomenclature

The International Union of Pure and Applied Chemistry (IUPAC) provides a systematic method for naming chemical compounds. This includes rules for identifying the longest carbon chain, numbering the chain to give the lowest possible numbers to substituents and double bonds, and using prefixes and suffixes to indicate functional groups and unsaturation. Mastery of IUPAC nomenclature is necessary for accurately conveying the structure of organic molecules.
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The different parts of an IUPAC name