Write structural formulas or build molecular models and give the IUPAC names for all the alkenes of molecular formula C6H12 that contain a trisubstituted double bond

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Write structural formulas or build molecular models and give the IUPAC names for all the alkenes of molecular formula C6H12 that contain a trisubstituted double bond. (Don’t forget to include stereoisomers.)

The correct answer and explanation is :

Structural Formulas and IUPAC Names for Trisubstituted Alkenes (C₆H₁₂)

The molecular formula C₆H₁₂ corresponds to alkenes (CnH₂n) with one double bond. A trisubstituted alkene has a double bond where three carbon atoms are directly attached to the sp² hybridized carbons.

Here are all the possible trisubstituted alkenes for C₆H₁₂, including their structural formulas and IUPAC names:

1. 2-Methylpent-2-ene

Structural Formula:

      CH3  
       |  
CH3-CH=C-CH2-CH3
  • IUPAC Name: 2-Methylpent-2-ene
  • Has E/Z isomers due to different groups attached to the double bond:
  • (E)-2-Methylpent-2-ene
  • (Z)-2-Methylpent-2-ene

2. 3-Methylpent-2-ene

Structural Formula:

      CH3  
       |  
CH3-CH=C-CH-CH3  
         |  
        CH3
  • IUPAC Name: 3-Methylpent-2-ene
  • Has E/Z isomers:
  • (E)-3-Methylpent-2-ene
  • (Z)-3-Methylpent-2-ene

3. 2,3-Dimethylbut-2-ene

Structural Formula:

    CH3     CH3  
      \     /  
       C=C  
      /     \  
    CH3     CH3
  • IUPAC Name: 2,3-Dimethylbut-2-ene
  • No E/Z isomerism because both sides of the double bond have identical groups.

Explanation (300 words)

A trisubstituted alkene has three carbon groups attached to the doubly bonded carbons. For C₆H₁₂, we must systematically find structures that satisfy this criterion.

Step 1: Identify the Carbon Skeleton
Since C₆H₁₂ has six carbons and one double bond, we consider various straight-chain and branched structures while ensuring three carbon groups are attached to the alkene carbon atoms.

Step 2: Positioning the Double Bond
By placing the C=C bond at different positions in the pentane and butane skeletons, we identify potential trisubstituted configurations:

  • Pentane backbone: 2-Methylpent-2-ene, 3-Methylpent-2-ene
  • Butane backbone: 2,3-Dimethylbut-2-ene

Step 3: Stereoisomerism Consideration
Alkenes with different substituents on each double-bonded carbon exhibit E/Z (cis-trans) isomerism due to restricted rotation around the double bond.

  • 2-Methylpent-2-ene and 3-Methylpent-2-ene each have E/Z isomers because of distinct groups on both sp² carbons.
  • 2,3-Dimethylbut-2-ene does not have E/Z isomerism since both sp² carbons have identical groups.

Thus, the final answer includes five unique structures: three base structures and two E/Z isomers for two of them.

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