trans-2-Butene is more stable than cis-2-butene by only 4 kJ/mol, but trans-2,2,5,5-tetramethyl-

step 1 Sysbutin is less stable than trisbutin by 4 kilojoules per mole, while 225 tetra -methal 3 hexen

Trans-2-Butene is more stable than cis-2-butene by only 4...

Key Concepts

Alkene Substitution and Stability

The degree of substitution on an alkene (how many alkyl groups are attached to the sp2 carbons) is a key factor in its stability. More substituted alkenes are generally more stable due to hyperconjugation, but when large substituents are present, the spatial arrangement (cis vs. trans) becomes critical. With bulky substituents, the trans isomer is favored as it minimizes steric clashes, thereby enhancing the overall stability disparity.

Substituent Effects

Substituent effects involve the influence of alkyl or other groups attached to a double bond on the molecule’s stability. Larger or more numerous substituents can create significant steric hindrance and, in addition, may participate in stabilizing interactions like hyperconjugation. In cases where substituents are very bulky, the arrangement that minimizes repulsions (typically the trans configuration) is markedly more stable.

Cis/Trans Isomerism

Cis/trans isomerism refers to the spatial arrangement of groups around a double bond, where in the cis configuration similar groups are on the same side and in the trans configuration they are on opposite sides. This geometric difference can significantly affect the physical and chemical properties, including the overall stability of the isomers.

Steric Strain

Steric strain arises when bulky groups are forced into close proximity, leading to repulsive interactions. In cis isomers, bulky substituents are adjacent, which can increase repulsive forces and strain, whereas in trans isomers these groups are positioned farther apart, reducing the steric hindrance and leading to greater stability.

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