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Ch. 9 - Alkenes and AlkynesWorksheetSee all chapters
All Chapters
Ch. 1 - A Review of General Chemistry
Ch. 2 - Molecular Representations
Ch. 3 - Acids and Bases
Ch. 4 - Alkanes and Cycloalkanes
Ch. 5 - Chirality
Ch. 6 - Thermodynamics and Kinetics
Ch. 7 - Substitution Reactions
Ch. 8 - Elimination Reactions
Ch. 9 - Alkenes and Alkynes
Ch. 10 - Addition Reactions
Ch. 11 - Radical Reactions
Ch. 12 - Alcohols, Ethers, Epoxides and Thiols
Ch. 13 - Alcohols and Carbonyl Compounds
Ch. 14 - Synthetic Techniques
Ch. 15 - Analytical Techniques: IR, NMR, Mass Spect
Ch. 16 - Conjugated Systems
Ch. 17 - Aromaticity
Ch. 18 - Reactions of Aromatics: EAS and Beyond
Ch. 19 - Aldehydes and Ketones: Nucleophilic Addition
Ch. 20 - Carboxylic Acid Derivatives: NAS
Ch. 21 - Enolate Chemistry: Reactions at the Alpha-Carbon
Ch. 22 - Condensation Chemistry
Ch. 23 - Amines
Ch. 24 - Carbohydrates
Ch. 25 - Phenols
Ch. 26 - Amino Acids, Peptides, and Proteins
Ch. 26 - Transition Metals
Alkene Stability
Zaitsev Rule
Double Elimination
Hydrogenation of Alkynes
Dehydration Reaction
POCl3 Dehydration
Alkynide Synthesis

Not all alkenes were created equal. Like carbocations, alkenes are stabilized through a phenomenon called hyperconjugation

Hyperconjugation allows adjacent -R groups (mostly C-C and C-H σ-bonds) to create shared molecular orbitals with π-bonds, stabilizing the bond.

Concept #1: Understanding trends of alkene stability.

So basically, the more –R groups attached to the double bond, the more stable the double bond will be.

Specifically, when it comes to di-substituted bonds, the order os stability is gem > trans >  cis.

  • trans > cis due to steric hindrance. Groups have less freedom of movement in the cis position.
  • gem > trans due to better hyperconjugation. The full explanation for this trend is beyond the level of this course. Just memorize it.

Rank the following alkenes in order of lowest to highest heat of combustion. 

Example #1: Rank the following alkenes in order of lowest to highest heat of combustion.