Chapter 7: Alkenes

Groups with c-c pi bonds.

CNH2N 2 less hydrogens than alkanes CNH2N + 2 which makes alkenes unsaturated because they do not have the max amount of H on the molecule

DBE= 2C + 2 - H - x + N/2 Helps calculate the number of pi bonds or rings in a molecule which helps solve for structure (will be important in spectroscopy)

Double bonds are 2 carbons that share a sigma and pi bond.

• Alkene demands priority so it has to be on the lowest number of carbons regardless of substituents • Find the largest continuous carbon chain that has the alkene (ring or chain) • Drop the -ane and add -ene

• cis/trans disubstituted alkenes • E/Z designation for alkenes

• Use Cahn-Ingold-Prelog rules of priority • # 1 falls on the same side then (Z) • # 1 falls on the opposite side then (E)

False.

An atom or substituent is in the vinylic position when they are directly attached to an alkene.

A group is in the allylic position on an alkene when it is next to the alkene.

Use bond energies to calculate delta Horxn

delta Horxn = (sum Hobonds broken) - (sum Hobonds formed)

(-) exothermic. Energy occurs on the product side of rxn because alkenes will give off energy if you reduce or hydrogenate it.

Mono substituted, disubstituted, and trisubstituted. Substitution matters

trisub > disub > monosub Trisubstituted is the most stable, Monosubstituted is the least stable

More substituted alkenes are more thermodynamically stable. Giving off less heat (less energy) creates more stability. Giving off more heat (more energy) creates less stability.

Trans are more stable because it gives off less heat and is lower in energy than cis due to avoidance of steric strain.

Cis alkenes create very close electron clouds called steric strain (electrons bumping into each other). Steric strain adds energy to a system making it less stable.

A carbon that only has 6 electrons in its valence shell and is covalently bonded to 3 atoms. Carbon can have 6 electrons because it is not super electronegative.

+CH3 - methyl (C+ nothing attached) 1o primary (1 Carbon attached) 2o secondary (2 Carbons attached) 3o tertiary (3 Carbons attached)

3 >> 2 > 1 more substitution=more stable or lower in energy

Hyperconjugation. Electron delocalization called hyperconjugation which is an overlap of a pair of electrons between a filled and empty orbital that can’t be described by resonance.

More hyperconjugation=more stable The more bonds that you have next to a carbocation the more hyperconjugation. The more occurrences of hyperconjugation, the more stable the carbocation.

H-X Addition