MCAT Organic Reactions Flashcards
What are reaction intermediates?
Short- lived transient products that are short lived and not found in the final product.
Describe the shape of carbocations
Trigonal planar , 120 degrees.
contains unoccupied unhybrized P orbitals that’s perpendicular to SP2 hybridized orbitals.
Contains 3 sigma bonds
They’re electrophilic
How does alkyl groups effect carbocation stability?
More alkyl groups makes it more stable due to the inductive effect ( pushing electron density into the carbocation).
They also stabilize the unhybridized P orbital via hyperconjugation ( when SP3 orbital overlaps with unhybridized P orbital).
How does resonance effect carbocation stability?
Through carbocation rearrangement.
- 1,2 hydride shift in which a hydrogen switch places with carbocation so carbocation is on carbon with more methyl groups.
- 1,2 methyl groups in which a methyl group switches places with carbocation so carbocation is on carbon with more methyl groups.
Describe the structure of carboanions
Contains 3 sigma bonds.
SP3 hybridized, tetrahedral geometry, 109.5 degrees.
They’re electron rich and so act as nucleophiles ( and so lewis bases)
The lone pair is located in the unhybridized P orbital.
Which one is a stronger base? Methyl carboanions or hydroxide ions?
Methyl carboanions are stronger than hydroxide ions.
How are carboanions and carbocations are described?
By the number of alkyl groups they have attached directly to the carbocation or the carboanion.
- Methyl = 0 alkyl groups.
- Primary = 1 alkyl group
- Secondary = 2 alkyl groups
- Tertiary = 3 alkyl groups.
How does alkyl groups effect carbanion strength?
Due to the inductive effect of alkyl groups pushing electron density into the carbanion it destabilizes it.
Thus the trend of stability is opposite of carbocations.
How does resonance effect carbanions?
When they’re next to alkenes or carbonyls they’re more stable because of resonance.
This is because the negative charge is able to spread out.
Describe the structure of free radicals
Contains 3 sigma bonds, unpaired/ nonbonded electron ( difference is that it’s only 1 electron rather than a pair).
They’re also SP2 hybridized like carbanions.
How does alkyl groups and resonance effect free radical stability?
More alkyl groups and resonance stabilizes it.
Resonance happens by breaking up electron pairs, represented by half an arrow and a dot that represents the free radical.
Oxidation v. Reduction in organic reactions
Oxidation is adding bonds to oxygen while removing bonds from hydrogen.
Reduction is adding bonds to hydrogen while removing bonds from oxygen.
Decarboxylation
Removal of a carboxyl group in the form of CO2.
The beta carbonyl is the group that’s removed.
Describe terpenes and how we classify them.
Terpenes are lipid precursors used to make steroids and lipid signaling molecules.
Isoprenes are precursors to terpenes. Isoprenes consist of a 5-carbon structure with a branched end (called the head) and the unbranched end (called the tail).
Terpenes are categorized by how many isoprene units they have:
2 - monoterpenes
3- sesquiterpenes
4- diterpenes
5- sesterterpenes
6- Triterpenes
