Integrated SequencePhysics Chemistry Organic Biology

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Special points of emphasis

Electricity

Thermochemistry

Chemical Kinetics

Nucleophiles and Electrophiles

Reactions of Alcohols and Ethers

Regioselectivity in epoxide ring opening is characteristic of an organic chemistry passage subject on the MCAT, but which is a bit too abstruse to be prior required knowledge for the exam. A shift in conditions to acid catalysis shifts the regioselectivity of epoxide ring opening from less highly substituted carbon to the carbon with more aliphatic substituents. In other words, anionic nucleophiles attack the less hindered carbon, while with acid catalysis, the other carbon is favored for attack. Under acid conditions, the epoxide oxygen is first protonated, and then carbocation character develops at the carbon under attack by the nucleophile in the rate-determining step. More highly substituted carbons can better support positive charge because of the electron releasing character of aliphatic substituents.



Reactions of Alcohols and Ethers

Lipids

Integration of Metabolism

The Endocrine System

The MCAT tends to slant the organic towards the needs of future doctors and away from the needs of future chemical engineers (an influence, not a rule!). The epoxide form might be a minor MCAT favorite because of the importance of epoxides in lipid biosynthesis.

The biosynthesis of steroids involves epoxide formation in the terpene squalene to form squalene 2,3-epoxide. Multiple ring formation in squalene 2,3 epoxide is triggered by epoxide ring opening.








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