16 Epoxides And Regioselectivity 16 Epoxides And Regioselectivity

16 Epoxides And Regioselectivity

Sophomore Organic Chemistry By Inquisition: the first animated workbook for student self-study and flipped classes

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Publisher Description

Epoxidations of both cyclic and acyclic alkenes are stereospecific. Thus some isomers can be formed totally free of the others.

Unlike halonium ions, epoxides are readily isolated; then they can be combined with nucleophiles in separate reactions. Nucleophilic attack on unsymmetrical epoxides takes place via two competing pathways to give isomeric products. Preferred products are determined by reaction pH. Under neutral or basic conditions nucleophiles add to the least hindered epoxide end. Epoxides under acidic conditions, however, preferentially open at the terminus best able to support positive charge, which is usually the other end. Consequently, epoxide openings under acid and basic conditions have complementary regioselectivities and this is a way to exert regiocontrol over which ring-opened product forms preferentially. Regio-specificity, selectivity are two important concepts introduced in this book.

Another important conclusion from this chapter is different reaction mechanisms may apply under basic (or basic) and acidic conditions. This is important for epoxides and absolutely vital for carbonyl chemistry (featured later in this series). Under neutral and basic conditions nucleophiles tend to add directly to electrophilic substrates. However, under acidic conditions nucleophiles can be deactivated by protonation, but oxygen atoms on the substrates (here epoxides, later carbonyls) tend to be activated because they are also protonated.

GENRE
Science & Nature
RELEASED
2023
27 December
LANGUAGE
EN
English
LENGTH
32
Pages
PUBLISHER
By Inquisition Press
SELLER
Kevin Burgess
SIZE
25.3
MB

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