09 Advanced Reaction Mechanisms Free Online FlashCards

What three kinds of evidence help evaluate a reaction mechanism?

A strong analysis combines orbital compatibility, stereochemical outcomes, and reaction kinetics.

What happens in a 1,2-shift?

A group migrates with its bonding electron pair to a neighboring electron-deficient center, relocating the positive charge as the molecular skeleton changes.

What key events occur in a pinacol rearrangement?

Under acidic conditions, water leaves; a neighboring group migrates as oxygen forms a carbonyl. Product prediction depends on which migration pathway is favored.

What is the overall transformation in a Hofmann rearrangement?

A primary amide becomes an amine with loss of the carbonyl carbon, through bromination, rearrangement to an isocyanate, and hydrolysis.

What defines a pericyclic reaction?

It is a concerted reorganization of bonding electrons through a cyclic transition state, without discrete intermediates.

What does “symmetry-allowed” mean for a reaction?

Allowed means orbital symmetry permits the pathway; it does not guarantee that the reaction is fast or favorable under every condition.

How does a thermal 4π-electron system close electrocyclically?

A thermal 4π-electron system closes conrotatorily, with its terminal orbitals rotating in the same direction.

What is the thermal ring-closure mode for a 6π-electron system?

A thermal 6π-electron system closes disrotatorily; photochemical excitation reverses the thermal modes.

How do the diene and dienophile interact in a thermal Diels–Alder reaction?

The diene and dienophile interact suprafacially and form two bonds in one concerted step.

How can a suprafacial–suprafacial [2+2] cycloaddition be enabled?

A suprafacial–suprafacial [2+2] cycloaddition is thermally symmetry-disfavored but can be enabled photochemically.

What orbital pathway characterizes thermal [3,3] sigmatropic shifts?

Thermal [3,3] shifts proceed suprafacially on the participating systems and can transfer stereochemical information predictably.

What kinetic and stereochemical features characterize an SN2 reaction?

Its rate depends on both substrate and nucleophile concentrations, and it gives inversion at the reacting stereocenter.