The Bürgi-Dunitz angle describes the oblique approach of a nucleophile toward a carbonyl carbon, conventionally measured relative to C=O. A typical trajectory is near , with the optimum depending on the system.
The Bürgi-Dunitz trajectory describes the preferred approach of a nucleophile toward a carbonyl carbon, usually at an obtuse angle to the carbon-oxygen bond, often near . It is a geometrical trend, not a fixed angle obeyed by every reacting system.
An oblique approach balances favorable interaction with the carbonyl antibonding orbital against repulsion from occupied orbitals. Crystallographic observations of close contacts motivated this picture, linking static molecular structures with a possible path of nucleophilic addition. Steric constraints and the other substituents can modify the accessible trajectory.
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The Bürgi–Dunitz angle refers to a specific dihedral angle observed in the context of molecular structures, particularly in the study of how nucleophiles approach electrophiles during chemical reactions. It is defined as the angle between the plane of a nucleophile (such as a carbonyl or amine) and the bond axis connecting the electrophile (such as carbon in an electrophilic center) to the nucleophile.