text: In contrast to the Bürgi–Dunitz angle, , and using the case of carbonyl additions as example: the  angle adopted during an approach by the nucleophile to a trigonal electrophile depends in complex fashion on:
  * the relative steric size of the two substituents attached to (alpha to) the electrophilic carbonyl, which give rise to varying degrees of repulsive van der Waalss interactions (e.g., giving  ≈ 7° for hydride attack on pivaldehyde (see image), where R=tertiary-butyl, and R=H),
  * the electronic characteristics of substituents alpha to the carbonyl, where heteroatom-containing substituents can, through their stereoelectronic influence, function as overly intrusive steric groups (e.g., giving  ≈ 40-50° for esters and amides with small R' groups, since R is an O- and N-substituent, respectively), and
  * the nature of the bonds made by more distant atoms to the atoms alpha to the carbonyl, e.g., where the energy of the σ* molecular orbital (MO) between the alpha- and beta-substituents was seen to compete with the foregoing influences,
  as well as on the MO shapes and occupancies of the carbonyl and attacking nucleophile. Hence, the  observed for nucleophilic attack appears to be influenced primarily by the energetics of the HOMO-LUMO overlap of the nucleophile-electrophile pair in the systems studied—see the Bürgi–Dunitz article, and the related inorganic chemistry concept of the angular overlap model (AOM)—which leads in many cases to a convergence of  values (but not all, see below); however, the  required to provide optimal overlap between HOMO and LUMO reflect the complex interplay of energetic contributions described with examples above.