This entity is denoted 1 sub e in the trihydrogen cation, which raises its energy by forming a cyclic structure on a correlation diagram.
This entity experiences a "through-space" interaction based on its proximity to an alkene in foiled carbenes. Attack on this entity is prevented by steric hindrance in "frustrated" species, hindering the formation of a dative adduct. This entity is denoted 1 sub e in the trihydrogen cation, which raises its energy by forming a cyclic structure on a correlation diagram. The electron (*) affinity can be approximated by the eigenvalue of this entity, which is low-lying in soft species. The CO IR stretching frequency is decreased when a C-polarized example of this entity interacts with a metal's d sub xz. The major reason that carbonyls are useful ligands is that their degenerate example of this entity can act as a pi acceptor. In the first excited state, an electron is promoted to this entity, which is the site of reactivity for Lewis acids. For 10 points, name this frontier orbital that forms bonds with the HOMO.
This entity experiences a "through-space" interaction based on its proximity to an alkene in foiled carbenes.
LUMO [or lowest unoccupied molecular orbital; prompt on "frontier orbitals" or "FMOs"; prompt on "molecular orbitals" or "MOs"; prompt on sigma, pi, delta, s, p or d "orbitals" of any number; prompt on Lewis "acids" by asking, "With what entity do they react?"]