Open-shell Lewis structures and spin hybrids

5 OPEN-SHELL LEWIS STRUCTURES AND SPIN HYBRIDS 

Open-shell NBO hybridization and bonding patterns present some of the starkest conflicts with freshman textbook concepts. Indeed, elementary textbooks often give no hint of the open-shell (partial diradical) character of open-shell singlet systems 

Given the two spin-Lewis structures in (4.46), one can envision the composite spin hybrid as having average bond order of two, correctly indicative of bond 

A more complex and interesting illustration of DLDS behavior is provided by the ozone molecule (Section 3.3.2), an open-shell singlet species whose optimal Lewis-like bonding patterns are depicted in (4.47a,p)  

Abridged NBO output for the ozone ot-spin structure (4.47a) (cf. FO-3.9 for input and numbering) is shown in 1/0-4.15. (The corresponding p-spin output differs only in interchange of atom labels 1, 3.) Each spin-Lewis structure describes only 98.5% of the associated electron spin density, indicating significant same-spin resonance-type 

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Open-Shell Lewis Structures and Spin Hybrids 83... 

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