Out-of plane n-orbital

Disilyne 76 is emerald green in the solid state and shows two allowed n- n absorption bands in hexane at 259 (e 10300) and 328 (e 5800) nm and two forbidden n- n absorption bands at 483 (e 120) and 690 (e 14) nm.41 Theoretical calculations for 76 at the HF/6-311G(d)//B3LYP/6-31G(d) level have shown that HOMO and HOMO-1 are two split n orbitals and LUMO and LUMO+ 1 are two split lowest 7i orbitals. The out-of-plane n orbitals HOMO and LUMO+ 1 are represented by pure (p -p )7i orbitals, whereas the in-plane n orbitals HOMO-1 and LUMO are represented mainly by (py-py)n orbitals with a weak contribution of the a (Si-Si) orbital of the central bond. The presence of the nondegenerate n and ti molecular orbitals in 76 is responsible for the UV-vis absorption band feature of 76. 

Of the five symmetry-adapted combinations of the out of plane n orbitals of [B5H5]4-, the three lowest-lying ones (four electrons) have the proper symmetry to interact with the [Pg.354]

Calculations have been performed by Jafri and Phillips [84] to examine the low-lying electronic states of CH3O2. These reveal that the l A excited state, obtained by promotion of an in-plane oxygen lone-pair electron to the out-of-plane n orbital, is bound and lies in the near infrared, about 87 kJ mol above the ground state. The 2 A" state, which is reached by an oxygen n- n transition, lies in the UV and has been assigned to the... 

Based on experimental results and complementary calculations, an out-of-plane n-delocalization is suggested for thiirene dioxides39. As far as the thiirene oxide is concerned, theoretical calculations predict possible spiroconjugative-type53 interaction between the n c—c orbital of the ring and the jr-orbitals of the SO (which leads to aromatic stabilization and a n charge transfer backward from the SO to the C=C). There exists, however, a rather strong destabilization effect, due to the jr so(d )-orbital. 

Essentially, the n ag, b u) and n b g, b2u) orbitals are the four symmetry-adapted combinations of the in-plane n orbitals of the CN groups. It is important to distinguish between the two n orthogonal orbitals of the CN group. They are degenerate for CN itself because of the cylindrical symmetry but become nondegenerate in TCNQ. Because of the symmetry plane of the molecule, the two formally degenerate orbitals lead to one in-plane tt orbital, denoted as a (nr), which is symmetrical with respect to the molecular plane even if locally it is a nr-type orbital, and one out-of-plane nr orbital, denoted as n n), which is anti-symmetrical with respect to the molecular plane and is locally a nr-type orbital. 

What atomic orbuals on carbon in the planar C03- anion could be used (on the basts of symmetry) to construct in-plane and out-of-plane n bonds First answer the question by thinking about the orientations of the orbitals relative to the geometry of the ion then answer it by using reducible representations and the appropriate character table. 

Figure 3a Spin-coupled orbitals for the out-of-plane n system of CH2N2.

Reduction of F, (Eq. 3.1) shows that it is composed of 2 > ind The D, character table reveals that no orbitals transform as bin but that p. belongs to iu while djj. and dy. belong to e. That these three orbitals on platinum are allowed by symmetry to participate in out-of-plane 7t bonding is reasonable since they are all oriented perpendicular to the plane of the ion (the xy plane). Selection of orbitals on platinum suitable for in-plane n bonds is left as an exercise. (Hint In choosing vectors to represent the suitable atomic orbitals, remember that the in-piane and out-of-plane n bonds will be perpendicular to each other and that the regions of overlap for the former will be on each side of a bonding axis. Thus the in-plane vectors should be positioned perpendicular to the bonding axes.) °... 

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