Study 6.14 Synthesis of cage compounds octahedrane

Case Study 6.14 Synthesis of cage compounds - octahedrane 

Case Study 6.15 Mechanistic photochemistry - regioseiectivity of photosubstitution 

Explain the following concepts and keywords phototransposition photo-ring contraction meta-photocycloaddition photosubstitution photo-NOCAS. 

Carbonyl compounds also have two nonbonding lone pairs on the oxygen atom. In organic chemistry texts, these are sometimes shown as two equivalent sp2-hybridized lobes (rabbit s ears). While hybridization has no effect on the total energy, the two degenerate nsp2 orbitals are inappropriate as a basis set to discuss one-electron properties such as ionization potentials or n,jt transitions. Rather, the symmetry-adapted lone pairs 

The lowest excited state of simple ketones and aldehydes corresponds to excitation of an electron from the np lone pair to the 7t -MO. The transition is forbidden in compounds of C2v symmetry. The Tocal symmetry is the same in compounds such as acetaldehyde, so that n,7t transitions of ketones and aldehydes are generally weak, 20 50 m 1 cm and they are easily overlooked in absorption spectra or hidden by the red edge of stronger 71,71 absorption. The nature of the lowest excited state is, however, decisive for the photophysical properties and the photochemical reactivity of carbonyl compounds the reactivity of n,7t excited ketones is comparable to that of alkoxy radicals (see below). 

---