Unsymmetrical-top molecules

These values of W are then the allowed values for the rotational energy of the unsymmetrical-top molecule. Wang has evaluated the integrals Hue and shown that the secular equation can be further simplified. The application in the interpretation of the rotational fine structure of spectra has been carried out in several cases, including water, hydrogen sulfide, and formaldehyde.4... 

The palladium forms a Jt-complex 245 from the top face of the alkene, opposite the carboxylate leaving group. The nucleophile then adds from the opposite face to the palladium. The rf allyl cation complex is unsymmetrical and the nucleophile adds at the less hindered end. The selectivity is very marked in both steps because the starting material is a folded molecule and the palladium much prefers to add to the exo face of the alkene. The nucleophile has to add from the same face as the CH2C02- side chain so it prefers addition to the end of the complex as far from this side chain as possible 246. 

The topicity concept is also important in the reactions of trigonal centers, such as carbonyls and alkenes. In consideration of carbonyls, for example, the two faces are homotopic in a symmetrically substituted ketone, such as acetone or 2-pentanone, because the molecule has C2 symmetry. However, the faces are enantiotopic in an unsymmetrically substituted ketone, such as 2-butanone 190. While the reaction with hydride ion on the top face of the carbonyl group forms (M)-2-butanol 191, the reaction on the bottom face forms (5)-2-butanol 192. Extending this argument further, the two faces are diastereotopic in an unsymmetrical ketone bearing a chiral center elsewhere in it, e.g., (7 )-3-chloro-2-butanone 193. The delivery of hydride ion to the top face of the carbonyl group forms 2(/ ),3(/f)-3-chloro-2-butanol 194 and the delivery to the bottom face forms 2(,S ),3(A )-3-chloro-2-butanol 195. The molecules 194 and 195 are diastereoisomers. 

When the alkene is internal and unsymmetrical, as in 3-methyl-1-cyclohexene (22), the reaction is more complicated. In addition to the two faces (top and bottom) of the molecule, there are two different and reactive sp carbons of the alkene. Hydroboration leads to four products, 23, 24, 25, and 26. With diborane... 

The other possible class of mixed spiro compounds with a horizontal, or top-down , unsymmetric, 2,7-A-2, 7 -B substitution pattern is interesting due to the possibility of combining different functions (emitting properties, charge-transporting properties) in one molecule, which should lead to a reduced number of necessary layers in an OLED device. 

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