Cyclobutane, point group

Cycloaddition reactions, 162-165, 197-198 component analysis, 168 Diels-Alder, 162, 198 ethylene + ethylene, 198 orbital correlation diagram, 198 stereochemistry, 162-163 Cycloalkanols, synthesis, 277 Cyclobutadiene barrier, 91 ground state, 91 point group of, 5 self-reactivity, 97 SHMO, 151 structure, 309-310 Cyclobutane... 

Draw the formulae of all possible isomers of difluorocyclobutane and determine their symmetry elements and point groups. Assume that the cyclobutane ring is planar. Indicate which isomers are chiral. Use the flow chart in the appendix to assist you. 

Further examples for tetragonal point groups are the cyclic molecules cyclobutane (CB), cyclobutadiene (CBD), and their radical cations. Depending on whether CB is planar or puckered, the pertinent point group... 

From a preparative point of view the heteroatom in P-position has an influence because important latent cyclobutane cleavage pathways exist in the product. The prototypical reaction of this type is the [2 + 2]-photocycloaddition/retro-aldol reaction sequence (de Mayo reaction) [55-57], the course of which is illustrated for substrate A3 (Q = O, PG = protecting group) in the reaction with ethylene as a generic olefin. 

A different approach was utilized by Gassman and Richmond In order to prevent the flip process which equilibrates axial and equatorial positions in the cyclobutane product, benzyne was allowed to react with 7. The phenyl group assumes an endo position in the product, thereby confirming the assumption that the double bond attack takes place along an equatorial path (equation 72). It should be pointed out that the... 

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