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Photoelectrocyclic reactions

Woodward and Hoffmann define as electrocyclic reactions the formation of a single bond between the termini of a system containing k it electrons, and the reverse process [Pg.402]

Examples of this type of process are the conrotatory and disrotatory reactions of butadiene  [Pg.402]

In a concerted reaction, orbital and state symmetry is conserved throughout the course of the reaction. Thus a symmetric orbital in butadiene must transform into a symmetric orbital in cyclobutene and an antisymmetric orbital must transform into an antisymmetric orbital. In drawing the correlation diagram, molecular orbitals of one symmetry on one side of the diagram are connected to orbitals of the same symmetry on the other side, while observing the noncrossing rule. [Pg.403]

The alternate approach of Dewar and Zimmerman can be illustrated by an examination of the l,3,S-hexatriene system/ The disrotatory closure has no sign discontinuity (Hiickel system) and has An + 2 (where n — 1) n electrons, so that the transition state for the thermal reaction is aromatic and the reaction is thermally allowed. For the conrotatory closure there is one sign discontinuity (Mobius system) and there are 4n + 2 (n = l)w electrons, so that the transition state for the thermal reaction is antiaromatic and forbidden but the transition state for the photochemical reaction is aromatic or allowed (see Chapter 8 and Table 9.8). If we reexamine the butadiene [Pg.406]


Does the Curtin-Hammett principle apply to photoelectrocyclic reactions when more than one conformation of reactant is present in solution Why ... [Pg.513]

Scheme 14.15 Aryl—aryl bonds formations via photoelectrocyclic reactions. Scheme 14.15 Aryl—aryl bonds formations via photoelectrocyclic reactions.

See other pages where Photoelectrocyclic reactions is mentioned: [Pg.208]    [Pg.220]    [Pg.220]    [Pg.220]    [Pg.402]    [Pg.208]    [Pg.220]    [Pg.220]    [Pg.220]    [Pg.402]    [Pg.214]    [Pg.214]    [Pg.214]    [Pg.95]    [Pg.1749]   
See also in sourсe #XX -- [ Pg.402 ]

See also in sourсe #XX -- [ Pg.402 ]




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