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endo ‐cyclobutane ring strain in the cyclic isomers of 7‐coumarinyl diesters rooc(CH 2 ) n COOR
Author(s) -
Compernolle F.,
De Schryver F. C.
Publication year - 1976
Publication title -
organic mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.475
H-Index - 121
eISSN - 1096-9888
pISSN - 0030-493X
DOI - 10.1002/oms.1210110809
Subject(s) - cyclobutane , ring (chemistry) , chemistry , photodissociation , ring strain , strain (injury) , fragmentation (computing) , stereochemistry , cyclobutanes , structural isomer , cis–trans isomerism , photochemistry , organic chemistry , biology , ecology , anatomy
Upon electron impact the open form diesters ROOC(CH 2 ) n COOR where R = 7‐coumarinyl and 4‐methyl‐7‐coumarinyl and their cyclic isomers obtained by photolysis react via common fragmentation pathways. The cyclic isomers derived from 7‐coumarinyl by photolysis resist heating to 250 o C, but a thermal ring opening was observed for the more crowded cyclic isomers derived from 4‐methyl‐7‐coumarinyl. Differences in the appearance potentials for the ions [M OR] + produced from 7‐coumarinyl and its photocyclization isomers can be attributed to their different ground state enthalpies. The strain in the endo‐cyclobutane ring of the photocyclization isomers derived from 7‐coumarinyl (ring strain and strain due to nonbonded interactions) amounts to 38 ± 1 kcal mol −1 .