The meta photocycloaddition of benzene to ethylene semi-empirical calculations

NMR study of complex triquinanes and bulleranes derived from photoisomerization of aryl‐substituted norbornan‐2‐ones

“…This is reflected in the coupling constants J(5,l l), J(11,13), J(10,l I), J(9,lO) and J (6,9). The general trend of effects on vicinal coupling constants, predicted by the Karplus relationship" for changes in torsion angles, is in agreement with the observations.…”

“…Configuration and conformation. As the Dreiding model of 10 shows a torsion angle close to 90" for 8(4,5), 8 (5,6), O(5,ll) and cf(l1,13), very small coupling constants are expected." The torsion angles of 8 (6,9) and O(9,lO) are quasi-antiperiplanar, giving rise to a large coupling constant.…”

“…As the Dreiding model of 10 shows a torsion angle close to 90" for 8(4,5), 8(5,6), O(5,ll) and cf(l1,13), very small coupling constants are expected." The torsion angles of 8 (6,9) and O(9,lO) are quasi-antiperiplanar, giving rise to a large coupling constant. 12 The torsion angle O(l0,ll) is almost 0", which accounts for a large J(10,ll) value.12 Finally, in both ABX spin systems formed by H-6, H-7A, H-7B and by H-8A, H-8B and H-9, the projection of the C-9-H-9 or C-6-H-6 bonds is outside the angle of the other C-H bonds, leading to large coupling constants.…”

“…The H-8A and H-8B patterns allow the measurement of J(8A,9) = 3.5 Hz and J(8B,9) = 4.5 Hz. It follows from the H-9 absorption that J(9,lO) and 5 (6,9) should be cu. 4 and cu.…”

“…9 Hz, respectively (the order may be reversed). Since we already know from the H-6 arrangement that J (6,9) is ca. 8.4 Hz.…”