2 research outputs found
Conformation of eight-membered benzoannulated lactams by combined NMR and DFT studies
The title compounds were synthesized, and their
structure and conformational behavior in solution (NMR and DFT),
in the gas phase (DFT), and, for some of them, in the solid state (X-ray)
were investigated. The variable
-temperature NMR spectra were
employed to determine the conformational equilibria and the activation
energy of the conformational changes of the eight-membered ring. The
coalescence e
ff
ects are assigned to racemization of the chiral ground-
state conformation with a ring inversion barrier in the range of 38
−
100
kJ mol
−
1
depending on the relative setting of the two strong
conformational constraints: benzoannulation and the amide function.
The second conformational process, interconversion between two
di
ff
erent conformers, in the molecules of benzo[
c
]azocin-3-one,
benzo[
d
]azocin-2-one, and benzo[
d
]azocin-4-one was observed. The
natures of the conformers observed in solution were elucidated by
analysis of experimental and calculated NMR data. The present results are discussed in conjunction with previous experimental
and theoretical data on (
Z
,
Z
)-cyclooctadienes and their benzo analogues