Several 8-oxabicyclo[3.2.1]oct-6-en-3-one
derivatives have been prepared via the [3 + 4]
cycloaddition
between the oxyallyl carbocation generated from polybromoketones and
alkylfurans. The selective
effects of these compounds on the radicle growth of a monocotyledon
[sorghum (Sorghum bicolor
L.)] and a dicotyledon [cucumber (Cucumis sativus
L.)] were evaluated. All of the test compounds,
at the concentration of 100 μg mL-1,
stimulated cucumber root growth (5−30%), but they
inhibited
sorghum root growth (23−56%). None of the compounds had any
effect on the percent of germination
of the species tested.
Keywords: Plant growth regulators; oxyallyl cation; cucumber;
sorghum
Five new derivatives of 6α,7β-dihydroxyvouacapan-17β-oic acid
were prepared. The effect of these new furan diterpenes on the radicle growth
of Sorghum bicolor L. and
Cucumis sativus L. was evaluated. All compounds, at a
concentration of 100 ppm, showed an inhibitory effect (40–63%) on
the radicle growth of S. bicolor L. and a small
stimulatory growth effect (3–15%) on the radicle of
C. sativus L. None of the compounds had any effect on
the germination rate of both plants.
A reação entre metilamina e acetaldeído em pentano a 230 K leva à formação das aldiminas Ee Z-, sendo o isômero Z-o produto principal e gerado sob controle cinético. O isômero E-é mais estável do que o Z-por 3.3 kcal/mol (∆G*). Os cálculos ab initio mostraram que a etapa bimolecular de adição ocorre por um processo concertado, com formação da ligação C-N e transferência de próton através de um estado de transição de quatro centros. O intermediário zwiteriônico, frequentemente invocado neste tipo de reação, não existe como um mínimo na superfície de energia potencial. Entretanto, a energia livre de ativação para o mecanismo concertado é muito alta, e não é capaz de explicar a cinética deste processo. O mesmo acorre com a etapa de eliminação de água para formar a imina, ou seja, possui uma barreira de ativação muito alta. Estes resultados implicam que tanto a etapa de adição, como a de eliminação, devem ocorrer por um mecanismo de catálise.O isômero Z-pode se interconverter para a forma E-através de uma inversão sobre o nitrogênio sp 2 . A 298.15 K, a energia livre de ativação para este processo foi calculada como sendo 27.0 kcal/mol, o que leva a um tempo de vida de quatro meses para este isômero.The reaction of methylamine with acetaldehyde in pentane at 230 K leads to formation of both E-and Z-aldimines, the Z-isomer being the main product and generated upon kinetic control. The E-form is more stable than the Z-form by 3.3 kcal/mol (∆G*). Ab initio calculations have indicated that a tetrahedral zwitterion intermediate is not formed, and the bimolecular process, forming the aminoalcohol intermediate, occurs through a four center transition state, with concerted formation of C-N bond and proton transfer. However, the predicted ∆G* ≠ is very high, indicating that the true mechanism for this step is not bimolecular. A catalyzed pathway must be actuating. The following step, unimolecular elimination of water, also presents a very high activation free energy. Similarly, a catalyzed mechanism is needed. The isomerization from the Z-form to the E-form through inversion of the nitrogen atom has a predicted ∆G* ≠ of 27.0 kcal/mol at 298.15 K, resulting in a lifetime of four months for the Z-isomer.
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