α-Ocimene, β-ocimenes and alloocimenes are isomeric monoterpenes occurring naturally as oils within several plants and fruits. These thermally unstable compounds are employed in the pharmaceutical and fine-chemicals industries due to their natural plant defense properties and pleasant odors. In this work, and in the context of a recent revival in attention on the subject, we provide new theoretical insights concerning the nature of the electronic reorganization driving the decomposition of cis-β-ocimene to alloocimene. Our findings support the experimental proposal of a rearrangement via a six-membered cyclic transition state in a one-step concerted and highly synchronic process.
Two studies were performed to establish the best defoliation frequency in Brachiaria decumbens using the number of leaves per tiller as a criterion. In the first study, 3,500 tillers with 2, 3, 4, 5, or 6 leaves were collected in 10 farms. The number of green, senescent, and dead leaves was counted. A pooled sample of tillers by each farm with a given number of leaves was analyzed for nutritional quality; a complete randomized block design was used for this study. In a second study, it was implemented a complete ramdomized design with repeated measures over time (2 defoliations), and the effect of defoliating B. decumbens at 3, 4, or 5 leaves per tiller on its growth, dry matter yield, and nutritional quality were evaluated. In the first study, all leaves remained green until the tiller had 3 leaves. At the fourth leaf, few tillers (2.3%) had senescent leaves, but at 6 leaves, most tillers had senescent (40.6%) or dead (24.4%) leaves. Crude protein and digestibility decreased as the number of leaves in a tiller increased (P<0.001). In the second study, the rate of dry matter accumulation was the highest for plots defoliated at 4 leaves (P<0.05). Green stems (43.9%) represented a larger proportion of dry matter than green leaves (31.4%), and their proportions were similar among treatments. Crude protein and digestibility of stems decreased as the number of leaves per tiller increased (P<0.001), but the quality of leaves was similar. These findings suggest that these pastures should be defoliated at 4 leaves per tiller.
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