Effect of addition of phenols on the rate of Menschutkin reaction-Reaction , between phenacyl bromide and triethylamine

432-436Second order rate constants for the reaction between phenacyl bromide and triethylamine with and without phenols have been determined in aprotic solvents at 25°, 30° and 35°C. The addition of X - C6H4 - OH (X= H, p-OCH3, p-CH3, p-CI, p-Br and p-NO2) with pKa greater than 7.15 does not affeqt the rate of quaternization of triethylamine by phenacyl bromide, whereas strong acidic phenols such as 2,4-dinitrophenol and 2,4,6-trinitrophenol do affect the rate of quaternization. pKa of phenol is found to be driving force for quaternization or protonation of triethylamine. The active nucleophiles in these processes are predicted

Kinetic and theoretical studies on the reaction of phenacyl bromide with 4DMAP in the presence of certain phenols

414-417The quanternization reaction between phenacyl bromide an 4-(dimethylamino)pyridine (4DMAP) has been studied at 25, 30 and 35°C in acetone, Added phenols with pKa > 7.0 retard the rate of quaternization and there is no ether formation. This has been confirmed through product analysis by HPLC using paired ion chromatography (PIC) reagents –A. The reaction has been followed conductometrically using Gugenheim’s method. Theoretical calculations(PM3) confirm the formation of H-bonded complex between the phenoI(s) and 4DMAP, that could retard the rate of quaternization. Relative proton affinity (PA) values of various phenolates computed here explain the preferential formation of quaternary salt over ether in the reaction

Disentangling Population History and Character Evolution among Hybridizing Lineages

Understanding the origin and maintenance of adaptive phenotypic novelty is a central goal of evolutionary biology. However, both hybridization and incomplete lineage sorting can lead to genealogical discordance between the regions of the genome underlying adaptive traits and the remainder of the genome, decoupling inferences about character evolution from population history. Here, to disentangle these effects, we investigated the evolutionary origins and maintenance of Batesian mimicry between North American admiral butterflies (Limenitis arthemis) and their chemically defended model (Battus philenor) using a combination of de novo genome sequencing, whole-genome resequencing, and statistical introgression mapping. Our results suggest that balancing selection, arising from geographic variation in the presence or absence of the unpalatable model, has maintained two deeply divergent color patterning haplotypes that have been repeatedly sieved among distinct mimetic and nonmimetic lineages of Limenitis via introgressive hybridization

The molecular genetic basis of herbivory between butterflies and their host plants

International audienceInteractions between herbivorous insects and their host plants are a central component of terrestrial food webs and a critical topic in agriculture, where a substantial fraction of potential crop yield is lost annually to pests. Important insights into plant-insect interactions have come from research on specific plant defences and insect detoxification mechanisms. Yet, much remains unknown about the molecular mechanisms that mediate plant-insect interactions. Here we use multiple genome-wide approaches to map the molecular basis of herbivory from both plant and insect perspectives, focusing on butterflies and their larval host plants. Parallel genome-wide association studies in the cabbage white butterfly, Pieris rapae, and its host plant, Arabidopsis thaliana, pinpointed a small number of butterfly and plant genes that influenced herbivory. These genes, along with much of the genome, were regulated in a dynamic way over the time course of the feeding interaction. Comparative analyses, including diverse butterfly/plant systems, showed a variety of genome-wide responses to herbivory, as well as a core set of highly conserved genes in butterflies as well as their host plants. These results greatly expand our understanding of the genomic causes and evolutionary consequences of ecological interactions across two of nature's most diverse taxa, butterflies and flowering plants