Controlling Stereoselection in Aza-Cope-Mannich Reactions

The synthesis of 2-substituted cis-octahydroindolones from the reaction of cis-2-amino-1-alkenylcyclopentanols with aldehydes was studied to examine whether stereoselection in the aza-Cope–Mannich reaction could be controlled by the nature of the nitrogen substituent. 2-Alkylamino-1-(1-phenylethenyl)cyclopentanols 7 and 8 , which contain nitrogen substituents of widely differing size (Me and CHPh₂), were condensed with four aldehydes to give oxazolidines 9a–d and 10a-c. Rearrangement of these intermediates at 23–60 °C, in the presence of 0.9 equiv of (±)-10-camphorsulfonic acid in acetonitrile, gave cis-octahydroindolones 11a-d and 12a–c in yields of 77–95%. Using a combination of single-crystal X-ray crystallography, ¹H nOe measurements, and comparisons with known materials it was established that the N-methyl oxazolidines 9a–d provided exclusively cis-octahydroindolones having the 2-substituent trans to the angular substituents, while N-benzhydryl analogs 10a–c provided exclusively the all-cis products 12a–c. These results are interpreted to mean: (1) When the nitrogen substituent is small (Me), the stereochemistry-determining [3,3]-sigmatropic rearrangement occurs preferentially through a transition-state topography having the R² substituent oriented quasiequatorially ( 14 → 15 → 16 ); (2) When this substituent is large (CHPh₂), destabilizing steric interactions between the vicinal R¹ and R² substituents causes the rearrangement to occur preferentially through the alternate iminium ion stereoisomer ( 17 → 18 → 19 ).     

Conversion of Nuclear Waste to Molten Glass: Cold‐Cap Reactions in Crucible Tests

The feed‐to‐glass conversion, which comprises complex chemical reactions and phase transitions, occurs in the cold cap during nuclear waste vitrification. To investigate the conversion process, we analyzed heat‐treated samples of a simulated high‐level waste feed using X‐ray diffraction, electron probe microanalysis, leaching tests, and residual anion analysis. Feed dehydration, gas evolution, and borate phase formation occurred at temperatures below 700°C before the emerging glass‐forming melt was completely connected. Above 700°C, intermediate aluminosilicate phases and quartz particles gradually dissolved in the continuous borosilicate melt, which expanded with transient foam. Knowledge of the chemistry and physics of feed‐to‐glass conversion will help us control the conversion path by changing the melter feed makeup to maximize the glass production rate.     

The Effect of Homogenization Heat Treatment on the Texture Evolution in U-10Mo Alloy

Metallurgical and Materials Transactions A - Uranium alloyed with 10 wt pct Mo (U-10Mo) undergoes discontinuous precipitation (DP) when subjected to sub-eutectoid heat treatment. It is hypothesized...     

Ontogeny of place learning in children as measured in the Radial Arm Maze, Morris Search Task, and Open Field Task.

Children and adults were tested on 3 place learning tasks. Children under the age of 7 yrs were inferior to older Ss in solving the tasks by using spatial relational solutions, but Ss of all ages were equally proficient in solving the task by using simple stimulus-reward associations (cued solutions). Accurate performance on the cued versions suggests that neither the general response demands nor the large size of testing environments rendered the tasks differentially inappropriate for young children. Instead, the nature of the cognitive demands were responsible for different levels of performance across the age groups. Because, in animal studies, spatial relational solutions but not cued solutions of these tests require mature and undamaged medial temporal lobe structures, the results suggest that these systems are not fully developed in humans before approximately 7 yrs of age. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Coupling of dry matter and nitrogen accumulation in ryegrass

The logistic model has proven very useful in relating dry matter production of warm season perennial forage grasses to applied nitrogen. A recent extension of the model coupled dry matter and plant N accumulation through a common response coefficient c. The objective of this analysis was to apply the extended logistic model to cool season Gulf annual ryegrass (Lolium multiflorum Lam.) and to establish a common response coefficient c between accumulation of dry matter and plant N. Analysis of variance established the validity of this hypothesis. The model accurately described response of dry matter, plant N removal, and plant N concentration to applied N, with an overall correlation coefficient of 0.9954. Furthermore, the model closely described the relationship between yield and plant N removal, as well as between plant N concentration and plant N removal. The logistic equation is well-behaved and simple to use on a pocket calculator. It can be used to estimate yields and plant N removal in evaluation of agricultural production and environmental quality.     

Object recognition versus object discrimination: Comparison between human infants and infant monkeys.

Human infants (aged 12–32 mo old) and adults learned a delayed nonmatching-to-sample (DNMS) task and single- and multiple-pair discrimination tasks using nonverbal procedures previously used with monkeys. Infants learned discriminations rapidly and at a young age (12 mo), but they required prolonged training and maturation before learning the DNMS task. Adults learned all tasks rapidly. After learning the DNMS task to criterion, memory performance declined systematically in an inverse relation to age. The dissociation in ability of infants on the DNMS vs discrimination tasks closely resembles the dissociation previously reported with infant monkeys (J. Bachevalier & M. Mishkin, 1984). Results from both infant humans and monkeys support a neurocognitive maturational model. (PsycINFO Database Record (c) 2010 APA, all rights reserved)