(±)-2′-Phenyl­cyclo­hexa­nespiro-4′-(aze­pano[1,2-b]isoxazolidine)

In the crystal structure of the racemic title isoxazolidine, C19H27NO, the relative stereochemistry between the phenyl group and the bridgehead H atom is shown to be syn. There are two mol­ecules in the asymmetric unit, one of which is the 7R*,13R* enanti­omer, and one of which is the 7S*,13S* enanti­omer. These enanti­omers adopt different orientations of the phenyl ring with respect to the isoxazolidine ring, with C—C—C—C torsion angles of 63.6 (4) and 86.8 (4)°, respectively. In both enanti­omers, the six-membered ring adopts a chair conformation, while the seven-membered ring adopts a twist-chair conformation

Age-Corrected Trends and Toxic Equivalence of PCDD/F and CP-PCBs in Lake Trout and Walleye from the Great Lakes: 2004–2014

Our research reports polychlorinated dibenzo-<i>p</i>-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), and coplanar polychlorinated biphenyls (CP-PCBs) concentrations and age-corrected trends for lake trout and walleye in the Great Lakes over the 2004–2014 period. We determined that age–contaminant corrections are required to accurately report contaminant trends due to significant lake trout age structure changes. The age-trend model (ATM) described here uses a lake-specific age–contaminant regression to mitigate the effect of a fluctuating lake trout age structure to directly improve the log–linear regression model. ATM results indicate that half-life (<i>t</i>_1/2) and percent decreases for PCDD/Fs, CP-PCBs, and toxic equivalence (TEQ) (average −56 to 70%) were fairly uniform and consistent across the Great Lakes over the 2004–2014 period. The vast majority of TEQ associated with all Great Lakes lake trout and walleye samples is due to the nonortho CP-PCBs (average = 79%) as compared with PCDD/Fs (average = 21%). On average, CP-PCB_126 individually accounted for over 95% of the total CP-PCB TEQ. A retrospective analysis (1977–2014) of 2378-TCDF and 2378-TCDD raw concentrations in Lake Ontario lake trout revealed decreases of 94% and 96%, respectively. Tissue residue guidelines for wildlife protection based on lake trout and walleye total TEQ were uniformly exceeded in all the Great Lakes