1,2σ3λ3-Oxaphosphetanes and Their P-Chalcogenides-A Combined Experimental and Theoretical Study.

Although 1,2σ5λ5-oxaphosphetanes have been known for a long time, the "low-coordinate" 1,2σ3λ3-oxaphosphetanes have only been known since their first synthesis in 2018 via decomplexation. Apart from ligation of this P-heterocycle to gold(I)chloride and the oxidation using ortho-chloranil, nothing on their chemistry has been reported so far. Herein, we describe the synthesis of new 1,2σ3λ3-oxaphosphetane complexes (3a-e) and free derivatives (4a-e), as well as reactions of 4a with chalcogens and/or chalcogen transfer reagents, which yielded the P-chalcogenides (14-16a; Ch = O, S, Se). We also report on the theoretical results of the reaction pathways of C-phenyl-substituted 1,2 σ3λ3-oxaphosphetanes and ring strain energies of 1,2σ4λ5-oxaphosphetane P-chalcogenides.

Evolution of Game Demands From Young to Elite Players in Men's Volleyball.

PURPOSE: To assess the evolution of the volleyball's game demands throughout players' development in men's volleyball. METHODS: A total of 150 sets and 6.671 rallies were analyzed. The sample was composed of 30 sets each by under-14, under-16, under-19, national senior, and international senior teams (1.291, 1.318, 1.310, 1.372, and 1.380 rallies for each category, respectively). Sets included in the sample were stratified and then randomly selected. The variables studied included play time, rest time, rallies played, jumps, hits, types of ball contact, types of game interruptions, performance of the game phases, and performance of the actions. Student t and Mann Whitney U tests were used to analyze specific differences between categories. RESULTS: The results showed significant reductions in the play times of the rally (from 8.91 to 6.79 s) and the set (6 min 23 s to 4 min 30 s), significant increases in the rest times of the rally (19.64 to 26.53 s) and the set (13 min 44 s to 20 min 27 s), and a significant increase in the number of jumps per set (113.5 to 181.3). Significant improvements in the reception performance (1.57 to 2.45 out of 3), attack performance (2.13 to 2.67 out of 4), and side-out-phase success (48.4% to 69.6%) were found. Throughout the players' development, data show an increase in the speed, intensity, and efficacy of the side-out phase. CONCLUSIONS: The findings provide reference values to guide athletes' development and to monitor training and matches both physically and technically tactically.