Reference

Hydrolysis of cyclic phosphoramides

Hydrolysis of cyclic phosphoramides. Evidence for syn lone pair catalysis. Nunez, Andres; Berroteran, Dyanna; Nunez, Oswaldo (Departamento de Procesos y Sistemas, Laboratorio de Fisicoquimica Organica y Quimica Ambiental, Universidad Simon Bolivar, Venez.). Organic & Biomolecular Chemistry, 1(13), 2283-2289 (English) 2003 Royal Society of Chemistry. CODEN: OBCRAK. ISSN: 1477-0520. DOCUMENT TYPE: Journal CA Section: 29 (Organometallic and Organometalloidal Compounds) Section cross-reference(s): 22 Hydrolysis between 1.5 < pH < 4 of five- and six-membered cyclic phosphoramides was followed by UV and NMR 31P spectroscopy. The obsd. rates fit the equation: kobs = kH2O×[H+]/([H+] + Ka) + k'H2O, where kH2O and k'H2O are the pseudo first-order rate consts. of water attack on the protonated phosphoramide and its unprotonated form, resp., and Ka is the phosphoramide acidity equil. const. Although, faster hydrolysis rates on the five membered ring are expected due to the cyclic strain energy release in formation of a "strained free" trigonal-bipyramidal-pentacoordinated intermediate, in which one of the cyclic nitrogens occupy the apical position, the values of kH2O are only slightly higher, than for the corresponding six-membered analogs, whereas the k'H2O values were lower. The balance in reactivity is attributed to the addnl. stability gained in the six-membered rings by a syn orientation of the two lone pairs of the cyclic nitrogens to the water attack. This stabilization does not exist in the five membered phospholidines since the water attack is perpendicular to the electron pairs of the cyclic nitrogen atoms. In agreement with the incoming water orientation, the main products of the hydrolysis of the phospholidines arise from the endocyclic bond cleavage, whereas the diazaphosphorinanes gave the kinetic products originating from the exocyclic cleavage. The syn orientation of two electron pairs on nitrogen stabilizes the transition state of water approach to the phosphoramides by ca. 111-33-1 and 649759-42-2 are just another two chemicals used in this study. 3 kcal mol-1 when compared to the orthogonal attack. .

On the Importance of H-Bonding Interactions in Organic Ammonium Tetrathiotungstates

All Rights Reserved. On the Importance of H-Bonding Interactions in Organic Ammonium Tetrathiotungstates. Srinivasan, Bikshandarkoil R.; Naether, Christian; Dhuri, Sunder N.; Bensch, Wolfgang (Department of Chemistry, Goa University PO, Goa 403 206, India). Monatshefte fuer Chemie, 137(4), 397-411 (English) 2006 Springer Wien. CODEN: MOCMB7. ISSN: 0026-9247.Several reagents with their cas registry numbers 111-33-1 and 917611-34-8 are used here. DOCUMENT TYPE: Journal CA Section: 78 (Inorganic Chemicals and Reactions) Section cross-reference(s): 75 Four new org. ammonium tetrathiotungstates, (N-Me-enH2)[WS4] (1), (N,N'-dm-1,3-pnH2)[WS4] (2), (1,4-bnH2)[WS4] (3), and (mipaH)2[WS4] (4), (N-Me-enH2 = N-methylethylenediammonium, N,N'-dm-1,3-pnH2 = N,N'-dimethyl-1,3-propanediammonium, 1,4-bnH2 = 1,4-butanediammonium, and mipaH = monoisopropylammonium) were synthesized by the base promoted cation exchange reaction and characterized by elemental anal., IR, Raman, UV-visible and 1H NMR spectroscopy as well as single crystal x-ray crystallog. The structures of 1-4 consist of [WS4]2- tetrahedra which are linked to the org. ammonium cations via N-H×××S hydrogen bonding. The strength and no. of the S×××H interactions affect the W-S bond lengths as evidenced by distinct short and long W-S bonds. The IR spectra exhibit splitting of the W-S vibrations, which can be attributed to the distortion of the [WS4]2- tetrahedron. From a comparative study of several known tetrathiotungstates a difference of >0.033 ? between the longest and shortest W-S bonds in a tetrathiotungstate will result in the splitting of the asym. stretching vibration of the W-S bond. .