13C n.m.r. spectroscopy of diethyl alkyl- and benzyl-phosphonates. A study of phosphorus–carbon spin–spin coupling constants over one to seven bonds

¹³C chemical shifts and ³¹P? ¹³C spin–spin coupling constants are reported for 10 alkyl-, 20 benzyl- and 3 (naphthylmethyl)-phosphonates. While in saturated aliphatic chains P–C couplings over more than four bonds cannot be resolved, couplings over up to seven bonds are observed in the benzyl type systems. Conformational and substituent effects on J(PC) are studied and discussed. ⁿJ(PF) (n = 4, 5, 6) are reported for the isomeric (fluorobenzyl)phosphonates and ⁿJ(PP) (n = 5, 6, 7) were obtained from the ¹³C satellites in the ³¹P n.m.r. spectra of the isomeric diphosphonates, C₆H₄[CH₂P(O)(OEt)₂]₂. Comparison of those ¹³C absorptions of the latter, which represent the X parts of ABX or AA′X spin systems, with the spectra of the corresponding (methylbenzyl)phosphonates, CH₃C₆H₄CH₂P(O)(OEt)₂, yielded the relative signs of ⁿJ(PC) (n = 2–6).     

8 and 16-Membered ring phosphorus compounds. Ring size dependence of the NMR parameters

The ¹H NMR spectral analysis of four 8-membered rings, 2-thioxo- (or 2-oxo-) 2-R-1,3,6,2- trithiaphocane, is reported. The stereochemistry of the 8-membered ring is discussed. The ³¹P NMR spectral parameters [δ³¹P, ¹J(PC)] obtained on several cyclic 1,3,2-dithiaphospha compounds of variable size (5, 6, 8, 12 and 16-membered rings) are discussed as a function of the ring size and of the geometry of the molecule.     

Hochauflösungs-13c-nmr-spektroskopie—III: Strukturabhängigkeit der vicinalen methyl-13c,h-kopplungen in methylazulenen,methylaceheptylenen und anderen methyl-sub stituierten polycyclen mit fünf- und siebengliedrigen ringen

The vicinal couplings of ring hydrogens to methyl C atoms (³J_CH3H) in 22 methyl substituted non-benzenoid polycyclic conjugated hydrocarbons have been determined from the undecoupled ¹³C NMR spectra and have been correlated with bond lengths as well as with the corresponding vicinal H,H couplings, which are taken partly from own ¹H NMR analysis and partly from literature. As a result the (³J_CH3H) couplings of sterically unperturbated methyl groups in 7-membered rings are proportional to the corresponding ³J_HH values which is indicative of comparable influences, but both types of vicinal couplings are not dependent on bond lengths only. Moreover they are to a large extent determined by the CCH bond angles θ and θ', which show a significant variation in condensed 7-membered rings so that this twofold dependence has to be taken into account for structure determinations.     

Massenspektrometrische Untersuchungen an Organophosphorverbindungen. II—Elektronenstoßinduzierte Fragmentierungen von Tetraorganodiphosphandisulfiden

The behaviour under electron impact (70 eV) which includes some rearrangement processes of some tetraorganodiphosphanedisulfides R₂P(S)-P(S)R₂ (R ? CH₃, C₂H₅, n-C₃H₇, n-C₄H₉, C₃H₅, C₆H₅) and CH₃RP(S)–P(S)CH₃R (R ? C₂H₅, n-C₃H₇, n-C₄H₉, C₆H₅, C₆H₅, C₆H₅,CH₂) is reported and discussed. Fragmentation patterns which are consistent with direct analysis of daughter ions and defocusing metastable spectra are given. The atomic composition of many of the fragment ions was determined by precise mass measurements. In contrast to compounds R₃P(S) loss of sulphur is not a common process here. The first step in the fragmentation of these compounds is cleavage of one P–C bond and loss of a substituent R?. The second step is elimination of RPS leading to [R₂PS]⁺ from which the base peaks in nearly all the spectra arise. The phenyl substituted compounds give spectra with very abundant [(C₆H₅)₃P]^+. and [(C₆H₅)₂CH₃P]^+. ions respectively, resulting from [M]^+. by migration of C₆H₅. Rearrangement of [M]^+. to a 4-membered P-S ring system prior to fragmentation is suggested.     

An iron(III) 18-metallacrown-6 complex: synthesis,crystal structure,and bioactivity

A macrocyclic hexanuclear iron(III) 18-metallacrown-6 complex, [Fe₆(C₉H₆BrN₂O₃)₆(CH₃OH)₄(H₂O)₂]?·?7CH₃OH?·?4H₂O, has been prepared using a trianionic pentadentate ligand N-acetyl-5-bromosalicylhydrazidate, abshz^3–, and characterized by X-ray diffraction. The crystal structure contains a neutral 18-membered metallacrown ring consisting of six Fe(III) and six abshz^3– ligands. The 18-membered metallacrown ring is formed by combination of six structural moieties, [Fe(III)–N–N]. Due to meridional coordination of ligand to Fe³⁺, the ligand enforces the stereochemistry of the Fe³⁺ ions as a propeller configuration with alternating Δ/Λ forms. Methanol and water are linked with Fe1, Fe1A, Fe,3 and Fe3A. The ratios of methanol to water are 0.76?:?0.24 for Fe1 and Fe1A, and 0.30?:?0.70 for Fe3 and Fe3A, which results in four component crystals of metallacrown rings with ratio of 0.168?:?0.072?:?0.532?:?0.228. Antibacterial screening data showed that the iron metallacrown has moderate antimicrobial activity against Bacillus subtilis.     

Effects of fused benzene rings on tautomerizations and inversions of benzo, azabenzo, and oxabenzocycloheptatrienes at theoretical levels

Biologically important bicyclic species, including 6H-, 6H-6-aza-, and 6-oxabenzocycloheptatrienes (in which the benzene moiety is fused meta with respect to the tetrahedral constituents: –CH₂–, –NH–, and –O–, respectively), show strong shifts of tautomerizations in favor of the corresponding tricyclic benzonorcaradienes (with ΔH values of −11.49, −14.55, and −19.20 kcal mol⁻¹, respectively), at B3LYP/6-311++G**//B3LYP/6-31G*, and MP2/6-311++G**//MP2/6-31G* levels, and at 298 K. In contrast, such shifts are strongly disfavored by the isomeric bicyclic species in which the benzene moieties are fused ortho or para with respect to –CH₂–, –NH–, and –O–, respectively. Hence for species with ortho benzene rings including 5H-, 5H-5-aza- and 5-oxabenzocycloheptatrienes, tautomerization ΔH values are 30.76, 31.89, and 25.27 kcal mol⁻¹, respectively, while for species with para fused benzene moieties including 7H-, 7H-7-aza-, and 7-oxabenzocycloheptatrienes, tautomerization ΔH values are 24.12, 26.00, and 19.55 kcal mol⁻¹, respectively. NICS calculations are successfully used to rationalize these results. The calculated energy barriers for inversion of the seven-membered rings of bicyclic species predict a dynamic nature for all the structures except for the virtually planar 6H-6-aza- and 6-oxabenzocycloheptatrienes. Finally, our theoretical data are compared to the experimental results where available. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Carbon-13 NMR of some organophosphorus compounds. 2—chemical shifts and P?C coupling constants of diaryl-, dialkoxy- and diaryloxy-phosphine amines with general formula Y2PNRR'

Carbon-13 chemical shifts and ²J(POC), ³J(POCC), ²J(PNC) and ³J(PNC) coupling constants of 30 compounds containing the amine moiety, with the general formula Y₂PNRR' (Y ? C₆H₅, CH₃O, CH₃CH₂O, CH₂O; Y₂ ? 1,2-dioxybenzene) have been determined. J(PNC) values have been used to explain the preferred conformation around the P? N bond. A comparison between ²J(PNC) and ²J(PNH) was accomplished.     

3J(HH)?Pμ,ν correlation for planar 7-membered cyclic π-systems—structural effects on 3J(HH)

It is shown that sterically unperturbed vicinal HH coupling constants in planar 7-membered π-systems correlate linearly with the HMO π-bond order: ³J(HH) = 20.91P_μ,_ν–3.85 (r.m.s. error 0.26 Hz, correlation coefficient =0.988). Systematic deviations from this relationship which most probably originate from valence angle changes are found for fused π-systems containing rings of different size. Model calculations using the CNDO/2 method as well as finite perturbation theory and INDO wave functions support the experimental findings. An improvement of existing ³J(HH)? P_μ,_ν correlations for planar 6-membered rings is possible if CNDO/2 π-bond orders are used instead of HMO or PPP-SCF data.     

1H and 13C NMR study of α-acetylenic PIII and PIV derivatives. Signs and magnitudes of J(P?C) and J(P?H)

All J(P? H) and J(P? C) values, including signs, have been obtained in acetylenic and propynylic phosphorus derivatives, R₂P(X)? C?C? H and R₂P(X)? C?C? CH₃ (X ? oxygen, lone pair and R ? C₆H₅, N(CH₃)₂, OC₂H₅, N(C₆H₅)₂, Cl) from ¹H and ¹³C NMR spectra. In P^IV derivatives the following signs are obtained: ¹J(P? C)+, ²J(P? C)+, ³J(P? C)+, ³J(P? H)+, ⁴J(P? H)? . Linear relations are observed between ¹J(P? C), ²J(P? C) and ³J(P? C) versus ³J(P? H), indicating that these coupling constants are mainly dependent on the Fermi contact term, though the other terms of the Ramsey theory do not seem to be negligible for ¹J(P? C) and ²J(P? C). In P^III derivatives these signs are: ¹J(P? C)- and +, ²J(P? C)+, ³J(P? C)-, ³J(P? H)-, ⁴J(P? H)+. Only ³J(P? C) and ³J(P? H) reflect a small contribution of the Fermi contact term while in ¹J(P? C) and ²J(P? C) this contribution seems to be negligible relative to the orbital and/or spin dipolar coupling mechanisms.     

Beiträge zur Chemie des Phosphors. 167 [1, 2]. Konstitutions- und Konfigurationsisomere von Pentaphosphan(7), P5H7

Contributions to the Chemistry of Phosphorus. 167. Constitutional and Configurational Isomers of Pentaphosphane(7), P₅H₇ Phosphane mixtures containing 10—15 P-% of pentaphosphane(7), P₅H₇, are obtained by thermolysis of diphosphane, P₂H₄, or as residue from distillation of crude diphosphane [3]. According to the complete analysis of the ³¹P{¹H}-NMR spectrum on the basis of selective population transfer experiments, P₅H₇ exists as a mixture of three diastereomers of n-P₅H₇ — 1a (erythro, erythro), 1b (erythro, threo), 1c (threo, threo) — and of the constitutional isomer 2-phosphinotetraphosphane 2 (iso-P₅H₇, largest relative isomeric abundance). The correlation between the diastereomers and the observed spin systems results from the preferred gauche orientation of neighboring free electron pairs, the dependence of ¹J(PP) on dihedral angles, and the ³J(PP) long range couplings. From the ³¹P-NMR data of the phosphane molecules P_nH_n+2 with n = 1—5 general relationships for the δ(³¹P) values and the ¹J(PP) coupling constants of chain-type phosphorus hydrides as a function of their structural parameters are derived.     

N‐phosphinyl ureas: Synthesis,characterization, X‐ray structure,and in vitro evaluation of antitumor activity

A new series of N‐phosphinylureas 5b, 6a–7c was synthesized and characterized by ¹H, ¹³C, ³¹P NMR, IR, and elemental analysis. The three‐dimensional structure of 5b has been determined by X‐ray crystallography. The crystal structure revealed the existence of four independent molecules. All structures form two chains with different arrangements and connect to each other via hydrogen bonds to produce two‐dimensional polymeric chains. The cytotoxicity of cyclophosphamide (a standard antitumor compound) and its nine analogues with formula R¹C₆H₄ NHC(O)NHP(O)XCH₂C(R²)₂ CH₂Y(X = Y = NH, R² = CH₃, R¹ = H ( 5a ), CH₃ ( 5b ), NO₂ ( 5c ), X = O, Y = NH, R² = H, R¹ = H ( 6a , CH₃ ( 6b ), NO₂ ( 6c ), and X = Y = O, R² = CH₃, R¹ = H ( 7a ), CH₃ ( 7b ), NO₂ ( 7c )) as well as phenyl urea were evaluated in vitro against three human tumor cell lines K562, MDA‐MB‐231, and HepG2. The results showed that most of the compounds have significant activity against the selected cell lines. Also, HepG2 cells were more sensitive to all the tested compounds than other cell lines. © 2011 Wiley Periodicals, Inc. Heteroatom Chem 23:74–83, 2012; View this article online at wileyonlinelibrary.com . DOI 10.1002/hc.20754     

Organische Phosphorverbindungen XXXVIII. Darstellung und Eigenschaften von Tris-(dialkoxyphosphonyl-methyl)-, Tris-(alkoxyphosphinyl-methyl)-und Tris-(oxophosphoranyl-methyl)-phosphinsäureestern sowie der entsprechenden Säuren [1]

Tris-chloromethyl-phosphine oxide, (ClCH₂₎₃ P?O(I), is obtained by chlorination of (HOCH₂₎₃P?O with PCl₅ or (C₆H₅₎₃PCl₂, and also by oxidation of (CICH₂₎₃P?O and (ClCh₂₎₂(CH₃)P?O. High yields of tris-(dialkyloxyphosphonly-methyl)-phosphine oxides, [RO₂(O)PCH_2]2P?O (II) (R?CH₃, C₂H₅, iso-C₃H₇, n-C₄H₉, 2- ethyl-hexyl), tris (alkyloxyphosphinyl-methyl)-phosphine oxides, [R₂(O)PCH_2]3P?O(R = C₆H₅, CH₃) are obtained by heating tris-chloromethyl-phosphine oxides, [(RO) (R′) (O)PCH_2]3P?O (R = C₄H₉, R′? C₆H₅) and tris-(oxophosphoranyl-phosphine oxides with phosphites, phosphonites and phosphinites, respectively, at 170–180°C for several hours. Compounds II possess an extraordinarily high absorption capacity. Thus a warm. 2% solution of II (R = C₂H₅) in benzene solidifies completely on cooling so that no benzene can be poured off. Tris-dihydroxyphosphonyl-methyl)-phosphine oxide, [(HO)₂(O)PCH_2]3P?O, obtained by hydrolysis of II (R ? C₂H₅) with refluxing conc. HCl or by thermal decomposition of II (R ? iso-C₃H₇) at 190°, titrates in aqueous solution as a hexabasic acid with breaks at pH = 4,4 (three equivalents) and pH = 10,7 (three equivalents). It forms crystalline salts with amines, alkali and alkaline earth metals, and is an excellent chelating agent. The ¹H- and ^31?P-NMR. spectra of all the compounds prepared are discussed.     

Bis(diphenylphosphino)methane trimethylphosphine alkyl and η-cyclopentadienyl compounds of rhodium(I); P{H} two dimensional δ/J resolved and Overhauser effect nuclear magnetic resonance spectroscopy

Neutral mononuclear tertiary phosphine rhodium(I) complexes of the formula RhX(PMe₃)(dppm), X = Cl, CH₂SiMe₃, CH₂CMe₃, CH₂CMe₂Ph, η⁵-C₅H₅, DPPM = bis(diphenylphosphino)methane, RhCl(PPh₃)(dppm), RhX(dppm)₂, X = Cl, Me and Rh(η⁵-C₅H₅(dppm) have been synthesised. In Rh(η⁵-C₅H₅)(PMe₃)(dppm), the dppm ligand is unidentate according to ³¹P{¹H} NMR and X-ray data.The ³¹P{¹H} NMR spectral parameters of RhX(PR₃)(dppm) have been determined by a combination of two dimensional δ/J resolved spectroscopy and heteronuclear nuclear Overhauser effect difference spectroscopy (NOEDS) in conjunction with iterative analysis of the one dimensional spectra.     

Syntheses,crystal structures,and magnetic properties of five new coordination compounds bearing ferrocenedicarboxylate ligands

Five new coordination compounds, {[Mn(L)(CH₃OH)₂] · CH₃OH · H₂O} _n (1), {[Cd(L)(DMF)₂(H₂O)] · H₂O} _n (2), {[Co(L)(CH₃OH)₄] · CH₃OH}₂ (3), {[Cd(L)(phen)(CH₃OH)] · CH₃OH} _n (4), and {[Mn(L)(phen)(H₂O)] · CH₃OH} _n (5) (L = 5-ferrocene-1,3-benzenedicarboxylic acid, phen = 1,10-phenanthroline) were obtained from different metal salts and L with or without 1,10-phen under mild conditions. Complex 1 is a 1-D ladder-like chain composed of 8-membered rings A and 16-membered rings B, which arrange alternately. Complex 2 is an infinite linear chain, further bridged to form a parallel double chain through different hydrogen-bond interactions. Complex 3 is a discrete dinuclear structure, while 4 is a neutral 1-D infinite zigzag coordination chain. Complex 5 is a 1-D linear chain with phen and ferrocene groups of L as pendants hanging on the different sides of the main chain. Variable temperature magnetic susceptibilities of 1 were measured and weak antiferromagnetic exchange interactions between the neighboring Mn(II) ions were found with J = ?0.95 cm^?1.     

15N-NMR. and 31P-NMR. Studies of palladium and platinum complexes

¹⁵N-NMR. parameters for the complexes trans-[MCl₂ (¹⁵NH₂ (CH₂)₅CH₃)L] are reported; M = Pt, Pd, L = PBu, PMePh₂, P (p-CH₃? C₆H₄)₃, AsBuⁿ₃, AsMePh₂, As (p-CH₃C₆H₄)₃, NH₂ (CH₂)₅CH₃ and (for Pt) C₂H₄. For both metals, the NMR. parameters depend on the trans-influence of the ligand L. The values ¹J (¹⁹⁵Pt, ¹⁵N) vary from 138 to 336 Hz and can be shown to correlate with the values ¹J (¹⁹⁵Pt, ³¹P) in the complexes trans-[PtCl₂ (PBu)L]. There is a linear relation between the ¹⁵N chemical shifts in the complexes of the two metals. The reactions of the complexes sym-trans-[M₂Cl₄L₂], M = Pd, Pt, L = a tertiary phosphine or arsine, with neutral ligands are described. ¹⁹⁵Pt-, ³¹P- and ¹³C-NMR. data are reported.     

Synthesis,Spectroscopy, X‐ray Crystallography,and DFT Computations of Nanosized Phosphazenes

Nanoparticles of nine phosphazenes with general formula 4‐CH₃C₆H₄S(O)₂N=PX₃ [X = Cl ( A ), NC₄H₈ ( 1 ), NC₆H₁₂ ( 2 ), NC₄H₈N–C(O)OC₂H₅ ( 3 ), NC₄H₈N–C(O)OC₆H₅ ( 4 ), NC₄H₈O ( 5 ), NHCH₂–C₄H₇O ( 6 ), N(CH₃)(C₆H₁₁) ( 7 ), NHCH₂–C₆H₅ ( 8 ), and 2‐NH‐NC₅H₄ ( 9 )] were synthesized using ultrasonic method and characterized by ¹H, ¹³C, ³¹P NMR, FT‐IR, fluorescence, as well as UV/Vis spectroscopy and additionally with XRD, FE‐SEM, N₂ sorption, and elemental analysis. The ³¹P NMR spectra of compounds 1 – 9 reveal the most up field shift δ(³¹P) for 9 at –11.45 ppm reflecting the most electron donation of 2‐aminopyridinyl rings through resonance to the phosphorus atom. The ¹H, ¹³C NMR spectra of 7 exhibit two sets of signals for the hydrogen and carbon atoms of its two isomers present in the solution state in 1:4 ratio. The FE‐SEM micrographs illustrate that the nanoparticles of compounds 1 – 9 have spherical morphology and a size of 27–42 nm. From the XRD patterns, the crystal sizes were estimated to about 24–86 nm. The highest bandgap was measured for 3 (3.81 eV) whereas the smallest was measured for 8 (3.50 eV). The structures of two polymorphs of compound 5 ( 5 , 5′ ) were determined by X‐ray crystallography at 120 K. Both of these polymorphs are triclinic with P1 space group but 5 has a doubled unit cell volume and two symmetrically independent molecules ( 5a and 5b ). In structures 5a and 5′ , the phosphorus and all endocyclic atoms of two morpholinyl rings display disorder, whereas the molecule 5b does not show disorder. The strong intermolecular O–H ··· O hydrogen bonds plus weak intermolecular C–H ··· O and C–H ··· N interactions create three‐dimensional polymers in the crystalline networks of 5 and 5′ . The DFT computations illustrate that molecule 5b is more stable than 5a by –1.1062 and –0.9779 kcal · mol^–1 at B3LYP and B3PW91 levels, respectively. The NBO calculations presented sp³d hybridization for phosphorus and sulfur atoms and sp², sp³ hybrids for the nitrogen and oxygen atoms.     

Multiple magnetic resonance studies of some para-substituted derivatives of triphenyl phosphine

¹⁹F and ³¹P decoupling experiments are used to simplify the proton spectra of para-substituted derivatives of triphenyl phosphine, prior to ¹H-{¹H} tickling experiments. ³J(³¹P…?H) and ⁴J(³¹P…?H) are positive, and ⁵J(³¹P…?¹⁹F) is negative in the trivalent phosphorus derivatives, and all become more positive as the valency of the phosphorus atom is increased. A triple resonance experiment is used to show that ⁷J(³¹P…?H) in [p-CH₃C₆H₄CH₂P^⊕(C₆H₅)₃] is negative. The double resonance technique is used to relate the ³¹P chemical shifts to the tetramethylsilane resonant frequency.     

Synthesis and magnetic resonance studies of some phosphinous acids,phosphorylacetic acids,and some of their coordination compounds

The synthesis of phosphorylacetic acids, RR′P(O)CH₂COOH, where R = C₆H₅ and R′ = OC₂H₅, C₂H₅, i-C₃H₇, n-C₄H₉, sec-C₄H₉ and C₆H₅, from the appropriate phosphinous acids, several of which are previously unreported, is discussed. ³¹P nuclear magnetic resonance spectra are reported for the phosphinous acids, RR′P(O)H, the phosphorylacetic acids and the metal derivatives of the phosphinous acids, RR′POM, where M in Na or MgBr, which are intermediates in the synthesis. The diastereoisomers of Phsec-BuP(O)H exhibit different ³¹P NMR spectra. Diastereotopic protons of the phosphinous acids and phosphorylacetic acids do not exhibit complex PMR spectra, whereas the diastereotopic methyl groups of the isopropyl compounds do. Some metal complexes of the phosphorylacetic acids are reported.     

Platinum(II) and Palladium(II) Bis(chelate) Complexes Containing both Tri(1‐cyclohepta‐2, 4, 6‐trienyl)phosphane,P(C7H7)3, and Dichalcogenolato Ligands

Tri(1‐cyclohepta‐2, 4, 6‐trienyl)phosphane, P(C₇H₇)₃ ([P] when coordinated to a metal atom), was used to stabilize complexes of platinum(II) and palladium(II) with chelating dichalcogenolato ligands as [P]M(E∩E) [E = S, ∩ = CH₂CH₂, M = Pt ( 3a ); E = S, ∩ = 1, 2‐C₆H₄, M = Pt ( 5a ), Pd ( 6a ); E = S, ∩ = C(O)C(O), M = Pt ( 7a ), Pd ( 8a ); E = S, Se, ∩ = 1, 2‐C₂(B₁₀H₁₀), M = Pt ( 9a, 9b ), Pd ( 10a, 10b ); E = S, ∩ = Fe₂(CO)₆, M = Pt ( 11a ), Pd ( 12a )]. Starting materials in all reactions were [P]MCl₂ with M = Pt ( 1 ) and Pd ( 2 ). Attempts at the synthesis of [P]M(ER)₂ with non‐chelating chalcogenolato ligands were not successful. All new complexes were characterized by multinuclear magnetic resonance spectroscopy in solution (¹H, ¹³C, ³¹P, ⁷⁷Se and ¹⁹⁵Pt NMR), and the molecular structures of 5a and 12a were determined by X‐ray analysis. Both in the solid state and in solution the ligand [P] is linked to the metal atom by the P‐M bond and by η²‐C=C coordination of the central C=C bond of one of the C₇H₇ rings. In solution, intramolecular exchange between coordinated and non‐coordinated C₇H₇ rings is observed, the exchange process being markedly faster in the case of M = Pd than for M = Pt.     

Investigation of Polymerization and Cyclization of Dimethyldiethoxysilane by 29Si NMR and FTIR

Dimethyldiethoxysilane (DMDES) appears to be a very promising modifier to introduce functional groups to a silicate network. The polymerization and cyclization of DMDES under acid-catalyzed conditions (DMDES : Ethanol : water : HCl = 1:4:4:3.68 × 10^–4 in molar ratio) were investigated by high resolution liquid ²⁹Si nuclear magnetic resonance (NMR) and Fourier transform infrared spectrometry (FTIR). Time-dependent NMR and FTIR data illustrate that monomers of (CH₃)₂Si(OC₂H₅)₂, (CH₃)₂Si(OC₂H₅)(OH), and (CH₃)₂Si(OH)₂ reach meta-equilibrium in less than 4 minutes. 3-membered rings ((CH₃)₂SiO)₃ appear about half an hour later and 4-membered rings ((CH₃)₂SiO)₄ an hour later, which continue to be formed over 24 hours. The relative concentrations of monomers, linear structures and cyclic structures suggest a modified model for the kinetics of cyclization, where 4-membered rings are formed by dimer-dimer interactions, as opposed to monomer-trimer interactions previously proposed.