Spectroscopic and structural studies of the 2D Mn(II) coordination polymer from a bridging Noxa, Npy bidentate ligand; tetra-n-butylammonium[5-(3-pyridyl)-1,3,4-oxadiazole-2-thiolate]

A coordination polymer {[Mn(3-pyt)₂(H₂O)₂][N(n-Bu)₄]⁺[3-pyt]⁻}_n (3) has been synthesized from the reaction of tetra-n-butylammonium[5-(3-pyridyl)-1,3,4-oxadiazole-2-thiolate] {[N(n-Bu)₄]⁺[3-pyt]⁻} and Mn(OAc)₂ · 4H₂O. The ligand and the Mn(II) complex 3 have been characterized by elemental analyses, IR, ¹H and ¹³C NMR spectroscopy, in addition 3 has also been studied crystallographically. The single crystal X-ray structure of the 3 shows that the ligand is bonded to Mn(II) via its pyridyl and oxadiazole nitrogen atoms. This bonding pattern connects the Mn(II) centres to afford an uniform two dimensional coordination frame work where the [Mn(3-pyt)₂(H₂O)₂]_n molecules are stacked in a parallel layers. The overall arrangement of molecules in crystal lattice results in open channels in which the enclosed tetra-n-butylammonium cations are stabilized by anionic oxadiazole molecules through N⁺···S⁻ ionic interactions.     

Synthesis of a Novel Nickel(II) Complex with Dithiocarbimate from Sulfonamide

Potassium N-4-methylphenylsulfonyldithiocarbimate, K₂(4-CH₃C₆H₄SO₂N=CS₂), reacted with nickel(II) chloride hexahydrate and tetrabutylammonium bromide to form the bis(N-4-methylphenylsulfonyldithiocarbimate)nickelate(II) tetrabutylammonium salt (Bu₄N)₂[Ni(4-CH₃C₆H₄S₂C=NSO₂)₂]. The elemental analyses, IR and UV-Vis data obtained were consistent with the formation of a diamagnetic planar complex. The ¹H NMR and the ¹³C NMR spectra showed the expected signals for the dithiocarbimate moiety and the tetrabutylammonium cation. The single-crystal structure analysis showed that this substance crystallizes in the triclinic space group with a = 10.474(3) Å, b = 10.767(3) Å, c = 13.657(3) Å and = 81.54(2)°, = 80.44(2)°, = 67.63(2)°, V = 1398.5(8) ų, and Z = 2. The nickel atom is coordinated to four sulfur atoms.     

A new vanadium Schiff base complex as catalyst for oxidation of alcohols

The monoanionic bidentate Schiff base, N-(phenolyl)-benzaldimine (HL), has been employed to synthesize a new vanadium(IV) complex of general composition [VO(L)₂] (where L?=?O,?N donor of Schiff base). The ligand and complex have been fully characterized by elemental analyses, molar conductance data, FT-IR, ¹H- and ¹³C-NMR, and UV-Vis spectroscopies. Oxidation of alcohols to their corresponding aldehydes and ketones was conducted by this complex catalyst using Oxone as oxidant under biphasic reaction conditions (CH₂Cl₂/H₂O) and tetra-n-butylammonium bromide as phase transfer agent under air at room temperature.     

Synthesis, EPR spectrum and X-ray structure of tetra-n-butylammonium bis(benzene-1,2-dithiolato(2−)-κS,S′)platinate(III)

The new salt, tetra-n-butylammonium bis(benzene-1,2-dithiolato(2−)-κ²S,S′)platinate(III), [NBu₄][Pt(C₆H₄S₂)₂] (1), has been synthesized in ethanol/water, and fully characterized by single crystal X-ray structure determination. The central platinum in the complex ion [Pt(bdt)₂]⁻ is tetracoordinated by the S atoms of the bdt²⁻ ligands (bdt²⁻ is benzene-1,2-dithiolate) in a square-planar geometry. The well-resolved frozen solution EPR spectrum exhibits rhombic symmetry. The room temperature effective magnetic moment (μ_eff = 1.80 Bohr magneton) is in line with this spectrum and strongly supports the Pt(III) oxidation state in 1. This observation is in excellent agreement with previous results reported on closely related Ni(III), Pd(III) and Pt(III) species.     

Synthese und Röntgenstrukturanalyse von S4N4-Derivaten mit drei- und vierfach koordinierten Schwefelatomen

CF₃SO₂N?SCl₂ reagiert mit (CH₃)₂S[NSi(CH₃)₃]₂, (C₄H₈)S[NSi(CH₃)₃]₂ oder (C₅H₁₀)S[NSi(CH₃)₃]₂ unter Trimethylchlorsilanabspaltung zu den achtgliedrigen S₄N₄-Derivaten S₄N₄(NSO₂CF₃)₂(CH₃)₄ 3 , S₄N₄(NSO₂CF₃)₂(C₄H₈)₂ 4a und S₄N₄(NSO₂CF₃)₂(C₅H_{1 0})₂ 4b . In den achtgliedrigen SN-Ringen haben die Schwefelatome die Koordinationszahl 3 und 4. Die Röntgenstrukturanalyse von 4a ergab eine Sessel-Konformation. 4a kristallisiert orthorhombisch in der Raumgruppe Pna2₁ mit a = 17,641(4), b = 6,406(2), c = 19,130(4) Å, d_x = 1,815 g cm^?3 und Z = 4. Die mittleren S? N-Abstände betragen an den vierfach koordinierten Schwefelatomen 1,597 Å und an den Schwefelatomen mit der Koordinationszahl 3 1,650 Å. CF₃SO₂N? SCl₂ reagiert mit trimethylzinnhaltigen S? N-Verbindungen zum bekannten CF₃SO₂N[Sn(CH₃)₃]S(CH₃)NSO₂CF₃ und Dimethylzinndichlorid. Synthesis and X-Ray Structure Analysis of S₄N₄-Derivatives with Threefold and Fourfold Coordinated Sulfur Atoms CF₃SO₂N?SCl₂ reacts with (CH₃)₂S[NSi(CH₃)₃]₂, (C₄H₈)S[NSi(CH₃)₃]₂ or (C₅H₁₀S[NSi(CH₃)₂]₂ under elimination of (CH₃)₃SiCl to yield the eight-membered S₄N₄ derivatives S₄N₄?NSO₂CF₃)₂(CH₃)₄, 3 , S₄N₄(NSO₂CF₃)₂(C₄H₈)₂ 4a und S₄N₄(NSO₂CF₃)₂(C₅H_{1 0})₂ 4b . In the eight-membered SN-rings the sulfur atoms have the coordination number 3 and 4. The X-ray structure analysis of 4a revealed a chair conformation. 4a crystallizes in the orthorhombic space group Pna2₁ with a = 17.641(4), b = 6.406(2), c = 19.130(4) Å, d_x = 1.815 g cm^?3, and Z = 4. The average S? N distance was found to be 1.597 Å at fourfold coordinated sulfur atoms and 1.650 Å at sulfur with coordination number 3. CF₃SO₂N=SCl₂ reacts with trimethyl tin-containing S? N compounds to the known CF₃SO₂N[Sn(CH₃)₃]S(CH₃)NSO₂CF₃ and dimethyl tin dichloride.     

Pyrene-Terminated Tin Sulfide Clusters: Optical Properties and Deposition on a Metal Surface

Herein, we present the synthesis of two pyrene-functionalized clusters, [(R^pyrSn)₄S₆]⋅2 CH₂Cl₂ ( 4 ) and [(R^pyrSn)₄Sn₂S₁₀]⋅n CH₂Cl₂ (n=4, 5 a ; n=2, 5 b ; R^pyr=CMe₂CH₂C(Me)N-NC(H)C₁₆H₉), both of which form in reactions of the organotin sulfide cluster [(R^NSn)₄S₆] ( C ; R^N=CMe₂CH₂C(Me)N-NH₂) with the well-known fluorescent dye 1-pyrenecarboxaldehyde ( B ). In contrast, reactions using an organotin sulfide cluster with another core structure, [(R^NSn)₃S₄Cl] ( A ), leads to formation of small molecular fragments, [(R^pyrCl₂Sn)₂S] ( 1 ), (pyren-1-ylmethylene)hydrazine ( 2 ), and 1,2-bis(pyren-1-ylmethylene)hydrazine ( 3 ). Besides synthesis and structures of the new compounds, we report the influence of the inorganic core on the optical properties of the dye, which was analyzed exemplarily for compound 5 a via absorption and fluorescence spectroscopy. This cluster was also used for exploring the potential of such non-volatile clusters for deposition on a metal surface under vacuum conditions.     

Synthesis and characterization of glycol ether and oxime modified precursors of niobium(V) for soft transformation to niobia

A glycol ether modified precursor, [Nb{O(CH₂CH₂O)₂}(OPrⁱ)₃] (A) was prepared by the reaction of Nb(OPrⁱ)₅ with O(CH₂CH₂OH)₂ in 1:1 molar ratio in anhydrous benzene. Further reactions of A with a variety of internally functionalized oximes in different molar ratios, yielded heteroleptic complexes of the type, [Nb{O(CH₂CH₂O)₂}(OPrⁱ)_3?n{ON = C(CH₃)(Ar)}_n] (1–9) {where Ar = C₄H₃O-2, n = 1 [1], n = 2 [2], n = 3 [3]; C₄H₃S-2, n = 1 [4], n = 2 [5], n = 3 [6]; C₅H₄N-2, n = 1 [7], n = 2 [8], n = 3 [9]}. All the above derivatives have been characterized by elemental analyses, FT-IR, NMR (¹H, ¹³C {¹H}) and FAB mass studies. Spectral studies of 1–9 suggest the presence of mono- and bi-dentate mode of oxime moieties, in the solution and in the solid states, respectively. FAB mass studies indicate monomeric nature for 3 and dimeric nature for A. TG curves of A and 6 show their low thermal stability. Soft transformation of A and 3 to pure niobia, a and b, respectively have been carried out by sol–gel technique. The XRD patterns of niobia a and b suggest the formation of nano-size crystallites of average size of 10.8 and 19.5 nm, respectively. The XRD patterns also indicate the formation of monoclinic phase of the niobia in both the cases. Absorption spectra of a and b suggest energy band gaps of 4.95 and 4.39 eV, respectively.     

Partial molal heat capacities of tetraalkylammonium bromides in methanol from 10 to 50°C

Enthalpies of solution habe beenmeasured for tetraethyl-, tetra-n-propyl-, and tetra-n-butylammonium bromides in anhydrous methanol at several temperatures ranging from 5 to 55°C. The data were extrapolated to infinite dilution by an extended Debye-Hückel equation to obtain standard enthalpies of solution ΔH ₃ ⁰ , and the integral heat method was employed to obtain partial molal heat capacities , of the corresponding salts from 10 to 50°C. These data, along with similar data for tetramethylammonium bromide previously reported, were used to assign an, absolute heat capacity to the bromide ion in anhydrous methanol. Comparison of the absolute heat capacities of the bromide and tetraalkylammonium ions in water and methanol suggests that the processes occurring in the two solvents are quite dissimilar.     

1H and13C NMR study of tin-containing sulfoxide, sulfimide, and sulfoximide

Sulfoxide RS(O)R′ (1), sulfimide RS(=NSO₂Ar)R′ (2), and sulfoximide RS(O)(=NSO₂Ar)R′ (3) (R=Me₃Sn(CH₂)₃, R′=n-C₅H₁₁, Ar=4-C₆H₄Cl) were investigated by¹H and¹³C NMR spectroscopy. Unlike 3, compounds 1 and 2 have a cyclic structure due to the intramolecular donor-acceptor S→Sn interaction. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 1966–1969, November, 1997.     

The use of crystal data together with other experimental and computational results to discuss structure-reactivity and activity relationships

The understanding of chemical reactivity and biological activity requires knowledge of the three-dimensional structure of molecules and information about their conformational flexibility. Whereas crystallographic diffraction methods make ground-state structures easily available, the study of dynamic processes such as molecular transformations, intermediates, and transition states during chemical reactions; conformational interconversions; or drug-receptor interactions demand the combination of several complementary techniques. Because each of these methods has its inherent limitations, the results obtained from different sources must be checked. In the present study crystallographic data are used together with the results of spectroscopic, kinetic, and computational techniques (1) to discuss conformational flexibility and preferences of Ph-X-Ph [X=CH₂, C(CR _n )₂ (n=2, 3), C=0, NH, NR (R=C, N), O, S, SO₂], R₂N⁺ (n-Pr)₂ derivatives and caprylolactam, (2) to describe nucleophilic addition of N toward a carbonyl group during a ring-closure reaction in heterocylic systems, (3) to investigate S_N2 substitution at silicon, and (4) to visualize topochemical interconversion pathways in pentacoordinate complexes.     

19F,31P,1H NMR and X-ray crystallographic studies of (pentafluorophenyl)3−n (4-pyrazol-1-yl-2,3,5,6-tetrafluorophenyl) n=1,2,3 Phosphines

New phosphines1–3 have been synthetized by reaction of pyrazolate anion with tris(pentafluorophenyl)phosphine and characterized by¹H,³¹P, and¹⁹F NMR studies.¹⁹F NMR spectral data contribute to the evidence for apara-substitution of tetrafluorophenyl rings. The crystal structure of tris(4-pyrazol-1-yl-2,3,5,6-tetrafluorophenyl)phosphine 1 has been determined, proving that the assignment based on spectroscopic data was correct: C₂₇H₉F₁₂N₆P,M _r = 676.37, monoclinic, space group P2_l/c,a=10.754(2) å,b=10.316(2) å,c = 23.598(5) å,=95.36(3),V=2607(1), å³,Z=4,R ₁=0.042, andwR ₂=0.122.     

Relative viscosity and viscosity coefficients of aqueous azoniaspiroalkane bromides at 25°C

The relative viscosities η_r of dilute aqueous solutions of azoniaspiroalkane bromides, (CH₂) _n N⁺ (CH₂) _n Br^? (wheren=4, 5, and 6), have been measured at 25°C. The viscosityB _η andD _η coefficients were determined using the extended Jones-Dole equation $$\eta _r = 1 + A_\eta c^{1/2} + B_\eta c + D_\eta c^2$$ TheB _η coefficients obtained for the bicyclic azoniaspiroalkane bromides were compared with those of the corresponding homologous tetra-n-alkylammonium bromides. Based on the obtained sign and magnitude of (B _n ?0.0025ø _v ^° ) for the salts and for the bicyclic ions, the structural effects of cation geometry and alkyl group flexibility on water are discussed. The results indicate that the hydrophobic (clathrate hydrate-like) character of the larger tetra-n-alkylammonium ions is reduced significantly when cyclic groups are formed from the alkyl chains in symmetrical quaternary ammonium ions.     

Synthesis of polyphosphazenes bearing alkoxyethoxy and trifluoroethoxy groups

The synthesis of various phosphoranimines including (CH₃OCH₂CH₂O) (CF₃CH₂O)₂P?N? Si(CH₃)₃, (CH₃OCH₂CH₂OCH₂CH₂O) (CF₃CH₂O)₂P?N? Si (CH₃)₃, (CH₃OCH₂CH₂O)₂(CF₃CH₂O) P?N? Si(CH₃)₃, and (CH₃OCH₂CH₂OCH₂CH₂O)(CF₃CH₂O) P?N? Si(CH₃)₃ via the Staudinger reaction of (CH₃)₃SiN₃ with the suitably substituted phosphite is reported. These monomers were polymerized using tetra-n-butylammonium fluoride and N-methylimidazole in various solvents at several temperatures. In situ ³¹P-NMR kinetic studies and M_n versus time studies were also performed for the monomers to understand the propagation mechanism. © 1994 John Wiley & Sons, Inc.     

Ab initio molecular orbital study on structures and energetics of CH3O−(H2O)n and CH3S−(H2O)n in gas phase

The purpose of this article was to calculate the structures and energetics of CH₃O⁻(H₂O)_n and CH₃S⁻(H₂O)_n in the gas phase; the maximum number of water molecules that can directly interact with the O of CH₃O⁻; and when n is larger, we asked how the CH₃O⁻ and CH₃S⁻ moiety of CH₃O⁻(H₂O)_n and CH₃S⁻(H₂O)_n changes and how we can reproduce experimental ΔH ⁰_{n−1, n}. Using the ab initio closed-shell self-consistent field method with the energy gradient technique, we carried out full geometry optimizations with the MP2/aug-cc-pVDZ for CH₃O⁻(H₂O)_n (n=0, 1, 2, 3) and the MP2/6–31+G(d,p) (for n=5, 6). The structures of CH₃S⁻(H₂O)_n (n=0, 1, 2, 3) were fully optimized using MP2/6–31++G(2d,2p). It is predicted that the CH₃O⁻(H₂O)₆ does not exist. We also performed vibrational analysis for all clusters [except CH₃O⁻(H₂O)₆] at the optimized structures to confirm that all vibrational frequencies are real. Those clusters have all real vibrational frequencies and correspond to equilibrium structures. The results show that the above maximum number of water molecules for CH₃O⁻ is five in the gas phase. For CH₃O⁻(H₂O)_n, when n becomes larger, the C—O bond length becomes longer, the C—H bond lengths become smaller, the HCO bond angles become smaller, the charge on the hydrogen of CH₃ becomes more positive, and these values of CH₃O⁻(H₂O)_n approach the corresponding values of CH₃OH with the n increment. The C—O bond length of CH₃O⁻(H₂O)₃ is longer than the C—O bond length of CH₃O⁻ in the gas phase by 0.044 Å at the MP2/aug-cc-pVDZ level of theory. The structure of the CH₃S⁻ moiety in CH₃S⁻(H₂O)_n does not change with the n increment. ©1999 John Wiley & Sons, Inc. J Comput Chem 20: 1138–1144, 1999     

Synthesis and X-ray structural characterization of cobalt(II), copper(II), and silver(I) complexes of triphenylphosphoniopropionate

Four transition-metal carboxylate-like complexes have been synthesized from the reaction of the tertiary phosphine betaine triphenylphosphoniopropionate, Ph₃P⁺(CH₂)₂CO ₂ ^– , with Co(ClO₄)₂· 6H₂O, Cu(ClO₄)₂·6H₂O, Cu(BF₄)₂·xH₂O, and AgClO₄, respectively, and fully characterized by single-crystal X-ray analysis. [CoPh₃P(CH₂)₂CO_{2 4}(H₂O)₂](ClO₄)₂·2H₂O, 1, space groupP¯ l witha=9.195(2),b=13.000(2),c=18.795(3) Å,=102.52(1),=90.12(1),=109.28(2)° andZ=1; [CuPh₃P(CH₂)₂CO_{2 4}][Cu₂ -Ph₃P(CH₂)₂CO₂ -O,O ₄(H₂O)₂] (ClO₄)₆· 4H₂O, 2, space groupP2_l/c witha=14.225(3),b=24.624(6),c=24.297(5) Å,=94.18(1)°, andZ=2; [CuPh₃,P(CH₂)₂CO₂Me₂N(CH₂)₂NMe₂(H₂O)₂](BF₄)₂,3, space groupP2_l/c witha=17.668(2),b=13.454(3),c=15.876(2) Å,=116.45(1)°, andZ=4; [Ag₂Ph₃P(CH₂)₂CO_{2 2}(ClO₄)]₂(ClO₄)₂,4, space groupP¯ l witha=10.925(2),b=13.110(3),c=18.795(3) Å,=82.93(3),=87.45(3),=67.49(3)°, andZ=2. In complex1, the cobalt(II) atom is located in an inversion center and coordinated by four unidentate betaine ligands and a pair oftrans aqua ligands, and strong hydrogen bonds are formed between the aqua ligands and the pendant oxygen atoms of the betaine ligands. In complex2, mononuclear and dinuclear cations coexist in the asymmetric unit. In the mixed-ligand complex3 the betaine ligand acts in the unidentate coordination mode andN,N,N,N-tetramethylethylenediamine (tmen) in the chelate mode. Complex4 contains a discrete centrosymmetric tetranuclear cations in which one pair of betaine ligands act in the bidentate bridging mode and the other in both bidentate and one-atom bridging modes.     

A new and highly effective method for catalytic oxidation of alcohols to the corresponding carbonyl compounds using the tris[(2-oxazolinyl)phenolato]manganese(III)/Oxone®/n-Bu4NBr oxidation system

Oxone® (2KHSO₅·KHSO₄·K₂SO₄) in the presence of mer-tris[(2-oxazolinyl)phenolato]manganese(III), Mn(phox)₃, as catalyst under biphasic reaction conditions (CH₂Cl₂/H₂O) and tetra-n-butylammonium bromide as phase transfer agent efficiently oxidises alcohols to their corresponding aldehydes and ketones at room temperature with very short reaction times (5 min) and good to quantitative yields.     

Concentration Dependence of Thermoelectric Power in Aqueous Tetra-n-Butylammonium Hydroxide Using Hydrogen Electrodes

Using a hydrogen-electrode thermocell with a temperature difference of 8 K, initialthermoelectric power _in has been determined in aqueous tetra-n-butylammoniumhydroxide solutions for concentrations ranging from 0.001 to 0.2 molal at meantemperatures of 25 and 35°C. Graphs of a function of _in vs. m ^1/2/(1 + m ^1/2) yieldintercepts and infinite-dilution limiting slopes as m ^1/2 0. Using the value = 68.8±0.3 J-K^–1for the standard transported entropy of the hydroxideion, values for the enthalpy of transport of tetra-n-butylammonium hydroxide atinfinite dilution were determined to be 36.5±1.5 kJ-mol^–1 at25° and 37.7±2.0kJ-mol^–1 at 35°C.     

The synthesis and crystal structure of metal complexes S-alkyl-N-(ferrocenyl-1-methylmethylidene)-dithiocarbazate and the study on their quenching the luminescence of ruthenium(bipyridine)23+

The cobalt, nickel, copper, zinc and cadmium complexes of S-methyl-N-(ferrocenyl-1-methyl-methylidene)-dithiocarbazate (H-LSM) and S-benzyl-N-(ferrocenyl-1-methyl-methylidene)-dithiocarbazate (H-LSB) were synthesized and the crystal structure of Cd[Fe-C(CH₃) = NNCSS-(CH₃)]₂ was solved by X-ray diffraction. The crystal is in the orthorhombic system with space group Pbca, cell parameters a=19.741(3), b=19.924(5), c=15.452(4) Å, and the final factors of R=0.032. The study on quenching the luminescence of Ru(bpy)²⁺₃ by those complexes showed that bimolecular quenching constants obtained from the Stern-Volmer constant and the excited-state lifetime were related to the redox potential of the quencher. Linear relationship is shown in the plot of logk_q vs. E_1/2(Q⁺/Q). The main factor which influences the quenching rate constant and the redox potential is the coordinating ability of the metal in the complex.     

Synthesis and structures of cycloalkylidene-bridged biscyclopentadienyl-tetracarbonyldiiron complexes C(CH2) n [( η 5-C5H4)Fe(CO)]2( μ-CO)2(n = 4, 5 and 6)

A series of cycloalkylidene-bridged biscyclopentadienyldiiron complexes, C(CH₂) _n [(⁵-C₅H₄)Fe(CO)]₂(-CO)₂ (n = 4, 5 and 6) have been synthesized by the reacting C(CH₂) _n Cp₂ (Cp = C₅H₅) with Fe(CO)₅ in refluxing xylene. The molecular structures of C(CH₂)₅[(⁵-C₅H₄)Fe(CO)]₂(-CO)₂ (2) and trans-C(CH₂)₄[(⁵-t-BuC₅H₃)Fe(CO)]₂(-CO)₂ (4t) have been determined by X-ray diffraction. The Fe—Fe bond distance [2.466 Å], in (2) is the shortest reported to date for bridged biscyclopentadienyldiiron complexes.     

Kinetic Parameters of Alkyl,Alkoxy, and Peroxy Radical Isomerization

The parabolic model of radical abstraction reactions is used to analyze experimental data on monomolecular hydrogen-atom transfer in the reactionsRC^.H(CH₂) _n CH₂R¹ RCH₂(CH₂) _n C^.HR¹(n= 2, 3, 4)RCH(O^.)(CH₂)₂CH₂R¹ RCH(OH)(CH₂)₂C^.HR¹ RCH(OO^.)(CH₂) _n CH₂R¹ RCH(OOH)(CH₂) _n C^.HR¹(n= 1, 2).The activation energies and rate constants that specify each class of these reactions are calculated. Alkyl radical isomerization is characterized by the following activation energies of a thermally neutral reaction depending on the cycle size in the transition state (nis the number of atoms in a cycle): E _{e , 0}(kJ/mol) = 46.6 (n= 6), 59.4 (n= 5), and 57.1 (n= 7). Alkoxy radicals isomerize with E _{e , 0}(kJ/mol) = 53.4 (n= 6), whereas peroxy radicals isomerize with E _{e , 0}(kJ/mol) = 53.2 (n= 6) and E _{e , 0}(kJ/mol) = 54.8 (n= 7). The E _{e , 0}value varies with changes in the cycle size and the strain energy in cycloparaffin C _n H_2n in the same manner. The activation energies E _{e , 0}for the intra- and intermolecular H-atom abstractions are compared. It is found that E _{e , 0}(isomerization) < E _{e , 0}(R^.+ R¹H) for alkyl radicals and that E _{e , 0}(isomerization) E _{e , 0}(RO^.(RO^.) + R¹H) for alkoxy and peroxy radicals.