Search

Detailed NMR studies have shown that at 298 K optically-inactive saturated blue solutions of 2-chloro-2nitrosonorbornane in CDCl3 contain a mixture of the monomeric and dimeric forms of the compound in a ratio of dimer : monomer = 1: 40 (± 2): this ratio changes with a change in temperature. The analysis assigns the configuration at the C(2)(NO)(Cl) centre and shows that the monomeric form has the structure (4), in which the NO group is on the same side of the molecule as the bridging C(7)H2 group. White, solid 2-chloro-2-nitrosonorbornane is a 1:1:1:1 mixture of four diastereoisomeric forms of trans-diazodioxide (5). The white solid readily sublimes at ambient temperature and monomeric vapour forms a blue–green cast on its surface. Red-irradiation of the compound, in vacuo, produces white crystals and a viscous brown oil. The white crystals contain norbornan-2-one (6), the syn- and anti-forms of the norbornan-2-one oximes, (7) and (8), and a lactam, (9). These compounds are present in the viscous brown oil which also contains three other compounds to which the structures (10), (11) and (12) are assigned. The reaction mixture is EPR silent. The spectroscopic evidence enables some of the steps in the red photolysis reactions of (4) to be unravelled.

Chlorine-35 n.q.r. spectra for α-(NSClO)3, cis-(NSClO)2(NPCl2), and (NSClO)(NPCl2)2 have been recorded in the temperature range 77–300 K. Spectra have also been examined for these substances at 293 K when subjected to pressures within the range 1–700 kg cm–2 : the chlorine-35 resonance frequencies are linear functions of pressure. The partial differential coefficients (∂ν/∂P)T at 293 K, (∂ν/∂T)P, at 1 kg cm–2 and 293 K, and (∂ν/∂T)v, at 293 K have been evaluated for each resonance frequency and are related to the molecular conformers present in these solids. At 165 K (NSClO)(NPCl2)2 undergoes a phase change in which the conformation of the six-membered ring changes. The chlorine resonance frequencies, ν/MHz, are related to the corresponding bond lengths, d/A: these relationships are d=–0.0152ν+ 2.4166 for P–Cl bonds and d=–0.0172ν+ 2.636 for S–Cl bonds. The NSClO group is more electronegative than the NPCl2 group. Chlorine valence-electron populations, ϕ, can be deduced from the corresponding chlorine-35 n.q.r. frequencies at 77 K. The appropriate relationships are ϕ=–0.0345ν+ 8 for P–Cl bonds and ϕ=–0.0265ν+ 8 for SClO groups.

Chlorine-35 nuclear quadrupole resonance frequencies, ν, in N 3 P 3 Cl 6 and in N 3 P 3 Cl 5 NH Pr i are linear functions of the applied pressure, P , within the range 1 to 1000 kg·cm −2 . Chlorine-35 nuclear quadrupole resonance frequencies in N 3 P 3 Cl 5 NH Pr i , examined over the temperature range 100 to 320 K, have revealed that this solid undergoes a sharp phase change over the temperature range 220 to 235 K. Values of the partial differential coefficients. have been evaluated for each of the resonance frequencies in N 3 P 3 Cl 6 and in N 3 P 3 Cl 5 NH Pr i . The applied pressure discriminates between the two kinds of chlorine atoms in the PCl 2 groups in N 3 P 3 Cl 5 NH Pr i . The effects of pressure on the chlorine-35 nuclear quadrupole resonance frequencies of nine chlorine nuclei in similar environments in these two molecules are similar and appear to be characteristic of the functional groups involved.

Chlorine-35 NQR frequencies, ν, for (Cl 3 PN R ) 2 , where R = CH 3 , C 2 H 5 , or Ph, and for (ClOPNCH 3 ) 2 have been measured over the temperature range 77 ⩽ T ⩽ 350 K. Chlorine-35 asymmetry parameters have been measured for (Cl 3 PNCH 3 ) 2 at 295 K, and they show that π-character cannot contribute any more than 1–2% to the nature of the PCl bonds in this molecule. Chlorine-35 NQR frequencies for (Cl 3 PN R ) 2 , where R = CH 3 or Ph, also have been measured over the pressure range 1 ⩽ P ⩽ 1500 Kg cm −2 , at 295 K. These measurements enable three methods to be used to distinguish axial from equatorial chlorine atoms. Their resonance frequencies are different, the temperature coefficients of these frequencies are different, and the pressure coefficients of these frequencies are different. The partial differential coefficients have been evaluated for (Cl 3 PN R ) 2 , where R = CH 3 and Ph. Bayer-type analyses show that the characteristic effects of temperature and pressure on these compounds originate in the typical ionic characters of the PCl bonds and in the characteristic 64 cm −1 PCl 3 torsional-bending modes in these solids. The analyses also indicate that it should be possible to distinguish between different kinds of PCl systems by measuring the effects of applied pressures or changes in temperature on their chlorine-35 NQR frequencies.

Analysis of the 1H n.m.r. spectrum of (–)-2-chloro-2-nitrosocamphane (3) defines its molecular structure. Irradiation of the blue solid rapidly inverts the configuration at C(2) and causes a photochemically initiated Beckmann rearrangement to the nitroxide radical (7). Extended irradiation generates two additional nitroxide radicals (8) and (9), camphor oxime (10), camphor (11), 2-chloro-2-nitrocamphane (12), and 2-chloro-2-nitratocamphane (13). N.m.r. methods show that in (12) the configuration at C(2) is inverted relative to that in the parent chloro-nitroso compound (3). The combination of chemical and spectroscopic evidence enables some of the steps in the solid-state red photolysis reactions of (3) to be unravelled.

The 35Cl n.q.r. spectra of a series of chlorine-containing phosphorus–nitrogen compounds including [Cl(X)PNR]2(X = lone pair, R = But; X = O, R = But or Me), PCl2(NButH)O, Cl2P·NBut·PCl2, Cl2P·NMe·P(O)Cl2, Cl2(X)P·NMe·P(X)Cl2(X = O or S), Cl2(O)P·NR·P(S)Cl2(R = Me or Ph), the heterocycle C17H20ClN2OP (see Table 1), and Cl2(O)P·N:PPh3 have been recorded at ambient temperatures and/or 77 K. The results are discussed in terms of the structures, where known, and a linear correlation between P–Cl bond lengths and n.q.r. frequencies has been deduced for phosphoryl compounds : this is different from the correlation previously deduced for cyclophosphazenes. Data for Cl2(O)PCH2P(O)Cl2 are also included. The n.q.r. results enable some comparisons to be made of the relative electron supply of some common substituents encountered in phosphorus chemistry.

Bromine NQR frequencies, v (MHz), for N 3 P 3 Br 6 , N 3 P 3 Br 5 NHPr i and for cis -N 3 P 3 Br 4 (NMe 2 ) 2 have been examined over the temperature range 77⩽=T⩽=300K. Bromine-81 resonance frequencies in these compounds are approximately linearly related Co the chlorine-35 resonance frequencies observed in the corresponding chloro-derivatives: v ( 81 Br) ≈ 8.121 v ( 35 Cl) - 29.4. Bromine nuclei are more sensitive monitors of physical and chemical change than chlorine nuclei. In the cyclotriphosphazatrienes, bromine is more electronegative than amino-nitrogen. Asymmetry parameters for N 3 P 3 Br 6 show that π-character cannot contribute any more than about 0.2% to the nature of the P-Br bonds in this molecule. One phase change, at 125K, has been detected for N 3 P 3 Br 6 and two, at 135K and 215K, for N 3 P 3 Br 5 NHPr i . In cis -N 3 P 3 Br 4 (NMe 2 ) 2 bromine-81 spectra fade out at 215K. Bromine NQR spectra for N 3 P 3 Br 5 NMe 2 have not been detected in the temperature range 77⩽=T⩽=300K. The NQR data enable conformations to be assigned to these molecules.

Chlorine-35 NQR frequencies, v (MHz), in the chlorocyclotriphosphazatrienes are related to the corresponding PC1 bond lengths, d ( A ): d = −0.012 8 v + 2.355. v is also related to θCl, the valence shell electronic population localized on the chlorine atom: θCl = −0.0345v + 8. Chlorine-35 NQR frequencies discriminate between the positional isomers of N3P3C13(NMe2)3. Chlorine-35 NQR frequencies in N1P3Cl6, N3P3Cl5NHPri, N3P3Cl5NC5H10, cis-N3P3Cl4(NMe2)2, and trans-N3P3Cl4(NMe2)2 are linear functions of the applied pressure, P, within the range 1 to 700 kg cm−2. N3P3CI5NC5H10, cis-N3P3Cl4(NMe2)2 and trans-N3P3Cl4(NMe2)2 undergo minor phase changes at about 150 K. The partial differential coefficients (ϖv ϖP) T=293 K′ (ϖv ϖT) P=1kgcm −2 , T=293 K′ and (ϖv ϖT) V,T=293K have been evaluated for each of the resonance frequencies in N3P3Cl6, N3P3Cl5NHPri, N3P3Cl5NC5H10, cis-N3P3Cl4(NMe2)2, and trans-N3P3Cl4(NMe2)2. The pressure derivatives, (ϖv ϖP) T , discriminate between geometric isomers. The temperature derivatives, (ϖv ϖT) , and the pressure derivatives together discriminate between molecular conformers and give detailed information about molecular dynamics in these solids.

X-Band e.p.r. spectra of magnetically dilute glasses containing (π-C5H5)2VX2 and (π-C5H5)2NbX2(X = Cl, SCN, OCN, and CN) have been recorded at 77 and 290 K and are analysed in detail. The metal-ion spin–orbit coupling constants, ξv and ξNb, for these molecules are estimated to be +133 and +490 cm–1 respectively. Spin Hamiltonian parameters are listed for each substance and are equated to the atomic orbital coefficients in some of the molecular orbitals involved in bonding in these molecules. Except for the cyanides, in each case the unpaired electron lies essentially in a non-bonding ndz2 metal-ion orbital mixed with a small amount of the corresponding metal ion ndx2–y2 orbital, the z-axis coinciding with the C2 axis of the compound; in the cyanides this unpaired electron is delocalised into px orbitals on the ligands. π-Electrons of the cyclopentadienide rings and σ-bonding electrons derived from the other ligands X are almost completely delocalised, π-bonding to the cyclopentadienide residues being stronger than σ-bonding to the ligands X. Several redistribution complexes (π-C5H5)2NbXY have been detected. E.p.r. techniques can be used to distinguish compounds of the type (π-C5H5)2MX2 from other compounds which contain vanadium(IV) or niobium(IV). Huckel LCAO molecular orbital calculations carried out on these molecules appear to give reasonable descriptions of their ground states.

The electron paramagnetic resonance spectra of the trigonal prismatic complexes, [Re(S2C2Ph2)3] and [Re(tdt)3](tdt = toluene-3,4-dithiolate), are characteristic of sulphur-containing organic radicals and they show that the unpaired electron in these compounds is in a non-bonding molecular orbital derived from the ligand π orbitals, E.p.r. properties, visible-u.v. absorption spectra, voltammetric properties, the magnetic properties of ions derived from [Re(S2C2R2)3], and the unusually high electrical conductivities exhibited by the solids are all consistent with an electronic ground state configuration (3a1′)2(4e′)4(2a2′)1 for these complexes.

X-Band e.p.r. spectra of magnetically dilute solutions of MnO2Cl2 in CCl4 have been recorded at 77 K and at 298 K and are analysed in detail. The spin–orbit coupling constants, ξMn and ξCl, at the manganese and chlorine atoms in this compound are estimated to be 248 and 587 cm–1 respectively. At 77 K, MnO2Cl2 rotates about its X-axis in CCl4 solution. Spin-Hamiltonian parameters are listed for 298 K, for 77 K, and for the rigid molecule, and are equated to the atomic orbital coefficients in the molecular orbitals involved in bonding in this molecule. The unpaired electron lies in the metal ion 3dx2–y2 orbital mixed with a small amount (8%) of the 3dz2 orbital, and it is strongly (55%) delocalised on to the ligands. Two of the principal components of the g-tensor are larger than the spin-only value, a situation unusual in d1 complexes. This is shown to be due to relatively large spin–orbit coupling at the chlorine atoms. It is pointed out that principal values of the g-tensor may be used to distinguish distorted tetrahedral complexes which are stretched along their z-axes from the corresponding complexes compressed in this direction, provided that spin–orbit interactions at the ligands are relatively large.

The 35Cl n.q.r. spectra of a series of chlorine-containing phosphorus–nitrogen compounds including [Cl(X)PNR]2(X = lone pair, R = But; X = O, R = But or Me), PCl2(NButH)O, Cl2P·NBut·PCl2, Cl2P·NMe·P(O)Cl2, Cl2(X)P·NMe·P(X)Cl2(X = O or S), Cl2(O)P·NR·P(S)Cl2(R = Me or Ph), the heterocycle C17H20ClN2OP (see Table 1), and Cl2(O)P·N:PPh3 have been recorded at ambient temperatures and/or 77 K. The results are discussed in terms of the structures, where known, and a linear correlation between P–Cl bond lengths and n.q.r. frequencies has been deduced for phosphoryl compounds : this is different from the correlation previously deduced for cyclophosphazenes. Data for Cl2(O)PCH2P(O)Cl2 are also included. The n.q.r. results enable some comparisons to be made of the relative electron supply of some common substituents encountered in phosphorus chemistry.

The electron paramagnetic resonance spectra of the trigonal prismatic complexes, [Re(S2C2Ph2)3] and [Re(tdt)3](tdt = toluene-3,4-dithiolate), are characteristic of sulphur-containing organic radicals and they show that the unpaired electron in these compounds is in a non-bonding molecular orbital derived from the ligand π orbitals, E.p.r. properties, visible-u.v. absorption spectra, voltammetric properties, the magnetic properties of ions derived from [Re(S2C2R2)3], and the unusually high electrical conductivities exhibited by the solids are all consistent with an electronic ground state configuration (3a1′)2(4e′)4(2a2′)1 for these complexes.

Humulene nitrosite (3), dinitrohumulene (5), and nitronitratohumulene (4) are obtained as crystalline products when nitrogen dioxide and nitric oxide react with humulene. 1H N.m.r., 13C n.m.r., i.r., and mass spectroscopy enable the molecular structures for each of these compounds to be deduced. The yellow oil, obtained when humulene nitrosite reacts with nitric oxide and nitrogen dioxide, contains dinitrohumulene (5), nitronitratohumulene (4), 1,1,4-trimethyl-8-methylene-7-nitrocycloundeca-3,10-diene (9), isomers (11) and (12) of compound (9), the caryophyllene derivative 4,11,11-trimethyl-8-methylene-2,5-dinitrobicyclo[7.2.0]undec-3-ene (10), three nitroxide radicals, and several olefinic compounds derived from further reaction at position C(10)C(11) of the humulene structure with oxides of nitrogen. These compounds originate from reactions in which a ‘master’ aliphatic radical (15) takes part, and their characterization enables details of the mechanisms of reaction of N2O3 with humulene nitrosite to be unravelled.

E.p.r. studies of the first radical that is produced when a single crystal of the platelet form of humulene nitrosite is irradiated with red light enable the tensor components of its spin-Hamiltonian to be evaluated, and the principal directions of its g, A(14N), and A(1H) tensors to be orientated with respect to the crystallographic axes of the monoclinic unit cell. The radical is a monoalkyl nitroxide to which the structure (2) is assigned: it is a geometric isomer of the corresponding cycloundecatriene derivative that is obtained when the needle form of humulene nitrosite is red-irradiated. Superimposition of relatively minor librational motions in the solid, causes the principal directions within its different nitroxides to become effectively parallel, so that the two crystallographically distinguishable molecules of (2) in the unit cell can not be distinguished by e.p.r. methods at 293 K.

Humulene nitrosite (1) exhibits needle and platelet crystalline forms. Photolysis of compound (1) with red light generates N2, NO, NO2, dinitrohumulene (2), 1,4,4-trimethyl-8-methylene-9-nitrocycloundeca-1,5-diene (3), isomers (4) and (5) of compound (3) and, in the case of the platelets, caryophyllene derivatives. Several nitroxide radicals are also generated, and changes in their e.p.r. spectra have been monitored as a function of irradiation time. These spectra have been analysed to yield spin-Hamiltonian parameters, and they give information about the molecular structures of the nitroxides and about their formation and decay in the solid. The combination of chemical and spectroscopic evidence enables some of the steps involved in the solid photolysis reaction to be unravelled.

X-Band e.p.r. spectra of Re(O)Cl4, [Re(O)Cl4(NCMe)], [Re(O)Cl4(OPCl3)], and [Ph4As][Re(O)Cl5] have been recorded at 77 K and are analysed in detail. The metal-ion spin–orbit coupling constant and the parameter P= 2·002gReβeβN〈ψ|r–3|ψ〉 have been estimated to be ca. 2 400 and 0·033 cm–1 respectively. Spin-Hamiltonian parameters are listed for each substance and are equated to the atomic-orbital coefficients in some of the molecular orbitals involved in bonding in these molecules. The unpaired electron lies in the metal-ion 5dxy orbital and is strongly delocalised (33%) on to the chloride ligands. g∥ Is greater than g⊥ and this is shown to be essentially due to charge-transfer mixing through spin–orbit coupling at the chlorine atoms. Changes in the spin-Hamiltonian parameters when a sixth ligand is added to Re(O)Cl4 are accounted for. Huckel LCAO molecular-orbital calculations on Re(O)Cl4 appear to give a reasonable description of its ground state.

X-Band e.p.r. spectra of magnetically dilute solutions of MnO2Cl2 in CCl4 have been recorded at 77 K and at 298 K and are analysed in detail. The spin–orbit coupling constants, ξMn and ξCl, at the manganese and chlorine atoms in this compound are estimated to be 248 and 587 cm–1 respectively. At 77 K, MnO2Cl2 rotates about its X-axis in CCl4 solution. Spin-Hamiltonian parameters are listed for 298 K, for 77 K, and for the rigid molecule, and are equated to the atomic orbital coefficients in the molecular orbitals involved in bonding in this molecule. The unpaired electron lies in the metal ion 3dx2–y2 orbital mixed with a small amount (8%) of the 3dz2 orbital, and it is strongly (55%) delocalised on to the ligands. Two of the principal components of the g-tensor are larger than the spin-only value, a situation unusual in d1 complexes. This is shown to be due to relatively large spin–orbit coupling at the chlorine atoms. It is pointed out that principal values of the g-tensor may be used to distinguish distorted tetrahedral complexes which are stretched along their z-axes from the corresponding complexes compressed in this direction, provided that spin–orbit interactions at the ligands are relatively large.

The stereochemistries and conformations of humulene nitrosite (2), dinitrohumulene (3), and nitronitratohumulene (4) have been determined by X-ray analyses of their crystal structures. The compounds are shown to result from cis addition to humulene (1). The common ring conformation in compounds (2), (3), and (4) differs from that in humulene. A spread of C–C–C angles in the eleven-membered rings indicates steric strain and these results are reproduced in force-field calculations on the hexamethylcycloundecadiene (5). Crystallographic data are humulene nitrosite, a= 6.484(2), b= 18.139(8), c= 14.294(3)A, β= 101.33(2)°, Z= 4, space group P21/n; dinitrohumulene, a= 6.422(2), b= 18.177(2), c= 14.218(2)A, β= 100.69(2)°, Z= 4, space group P21/n; nitronitratohumulene, a= 7.665(2), b= 11.908(2), c= 18.170(4)A, Z= 4, space group Pc21n. X-Ray intensity measurements were made on an automatic four-circle diffractometer and least-squares adjustment of the atomic co-ordinates and thermal parameters converged at R 0.071 for compound (2), 0.042 for compound (3), and 0.052 for compound (4).

The 35Cl nuclear quadrupole resonance spectra of a series of aminochlorocyclotriphosphazatrienes N3P3Cl6–nRn(R = NMe2, n= 1–4; R = NC5H10, n= 1–3) have been recorded at 77 and/or 273 K. These data show that positional isomers may be distinguished, but that unambiguous structural assignments to geometrical isomers are not generally possible. Similar conclusions may be drawn for other aminochloro- and phenylchloro-cyclotriphosphazatrienes. Resonance frequencies diagnostic of PCl2, PCl·NR2, and PClPh groups fall in the ranges 26–29, 22–25, and 23–25 MHz respectively, but the last two groups cannot be distinguished by this technique.

Two conformational isomers of humulene nitrosite have been isolated as distinct crystalline forms, needles and platelets. The conformations have been characterized by X-ray diffraction studies and molecular mechanics calculations. Crystallographic data for the platelet form are: a= 7.873(6), b= 16.660(9), c= 12.140(6)A, β= 101.94(5)°, Z= 4, space group P21/c. X-Ray intensity measurements were made on an automatic four-circle diffractometer and least-squares adjustment of the atomic parameters converged at R 0.059 for 2 690 |F0| values.

The stereochemistries of caryophyllene nitrosite (3) and dinitrocaryophyllene (5) have been determined by X-ray analyses of their crystal structures. Crystallographic data are: caryophyllene nitrosite, a=6.476(4), b=13.199(2), c=18.784(2)A, Z=4, space group P212121; dinitrocaryophyllene, a=6.405(4), b=12.991(2), c=9.797(3)A, β=93.04(4)°, Z=2, space group P21. The molecular conformations are very similar and caryophyllene nitrosite forms solid solutions in dinitrocaryophyllene. Irradiation of these solid solutions with red light generates a monoalkyl nitroxide radical (11). in two symmetry-related orientations, whose spin- Hamiltonian parameters and orientations in the unit cell of the dinitrocaryophyllene crystal have been determined by detailed analyses of single-crystal e.p.r. spectra. Photolysis of pure solid caryophyllene nitrosite with red light generates N2, NO, NO2, dinitrocaryophyllene (5), nitro-nitratocaryophyllene (7), isocaryophyllene (6), and 4,8-bismethylene-11,11 -dimethyl-5-nitrobicyclo[7.2.0]undecane (8) and its isomers, compounds (9) and (10). Three nitroxide radicals, two of which have been identified as compounds (11) and (15) are also generated. The combination of chemical, X-ray, and spectroscopic evidence enables the steps in the solid photolysis reactions to be unravelled.