Showing papers on "Dihedral angle published in 1970"
TL;DR: In this article, a complete description of the polyhedra of finite volume with dihedral angles not exceeding 90° in three-dimensional Lobacevski space is given, where the dihedral angle is fixed.
Abstract: The paper contains a complete description of the polyhedra of finite volume with dihedral angles not exceeding 90° in three-dimensional Lobacevskiĭ space. Bibliography: One item.
254 citations
TL;DR: In this paper, a proposed intramolecular hydrogen bond in the 2−haloethanols has been investigated with analysis of the microwave spectra of 2−chloroethanol and 2−bromo-ethanol, for each moledule, only a form gauche about the CC bond has been observed.
Abstract: A proposed intramolecular hydrogen bond in the 2‐haloethanols has been investigated with analysis of the microwave spectra of 2‐chloroethanol and 2‐bromoethanol. For each moledule, only a form gauche about the CC bond has been observed. For the chloro compound nine isotopic species have been studied to yield the molecular coordinates of the chlorine, oxygen, hydroxyl hydrogen, and carbon atoms, and thus a molecular structure. For bromoethanol a molecular structure has been found based upon the coordinates of the bromine and hydroxyl hydrogen atoms. Principal structural conclusions are that, of the probable rotameric forms, the lowest energy form is the one allowing close approach of hydrogen and halogen—namely, the gauche–gauche for dihedral angles (CCX) (COH) close to 60°. The O–H bond length in chloroethanol is 1.008 A, about 5% longer than in ethanol. The H···X distance is ∼ 0.5 A less than the sum of the atom van der Waals radii for X = Cl, Br. The O···X distance is approximately equal to the sum of t...
107 citations
TL;DR: The microwave spectra of two isotopic species of 2-fluoroethanol (FCH2CH2OH and FCH2 CH2OD) have been analyzed to yield some information about a proposed intramolecular hydrogen bond in the molecule as mentioned in this paper.
Abstract: The microwave spectra of two isotopic species of 2‐fluoroethanol (FCH2CH2OH and FCH2CH2OD) have been analyzed to yield some information about a proposed intramolecular hydrogen bond in the molecule A molecular structure has been derived which reveals that the most stable rotamer is that which allows close approach of fluorine and hydrogen atoms The F···H distance is 242 ± 002 A; the dihedral angle FCCO is 62°12′ ± 10°, and the dihedral angle CCOH is 55°30′ ± 3° The dipole moment components are μa = 038 ± 002 D, μb = 147 ± 001 D, and μc ≈ 00 D; these are consistent with bond moment calculations A vibrational state attributed to the CC torsional motion has been assigned and determined to be 152 ± 10 cm−1 above the ground state Our results suggest a hydrogen–fluorine interaction which does not grossly distort the normal molecular charge distribution
92 citations
TL;DR: In this article, the electron-diffraction intensities for bicyclo[2.2] octane in gas phase measured at 28°C have been given the following structural parameters: rg(C-C) (average)=1.542±0.004A, rg(H) ( average)= 1.107± 0.015A, etc.
Abstract: A least-squares analysis of the electron-diffraction intensities for bicyclo[2.2.2]octane in gas phase measured at 28°C has given the following structural parameters: rg(C–C) (average)=1.542±0.004A, rg(C–H) (average)=1.107±0.009A, rg(C1–C2)=1.538±0.015A, rg(C2–C3)=1.552±0.029A, ∠C1–C2–C3=109.7°±0.7°, and ∠H–C–H=110·1°±5·6°, where the uncertainties represent estimated limits of error. The potential function for the twisting motion around the D3h symmetry axis is found to have a broad minimum; in terms of the dihedral angle of torsion about the C2–C3 axis, φ, the potential has an rms angle of 12.0°±1.5° and a “classical turning point” of 21.5°±0.5° (7.2° and 12.8°, respectively, in terms of the dihedral angle of twist, τ). Best fit to the observed intensities has been achieved when a quartic function, V(φ)=k2φ2+k4φ4 with k2=−4.0 kcal/mol and k4=54.2 kcal/mol, is assumed. The potential function probably has a hump of the order of 100 cal/mol at the D3h conformation. Hence, this molecule may be regarded as ha...
67 citations
TL;DR: In this article, the Jahn-Teller distorted equilibrium geometries of the radical cations of cyclopropane and allene have been investigated using the MINDO/2 method.
65 citations
TL;DR: An ab initio SCF-LCAO-MO study of the relaxation process during internal rotation has been performed for ethane and hydrogen peroxyde, with polarization functions.
Abstract: An ab initio SCF-LCAO-MO study of the relaxation process during internal rotation has been performed for ethane and hydrogen peroxyde. A large gaussian basis set has been used, with polarization functions. The total energy has been optimized with respect to the bond lengths and bond angles. The computed barrier for the ethane molecule is 3.07 kcal/mole with the optimized geometry (experimental 2.93 kcal/mole). For hydrogen peroxyde, this yields a cis-barrier of 10.9 kcal/mole (experimental 7.0 kcal/mole) and a trans barrier of 0.6 kcal/mole (experimental 1.1 kcal/mole), with a dihedral angle equal to 123‡ (experimental 111‡–120‡). The eclipsed or cis conformations are found to have more “open” structures than the staggered or equilibrium conformations.
58 citations
TL;DR: Correlation between the Karplus-Bystrov relationship for (3)J(NC) and the peptide conformational potential energy map limits the possible values of the N-C(alpha) dihedral angle varphi of each amino acid residue in a polypeptide and protein, and therefore presents a method of conformational analysis in solution superior to the use of either nmr or conformational maps alone.
Abstract: Simple criteria, based on the combined use of nmr spectral parameters and potential energy maps, are proposed for the conformational analysis of polypeptides and proteins. Experimentally determined coupling constants 3JNC for the N-Cα bond are consistent with the Karplus-Bystrov relationship. It is proposed therefore that 3JNC can be used to distinguish (a) between right-and left-handed α-helices, (b) between α-helical, β-pleated sheet, and randomly coiled forms of peptides. The average 3JNC for the random coil is predicted. The criteria proposed are valid for both L- and D-amino acids. Correlation between the Karplus-Bystrov relationship for 3JNC and the peptide conformational potential energy map limits the possible values of the N-Cα dihedral angle ϕ of each amino acid residue in a polypeptide and protein, and therefore presents a method of conformational analysis in solution superior to the use of either nmr or conformational maps alone. Nmr studies of hydrogen bonding or neighboring-group diamagnetic anisotropy reduce the number of possibilities consistent with the above criteria. A suggestion for evaluating the dihedral angle is presented. These criteria are useful provided the coupling constant is not obscured by line broadening.
52 citations
TL;DR: The structure of dibenzothiophen was determined with Mo-Kα diffractometer data by Patterson, electron-density, and least-squares methods, the final R being 0·083 for 1176 observed reflexions as discussed by the authors.
Abstract: Crystals of dibenzothiophen are monoclinic, a= 8·67 ± 1, b= 6·00 ± 1, c= 18·70 ± 2 A, β= 113·9°, Z= 4, space group P21/c. The structure was determined with Mo-Kα diffractometer data by Patterson, electron-density, and least-squares methods, the final R being 0·083 for 1176 observed reflexions. The molecule is slightly folded, the dihedral angles between the five-membered ring and the six-membered rings being 0·4 and 1·2°(σ∼ 0·2°). The bond distances and valency angles are similar to those in related molecules. The C–S bond length is 1·740(8)A, and the C–S–C angle is 91·5(4)°.
51 citations
TL;DR: In this paper, the Zimm-Bragg parameters s and σ for the helix-coil transition in polyglycine and polyl-alanine are calculated in terms of molecular quantities, based on the earlier formulation which is modified here to take effects at junctions between helical and coil sequences into account more properly.
Abstract: The Zimm–Bragg parameters s and σ for the helix‐coil transition in polyglycine and poly‐l‐alanine are calculated in terms of molecular quantities, based on our earlier formulation which is modified here to take effects at junctions between helical and coil sequences into account more properly The statistical weight of a helical sequence is computed for both regular and nonregular helices In the latter, the dihedral angles φ and ψ (and χ for alanine) near the ends of helical sequences differ from those in the interior; this diffuseness, which extends over about five residues at each end, reduces the values of σ by a factor of 1000−1008 The dihedral angles and the corresponding conformational energies of both regular and nonregular helices are obtained by energy minimization The entropy factor in the statistical weight of a helical sequence consisting of j residues [(j + 1) peptide units] is obtained from the second derivatives of the energy surface in the 2j‐dimensional space for both regular and non
51 citations
TL;DR: The structure of tetrasilylhydrazine (SiH3)4N2 has been determined by the sector microphotometer method of electron diffraction as mentioned in this paper, and the data are consistent with planar Si2NN groups, and a dihedral angle of 82·5 ± 0·8°.
Abstract: The structure of tetrasilylhydrazine, (SiH3)4N2, has been determined by the sector microphotometer method of electron diffraction. The data are consistent with planar Si2NN groups, and a dihedral angle of 82·5 ± 0·8°; the deviation of this angle from 90° may possibly be explained by torsional effects. The Si–H, N–Si, and N–N bond lengths are 1·487 ± 0·014, 1·731 ± 0·004, and 1·457 ± 0·016 A respectively; the Si–N–Si angle is 129·5 ± 0·7° and the N–Si–H angle is 109·0 ± 1·4°.
37 citations
TL;DR: In this article, the authors used the nonempirical self-consistent field molecular orbital method with a basis set of groups of accurate Gaussian atomic orbitals to study formic acid for three different geometries.
Abstract: The nonempirical self‐consistent‐field molecular‐orbital method with a basis set of groups of accurate Gaussian atomic orbitals has been used to study formic acid, HCOOH, for three different geometries. The conformer with the hydroxyl hydrogen cis to the carbonyl oxygen is correctly computed to be the most stable. This geometry is 13.0 kcal lower in energy than the geometry with the hydroxyl hydrogen at a 90° dihedral angle with the carbonyl oxygen (experimental estimate: 13.4 kcal) and 8.1 kcal lower than the trans form (experimental estimate: ≥ 4 kcal). The population analysis suggests a screening of the carbonyl oxygen in the high nuclear repulsion cis form and a partial breaking of the hydroxyl oxygen–carbon bond from cis to 90°. The electronic contribution to the calculated dipole moment shows shifts of electronic charge toward the carbonyl end of the molecule in cis and trans forms compared to the 90° form. Molecular properties related to the nuclear–nuclear and nuclear–electron potentials at the va...
TL;DR: Terui, Aono, and Tori have recently demonstrated a geometrical dependence of the vicinal ^(14)N-H coupling in compounds of types 1 and 2 for dihedral angles of 0, 60, and 120o.
Abstract: In contrast to the extensive investigations of the dependence of vicinal proton-proton and protonfluorine coupling constants on dihedral angle, relatively little is known about the angular dependence of vicinal proton-nitrogen couplings in saturated systems. The principal reasons for this are experimental difficulties associated with the quadrupole-induced relaxation of ^(14)N and the relatively small magnitudes of ^(14)N-H coupling constants. However, Terui, Aono, and Tori have recently demonstrated a geometrical dependence of the vicinal ^(14)N-H coupling in compounds of types 1 and 2 for dihedral angles of 0, 60, and 120o.
TL;DR: The molecular structure of tetramethyldiphosphine in the gas phase has been determined by electron diffraction as mentioned in this paper, which required a gas-nozzle temperature of 170°C, obtained by using hot compressed air.
Abstract: The molecular structure of tetramethyldiphosphine in the gas phase has been determined by electron diffraction. The study required a gas-nozzle temperature of 170°C, obtained by using hot compressed air. The molecule can be described by seven structural parameters from which all the 52 different interatomic distances can be calculated. All 52 distances were included in the full-matrix least-squares refinements which were performed. The final values of the seven independent parameters are C—H = 1.109±0.009 A, C—P = 1.853±0.003 A, P—P = 2.192±0.009 A, ∠CPC = 99.6±1.0°, ∠PCH = 108.8±2.5°, ∠CPP = 101.1±0.7°, and ϕ, the dihedral angle expressing the relative orientation of the dimethylphosphino groups, is 164±23°, measured from the cis configuration. The parameters of the dimethylphosphino groups are very similar to the corresponding values for the methyl phosphines. The P—P bond length is at the low end of a range of literature values for this bond. The apparent deviation of 16° from the trans configuration is possibly due to a shrinkage effect involving a low frequency torsional oscillation about the P—P bond.
TL;DR: In this article, the molecular structure of trimethylcyclopentadienylsilane, C 5 H 5 Si(CH 3 ) 3, has been studied by electron diffraction in the vapour phase.
TL;DR: In this article, it was shown that there are separate correlations for the trivalent and pentavalent phosphorus systems, each of which takes the form of a curved band even when the dihedrals are known quite accurately.
TL;DR: In this article, the p.m. spectrum of 3- O -benzoyl-1,2,4- O-benzylidyne-α- d -ribopyranose 1 (1 ) at 100 MHz has been analyzed by an iterative, least-squares method.
TL;DR: In this paper, the crystal structure of deoxycytidine hydrochloride (C_9H_(14)N_3Q_4Cl) was determined by a three-dimensional X-ray diffraction analysis.
Abstract: 2'-Deoxycytidine hydrochloride (C_9H_(14)N_3Q_4Cl) was crystallized from water as monoclinic needles, space group P2_1, with ɑ = 6-561, b= 17·659, c=5·125 A, β = 108·08° and two molecules per cell. The crystal structure has been determined by a three-dimensional X-ray diffraction analysis. A complete hemisphere of data (positive and negative values of both hand k) was collected with a General Electric XRD-5 automatic diffractometer and nickel-filtered Cu Kɑ radiation. The structure was solved by the
heavy-atom method. Full-matrix least-squares refinement of both the D and L enantiomorphs has led to respective R values of 0·035 and 0·061; the configuration that gave the lower R value confirms previous conclusions regarding the absolute configuration of the D sugar. The atoms in the pyrimidine ring exhibit small but significant deviations from planarity. The torsion angle describing the conformation about the glycosidic bond is 0°. The least-squares planes through any four ring atoms of the sugar residue, normally used to describe its conformation, are unsatisfactory in that the deviations of the atoms from the planes are rather large. The conformation can, perhaps, be best described relative to the plane through C(l'), C(4'), and 0(1'), with respect to which C(3') is displaced endo by 0·361 A and C(2') is 0·245 A exo.
TL;DR: In this article, the synthesis of homoadamantanone and some derivatives thereof is described, and the dihedral angle between the carbonyl groups is shown to be small.
TL;DR: In this article, a theory governing the change of the vicinal coupling parameters L and N in the A2B2 PMR spectra of nonsymmetrical 1,2-disubstituted ethanes, as evidenced in the studies of substituent effect and solvent effect, has been developed in terms of the potential function characteristics to internal rotation about the C-C bond.
Abstract: Based on rotational averaging, a theory governing the change of the vicinal coupling parameters L and N in the A2B2 PMR spectra of nonsymmetrical 1,2‐disubstituted ethanes, as evidenced in the studies of substituent effect and solvent effect, has been developed in terms of the potential function characteristics to internal rotation about the C–C bond. By taking the average over the entire period of dihedral angle with respect to an appropriate potential function for internal rotation of the compound, a refined Karplus equation for the vicinal H–H coupling constant as a function of dihedral angle, J = A cos2φ + B cosφ + C, could yield the expression for L / A and/or N / A in terms of hyperbolic Bessel functions which describes an explicit functional dependence of L and/or N on both the ethane barrier and the maximum dipole interaction potential between the two bonds C–X and C–Y. These expressions enable one to determine the physical parameters related to internal rotation upon measurement of L and/or N fro...
TL;DR: In this paper, a vibrational assignment of the fundamentals is proposed which is consistent with the Cs equilibrium configuration, based on the gas phase band contours, the depolarization values, and group frequency correlations.
Abstract: The infrared spectrum of gaseous 1‐pyrazoline has been measured from 33 to 4000 cm−1. The infrared and Raman spectra of the corresponding liquid sample have also been recorded. A vibrational assignment of the fundamentals is proposed which is consistent with the Cs equilibrium configuration. The assignment is based on the gas‐phase band contours, the depolarization values, and group frequency correlations. A series of 13 pronounced Q branches was observed in the far‐infrared spectral region, and they have been attributed to the strongly anharmonic ring‐puckering vibration. Although the far‐infrared frequencies could be reproduced by two different potential functions, a double minimum potential of the form V = 23.40(z4 − 4.40z2) where z is the reduced ring‐puckering coordinate provides the most satisfactory interpretation of all the spectral data. The height of the inversion barrier is calculated to be 113 cm−1, and the equilibrium angle between the two dihedral planes of the puckered ring is 19.7° ± 1.0°....
TL;DR: The crystal and molecular structures of di-μ-chloro-bis-(π- 1-ethoxycarbonyl-2-hydroxyallyl)-dipalladium, (C6H9O3PdCl)2 have been determined from the three-dimensional data.
Abstract: The crystal and molecular structures of di-μ-chloro-bis-(π- 1-ethoxycarbonyl-2-hydroxyallyl)-dipalladium, (C6H9O3PdCl)2 have been determined from the three-dimensional data. The crystals are triclinic; space group Pl; with one dimeric molecule per unit-cell; a=4.80, b=10.31, c=10.64 A, α=117.4, β=102.3, and γ=84.1°. The final discrepancy index is 14.0% for 1208 reflections. The two palladium atoms are joined by two chlorine bridges to form a square planar arrangement. The molecule possesses a center of symmetry which coincides with a crystallographic center of symmetry in the crystal; the overall coordination scheme of the palladium atom is similar to that established for the π-allyl palladium chloride dimer. The dihedral angle between the plane of four atoms [Pd, Pd′, Cl, and Cl′] and the π-allyl plane is 108. There are intermolecular hydrogen-bonds between the enolic hydroxyl group of one molecule and the carbonyl-group of the other molecule related by the center of symmetry.
TL;DR: The crystal structure of [16] annulene has been determined by two independent groups as mentioned in this paper, one determination was at 4° with equi-inclination Weissenberg film X-ray data, and was refined to an R of 0·12 on 1204 observed reflexions; the other determination is at 23° with counter data and has been refined to 0·06 on 822 reflexions.
Abstract: The crystal structure of [16]annulene has been determined by two independent groups. One determination was at 4° with equi-inclination Weissenberg film X-ray data, and was refined to an R of 0·12 on 1204 observed reflexions; the other determination was at 23° with counter data and has been refined to an R of 0·06 on 822 reflexions. The crystals are monoclinic, a= 8·779, b= 8·152, c= 18·643 A, and β= 109° 30′, (room temperature data), Z= 4, space group P21/c. The molecule is non-planar, with almost complete bond alternation. The single bonds (1·454 A) are alternately trans and gauche and the double bonds (1·333 A)cis and trans. The average torsion angle at a gauche bond is 41° so that the molecule is relatively flat with S4 non-crystallographic symmetry. These determinations confirm the lack of aromaticity of this [4n]annulene.
TL;DR: In this paper, the rotational constants for seven vibrational states of the ring bending mode for the most abundant isotopic species were determined from the microwave spectrum of trimethylene selenide (TMSe).
Abstract: The microwave spectrum of trimethylene selenide (TMSe) was measured in the region 7.3–32 GHz. The rotational constants for seven vibrational states of the ring bending mode for the most abundant isotopic species were determined. From the variation of the rotational constants with vibrational state a potential function was obtained for the ring bending vibration, V(Q) = 8.7056[Q4 − 13.2669Q2]. This potential function is in good agreement with that obtained from an analysis of the far ir spectrum, V(Q) = 8.7056[Q4 − 13.19Q2], and predicts a barrier height to the planar configuration of 383.1 ± 4 cm−1 as compared with 378.1 ± 4 cm−1 obtained from the far infrared. The equilibrium dihedral angle was calculated to be 29.5 ± 1°.
TL;DR: In this article, the electronic structure and conformational analysis of the acetanilide were carried out using the CNDO/2 method, and the results showed that the endo form is 1.2 Kcal/mole more stable than the exo form.
Abstract: The calculations of the electronic structure and conformational analysis of the acetanilide were carried out using the CNDO/2 method. The results show that the endo form is 1.2 Kcal/mole more stable than the exo form. The most stable conformation of the exo isomer corresponds to the dihedral angle of 90 ° between the phenyl and acetamide plane, whereas the minimum energy conformation of the endo isomer corresponds to the dihedral angle 50 °–60 °. A comparison of the calculated and experimental dipole moments suggests also the dihedral angle of 50 °–60 °. A comparison with experiment indicates that this molecular orbital method is good for conformational analysis and gives electronic structure which is compatible with spectroscopic measurement. The calculated conformational analysis and electronic structure of the acetanilide are in excellent agreement with experiments.
TL;DR: In this article, the cumulative frequency distribution curves of apparent dihedral angles expected on extraction replicas are derived from distributions of true dihedral angle by analysis of the projected image shapes of lenses situated on boundaries of random orientation in the solid.
TL;DR: In this paper, the relative orientation of the substituted phenyl group and the 4-cyanopyridinium group in compounds of the type: DCH 2 ǫA and DCH(R)CH(r′)A with R,R′ = H or alkyl was studied.
TL;DR: The two structure determinations of the trans-anti form showed that the molecules themselves have a centre of symmetry and consequently the four-membered rings must be planar, even though the packing and hydrogen bonding, if any, are quite different for the various materials.
Abstract: THERE is at present great interest in the chemical and biological effects of ultraviolet irradiation of nucleic acids. The possible correlation between the stereochemistry of the photoproducts and the biological consequences requires a detailed knowledge of the structures of these photo products. In addition to the methods of nuclear magnetic resonance1,2, mass spectra3, topochemistry4–7 and chemical analysis8–10, X-ray analysis is most conclusive. Consequently, crystal structure analyses have been performed on an adduct of thymine11–13 and a trimer of thymine (unpublished) in addition to the cis-syn14–16, cis-anti17 and trans-anti18,19 cyclobutyl dimers of uracil and thymine derivatives. The analyses of various dimers show remarkable agreement in bond lengths and angles of the molecules even though the packing and hydrogen bonding, if any, are quite different for the various materials. The cis-syn and cis-anti forms all have a puckered four-membered ring with a dihedral angle ∼155° except for the cis-syn photoproduct from 1,1′-trimethylene bis-thymine where the trimethylene bridge seems to force the cyclobutyl ring into a planar configuration16. The two structure determinations of the trans-anti form showed that the molecules themselves have a centre of symmetry and consequently the four-membered rings must be planar.
TL;DR: The crystal structure of 1-p-(2-dimethylaminoethoxyphenyl)-1,2-cis-diphenylbut-1-ene, a compound with oestrogenic activity, has been determined from diffractometer data and refined to R 0·101 for 3082 planes.
Abstract: The crystal structure of the hydrobromide of 1-p-(2-dimethylaminoethoxyphenyl)-1,2-cis-diphenylbut-1-ene, a compound with oestrogenic activity, has been determined from diffractometer data and refined to R 0·101 for 3082 planes. The compound crystallizes in the triclinic system with Z= 4; the structure has refined satisfactorily in the space group P. There are two crystallographically distinct conformational isomers of the cation in the crystal, differing mainly in the torsion angle in the O–CH2–CH2–N+ chain [+60° and –176°, syn-clinal-(gauche) and anti-periplanar(trans) conformations respectively]. The average dihedral angle between the planes of the aromatic rings and the plane of the ethylenic double bond is 54°. The identification of the isomers of similar related tri-aryl ethylenes from their n.m.r. spectra can now be made with confidence by reference to this known structure.
TL;DR: In this paper, the configuration and conformation of α-hydroxy-N-caproylhydrazobenzene (5) were discussed and an HCOH dihedral angle of 145° was calculated.
Abstract: —Intramolecular OH… N hydrogen bonding between the hydroxylic and terminal amino groups of α-hydroxy-N-caproylhydrazobenzene (5) permits J(HCOH) to be observed in most solvents. The configuration and conformation of 5 are discussed and an HCOH dihedral angle (ϕ) of 145° is calculated. Solvent effects on J(HCOH) as well as the role they appear to exert in restricting internal rotation of the phenyl substituents of 5 are discussed.
TL;DR: The structure of 2,6-dimethyl-4-phenylphosphorin, C13H13P, has been determined by single-crystal X-ray methods.
Abstract: The structure of 2,6-dimethyl-4-phenylphosphorin, C13H13P, has been determined by single-crystal X-ray methods. The space group is P212121 with a= 7·312(5), b= 14·333(7), and c= 10·820(8)A. The intensities of 935 planes, measured on a linear diffractometer; the final R was 0·052. Hydrogen-atom positions were located. The molecule possesses an approximate two-fold symmetry axis and the two planar six-membered rings have a dihedral angle of 38·6°. Phosphorin is the phosphorus analogue of pyridine and the planar C5P ring has two equal phosphorus–carbon bond-lengths of 1·743(5)A, and four equal carbon–carbon bond-lengths [mean 1·388(9)A]. The CPC angle is 102·4(2)°.