N-2-hydroxy-4-methoxyacetophenone-N'-4-nitrobenzoyl hydrazine: synthesis and structural characterization

A new aroyl hydrazone, N-2-hydroxy-4-methoxyacetophenone-N'-4-nitrobenzoyl hydrazine was prepared by the condensation reaction of 2-hydroxy-4-methoxyacetophenone and 4-nitrobenzoyl hydrazine. Characterization of the compound was done by elemental analysis and electronic, infrared and NMR spectral analyses. The complete structural assignment of the compound was done by NMR studies by using COSY homonuclear and HSQC heteronuclear techniques. The crystal and molecular structure was determined by single crystal X-ray diffraction studies: crystallized in the monoclinic system, space group P2(1)/n, Z=4, a=7.3343(9)A, b=20.3517(9)A, c=10.1375(5)A, alpha=90.00 degrees, beta=95.735(7) degrees and gamma=90.00 degrees. From the crystal structure, it is concluded that the compound exists as the keto isomer in the solid state. There is a completely extended conformation in the central part of the molecule C5C8N1N2C10O2 with an E configuration at the double bond of the hydrazinic bridge.     

Vibrational spectra and structure of cyclopropane-d1 and dicyclopropyl ketone

Infrared spectra have been obtained for cyclopropane-d₁, C₃H₅D(CP-d₁), in the vapor phase and for dicyclopropyl ketone (C₃H₅)₂ CO (DCPK) in the liquid state. Raman spectra of the latter compound in the liquid and solid phases have also been recorded. By comparing the experimental with the theoretical spectra of CP-d₁ it has been possible to assign most of the fundamental frequencies of the molecule. Additionably, empirical spectra—structure correlations from the literature for cyclopropyl derivatives containing the COX moiety (X=halogen) have been used to investigate the conformational preference of DCPK. The experimental results confirm that the molecular configuration with the carbonyl group cis to the planes of the two rings is the predominant species in the liquid state, though evidence for a second conformer, which we tentatively identify as the cis—trans conformer, is presented.     

Molecular structure and conformational preferences of 1-chloro-1-silacyclohexane,CH<Subscript>2</Subscript>(CH<Subscript>2</Subscript>CH<Subscript>2</Subscript>)<Subscript>2</Subscript>SiH-Cl,as studies by gas-phase electron diffraction and quantum chemistry

The molecular structure of axial and equatorial conformer of the 1-chloro-1-silacyclohexane molecule, CH₂(CH₂CH₂)₂SiH-Cl, as well as thermodynamic equilibrium between these species were investigated by means of gas-phase electron diffraction and quantum chemistry on the MP2(full)/AUG-cc-PVTZ level of theory. According to electron diffraction data, the compound exists in the gas-phase as a mixture of conformers possessing the chair conformation of the six-membered ring and Cs symmetry and differing in the axial and equatorial position of the Si-Cl bond at 352 K. NBO analysis revealed that axial conformer of 1-chloro-1-silacyclohexane molecule is an example of the stabilization of the form that is unfavorable from the point of view steric effects and effects of conjugations and that stabilization is achieved due to electrostatic interactions.     

新型含硫半抗原的晶体结构、构象分析及其电性研究

分析了一种新设计的含硫半抗原N-苯甲酰牛磺酰基苯丙氨酸的晶体结构,确证了其中的S原子为四面体构型,可以用来模拟酰胺键水解的过渡态,并且发现了几个分子间氢键.运用分子力学程序MOLGEN对此化合物进行了优化,并与含P半抗原进行了比较.然后又比较了N_S_C键和N_P_C键的旋转构象分析图,发现N_S_C键只有一个低能构象.最后用MOPAC程序(AM1参数)计算了S原子周围的电荷分布.发现S原子周围的电荷分布与P原子周围的电荷分布相似.     

Synthesis, spectral characterization and crystal structure of N-2-hydroxy-4-methoxybenzaldehyde-N'-4-nitrobenzoyl hydrazone and its square planar Cu(II) complex

A new aroyl hydrazone, N-2-hydroxy-4-methoxybenzaldehyde-N'-4-nitrobenzoyl hydrazone (H2L) and its mixed ligand Cu(II) complex [CuLpy] [py, pyridine] have been prepared. The ligand is characterized by elemental analysis, electronic, infrared and NMR spectral studies and the complex by electronic, infrared, EPR spectral studies and the magnetic susceptibility data. The structures of the compounds were determined by single crystal X-ray diffraction studies. Both the ligand and the Cu complex crystallize into a triclinic lattice with a space group of PI. From the crystal studies, it is concluded that the ligand molecule exits in the keto form in the solid state, while at the time of complexation, it tautomerises into the enol form. The complex is formed by the double deprotonation of the ligand molecule--both the phenolic and the enolic protons.     

Dendron-combined poly(4-diphenyl- aminium-1,2-phenylenevinylene): an isolated multiplet molecule

[structure: see text] Poly[4-(N,N-bis(4-3,5-bis(3,5-bis(benzyloxy)benzyloxy)benzyloxyphenyl)amino)-1,2-phenylenevinylene] was prepared by the palladium-catalyzed polycondensation of the dendron-coupled bromostyrene and oxidized to yield the corresponding poly(aminium cationic radical): The dendron-combined polyradical molecule displayed both a substantial chemical stability and a multiplet state without any intermolecular interaction.     

Computational study of sulfoxides of thiacyclohexane, 4‐silathiacyclohexane, 4‐fluoro‐4‐silathiacyclohexane,and 4,4‐difluoro‐4‐silathiacyclohexane: Relative energies of conformations and sulfinyl oxygen stabilized pentacoordinate silicon in boat and twist structures

Second‐order Møller‐Plesset theory (MP2) has been used to calculate the equilibrium geometries and relative energies of the chair, 1,4‐twist, 2,5‐twist, 1,4‐boat, and 2,5‐boat conformations of thiacyclohexane 1‐oxide (tetrahydro‐2H‐thiopyran 1‐oxide), 4‐silathiacyclohexane 1‐oxide, cis‐ and trans‐4‐fluoro‐4‐silathiacyclohexane 1‐oxide, and 4,4‐difluoro‐4‐silathiacyclohexane 1‐oxide. At the MP2/6‐311+G(d,p) level of theory, the chair conformer of axial thiacyclohexane 1‐oxide is 0.99, 5.61, 5.91, 8.57, and 7.43 kcal/mol more stable (ΔE) than its respective equatorial chair, 1,4‐twist, and 2,5‐twist conformers and 1,4‐boat and 2,5‐boat transition states. The chair conformer of equatorial thiacyclohexane 1‐oxide is 4.62, 6.31, 7.56, and 7.26 kcal/mol more stable (ΔE) than its respective 1,4‐twist and 2,5‐twist conformers and 1,4‐boat and 2,5‐boat transition states. The chair conformer of axial 4‐silathiacyclohexane 1‐oxide is 1.79, 4.26, 3.85, and 5.71 kcal/mol more stable (ΔE) than its respective equatorial chair, 1,4‐twist, and 2,5‐twist conformers and 2,5‐boat transition state. The 2,5‐twist conformer of axial 4‐silathiacyclohexane 1‐oxide is stabilized by a transannular interaction between the sulfinyl oxygen and silicon, to give trigonal bipyramidal geometry at silicon. The chair conformer of equatorial 4‐silathiacyclohexane 1‐oxide is 2.47, 7.90, and 8.09 kcal/mol more stable (ΔE) than its respective 1,4‐twist, and 2,5‐twist conformers and 2,5‐boat transition state. The chair conformer of axial cis‐4‐fluoro‐4‐silathiacyclohexane 1‐oxide is 4.18 and 5.70 kcal/mol more stable than its 1,4‐twist conformer and 2,5‐boat transition state and 1.51 kcal/mol more stable than the chair conformer of equatorial cis‐4‐fluoro‐4‐silathiacyclohexane 1‐oxide. The chair conformer of axial trans‐4‐fluoro‐4‐silathiacyclohexane 1‐oxide is 5.02 and 6.11 kcal/mol more stable than its respective 1,4‐twist conformer and 2,5‐boat transition state, but is less stable than its 2,5‐twist conformer (ΔE = ?1.77 kcal/mol) and 1,4‐boat transition state (ΔE = ?1.65 kcal/mol). The 2,5‐twist conformer and 1,4‐boat conformer of axial trans‐4‐fluoro‐4‐silathiacyclohexane 1‐oxide are stabilized by intramolecular coordination of the sulfinyl oxygen with silicon that results in trigonal bipyramidal geometry at silicon. The chair conformer of axial 4,4‐difluoro‐4‐silathiacyclohexane 1‐oxide is 3.02, 5.16, 0.90, and 6.21 kcal/mol more stable (ΔE) than its respective equatorial chair, 1,4‐twist, and 1,4‐boat conformers and 2,5‐boat transition state. The 1,4‐boat conformer of axial 4,4‐difluoro‐4‐silathiacyclohexane 1‐oxide is stabilized by a transannular coordination of the sulfinyl oxygen with silicon that results in a trigonal bipyramidal geometry at silicon. The relative energies of the conformers and transition states are discussed in terms of hyperconjugation, orbital interactions, nonbonded interactions, and intramolecular sulfinyl oxygen–silicon coordination. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2005     

Synthesis and characterization of novel aliphatic polycarbonates

A new six‐membered cyclic carbonate monomer, 5‐benzyloxy‐trimethylene carbonate, was synthesized from 2‐benzyloxy‐1,3‐propanediol, and the corresponding polycarbonate, poly(5‐benzyloxy‐trimethylene carbonate) (PBTMC), was further synthesized by ring‐opening polymerization in bulk at 150 °C using aluminum isobutoxide [Al(OⁱBu)₃], aluminum isopropoxide, or stannous octanoate as an initiator. The results showed that a higher molecular weight polycarbonate could be obtained in the case of Al(OⁱBu)_3. The protecting benzyl group was removed subsequently by catalytic hydrogenation to give a polycarbonate containing a pendant hydroxyl group (PHTMC). The polycarbonates obtained were characterized by Fourier transform infrared spectroscopy, ¹H NMR,¹³C NMR, gel permeation chromatography, and DSC. NMR results of PBTMC offered no evidence for decarboxylation occurring during the propagation. The pendant hydroxyl group in PHTMC resulted in an enhancement of the hydrophilicity of the polycarbonate. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 40: 70–75, 2002     

Molecular structures of some hydroxyazo compounds and their derivatives

The i.r. absorption spectra of 14 o-hydroxyazophenyl derivatives with increasing number of fused benzene rings of the aryl moiety are studied in solid state, in CCl₄ solution and in nujol mull. The i.r. spectral bands are assigned and indicate that these compounds exist in two tautomer forms. The OH group of the aryl moiety ortho to the azo group is responsible for the hydrazone structure. If solutions in CCl₄ are exposed to sunlight the strongly coloured compounds undergo a rapid bleaching, leading to a destruction of the azo group accompanied by an increase of hydrazone structures.     

Infrared and Raman spectra, conformational stability, normal coordinate analysis, ab initio calculations, and vibrational assignment of 1-fluoro-1-methylsilacyclobutane

The infrared (3500–40 cm⁻¹) spectra of gaseous and solid 1-fluoro-1-methylsilacyclobutane, c-C₃H₆SiF(CH₃), have been recorded. Additionally, the Raman spectrum (3500–30 cm⁻¹) of the liquid has been recorded and quantitative depolarization values have been obtained. Both the axial and equatorial (with respect to the methyl group) conformers have been identified in the fluid phases. Variable temperature (−55–−100°C) studies of the infrared spectra of the sample dissolved in liquid xenon have been carried out. From these data, the enthalpy difference has been determined to be 267±10 cm⁻¹ (3.19±0.12 kJ mol⁻¹), with the axial conformer being the more stable form and the only conformer remaining in the polycrystalline solid. A complete vibrational assignment is proposed for the axial conformer and many of the fundamentals for the equatorial conformer have also been identified. The vibrational assignments are supported by normal coordinate calculations utilizing ab initio force constants. Complete equilibrium geometries have been determined for both rotamers by ab initio calculations employing the 6-31G* and 6-311++G** basis sets at the levels of restricted Hartree–Fock (RHF) and/or Moller–Plesset (MP) to second order. The results are discussed and compared to those obtained for some similar molecules.     

Experimental and computational study of crystalline formic acid composed of the higher-energy conformer

Crystalline formic acid (FA) is studied experimentally and by first-principles simulations in order to identify a bulk solid structure composed of the higher-energy (cis) conformer. In the experiments, deuterated FA (HCOOD) was deposited in a Ne matrix and transformed to the cis conformer by vibrational excitation of the ground state (trans) form. Evaporation of the Ne host above 13 K prepared FA in a bulk solid state mainly composed of cis-FA. Infrared absorption spectroscopy at 4.3 K shows that the obtained solid differs from that composed of trans-FA molecules and that the state persists up to the annealing temperature of at least 110 K. The first-principles simulations reveal various energetically stable periodic chain structures containing cis-FA conformers. These chain structures contain either purely cis or both cis and trans forms. The vibrational frequencies of the calculated structures were compared to the experiment and a tentative assignment is given for a novel solid composed of cis-FA.     

Polymorphism of N,N'-diacetylbiuret studied by solid-state 13C and 15N NMR spectroscopy, DFT calculations, and X-ray diffraction

The molecular configuration and crystal structure of solid polycrystalline N,N′′‐diacetylbiuret (DAB), a potential nitrogen‐rich fertilizer, have been analyzed by a combination of solid‐ and liquid‐state NMR spectroscopy, X‐ray diffraction, and DFT calculations. Initially a pure NMR study (“NMR crystallography”) was performed as available single crystals of DAB were not suitable for X‐ray diffraction. Solid‐state ¹³C NMR spectra revealed the unexpected existence of two polymorphic modifications (α‐ and β‐DAB) obtained from different chemical procedures. Several NMR techniques were applied for a thorough characterization of the molecular system, revealing chemical shift anisotropy (CSA) tensors of selected nuclei in the solid state, chemical shifts in the liquid state, and molecular dynamics in the solid state. Dynamic NMR spectroscopy of DAB in solution revealed exchange between two different configurations, which raised the question, is there a correlation between the two different configurations found in solution and the two polymorphic modifications found in the solid state? By using this knowledge, a new crystallization protocol was devised which led to the growth of single crystals suitable for X‐ray diffraction. The X‐ray data showed that the same symmetric configuration is present in both polymorphic modifications, but the packing patterns in the crystals are different. In both cases hydrogen bonds lead to the formation of planes of DAB molecules. Additional symmetry elements, a two‐fold screw in the case of α‐DAB and a c‐glide plane in the case of β‐DAB, lead to a more symmetric (α‐DAB) or asymmetric (β‐DAB) intermolecular hydrogen‐bonding pattern for each molecule.     

Conformational analysis,barriers to internal rotation and vibrational assignment for dimethylethylamine

The IR (50–3500 cm^?1) and Raman (20–3500 cm^?1) spectra have been recorded for gaseous and solid dimethylethylamine. Additionally, the Raman spectrum of the liquid has been recorded and qualitative depolarization values have been obtained. Due to the fact that three distinct Raman lines disappear on going from the fluid phases to the solid state, it is concluded that the molecule exists as a mixture of the gauche and trans conformers in the fluid phases with the gauche conformer being more stable and the only one present in the spectra of the unannealed solid. From the temperature study of the Raman spectrum of the liquid a rough estimate of 3.9 kcal mol^?1 has been obtained for ΔH. Relying mainly on group frequencies and relative intensities of the IR and Raman lines, a complete vibrational assignment is proposed for the gauche conformer. The potential functions for the three methyl rotors have been obtained, and the barriers to internal rotation for the two CH₃ rotors attached to the nitrogen atom have been calculated to be 3.51 and 3.43 kcal mol^?1, whereas the barrier for the CH₃ rotor of the ethyl group has been calculated to be 3.71 kcal mol^?1. The asymmetric torsional mode for the gauche conformer has been observed in both the IR and Raman spectra of the gas at 105 cm^?1 with at least one hot band at a lower frequency. Since the corresponding mode has not been observed for the trans conformer, it is not possible to obtain the potential function for the asymmetric rotation although estimates on the magnitudes of some of the terms have been made. Significant changes occur in the low-frequency IR and Raman spectra of the solid with repeated annealing; several possible reasons for these changes are discussed and one possible explanation is that a conformational change is taking place in the solid where the trans form is stabilized by crystal packing forces. These results are compared to the corresponding quantities for some similar amines.     

Isolation of axial conformers of chloro- and bromocyclohexane in a pure state as inclusion complexes with 9,9'-bianthryl, and the discovery of a novel 1,3 diaxial Cl...H weak interaction

The axial conformers of chloro- and bromocyclohexane were isolated in a pure state as inclusion complexes with 9,9'-bianthryl, and a 1,3 diaxial Cl...H weak interaction was discovered by X-ray analysis of the axial conformer of chlorocyclohexane.     

Spectra and structure of small ring compounds. LXVII vibrational spectra, variable temperature FT-IR spectra of krypton solutions, conformational stability and ab initio calculations of 1-bromosilacyclobutane

The infrared (3,200-30 cm(-1) spectra of gaseous and solid 1-bromosilacyclobutane, c-C3H6SiBrH, have been recorded. Additionally, the Raman spectra of the liquid (3,200- 30 cm(-1) with quantitative depolarization values and the solid have been recorded. Both the equatorial and the axial conformers have been identified in the fluid phases, Variable temperature ( - 105 to - 150 degrees C) studies of the infrared spectra of the sample dissolved in liquid krypton have been carried out. From these data the enthalpy difference has been determined to be 182 +/- 18 cm(-1) (2.18 +/- 0.22 kJ/mol) with the equatorial conformer the more stable rotamer and only conformer remaining in the annealing solid. At ambient temperature there is approximately 22% of the axial conformer present in the vapor phase. A complete vibrational assignment is proposed for both conformers based on infrared contours, relative intensities, depolarization values and group frequencies. The vibrational assignments are supported by normal coordinate calculations utilizing the force constants from ab initio MP2/6-31G(d) calculations. From the frequencies of the Si-H stretch, the Si-H bond distance of 1.483 A has been determined for both the equatorial and the axial conformers. Complete equilibrium geometries have been determined for both rotamers by ab initio calculations employing the 6-31G(d) and 6-311 +/- G(d,p) basis sets at levels of Hartree Fock (RHF) and/or Moller- Plesset with full electron correlation by the perturbation method to the second order (MP2). The results are discussed and compared to those obtained for some similar molecules.     

Synthesis and NMR investigation of 3,4-diazabicyclo[4.3.0]non-2-ene and N,N'-azo-3-azabicyclo[3.3.0]octane. X-ray crystal structure analysis of a new tetrazene derivative

3,4-Diazabicyclo[4.3.0]non-2-ene and N,N'-azo-3-azabicyclo[3.3.0]octane are the main products of the oxidation of N-amino-3-azabicyclo[3.3.0]octane by chloramine. These new compounds have been isolated and characterized. A structural study has been performed with the goal of establishing the cis—trans configuration at the bicyclic junction. Multinuclear proton decoupling carried out on the endocyclic hydrazone has allowed the determination of the coupling constant of the bridgehead hydrogens. A low temperature conformational study shows splitting of the ¹³C signal of the carbon atom located α with respect to the ammonia nitrogen. This result, consistent with a cis structure, was confirmed by a nmr analysis conducted on the solid tetrazene derivative. The X-ray data collection on a single cyrstal of the tetrazene has permitted us to determine the crystallographic properties of this compound. Data processing by direct methods reveals that the geometry of the molecule presents a cis configuration for the bicyclic bridge link and a trans one for the azo group, confirming thus the main results obtained by nmr studies.     

Infrared and Raman spectra, conformational stability, ab initio calculations of structure, and vibrational assignment of ethynylmethyl cyclobutane.

The infrared spectra (3200-300 cm(-1)) of the gas and solid and the Raman spectra (3200-30 cm(-1) of the liquid with quantitative depolarization values and the solid have been recorded of ethynylmethyl cyclobutane (cyclobutylmethyl acetylene), c-C4H7CH2C[ triple bond]CH. Both the equatorial and the axial conformers have been identified in the fluid phases and both the gauche and trans conformations of the methyl acetylenic group have been identified for each ring conformer. Variable temperature (-105 to -150 degrees C) studies of the infrared spectra of the sample dissolved in liquid krypton have been carried out. From these data the enthalpy differences have been determined to the 112 +/- 11 cm(-1) (1.34 +/- 0.13 kJ mol) between the most stable equatorial-trans (Et) conformer and the equatorial-gauche (Eg) conformer which is the second most stable conformer and 327 +/- 35 cm(-1) (3.91 + 0.42 kJ/mol) with the axial-gauche (Ag) conformer which is the least stable conformer. The enthalpy difference between the axial-trans (At) and the equatorial-gauche(Eg) is 56 +/- 6 cm(-1). At ambient temperature there is approximately 33% of the Et conformer, 38% of the Eg form, 15% of the At and 14% of the Ag conformer. For the polycrystalline solid the Eg conformer is the only form present which probably results form the packing in the crystal. A complete vibrational assignment is proposed for both equatorial conformers and additionally a few of the fundamentals of the At and Ag conformers have been assigned. The vibrational assignments are supported by normal coordinate calculations utilizing the force constants from ab initio MP2/6-31G(d) calculations. Complete equilibrium geometries have been determined for all four possible rotamers by ab initio calculations employing the 6-31G(d) and 6-311 + + G(d,p) basis sets at levels of restricted Hartree-Fock (RHF) and /or Moller-Plesset (MP2) with full electron correlation by the perturbation method to second order. The results are discussed and compared to those obtained for some similar molecules.     

Generation of a spin polymer through a charge-transfer complex of a ferrocenyl mesogen with tetracyanoethylene in the solid state

Some disubstituted ferrocenes and a polymer with flexible pendant ferrocenyl mesogens were found to form a complex with tetracyanoethylene to give a spin molecule even in the solid state at ambient temperature.     

Crystal structures and topochemical polymerizations of 7,7,8,8-tetrakis(alkoxycarbonyl)quinodimethanes

Highly conjugated monomers, 7,7,8,8-tetrakis(alkoxycarbonyl)quinodimethanes (methoxy (1a), ethoxy (1b), isopropoxy (1c), benzyloxy (1d), chloroethoxy (1e), and bromoethoxy (1f)), were synthesized. Recrystallizations of 1a, 1c, 1e, and 1f yielded two crystal forms (prisms (1a-A) and needles (1a-B), needles (1c-A) and plates (1c-B), prisms (1e-A) and plates (1e-B), and prisms (1f-A) and needles (1f-B)), which have different molecular packing modes by X-ray crystal structure analysis, indicating that the crystals are polymorphic. In the photopolymerizations of these monomer crystals in the solid state, 1a-A, 1e-A, and 1f-A polymerized topochemically to give crystalline polymers. For their thermal polymerizations in the solid state, in addition to 1a-A, 1e-A, and 1f-A, 1e-B and 1f-B polymerized, but polymers formed from the 1e-B and 1f-B were amorphous. The packing of quinodimethane molecules in the crystals was defined by four kinds of parameters, stacking distance (d(s)), the distance between the reacting exomethylene carbon atoms (d(cc)), the angles formed between the stacking axis and longer axis of the monomer molecule (theta(1)), and the shorter axis of the monomer molecule (theta(2)), and then the polymerization reactivity of these quinodimethanes in the solid state was discussed on the basis of these parameters.     

Infrared, and Raman spectra, conformational stability, normal coordinate analysis, ab initio calculations, and vibrational assignment of 1-chlorosilacyclobutane

The infrared spectra (3500–40 cm⁻¹) of gaseous and solid and the Raman spectra (3500–30 cm⁻¹) of liquid and solid 1-chlorosilacyclobutane, c-C₃H₆SiClH, have been obtained. Both the axial and equatorial conformers with respect to the chlorine atom have been identified in the fluid phases. Variable temperature (−105 to −150°C) studies of the infrared spectra of the sample dissolved in liquid krypton have been carried out. From these data, the enthalpy difference has been determined to be 211±17 cm⁻¹ (2.53±0.21 kJ/mol), with the equatorial conformer being the more stable form and the only conformer remaining in the annealed solid. At ambient temperatures, approximately 26% of the axial conformers are present in the vapor phase. A complete vibrational assignment is proposed for the equatorial conformer, and many of the fundamentals of the axial conformers have also been identified. The vibrational assignments are supported by normal coordinate calculations utilizing ab initio force constants. Complete equilibrium geometries, conformational stabilities, harmonic force fields, infrared intensities, Raman activities, and depolarization ratios have been determined for both rotamers by ab initio calculations employing the 6-31G(d) basis set at the levels of restricted Hartree–Fock (RHF) and/or Moller–Plesset (MP) to second order. Structural parameters have also been obtained using MP2/6-311+G(d,p) ab initio calculations. The r₀ parameters for both conformers are obtained from a combination of the ab initio predicted values and the twelve previously reported microwave rotational constants. The results are discussed and compared to those obtained for some similar molecules.