Spectra and structure of organophosphorus compounds—XXX. Vibrational and conformational study of methoxy difluorophosphinoxide-d0 and -d3

The i.r. (4000-40 cm⁻¹) and Raman (4000-10 cm⁻¹) spectra of gaseous, liquid and solid methoxy difluorophosphinoxide, CH₃OP(O)F₂, and the deuterated analog have been recorded. Results obtained from variable solvent and matrix isolation studies are consistent with the existence of both trans (CO bond trans to the PO bond) and gauche (dihedral angle approximately 120° from the trans form) conformers in the fluid phases. From simulations of observed gas phase i.r. band profiles, it was possible for assignments to be made to the individual conformers for a number of the fundamentals. Variable temperature studies carried out for the gaseous and liquid phases give energy differences between the gauche and trans conformers of 451 ± 100 cm⁻¹ (1.29 ± 0.3 kcal/mol) and 69 ± 20 cm⁻¹ (197 ± 57 cal/mol), respectively. Furthermore, these data are consistent with the gauche form being the thermodynamically preferred conformer for the gas phase whereas the trans conformer is preferred in the liquid phase and the only conformer present in the annealed solid. The methoxy torsional mode of the gauche conformer has been assigned to a very strong band observed in the far i.r. spectrum of the gas phase at 42 cm⁻¹. The matrix isolation spectra of the normal compound in Ar, CO and N₂ matrices indicated no changes in the conformational equilibrium among these different matrices and this equilibrium remains unchanged upon annealing the matrices.     

Infrared and Raman spectra,conformational stability,barriers to internal rotation,ab initio calculations and vibrational assignment of ethyl methyl selenide

The Raman spectra (3200–10 cm⁻¹) of ethyl methyl selenide in the gas, liquid and solid phases and the infrared spectra (3200–30 cm⁻¹) of the gas and solid have been recorded. Qualitative depolarization ratios have been obtained for the lines in the Raman spectrum of the liquid. By a variable temperature Raman study of the liquid, it has been determined that the gauche conformer is more stable than the trans rotamer by 158±16 cm⁻¹ (452±46 cal mol⁻¹), and the gauche conformer is the rotamer present in the solid. A complete vibrational assignment for the gauche conformer is presented. All of these data are compared to the corresponding quantities obtained from ab initio Hartree—Fock gradient calculations employing the STO-3G* and 4–31G*/MIDI-4* basis sets. Complete equilibrium geometries have been calculated for both rotamers and the results are discussed and compared with the corresponding quantities for some similar molecules.     

A conformational study of ethylene glycol

Ab initio calculations were performed for some different conformers of 1,2-ethanediol in order to reveal their relative energies. The equilibrium conformation is of gauche type with a comparatively weak intramolecular hydrogen bond. The energy of the all-trans conformer is 3 kcal/mol above the minimum.     

Solid state and theoretical evaluation of β-fluoroethyl esters indicate a fluorine-ester gauche effect

Single crystal X-ray diffraction studies and a theoretical analysis indicate a preferred conformation for O-β-fluoroethyl esters, where the CF and CO(CO) bonds are gauche rather than anti to each other. The OCCF dihedral angles for three compounds and five independent structures indicate a range of only 63.4-69.6°. Evaluation of a rotational energy profile around this bond in a model system (β-fluoroethyl acetate) predicted a similar dihedral angle and the gauche conformation to be the minimum on the rotational energy profile. High level ab initio calculations measured the gauche conformer to be 0.95 kcal mol⁻¹ lower in energy than the anti conformer and application of a solvation model further increased this differential to 1.6 kcal mol⁻¹, consistent with a previous solution state (NMR) evaluation of this system.     

Far infrared and low frequency gas phase Raman spectra,vibrational assignment,and conformational stability of 1-chloro-2-methylpropane and 1-bromo-2-methylpropane

The Raman (3200—10cm⁻¹) and infrared (3200—50 cm⁻¹) spectra of gaseous and solid 1-chloro-2-methylpropane and 1-bromo-methylpropane, as well as the Raman spectra of the liquids, have been recorded and assigned. The gauche asymmetric torsion of the 1-chloro-2-methylpropane molecules has been observed at 110 cm⁻¹ in the Raman spectrum of the gas. For the 1-bromo-2-methylpropane molecule, both the trans and gauche asymmetric torsions have been observed at 106.70 and 103.94 cm⁻¹, respectively, along with three additional transitions for the gauche conformer. From these data, the asymmetric potential function for the bromide molecules to V₁ = —493 ±16, V₂ = 595 ± 18, and V₃ = 2006 ± 6 cm⁻¹ with the trans conformer being more stable than the gauche conformer by 44 ± 20 cm⁻¹. The trans form is found experimentally to be more stable in the liquid phase by 30 ± 14 cm⁻¹ (83 ± 40 cal mol⁻¹). From the relative intensities, in the Raman spectra, of the CCl stretches measured as a function of temperature, the gauche conformer of the chloride molecules to be 167 ± 71 cm⁻¹ (479 ± 203 cal mol⁻¹) more stable than the trans conformer in the gas phase, and 73 ± 10 cm⁻¹ (208 ± 29 cal mol⁻¹) more stable in the liquid phase. The methyl torsions for the gauche and trans conformers of both molecules are tentatively assigned in the gas phase and the barriers have been calculated. The results of this study are compared with previous studies on these molecules.     

Raman and infrared spectra, conformational stability, barriers to internal rotation, vibrational assignment, and ab initio calculations of 3-methyl-3-butenenitrile

The Raman (3500-30 cm⁻¹) spectra of liquid and solid and the infrared (3500-40 cm⁻¹) spectra of gaseous and solid 3-methyl-3-butenenitrile, CH₂C(CH₃)CH₂CN, have been recorded. Both cis and gauche conformers have been identified in the fluid phases but only the cis form remains in the solid. Variable temperature (−55 to −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 163±16 cm⁻¹ (1.20±0.19 kJ mol⁻¹), with the cis conformer the more stable rotamer. It is estimated that there is 48±2% of the gauche conformer present at  25°C. A complete vibrational assignment is proposed for the cis conformer based on infrared band contours, relative intensities, depolarization ratios and group frequencies. Several of the fundamentals for the gauche conformer have also been identified. The vibrational assignments are supported by normal coordinate calculations utilizing ab initio force constants. Complete equilibrium geometries have been obtained for both rotamers by ab initio calculations employing the 6-31G(d), 6-311G(d,p), 6-311+G(d,p) and 6-311+G(2d,2p) basis sets at the levels of restricted Hartree-Fock (HF) and/or Møller-Plesset perturbation theory to the second order (MP2). Only with the 6-311G(2d,2p) and 6-311G(2df,2pd) basis sets with or without diffuse functions is the cis conformer predicted to be more stable than the gauche form. The potential energy terms for the conformational interchange have been obtained at the MP2(full)/6-311+G(2d,2p) level, and compared to those obtained from the experimental data. The results are discussed and compared to the corresponding quantities obtained for some similar molecules.     

Structure and conformational dynamics of the dicyclopropyl ketone in the ground electronic state

Geometric parameters, harmonic and anharmonic vibrational frequencies, conformer energy differences and barriers to internal rotation were obtained for dicyclopropyl ketone (DCPK) in the ground electronic state through MP2, DFT, CCSD and CCSD(T) calculations. VFPA was used to improve the estimations of conformer energy differences and heights of barriers to internal rotation. The ab initio calculations demonstrated that there are three stable conformations of DCPK: the cis–cis, the cis–trans and the gauche–gauche. The energy of the gauche–gauche conformer is noticeably higher than the energy of the two other conformers, so this conformer was not found experimentally. To study the conformational dynamics of the DCPK molecule, one- and two-dimensional sections of the potential energy surface corresponding to the rotations of the cyclopropyl groups were calculated. These sections were used to calculate torsion transition energies and vibrational wave functions in anharmonic approach. It was found that there is a strong coupling of large-amplitude torsion motions in the area of the cis–cis and gauche–gauche conformers.     

Far-infrared spectra and barriers to internal rotation of ethyl nitrate

The far-infrared spectra of gaseous and solid ethyl nitrate, CH₃CH₂ONO₂, have been recorded from 500 to 50 cm⁻¹. The fundamental asymmetric torsion of the trans conformer which has a heavy atom plane has been observed at 112.50 cm⁻¹ with two excited states failing to lower frequencies, and the corresponding fundamental torsion of the gauche conformer was observed at 109.62 cm⁻¹ with two excited states also falling to lower frequencies. The results of a variable temperature Raman study indicate that the trans conformer is more stable than the gauche conformer by 328 ± 96 cm⁻¹ (938 ± 275 cal mol⁻¹). An asymmetric potential function governing the internal rotation about the CH₂O bond is reported which gives a trans to gauche barrier of 894 ± 15 cm⁻¹ (2.56 ± 0.04 kcal mol⁻¹) and a gauche to gauche barrier of 3063 ± 68 cm⁻¹ (8.76 ± 0.20 kcal mol⁻¹) with the trans conformer more stable by 220 ± 148 cm⁻¹ (0.63 ± 0.42 kcal mol⁻¹). Transitions arising from the symmetric CH₃ and NO₂ torsions are observed for both conformers, from which the threefold and twofold periodic barriers to internal rotation have been calculated. For the trans conformer the values are 1002 cm⁻¹ (2.87 kcal mol⁻¹) and 2355 ± 145 cm⁻¹ (6.73 ± 0.42 kcal mol⁻¹) and for the gauche conformer they are 981 cm⁻¹ (2.81 kcal mol⁻¹) and 2736 ± 632 cm⁻¹ (7.82 ± 1.81 kcal mol⁻¹) for the CH₃ and NO₂ rotors, respectively. These results are compared to the corresponding quantities for some similar molecules.     

Evidence for a blue-shifting intramolecular hydrogen bond in the vibrational overtone spectrum of 1H-nonafluorobutane

We demonstrate that the gauche conformation of 1H-nonafluorobutane contains a blue-shifting intramolecular hydrogen bond by recording its 5th overtone spectrum with cavity ringdown spectroscopy and performing electronic structure calculations. The magnitude of the blue-shift is enhanced in the overtone spectrum as compared to the fundamental. The energy difference between the gauche conformer and the lowest energy zigzag conformer is calculated to be 288 cm⁻¹ using density functional theory and determined to be 280 ± 30 cm⁻¹ using temperature-dependent FTIR measurements. The –H⋯F– bonding interaction in the gauche conformer leads to changes in bond lengths as compared to the non-hydrogen bonded conformers.     

Spectra and structure of organophosphorus compounds—XXXVII. Infrared and Raman spectra,conformational stability,vibrational assignment and normal coordinate analysis of ethyldichlorophosphine-d0 and -d5

The infrared (3500 to 40 cm⁻¹) and Raman (3500 to 10 cm⁻¹) spectra have been recorded for the gaseous and solid phases of ethyldichlorophosphine, CH₃CH₂PCl₂, and CD₃CD₂PCl₂. Additionally, the Raman spectra of the liquids were recorded and qualitative depolarization values were obtained. In the spectrum of the gas the gauche conformer is predominant with about 65% abundance whereas in the spectrum of the liquid at ambient temperature the amount of gauche conformer is reduced compared to the gas phase and at −100°C the trans conformer predominates. The trans conformer is the more stable species in the solid. A variable temperature study was carried out on the Raman spectrum of the liquid and ΔH and ΔS values of 190 ± 30 cm⁻¹ (543 ± 87 cal/mol) and 2.86 ± 0.3 eu were determined, respectively, with the trans conformer being more stable. Similar variable temperature studies have been carried out on a number of conformer peaks in the infrared spectrum of the gas and a ΔH value of 53 ± 38 cm⁻¹ (152 ± 110 cal/mol) was obtained, again with the trans conformer being more stable. All the fundamental modes of both conformers have been assigned utilizing band contours, depolarization values, isotopic shift factors and group frequencies. A normal coordinate calculation has been carried out utilizing a modified valence force field to calculate the frequencies and potential energy distribution for both conformers. The barriers to methyl rotation of the trans and gauche conformers are 2.2 ± 0.1 and 2.3 ± 0.1 kcal/mol, respectively. These results are compared to similar quantities for some corresponding molecules.     

Spectra and structure of small ring compounds: Part XXXVIII. Cyclobutanol

The Raman spectrum of gaseous cyclobutanol has been recorded and the far infrared spectrum of the gas has been obtained at a resolution of 0.5 cm^?1. At least six Q-branches arising from the low frequency ring-puckering motion have been observed and assigned on the basis of a potential of the form V(X) = (6.32 ± 0.21) × 10⁵X⁴?(4.18 ± 0.04) × 10⁴X²+ (8.81 ± 1.20) × 10³X³ with a reduced mass of 170 amu. An energy difference between the equatorial and axial forms was found to be 50–150 cm^?1 with the equatorial being more stable and a barrier of 700–900 cm^?1 was found for the interconversion. Three O-H stretching modes were observed in the Raman spectrum. It is concluded that the O-H moiety has both the gauche and trans conformations present in the equatorial form but only the gauche conformer is present in the axial form of the ring. Three O-H torsional modes were observed at 244 (trans conformer), 226.5 and 181.5 cm^?1 (gauche conformer) for the equatorial form and one O-H torsion at 237.5 cm^?1 (gauche conformer) for the axial form. The potential function governing the O-H torsional motion for the equatorial form was found to be V₁ = 280 ± 7 cm^?1 (800 cal mole^?1) and V₃ = 425 ± 3 cm^? (121.5 cal mole^?1) with the trans conformer being more stable than the gauche by approximately 206 cm^?1 (589 cal mole^?). The barriers to trans-gauche and gauche-gauche interconversion have essentially the same values, 500 cm^?1 (1430 cal mole^?1).     

On the transferability of conformation in FC(O)S-containing compounds: Conformation and properties of methylfluorocarbonyl disulphide FC(O)SSCH3

Methylfluorocarbonyl disulphide, FC(O)SSCH₃, was prepared for the first time by reaction of FC(O)SCl with CH₃SH at room temperature. Infrared data for the vapour and matrices (Ar, Ne and N₂) as well as Raman, UV, mass and ¹⁹F, ¹³C and ¹H NMR spectra have been obtained and interpreted.From these data, the most stable conformer was deduced to have the gauche conformation with respect to the FC(O) and CH₃ groups with the syn conformation between the CO and SS bonds having C₁ molecular symmetry. This conformer is in equilibrium with another, possibly the corresponding anti, referring to the CO and SS bonds.The main structure found for FC(O)S-containing compounds seems to be the syn conformation.     

Vibrational spectra,methyl torsional potential functions,internal rotational potential functions,and conformational properties of ethyl vinyl ether

The vibrational spectra of ethyl vinyl ether in both the fluid and solid states have been recorded from 20 to 3500 cm^?1. The 33 fundamental modes of vibration have been assigned. Three rotational isomers have been observed and their structures have been determined. The most stable conformer, s-cis/s-trans, is planar and of C_s symmetry. The two less stable rotamers, skew/s-trans and skew/gauche, are non-planar and of C_i molecular symmetry. The barrier to internal rotation of the methyl rotor has been determined for each conformation; these barriers are 3.43 kcal mol^?1 (s-cis/s-trans), 3.35 kcal mol^?1 (skew/s-trans) and 3.19 kcal mol^?1 (skew/gauche). A potential function for each of the two asymmetric internal rotations has been calculated and barriers to conformer interconversion have been determined. From the asymmetric potential function calculations, ΔH, the enthalpy difference between the conformers, has been determined. The s-cis/s-trans conformer is 1.87 kcal mol^?1 more stable than the skew/s-trans conformer; the skew/s-trans conformer is more stable than the skew/gauche conformer by 1.10 kcal mol^?1. The energetics of conformer interconversion and methyl internal rotation have been described in terms of molecular geometry and non-bonded interactions. These results are compared to those found in other alkyl vinyl and dialkyl ethers.     

Conformational equilibrium of dicyclopropyl ketone

The i.r. and Raman spectra of liquid dicyclopropyl ketone have been reinvestigated from 4000 to 200 cm⁻¹ with higher resolution than previously obtained. In addition, the i.r. spectrum of the polycrystalline solid was recorded from 4000 to 400 cm⁻¹. Contrary to published results, evidence has been obtained for a conformational equilibrium between the predominant cis—cis form and the gauche—gauche conformer.     

Matrix isolation infrared and ab initio studies on conformers of 3-fluoropropene

The infrared spectra of the cis and gauche conformers of 3-fluoropropene, CH₂CHCH₂F, were studied in Ne, Ar, Kr and Xe matrices. An infrared-induced cis to gauche rotamerization was found in Ar, Kr and Xe matrices. A thermal interconversion process was also found. Its direction was dependent upon the host, being the same as that of the IR process in Kr but reverse in Ar and Xe. In Ar and Xe matrices considerable site-splitting occurs in the IR spectra and a detailed analysis of the processes in different sites is given. An energy difference of 2.5±0.3 kJ mol⁻¹ between the cis and gauche species was obtained on assuming that the gas phase equilibrium between the conformers is trapped upon deposition. A slow dark process from cis to gauche conformer was observed in Kr matrices at temperatures above 15 K, possibly due to tunnelling. Ab initio calculations were carried out on 3-fluoropropene. The torsional potential energy curve and spectra of the conformers were calculated at the MP2(full)16-31G** level and were compared with the experimental results.     

Far-IR spectrum,conformation stability,barriers to internal rotation,vibrational assignment,and ab initio calculations of 3-chloro-2-methylpropene

The far-IR spectrum from 375 to 30 cm⁻¹ of gaseous 3-chloro-2-methylpropene, CH₂=C(CH₃)CH₂Cl, has been recorded at a resolution of 0.10 cm⁻¹. The fundamental asymmetric torsional mode for the gauche conformer is observed at 84.3 cm⁻¹ with three excited states falling to lower frequency. For the higher energy s-cis conformer, where the chlorine atom eclipses the double bond, the asymmetric torsion is observed at 81.3 cm⁻¹ with two excited states falling to lower frequency. Utilizing the s-cis and gauche torsional frequencies, the gauche dihedral angle and the enthalpy difference between conformers, the potential function governing the interconversion of the rotamers has been calculated. The determined potential function coefficients are (in reciprocal centimeters): V₁=189±12, V₂=−358±11, V₃=886±2 and V₄=−12±2 with an enthalpy difference between the more stable gauche and s-cis conformers of 150 ±25 cm⁻¹ (430 ± 71 cal mol⁻¹). This function gives values of 661 cm⁻¹ (1.89 kcal mol⁻¹), 1226 cm⁻¹ (3.51 kcal mol⁻¹) and 812 cm⁻¹ (2.32 kcal mol⁻¹), for the s-cis to gauche, gauche to gauche, and gauche to s-cis barriers, respectively. From the methyl torsional frequency of 170 cm⁻¹ for the gauche conformer, the threefold barrier of 678 cm⁻¹ (1.94 kcal mol⁻¹) has been calculated. The asymmetric potential function, conformational energy difference and optimized geometries of both conformers have also been obtained from ab initio calculations with both the 3–21G^* and 6–31G^* basis sets. A normal-coordinate analysis has also been performed with a force field determined from the 3–21G^* basis set. These data are compared with the corresponding data for some similar molecules.     

Proposed molecular structures for 3-butenenitrile, 2-methyl-3-butenenitrile,and 3-methyl-3-butenenitrile

Molecular structures are proposed for the two conformers, s-cis and gauche, existing for 3-butenenitrile and 3-methyl-3-butenenitrile, and for the three predicted conformers of 2-methyl-3-butenenitrile, using structural parameters transferred from related molecules. The proposed structures for the two conformers of 3-butenenitrile have principal moments of inertia which agree well with experimental values obtained by microwave spectroscopy, except for the gauche I_A moment. The experimental value of I_A for the gauche conformer of 3-butenenitrile could only be determined at the time with a low degree of precision, hence the microwave spectrum of this conformer should probably be reexamined.     

The role of internal H-bonding in the conformational preferences of some molecules of the formula CH3CHYCH2X

The conformational energies of 1-amino-2-propanol, 2-amino-1-propanol and 1,2-diaminopropane are studied using ab initio molecular orbital theory employing minimal (STO-3G) and extended (4-31G) basis sets. Calculations at both levels of theory generally favor conformations stabilized by internal H-bonding for all molecules considered. Results are first presented for conformations employing assumed geometries. Since the conformational energy differences as found by the initial set of calculations are in some cases rather small it then becomes necessary to introduce geometry optimizations into the study at the minimal STO-3G level. In addition, to get a better estimate of the energy differences of the various conformations 4-31G calculations are performed on the STO-3G optimized structures. These latter results indicate the following, (a) For 1-amino-2-propanol only one conformation that is stabilized by intramolecular H-bonding is low in energy; this has the methyl and amino groups anti. The other H-bonded conformer, where the methyl and amino groups are gauche, is predicted to be ca. 1.2 kcal mol^?1 less stable. Similar findings for this molecule have recently been provided by micro-wave spectroscopy. (b) For 2-amino-1-propanol the two H-bonded conformers are only separated by about 0.5 kcal mol^?1, with the anti conformer being more stable. Micro-wave spectroscopy again supports these calculations. (c) For 1,2-diaminopropane the gauche conformer is predicted to be of rather high energy (ca. 2.5 kcal mol^?1) compared to the corresponding anti H-bonded conformer. The value of 2.5 kcal mol^?1should be taken as an upper limit, since the geometry optimization of the gauche conformer of 1,2-diaminopropane is incomplete compared to the optimization carried out for the anti conformer.     

The infrared and Raman spectra, ab initio calculations and spectral assignments of cyclopropylmethyl dichlorosilane (c-C3H5)SiCl2CH3

Raman spectra of cyclopropylmethyl dichlorosilane (c-C₃H₅)SiCl₂CH₃ as a liquid were recorded at 293 K and polarization data were obtained. Additional Raman spectra were recorded at various temperatures between 293 and 163 K, and intensity changes of certain bands with temperature were detected. No crystallization was ever obtained in the Raman cryostat in spite of extensive annealing. The infrared spectra have been studied as a vapour, as an amorphous solid at 78 K and as a liquid in the range 600-100 cm⁻¹. No infrared bands present in the vapour or liquid seemed to vanish upon cooling, and the sample never formed crystals on the CsI window of an infrared cryostat.The compound exists a priori in two conformers, syn and gauche, and the experimental results suggest an equilibrium in which the gauche conformer has 1.64 kJ mol⁻¹ lower enthalpy than syn in the liquid, leading to 20% syn at ambient temperature. Most of the syn bands were situated close to the corresponding gauche bands and it was difficult to obtain reliable ΔH values.B3LYP calculations with various basis sets and the CBS-QB3 and G2 and G3 models were employed, yielding the conformational enthalpy difference ΔH (syn-gauche) between 2.6 and 3.4 kJ mol⁻¹. Infrared and Raman intensities, polarization ratios and vibrational frequencies for the syn and gauche conformers were calculated. Instead of scaling the calculated wavenumbers in the harmonic approximation, calculations from B3LYP/cc-pVTZ were derived in the anharmonic approximation. In most cases these values were in good agreement with the experimental results for 38 observed modes of the gauche and 8 modes of the syn conformer with a deviation of ca. 1%.     

Molecular conformational structures of 2-fluorobenzoyl chloride, 2-chlorobenzoyl chloride, and 2-bromobenzoyl chloride by gas electron diffraction and normal coordinate analysis aided by quantum chemical calculations

The gas phase molecular structures and conformational compositions of 2-fluorobenzoyl chloride, 2-chlorobenzoyl chloride, and 2-bromobenzoyl chloride have been investigated using gas electron diffraction data obtained from experiments performed in the laboratories of the University of Oslo and Oregon State University. The refinements on the experimental data have been aided by normal coordinate calculations as well as extensive ab initio molecular orbital and density functional theory calculations up to the levels of MP4(SDQ) and B3LYP with larger basis sets up to the level of 6-311 + G(2d,p) for the computed molecular geometries, electronic energies, vibrational zero-point energies and entropy corrections, gas mixture conformational compositions, and MP2(fc) quantum mechanical force fields. The three title molecules each exist in the gas phase as two stable non-planar conformers anti and gauche with respect to the halogen atom positions with anti the lower energy conformer in each case. Among the three title molecules there have been found considerable experimental and theoretical support for several trends in molecular or conformational behavior with increasing ortho halogen atomic size: An increasing although disputable trend in the C=O bond distance values; an increasing trend in the average phenyl ring C–C bond distance values; an increasing trend in the contribution of the gauche conformer to the gaseous mixture lowering the standard free energy difference values (ΔG ^o) correspondingly; and an increasing deviation from full planarity (C _s symmetry) in both the anti and the gauche conformers of the title molecules with increasing ortho halogen atomic size. Only in the anti conformer of 2-fluorobenzoyl chloride does the experimental data refinements suggest close to full planarity for these 2-halobenzoyl chloride molecules.