Abstract
The structural and conformational properties of 2,2,2-trichloroethylacetate, H3CCO2CH2CCl3, have been determined in the gas phase using gas electron diffraction (GED). The experimental measurements were complemented by MP2 and DFT quantum-chemical calculations. Two conformers separated by a shallow rotational barrier have been identified, one of C1 (syn-gauche) and the other of Cs symmetry (syn-anti). All calculations indicate that syn-gauche is preferred in terms of enthalpy, whereas syn-anti seems to be slightly more stable regarding Gibbs free energy. In the gas-phase structure determination, dynamic models based on different potential energy surface scans were used. The one from dispersion-corrected density functional theory, predicting a preference of syn-gauche by 1.7kJmol−1, was found to describe the experimental data best. One- and two-conformer models had to be rejected due to correlations and unrealistically large amplitudes. Experimentally determined structural parameters are in good agreement with both, quantum-chemical calculations as well as GED data for related compounds. Interacting quantum atoms (IQA) analyses revealed that interplay between the carbonyl group and the hydrogen as well as chlorine atoms of the trichloroethyl group accounts for most of the stabilisation of the C1 conformer. With intramolecular symmetry-adapted perturbation theory (I-SAPT) analyses it was possible to further elucidate the nature of dominant interactions in the two conformers. Herein, preference of syn-gauche can for the most part be attributed to electrostatic and to some extent to induction and dispersion interplays. In contrast this conformer is severely destabilised through steric repulsion. These results were supported by NBO analyses.
1 Introduction
2,2,2-Trichloroethyl acetate (H3CC(O)OCH2CCl3, abbreviated as TCEA) is widely used in enzymatic transesterification, ranging from regioselective acylation of different sugars [1], [2] to enantioselective acetylation yielding prostaglandin intermediates [3]. Several partially substituted ethyl oxo- and thioesters have already been characterised with consideration of their electronic and, in part, molecular structure. Besides the elementary compounds methyl [4] and ethyl acetate [5] as well as S-methyl [6] and S-ethyl thioacetate [7] a series of different fluorinated derivatives F3CC(O)XR (XR=OCH2CH3 [8], OCH2CF3 [9], SCH2CH3 [10]) has been investigated. We recently elucidated the molecular and electronic structure of the related 2,2,2-trichloroethyl ester, namely 2,2,2-trichloroethyl chloroformate, by gas electron diffraction (GED), various spectroscopies and quantum-chemical calculations [11].
In a previous study we have investigated the conformational preference and vibrational properties of TCEA using MP2 and DFT techniques [12]. These studies led to the conclusion that the electrostatic and steric contributions included in the Lewis term tend to promote the syn-anti conformer, whereas the delocalisation contribution tends to favour the syn-gauche conformer, as is expected from the anomeric effect. In accordance with the analysis of the vibrational spectra (IR and Raman), it was possible to determine the presence of both conformations in solid and liquid phases. Similar results were obtained for the previously mentioned 2,2,2-trichloroethyl chloroformate which was studied using GED and vibrational spectroscopy [11].
In this contribution, we report the experimental molecular structure of TCEA determined using gas-phase electron diffraction (GED). The experimental data are complemented by ab-initio (MP2) and DFT (B3LYP) quantum-chemical calculations. Martín Pendás’ interacting quantum atoms (IQA) [13], [14], [15], [16], [17] analyses reveal that the interplay between the carbonyl group and the hydrogen as well as chlorine atoms of the trichloroethyl group accounts for most of the stabilisation of the C1 conformer. Thus, the most important non-bonding interaction for stabilisation of the syn-gauche conformer is observed between O(1) and H(11). This hydrogen bridge is confirmed by the study of hyperconjugative interactions using natural bond orbital (NBO) analyses.
2 Experimental section
2.1 Sample preparation
A sample of TCEA was purchased from Sigma-Aldrich and used without further purification. The identity and purity of the compound were verified by IR, Raman and NMR spectroscopy.
2.2 Gas-phase electron diffraction (GED)
Electron diffraction patterns were recorded using the heavily modified KD-G2 gas diffractometer at Bielefeld University [18], [19] with an accelerating voltage of 60kV at two nozzle-to-plate distances (250 and 500mm). The samples as well as the inlet system and nozzle tip were heated to 50 °C throughout the GED experiments. Details of the latter are summarised in TableS2 (Supporting Information available online). The electron wavelength was determined from diffraction patterns of carbon tetrachloride standard measurements, carried out at ambient temperature [20]. Molecular intensities Imol(s) were obtained in the s-range from 2.0 to 32.0Å−1. Molecular structure refinements were performed using the Unex programme [21], [22]. Starting parameters, fixed differences between parameters as well as relative potential energies for all pseudoconformers were based on quantum-chemical calculations at MP2/cc-pVTZ, B3LYP-D3/6-311++G(d,p) and B3LYP/6-311++G(d,p) levels of theory and are summarised in Tables 4 and 5.
2.3 Computational details
Quantum-chemical calculations were performed using the Gaussian09 programme package [23]. Geometry optimisations as well as potential energy surface scans were performed using second-order perturbation theory (MP2) and the DFT functional B3LYP with and without Grimme’s D3 dispersion correction as implemented. For the geometry optimisations, very tight convergence criteria were applied in all calculations and stationary points were proved to be minima by frequency analyses. Potential energy surface scans about the C(2)–O(4)–C(5)–C(6) dihedral angle were carried out with a step size of 10° applying tight convergence criteria.
Mean square amplitudes and vibrational corrections to the equilibrium structures were calculated with the Vibmodule [24] programme using quadratic and cubic force fields at MP2/6-311G(d,p) level of theory. Analyses within Bader’s quantum theory of atoms in molecules (QTAIM) [25] as well as Martín Pendás’ IQA approach [13], [14], [15], [16], [17] were carried out on the basis of B3LYP-D3/6-311++G(d,p) wave-functions using the AimAll [26] code. Zeroth-order intramolecular symmetry-adapted perturbation theory (I-SAPT) [27] analyses were carried out on MP2/cc-pVTZ-optimised geometries using Psi4 [28], [29] and applying the jun-cc-pVDZ basis set as recommended. NBO analyses were carried out at B3LYP-D3/6-311++G(d,p) level of theory through the interface with Gaussian 09 [23].
3 Results and discussion
3.1 Quantum-chemical calculations
3.1.1 Geometry optimisations and potential energy surface scans
Two minima can be found on the potential energy surface obtained by relaxed energy scanning about the O(4)–C(5) bond at different levels of theory (see Fig. 1). The syn-anti conformer (Cs symmetry) exhibits a C(2)–O(4)–C(5)–C(6) dihedral angle of 180°, whereas the syn-gauche conformer (C1 symmetry) is characterised by an analogous COCC dihedral angle of 110° (MP2/cc-pVTZ). While all quantum-chemical methods used in this investigation suggest the syn-gauche conformer to be the most stable, they severely differ in predicting the energy difference between as well as barrier height separating the conformers. The corresponding structures and atom numbering for both conformers of TCEA are depicted in Fig. 2.
The results obtained from B3LYP-D3 and MP2 calculations with 6-311G(d,p) and 6-311G++(d,p) basis set, respectively, differ hardly. Compared to these, MP2/cc-pVTZ predicts the Cs conformer to be slightly more stable by 0.4kJmol−1 and the barrier to be higher by 0.6kJmol−1. The potential energy curve obtained from a B3LYP/6-311++G(d,p) calculation deviates most from the others, since all pseudoconformers in the range of 110< Φ<180° are found within 0.5kJmol−1 in energy.
As can be seen in Table 1, the analysis of the calculated Gibbs free energies at the temperature of the GED experiments indicates the syn-anti conformer to be slightly preferred by 0.4–1.8kJmol−1; this corresponds to a mole fraction of 54–66%. We cannot draw any distinct conclusion on any conformational preference from calculated thermodynamic data apart from the fact that the dihedral angle COCC and the potential energy are very weakly correlated in the range of 110<Φ<180°.
ΔEa/kJmol−1 | Ebarrierb/kJmol−1 | ΔG323 Kc/kJmol−1 | Cs:C1 ratiod | |
---|---|---|---|---|
B3LYP/6-311++G(d,p) | −0.1 | +0.3 | +1.8 | 0.66:0.34 |
B3LYP-D3/6-311++G(d,p) | −1.7 | +0.3 | +1.2 | 0.61:0.39 |
MP2/6-311G(d,p) | −1.8 | +0.6 | +0.9 | 0.58:0.42 |
MP2/6-311++G(d,p) | −1.5 | +0.2 | +1.5 | 0.64:0.36 |
MP2/cc-pVTZ | −1.2 | +1.2 | +0.4 | 0.54:0.46 |
aΔE=E (syn-gauche)−E (syn-anti); bEbarrier=E (TS)−E (syn-anti); cΔG323 K=G323 K(syn-gauche)−G323 K(syn-anti); dBoltzmann ratio at 323 K.
Giletal. attributed the existence and relative stability of the syn-gauche conformer of H3CC(O)OCH2CCl3 to the anomeric effect and found proof in NBO analyses in the form of an LP(O(4))→σ*(C(5)–C(6)) interaction, which dominantly stabilises the C1 conformer [12]. In addition to this, Martín Pendás IQA approach as well as the I-SAPT formalism of Parrish et al. allow us to further investigate the nature of the intramolecular interactions that are responsible for the stabilisation of the C1 conformer over the one of Cs symmetry.
3.1.2 IQA analyses
The standard expression of the total molecular energy in the QTAIM formalism, as a sum of atomic energies, gave no clear reason for conformational preferences. With IQA analyses it is possible to decompose the total molecular energy into chemically interpretable components, such as interatomic interaction energies.
The most important non-bonding interactions for stabilisation of the syn-gauche conformer is observed between O(1) and H(11). This hydrogen bridge is obviously stronger in the C1 conformer due to the O(1)–C(2) bond being nearly collinear to the C(5)–H(11) bond but this is accompanied by loss of the O(1)···H(10) hydrogen bond compared to the Cs conformer. Altogether, the O(1)···H(10/11) interaction energy is by 21.6kJmol−1 more stabilising in the C1 conformer. A similar behaviour can be observed for the atoms O(1), C(2) and Cl(12). In the syn-anti conformer Cl(12) is furthest away from the O(1)–C(2) moiety and the interatomic interaction energies are pretty small, −50kJmol−1 for C(2)···Cl(12) and +38kJmol−1 for O(1)···Cl(12). In the syn-gauche conformer, Cl(12) is situated closer to the carbonyl group and therefore the C(2)···Cl(12) interaction becomes more attractive by 27.4kJmol−1 and the O(1)···Cl(12) interplay more repulsive by 16.7kJmol−1, summing up to an overall stabilisation of the C1 conformer by 10.7kJmol−1. The most important stabilisation of the Cs conformers can be found in the C(2)–O(4) bond which is calculated to 74kJmol−1. The interactions that are most significantly responsible for the energy difference of the two conformers are listed in Table 2.
Atom pair | ΔEinter/kJmol−1 | ||
---|---|---|---|
O(1)···H(11) | −41.1 | ||
C(2)···Cl(12) | −27.4 | ||
O(1)–C(2) | −18.5 | ||
O(4)···H(11) | −18.2 | ||
C(2)···C(5) | −17.4 | ||
C(2)···H(10) | −16.4 | ||
C(3)–H(8) | +12.1 | ||
O(1)···C(5) | +12.2 | ||
C(5)–H(11) | +16.4 | ||
O(1)···Cl(12) | +16.7 | ||
O(1)···H(10) | +19.5 | ||
C(2)···H(11) | +28.2 | ||
C(2)–O(4) | +74.0 | ||
Einter | Eintra | EIQA | |
Σ | +23.4 | −26.8 | −3.4 |
Note that the 13 depicted interactions are those exhibiting the largest difference between the two conformers and not those with the overall largest stabilisation. For comparison the sum over all intra- and interatomic interaction energies are given below. Einter: potential energy contribution to IQA interaction energy. ΔE=E (syn-gauche)−E (syn-anti). Thus, positive values indicate stabilisation of the conformer of Cs symmetry over the one of C1 symmetry.
3.1.3 I-SAPT analyses
In the I-SAPT formalism, the total interaction energy between two intramolecular fragments, EI-SAPT, can be written as a sum of electrostatic, exchange, induction and dispersion terms. The fragments are separated by linkers, which can consist of a bond, an atom or even a whole group; they do not contribute to the interaction energy. The main interaction components stabilising one of the conformers of H3CC(O)OCH2CCl3 are supposed to occur between the CH2CCl3 group and the carbonyl group. Since there is no obviously suitable site to fragment the molecule, we decided to perform this analysis using three different linkers, namely the C(2)–O(4), O(4)–C(5) as well as C(5)–C(6) bonds (see Table 3). Partition schemes that use one or several atoms as linker were rejected in order to cover as many interacting atoms as possible.
Fragmentation | ΔEelectrostatica | ΔEexchange | ΔEinduction | ΔEdispersion | ΔEI-SAPT |
---|---|---|---|---|---|
H3CC(O)–OCH2CCl3 | −11.7 | +4.0 | +2.3 | −2.9 | −8.3 |
H3CC(O)O–CH2CCl3 | −13.2 | +20.3 | −5.1 | −3.6 | −1.6 |
H3CC(O)OCH2–CCl3 | −20.5 | +7.8 | −0.1 | −2.8 | −15.6 |
aΔEi=E (syn-gauche)−Ei (syn-anti), energies in kJmol−1.
If an I-SAPT analysis is carried out on a system with well separated interacting fragments, the total I-SAPT energy of different conformers should be close to their relative energy. According to the afore-mentioned quantum-chemical calculations (see Table 1), the difference in energy between the two conformers is approximately 1.5kJmol−1. Thus, it seems that the best way of analysing H3CC(O)OCH2CCl3 in terms of intramolecular interactions is by defining two fragments separated by the O(4)–C(5) bond, because herein, the interaction energy amounts to 1.6kJmol−1. Nonetheless, this might also be due to fortuitous error cancellation, since all fragmentation schemes neglect some intramolecular interaction energies, both, those involving the linking σ-bond electrons as well as the ones occurring within the fragments. Therefore, we hesitate to discuss particular parameters but want to focus on the overall tendency (see Table 3).
Irrespective of the fragmentation scheme, the electrostatic interaction component stabilises the syn-gauche conformer by 12–21kJmol−1, whereas the conformational difference in the exchange term is calculated to 4–20kJmol−1, indicating a steric preference for syn-anti. The contribution of induction to the total difference in interaction energy is smaller and more ambiguous, ranging from +2 to−5kJmol−1. In all cases, the C1 conformer experiences a stabilisation through dispersion forces with a magnitude of about 3kJmol−1.
3.1.4 NBO analyses
The most relevant hyperconjugative interactions resulting from NBO analyses for both conformers of H3CCO2CH2CCl3 are shown in Table S1. In accordance with Gil et al. [12] the hyperconjugative interactions are more stabilising in the Cs than in the C1 conformer, whereas the LP(O(2))→σ*(O(4)–C(5)) interaction is dominant in the syn-gauche by 19kJmol−1. In this conformer, the anomeric orbital interaction LP(O(2))→σ*(C(5)–H(11)) is calculated as 3kJmol−1, whereas in the syn-anti conformer this interplay is negligible. This interaction is significantly responsible for the higher occupancy of the σ*(C(5)–H(11)) in the C1 conformer and confirms the presence of an intramolecular hydrogen bond in this conformation. Furthermore, lone pairs of the chlorine atoms in both conformers transfer electronic charge to the virtually empty antibonding σ* orbital of the C(5)-H(10,11) link. The magnitude of this interaction is higher in the syn-anti form.
3.2 Gas-phase structure by GED
Different types of GED data refinement were carried out on the basis of the aforementioned calculations. Two single-conformer models and a two-conformer model based on MP2/cc-pVTZ con- and restraints were written. Additionally, dynamic models using different sets of starting geometries, constraints, restraints and potential energy curves from MP2/cc-pVTZ (dyn1), B3LYP-D3/6-311++G(d,p) (dyn2) as well as B3LYP/6-311++G(d,p) (dyn3) calculations were used in structure refinement.
Investigations of the molecular structures of ethyl acetate [5], F3CC(O)OCH2CH3 [8], F3CC(O)OCH2CF3 [9] and ClC(O)OCH2CCl3 [11] revealed similar conformational behaviour as found for H3CC(O)OCH2CCl3. For the first a two-conformer model could be applied, as the barrier of intramolecular rotation was calculated as 4kJmol−1, twice as high as for H3CC(O)OCH2CCl3. Ethyl acetate exhibits a rotational barrier of about 4–5kJmol−1. Nevertheless, for analysis of its GED data a rough dynamic model showed up to be the best choice [5]. Rotation about the COCC dihedral angle in the afore-mentioned chloroformate derivative is characterised by a barrier of 1–2kJmol−1, depending on the quantum-chemical method used. Determination of the molecular structure for this compound was therefore aided by a dynamic model, too.
As can be seen in Fig. 3, the single conformer models do not describe the experimental data sufficiently compared to the other models. With all dynamic models nearly the same R-factors can be obtained. Here, the B3LYP-D3/6-311++G(d,p) model describes the experimental data best. Using the two-conformer model an R-factor of 4.6% can be obtained and the mole fraction of syn-gauche is refined to 56(9)%,
Nevertheless, we eventually decided to reject this model due to strong correlations between geometrical parameters plus unusually large amplitudes for long intramolecular distances. We attribute these artefacts to the overall high flexibility of the molecule, which leads to broadening of long-range atomic distance peaks on the radial distribution curve. These can either be described by numerous distinct geometrical terms (dynamic model) or few terms that are strongly broadened by large amplitudes in the refinement procedure (one- or two-conformer models). Consequently, it is actually misleading to describe the vapour of H3CC(O)OCH2CCl3 as a mixture of rigid conformers only exhibiting small-amplitude motions. We think that the dynamic model is clearly the method of choice for refining the obtained data, regardless of the fact that with this model it was not possible to refine a potential energy curve and therefore a ratio of conformers in the dynamic model.
The dynamic models eventually yield the same structural parameters within the 1σ error limit. Thus, the different R-factors can largely be attributed to the varying potential energy surfaces and different con- and restraints. The latter affect only the C–H and C–Cl distances as well as three angles, which do not differ severely between the quantum-chemical methods. Consequently, the potential for rotation about the C(2)–O(4)–C(5)–C(6) dihedral angle is the most influential parameter and thus, the pseudoconformers that are Boltzmann-weighted on the basis of B3LYP-D3/6-311++G(d,p) calculations seem to describe the vapour composition best. Relative abundances used herein as well as structural parameters obtained from this model are listed in Tables 4 and 5.
Φ/deg | Multiplicity | χ/% | ||
---|---|---|---|---|
MP2/cc-pVTZ | B3LYP-D3/6-311++G(d,p) | B3LYP/6-311++G(d,p) | ||
90 | 2 | 2.2 | 1.8 | 0.6 |
100 | 2 | 12.0 | 10.2 | 4.3 |
110 | 2 | 19.2 | 17.8 | 10.9 |
120 | 2 | 15.5 | 16.1 | 13.8 |
130 | 2 | 10.4 | 12.5 | 13.8 |
140 | 2 | 7.8 | 9.6 | 12.5 |
150 | 2 | 7.5 | 9.6 | 11.8 |
160 | 2 | 8.7 | 8.5 | 12.4 |
170 | 2 | 10.8 | 9.1 | 13.2 |
180 | 1 | 6.0 | 4.7 | 6.7 |
Parametera | Syn-gauche (re) | Syn-anti (re) | GED(re)b | ||||
---|---|---|---|---|---|---|---|
B3LYP | B3LYP-D3 | MP2 | B3LYP | B3LYP-D3 | MP2 | ||
d(O(1)=C(2)) | 1.202 | 1.201 | 1.202 | 1.204 | 1.203 | 1.205 | 1.218(5) |
d(C(2)–C(3)) | 1.503 | 1.502 | 1.490 | 1.503 | 1.503 | 1.490 | 1.493(3) |
d(C(2)–O(4)) | 1.371 | 1.372 | 1.364 | 1.362 | 1.361 | 1.355 | 1.346(5) |
d(O(4)–C(5)) | 1.422 | 1.422 | 1.411 | 1.425 | 1.425 | 1.414 | 1.411(5) |
d(C(5)–C(6)) | 1.531 | 1.534 | 1.516 | 1.527 | 1.527 | 1.510 | 1.517(4) |
d(C(6)–Cl)mean | 1.798 | 1.800 | 1.766 | 1.798 | 1.800 | 1.766 | 1.769(1) |
d(C(3)–H)mean | 1.091 | 1.091 | 1.083 | 1.091 | 1.091 | 1.083 | 1.100(6)b1.0 |
d(C(5)–H)mean | 1.091 | 1.090 | 1.084 | 1.091 | 1.091 | 1.085 | 1.097(6)b1.0 |
α(O(1)–C(2)–C(3)) | 126.4 | 126.6 | 126.5 | 126.6 | 126.8 | 126.7 | 126.7(15)0.5 |
α(O(1)–C(2)–O(4)) | 123.5 | 123.7 | 123.9 | 122.7 | 122.7 | 122.8 | 122.1(10)0.5 |
α(C(2)–O(4)–C(5)) | 117.7 | 117.9 | 116.0 | 115.7 | 115.6 | 113.6 | 113.5(10)0.5 |
α(O(4)–C(5)–C(6)) | 110.3 | 110.4 | 109.8 | 108.4 | 108.3 | 107.6 | 107.3(7) |
Φ(C(2)–O(4)–C(5)–C(6)) | 122.9 | 112.7 | 110.4 | 180.0 | 180.0 | 180.0 | – |
Φ(O(4)–C(5)–C(6)–Cl(14)) | 178.8 | 179.3 | 179.2 | 180.0 | 180.0 | 180.0 | 179.3(15) |
aBond lengths in Å, angles in degrees. See Fig. 2 for numbering of atoms. bValues for the conformer of Cs symmetry from refinement using model dyn2. Standard deviations are given as 3σLS. Superscript numbers indicate the regularisation coefficient. Subscript letters state if parameters were refined in groups with fixed differences between them. The C(3)–C(2)–O(4) angle was not refined explicitly but results from the O(1)=C(2)–C(3), O(1)=C(2)–O(4) angles and the assumed planarity of the C(3)–C(2)–O(1)–O(4) moiety in the conformer of Cs symmetry.
For some of the structural parameters, conspicuous differences between theory and experiment are observed. All parameters discussed in the following are the ones obtained for the syn-anti pseudo-conformer. The O(1)=C(2) distance at 1.218(5)Å is by 0.013Å longer in the experiment than in all calculations, a fact that was already observed for the afore-mentioned 2,2,2-trichloroethyl chloroformate [11].
In H3CC(O)OCH2CCl3, the C(2)–O(4) distance determined by GED is shorter by 0.009Å than in all calculations. The C(3)–C(2)–O(4) angle at 107.3(25)°, resulting from O(1)–C(2)–C(3), O(1)–C(2)–C(3) and planarity of the C(3)–C(2)–O(1)–O(4) moiety, is by nearly 4° narrower than in ethyl acetate [5].
The remaining experimentally determined parameters are in good agreement with the quantum-chemically calculated ones, especially with those from MP2 calculations. The O(4)–C(5)–C(6)–Cl(14) dihedral angle at 179.3(15)° can only be interpreted as a thermally averaged value since the relative potential energy correlated with rotation about this dihedral angle exhibits a very shallow minimum at 180°. Displacing this angle by 10° results in an increase in energy of only 2.3kJmol−1 (Cs conformer, MP2/cc-pVTZ). Compared to ClC(O)OCH2CCl3 [11], the O(1)=C(2) and C(2)–O(4) bonds in H3CC(O)OCH2CCl3 are longer by 0.034Å and 0.019Å, respectively. This might be ascribed to the higher polarity of these bonds caused by the electron-withdrawing nature of the chlorine atom attached to the carbonyl group. The O(4)–C(5) bond being shorter in H3CC(O)OCH2CCl3 is also supported by this interpretation. All other parameters are in good compliance within the error limit.
4 Conclusion
The conformational behaviour of 2,2,2-trichloroethyl acetate has been investigated using MP2 and DFT quantum-chemical methods. Two conformers separated by a shallow rotational barrier have been identified, one of C1 (syn-gauche) and the other of Cs symmetry (syn-anti). All calculations indicate that syn-gauche is preferred in terms of enthalpy, whereas syn-anti seems to be slightly lower in Gibbs free energy.
The molecular structure of H3CC(O)OCH2CCl3 could be determined experimentally using GED. For this purpose dynamic models based on different potential energy surface scans were used. The one from B3LYP-D3/6-311++G(d,p), predicting a preference of syn-gauche by 1.2kJmol−1, was found to describe the experimental data best. One- and two-conformer models had to be rejected due to correlations and convergence to unrealistically large vibrational amplitudes. Experimentally determined structural parameters are in good agreement with both, quantum-chemical calculations as well as GED data for related compounds.
IQA analyses revealed that interplay between the carbonyl group and the hydrogen as well as chlorine atoms of the trichloroethyl group accounts for most of the stabilisation of the C1 conformer. With I-SAPT analyses it was possible to further elucidate the nature of dominant interactions in the two conformers. Preference of syn-gauche can for the most part be attributed to electrostatic and to some extent to induction and dispersion interplays. In contrast it is severely destabilised through steric repulsion. These results have been supported by NBO analyses.
5 Supporting information
Details of the quantum-chemical calculations, GED experiment and structure refinement including the final Cartesian coordinates of the most abundant pseudoconformers as well as other supporting data associated with this article are given as Supporting Information available online (DOI: 10.1515/znb-2016-0166).
Acknowledgments
This work was supported by Deutsche Forschungsgemeinschaft (DFG, core facility GED@BI, grant MI477/21-1). DMG, MET and ABA thank CIUNT, CONICET (PIP 0205) and ANPCyT (PICT-2013-0697) for financial support. We thank the “Regionales Rechenzentrum der Universität zu Köln (RRZK)” for providing the necessary computational resources.
References
[1] M. Therisod, A. M. Klibanov, J. Am. Chem. Soc.1986, 108, 5638.10.1021/ja00278a053Search in Google Scholar
[2] G. Carrea, S. Riva, F. Secundo, B. Danieli, J. Chem. Soc. Perkin Trans.1989, 1, 1057.10.1039/P19890001057Search in Google Scholar
[3] M. A. Djadchenko, K. K. Pivnitsky, F. Theil, H. Schick, J. Chem. Soc. Perkin Trans.1989, 1, 2001.10.1039/p19890002001Search in Google Scholar
[4] J. M. O’Gorman, W. Shand, V. Schomaker, J. Am. Chem. Soc.1950, 72, 4222.10.1021/ja01165a110Search in Google Scholar
[5] M. Sugino, H. Takeuchi, T. Egawa, S. Konaka, J. Mol. Struct.1991, 245, 357.10.1016/0022-2860(91)87110-4Search in Google Scholar
[6] C. O. Della Védova, R. M. Romano, H. Oberhammer, J. Org. Chem.2004, 69, 5395.10.1021/jo0493828Search in Google Scholar PubMed
[7] M. E. Defonsi Lestard, M. E. Tuttolomondo, A. Ben Altabef, Spectrochim. Acta A. Mol. Biomol. Spectrosc.2015, 135, 907.10.1016/j.saa.2014.07.054Search in Google Scholar PubMed
[8] M. E. Defonsi Lestard, M. E. Tuttolomondo, D. A. Wann, H. E. Robertson, D. W. H. Rankin, A. B. Altabef, J. Raman Spectrosc.2010, 41, 1357.10.1002/jrs.2550Search in Google Scholar
[9] M. E. Defonsi Lestard, M. E. Tuttolomondo, E. L. Varetti, D. A. Wann, H. E. Robertson, D. W. Rankin, A. Ben Altabef, J. Mol. Struct.2009, 917, 183.10.1016/j.molstruc.2008.08.012Search in Google Scholar
[10] M. E. Defonsi Lestard, M. E. Tuttolomondo, D. A. Wann, H. E. Robertson, D. W. H. Rankin, A. Ben Altabef, J. Chem. Phys.2009, 131, 214303.10.1063/1.3267633Search in Google Scholar PubMed
[11] D. M. Gil, M. E. Tuttolomondo, S. Blomeyer, C. G. Reuter, N. W. Mitzel, A. B. Altabef, Phys. Chem. Chem. Phys.2016, 18, 393.10.1039/C5CP05295ESearch in Google Scholar
[12] D. M. Gil, M. E. Tuttolomondo, A. Ben Altabef, Spectrochim. Acta A Mol. Biomol. Spectrosc.2014, 123, 290.10.1016/j.saa.2013.12.042Search in Google Scholar PubMed
[13] A. Martín Pendás, M. A. Blanco, E. Francisco, J. Chem. Phys.2004, 120, 4581.10.1063/1.1645788Search in Google Scholar PubMed
[14] A. Martín Pendás, E. Francisco, M. A. Blanco, J. Comput. Chem.2005, 26, 344.10.1002/jcc.20173Search in Google Scholar PubMed
[15] M. A. Blanco, A. Martín Pendás, E. Francisco, J. Chem. Theory Comput.2005, 1, 1096.10.1021/ct0501093Search in Google Scholar PubMed
[16] E. Francisco, A. Martín Pendás, M. A. Blanco, J. Chem. Theory Comput.2006, 2, 90.10.1021/ct0502209Search in Google Scholar PubMed
[17] A. Martín Pendás, M. A. Blanco, E. Francisco, J. Comput. Chem.2007, 28, 161.10.1002/jcc.20469Search in Google Scholar PubMed
[18] R. J. F. Berger, M. Hoffmann, S. A. Hayes, N. W. Mitzel, Z. Naturforsch.2009, 64b, 1259.10.1515/znb-2009-11-1204Search in Google Scholar
[19] C. G. Reuter, Y. V. Vishnevskiy, S. Blomeyer, N. W. Mitzel, Z. Naturforsch.2016, 71b, 1.10.1515/znb-2015-0186Search in Google Scholar
[20] S. Shibata, K. Iijima, R. Tani, I. Nakamura, Reports of Faculty of Science, Vol. 9, Shizuoka University (Japan) 1974, p. 33.Search in Google Scholar
[21] Y. V. Vishnevskiy, UNEX 1.6.0, Bielefeld University, Bielefeld (Germany) 2013; available online from www.unexprog.org.Search in Google Scholar
[22] Y. Vishnevskiy, J. Mol. Struct.2007, 833, 30.10.1016/j.molstruc.2006.08.026Search in Google Scholar
[23] M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria, M. A. Robb, J. R. Cheeseman, G. Scalmani, V. Barone, B. Mennucci, G. A. Petersson, H. Nakatsuji, M. Caricato, X. Li, H. P. Hratchian, A. F. Izmaylov, J. Bloino, G. Zheng, J. L. Sonnenberg, M. Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai, T. Vreven, J. A. Montgomery, Jr., J. E. Peralta, F. Ogliaro, M. Bearpark, J. J. Heyd, E. Brothers, K. N. Kudin, V. N. Staroverov, R. Kobayashi, J. Normand, K. Raghavachari, A. Rendell, J. C. Burant, S. S. Iyengar, J. Tomasi, M. Cossi, N. Rega, J. M. Millam, M. Klene, J. E. Knox, J. B. Cross, V. Bakken, C. Adamo, J. Jaramillo, R. Gomperts, R. E. Stratmann, O. Yazyev, A. J. Austin, R. Cammi, C. Pomelli, J. W. Ochterski, R. L. Martin, K. Morokuma, V. G. Zakrzewski, G. A. Voth, P. Salvador, J. J. Dannenberg, S. Dapprich, A. D. Daniels, Ö. Farkas, J. B. Foresman, J. V. Ortiz, J. Cioslowski, D. J. Fox, Gaussian 09 (revision D.01), Gaussian Inc., Wallingford, CT (USA) 2009.Search in Google Scholar
[24] Y. V. Vishnevskiy, Y. A. Zhabanov, J. Phys.: Conf. Ser.2015, 633, 12076.Search in Google Scholar
[25] R. F. W. Bader, Atoms in Molecules – A Quantum Theory, Oxford University Press, Oxford, 1990.Search in Google Scholar
[26] T. A. Keith, AIMAll (version 16.01.09), TK Gristmill Software, Overland Park KS (USA), 2016; available online from aim.tkgristmill.com.Search in Google Scholar
[27] R. M. Parrish, J. F. Gonthier, C. Corminbœuf, C. D. Sherrill, J. Chem. Phys.2015, 143, 51103.10.1063/1.4927575Search in Google Scholar PubMed
[28] Psi4 (version 0.3.543), An open-source ab initio electronic structure program, 2016, available online from www.psicode.org.Search in Google Scholar
[29] J. M. Turney, A. C. Simmonett, R. M. Parrish, E. G. Hohenstein, F. A. Evangelista, J. T. Fermann, B. J. Mintz, L. A. Burns, J. J. Wilke, M. L. Abrams, N. J. Russ, M. L. Leininger, C. L. Janssen, E. T. Seidl, W. D. Allen, H. F. Schaefer, R. A. King, E. F. Valeev, C. D. Sherrill, T. D. Crawford, WIREs Comput. Mol. Sci.2012, 2, 556.10.1002/wcms.93Search in Google Scholar
Supplemental Material:
The online version of this article (DOI: 10.1515/znb-2016-0166) offers supplementary material, available to authorized users.
©2016 Walter de Gruyter GmbH, Berlin/Boston