Twisted Imide Bond in Noncyclic Imides. Synthesis and Structural and Vibrational Properties of <i>N</i>,<i>N</i>-Bis(furan-2-carbonyl)-4-chloroaniline

A novel imide compound (C₁₆H₁₀ClNO₄) was synthesized in a single step by the reaction of 2-furoic acid with 4-chloroaniline in a 2:1 molar ratio using carbonyldiimidazole (CDI) in dry THF. The structure was supported by spectroscopic and elemental analyses and the single-crystal X-ray diffraction data. Crystallographic studies revealed that the compound crystallized in a monoclinic system with space group <i>P</i>2₁/<i>c</i> and unit cell dimensions <i>a</i> = 12.2575(5) Å, <i>b</i> = 7.7596(2) Å, <i>c</i> = 15.0234(7) Å, α = γ = 90°, β = 92.771(4)°, <i>V</i> = 1427.25(10) ų, <i>Z</i> = 4. The imide bond is twisted, and the OC–N–C­(O) units deviate significantly from planarity with dihedral angles around the imide group reaching ca. −150.3° (C1–N1–C2–O21 = −148.8° and C2–N1–C1–O11 = −151.9°). The nonplanarity of the imide moiety and the related conformational properties are discussed in a combined approach that includes the analysis of the vibrational spectra together with theoretical calculation methods, especially in terms of natural bond orbital (NBO) calculations

Toward an Intimate Understanding of the Structural Properties and Conformational Preference of Oxoesters and Thioesters: Gas and Crystal Structure and Conformational Analysis of Dimethyl Monothiocarbonate, CH₃OC(O)SCH₃

The molecular structure and conformational properties of dimethyl monothiocarbonate, CH3OC(O)SCH3, have been studied in the gas phase by gas electron diffraction (GED) and vibrational spectroscopy and in the solid state by X-ray crystallography. The experimental investigations were supplemented by quantum chemical calculations at the B3LYP/6-311++G(3df,2p) and MP2/6-311++G(2df,p) levels of approximation. The gaseous molecule exhibits only one conformation having Cs symmetry with synperiplanar orientation of both the CS and the CO single bonds relative to the CO double bond. The following skeletal geometric parameters were derived from the GED analysis (rhl values with 3σ uncertainties):  CO = 1.203(4) Å, C(sp2)O = 1.335(5) Å, C(sp3)O = 1.437(5) Å, C(sp2)S = 1.763(5) Å, and C(sp3)S = 1.803(5) Å; OCO = 125.9(8)°, OCS = 125.7(7)°, OCS = 108.4(9)°, and COC = 113.4(15)°. The structure of a single crystal, grown by a miniature zone-melting procedure, was determined by X-ray diffraction analysis at a low temperature. The crystalline solid [monoclinic, P21/n, a = 12.6409(9) Å, b = 4.1678(3) Å, and c = 19.940(1) Å, β = 98.164(1)°] exists exclusively as molecules in the synperiplanar conformation and with geometrical parameters that agree with those of the molecule in the gas phase. The results are discussed in terms of anomeric and mesomeric effects and in terms of a natural bond orbital analysis

Conformational Properties of Ethyl- and 2,2,2-Trifluoroethyl Thionitrites, (CX₃CH₂SNO, X = H and F)

The simple 2,2,2-trifluoroethyl thionitrite molecule, CF₃CH₂SNO, has been prepared in good yield for the first time using CF₃CH₂SH and NOCl in slight excess. The vapor pressure of the red-brown compound CF₃CH₂SNO follows, in the temperature range between 226 and 268 K, the equation log <i>p</i> = 12.0–3881/<i>T</i> (<i>p</i>/bar, <i>T</i>/K), and its extrapolated boiling point reaches 51 °C. Its structural and conformational properties have been compared with the ethyl thionitrite analogue, CH₃CH₂SNO. The FTIR spectra of the vapor of both thionitrites show the presence of bands with well-defined contours, allowing for a detailed conformational analysis and vibrational assignment on the basis of a normal coordinate analysis. The conformational space of both thionitrite derivatives has also been studied by using the DFT and MP2­(full) level of theory with extended basis sets [6-311+G­(2df) and cc-pVTZ]. The overall evaluation of the experimental and theoretical results suggests the existence of a mixture of two conformers at room temperature. The relative abundance of the most stable syn form (NO double bond syn with respect to the C–S single bond) has been estimated to be ca. 79 and 75% for CF₃CH₂SNO and CH₃CH₂SNO, respectively

Toward an Intimate Understanding of the Structural Properties and Conformational Preference of Oxoesters and Thioesters: Gas and Crystal Structure and Conformational Analysis of Dimethyl Monothiocarbonate, CH₃OC(O)SCH₃

The molecular structure and conformational properties of dimethyl monothiocarbonate, CH3OC(O)SCH3, have been studied in the gas phase by gas electron diffraction (GED) and vibrational spectroscopy and in the solid state by X-ray crystallography. The experimental investigations were supplemented by quantum chemical calculations at the B3LYP/6-311++G(3df,2p) and MP2/6-311++G(2df,p) levels of approximation. The gaseous molecule exhibits only one conformation having Cs symmetry with synperiplanar orientation of both the CS and the CO single bonds relative to the CO double bond. The following skeletal geometric parameters were derived from the GED analysis (rhl values with 3σ uncertainties):  CO = 1.203(4) Å, C(sp2)O = 1.335(5) Å, C(sp3)O = 1.437(5) Å, C(sp2)S = 1.763(5) Å, and C(sp3)S = 1.803(5) Å; OCO = 125.9(8)°, OCS = 125.7(7)°, OCS = 108.4(9)°, and COC = 113.4(15)°. The structure of a single crystal, grown by a miniature zone-melting procedure, was determined by X-ray diffraction analysis at a low temperature. The crystalline solid [monoclinic, P21/n, a = 12.6409(9) Å, b = 4.1678(3) Å, and c = 19.940(1) Å, β = 98.164(1)°] exists exclusively as molecules in the synperiplanar conformation and with geometrical parameters that agree with those of the molecule in the gas phase. The results are discussed in terms of anomeric and mesomeric effects and in terms of a natural bond orbital analysis

Trifluoromethyl Chloroformate, ClC(O)OCF₃: Structure, Conformation, and Vibrational Analysis Studied by Experimental and Theoretical Methods^†

The gas phase conformational properties and geometric structure of trifluoromethyl chloroformate, ClC(O)OCF3, have been studied by vibrational spectroscopy (IR (gas), IR (matrix), and Raman (liquid)), gas electron diffraction (GED), and quantum chemical calculation (HF, B3LYP and MP2 methods with 6-311G* basis sets). The molecule exhibits only one form having Cs symmetry with synperiplanar orientation of the O−C single bond relative to the CO double bond. If heated Ar:ClC(O)OCF3 mixtures are deposited as a matrix at 14 K, bands appear in the IR spectra which are assigned to the anti form. At room temperature, the contribution of the anti rotamer is estimated to be less than 1%. This high energy conformer is not observed in the GED experiment. The structure of solid ClC(O)OCF3 was determined by X-ray diffraction analysis from crystals obtained at low temperature, using a miniature zone melting procedure. The molecule crystallizes forming a dimeric structure belonging to the monoclinic crystal system and adopts the P21/n spatial group. Furthermore, we report the structure of the similar molecule trifluoroacetyl chloride, CF3C(O)Cl, in its crystalline phase by using the same method

Trifluoromethyl Chloroformate, ClC(O)OCF₃: Structure, Conformation, and Vibrational Analysis Studied by Experimental and Theoretical Methods^†

The gas phase conformational properties and geometric structure of trifluoromethyl chloroformate, ClC(O)OCF3, have been studied by vibrational spectroscopy (IR (gas), IR (matrix), and Raman (liquid)), gas electron diffraction (GED), and quantum chemical calculation (HF, B3LYP and MP2 methods with 6-311G* basis sets). The molecule exhibits only one form having Cs symmetry with synperiplanar orientation of the O−C single bond relative to the CO double bond. If heated Ar:ClC(O)OCF3 mixtures are deposited as a matrix at 14 K, bands appear in the IR spectra which are assigned to the anti form. At room temperature, the contribution of the anti rotamer is estimated to be less than 1%. This high energy conformer is not observed in the GED experiment. The structure of solid ClC(O)OCF3 was determined by X-ray diffraction analysis from crystals obtained at low temperature, using a miniature zone melting procedure. The molecule crystallizes forming a dimeric structure belonging to the monoclinic crystal system and adopts the P21/n spatial group. Furthermore, we report the structure of the similar molecule trifluoroacetyl chloride, CF3C(O)Cl, in its crystalline phase by using the same method

Preparation and Properties of Methoxycarbonylsulfenyl Isocyanate, CH₃OC(O)SNCO

Pure methoxycarbonylsulfenyl isocyanate, CH3OC(O)SNCO, is quantitatively prepared by the metathesis reaction between CH3OC(O)SCl and AgNCO. This novel species has been obtained in its pure form and characterized by 1H and 13C NMR, UV−vis, FTIR, and FT-Raman spectroscopy. The conformational properties of the gaseous molecule have been studied by vibrational spectroscopy and quantum chemical calculations (B3LYP and MP2 methods). The compound exhibits a conformational equilibrium at room temperature having the most stable form CS symmetry with the CO double bond synperiplanar with respect to the S−N single bond. A second form was observed in the IR spectrum and corresponds to a conformer possessing the C−S bond antiperiplanar with respect to the NC double bond of the isocyanate group. The structure of a single crystal of CH3OC(O)SNCO was determined by X-ray diffraction analysis at low temperature using a miniature zone melting procedure. The crystalline solid (triclinic, P1̄, a = 8.292(6) Å, b = 9.839(7) Å, c = 11.865(8) Å, α = 67.290(2)°, β = 71.5570(10)°, γ = 83.4850(10)° and Z = 6) shows the presence of molecules having exclusively a synperiplanar conformation with respect to the three φ(CO−CO), φ(OC−SN), and φ(CS−NC) dihedral angles

Preparation and Properties of Methoxycarbonylsulfenyl Isocyanate, CH₃OC(O)SNCO

Pure methoxycarbonylsulfenyl isocyanate, CH3OC(O)SNCO, is quantitatively prepared by the metathesis reaction between CH3OC(O)SCl and AgNCO. This novel species has been obtained in its pure form and characterized by 1H and 13C NMR, UV−vis, FTIR, and FT-Raman spectroscopy. The conformational properties of the gaseous molecule have been studied by vibrational spectroscopy and quantum chemical calculations (B3LYP and MP2 methods). The compound exhibits a conformational equilibrium at room temperature having the most stable form CS symmetry with the CO double bond synperiplanar with respect to the S−N single bond. A second form was observed in the IR spectrum and corresponds to a conformer possessing the C−S bond antiperiplanar with respect to the NC double bond of the isocyanate group. The structure of a single crystal of CH3OC(O)SNCO was determined by X-ray diffraction analysis at low temperature using a miniature zone melting procedure. The crystalline solid (triclinic, P1̄, a = 8.292(6) Å, b = 9.839(7) Å, c = 11.865(8) Å, α = 67.290(2)°, β = 71.5570(10)°, γ = 83.4850(10)° and Z = 6) shows the presence of molecules having exclusively a synperiplanar conformation with respect to the three φ(CO−CO), φ(OC−SN), and φ(CS−NC) dihedral angles

Conformational Behavior of CH₃OC(O)SX (X = CN and SCN) Pseudohalide Congeners. A Combined Experimental and Theoretical Study

Pure methoxycarbonylsulfenyl cyanide, CH3OC(O)SCN (I), and methoxycarbonylsulfenyl thiocyanate, CH3OC(O)SSCN (II), were prepared by reacting liquid CH3OC(O)SCl with either AgCN or AgSCN, respectively. Compounds I and II were characterized by 1H NMR, CG−MS, and vibrational (FTIR and FT-Raman) techniques. The conformational properties have been studied by using vibrational spectroscopy [infrared (gaseous, liquid, and Ar matrix isolated), Raman (liquid) spectroscopy] together with quantum chemical calculations at the B3LYP and MP2 methods with the extended 6-311++G** and aug-cc-pVTZ basis sets. Compound I exhibits a conformational equilibrium at room temperature having the most stable form Cs symmetry with a synperiplanar (syn) orientation of the carbonyl double bond (CO) with respect to both the CH3O− and −SCN groups (syn−syn). Several bands assigned to a second conformer have been observed in the IR matrix spectra. This rotamer presents an antiperiplanar orientation of the thiocyanate group (syn−anti). Evaluating the equilibrium compositions at different temperatures by quenching the gas phase mixtures as Ar matrices allowed us to determine the conformational enthalpy difference ΔH0 = H0(syn−anti) − H0(syn−syn) = 0.80(18) kcal mol−1. A similar conformational behavior has been determined for compound II. Thermodynamic properties were also computed at the high-level G2MP2 and G3 model chemistry methods. The importance of mesomeric (resonance) and anomeric (hyperconjugation) electronic interaction in the conformational behavior is evaluated by using the NBO approach for both species

Preparation and Properties of Methoxycarbonylsulfenyl Isocyanate, CH₃OC(O)SNCO

Pure methoxycarbonylsulfenyl isocyanate, CH3OC(O)SNCO, is quantitatively prepared by the metathesis reaction between CH3OC(O)SCl and AgNCO. This novel species has been obtained in its pure form and characterized by 1H and 13C NMR, UV−vis, FTIR, and FT-Raman spectroscopy. The conformational properties of the gaseous molecule have been studied by vibrational spectroscopy and quantum chemical calculations (B3LYP and MP2 methods). The compound exhibits a conformational equilibrium at room temperature having the most stable form CS symmetry with the CO double bond synperiplanar with respect to the S−N single bond. A second form was observed in the IR spectrum and corresponds to a conformer possessing the C−S bond antiperiplanar with respect to the NC double bond of the isocyanate group. The structure of a single crystal of CH3OC(O)SNCO was determined by X-ray diffraction analysis at low temperature using a miniature zone melting procedure. The crystalline solid (triclinic, P1̄, a = 8.292(6) Å, b = 9.839(7) Å, c = 11.865(8) Å, α = 67.290(2)°, β = 71.5570(10)°, γ = 83.4850(10)° and Z = 6) shows the presence of molecules having exclusively a synperiplanar conformation with respect to the three φ(CO−CO), φ(OC−SN), and φ(CS−NC) dihedral angles