Abstract
(C
6
F
5
)Te(CH
2
)
3
NMe
2
(
1
) wurde synthetisiert und charakterisiert. Das Perfluorphenyltellur‐Derivat ist in der Lage, intramolekulare N⋅⋅⋅Te‐Wechselwirkungen zu bilden. Die donorfreie ...Referenzsubstanz (C
6
F
5
)TeMe (
2
) und das nicht unterstützte Addukt (C
6
F
5
)(Me)Te⋅NMe
2
Et (
2 b
) wurden ebenso untersucht. Die Molekülstrukturen von
1
,
2
und
2 b
wurden durch Einkristall‐Röntgenbeugung und für
1
und
2
durch Gasphasen‐Elektronenbeugung bestimmt. Die Strukturen von
1
zeigen N⋅⋅⋅Te‐Abstände von 2.639(1) Å (Festkörper) und 2.92(3) Å (Gas). Ab‐initio‐ sowie NBO‐ und QTAIM‐Rechnungen zeigen erhebliche Ladungstransfereffekte innerhalb der N⋅⋅⋅Te‐Interaktionen und weisen auf σ‐Loch‐Wechselwirkungen hin.
The halogenotrinitromethanes FC(NO2)3 (1), BrC(NO2)3 (2), and IC(NO2)3 (3) were synthesized and fully characterized. The molecular structures of 1–3 were determined in the crystalline state by X‐ray ...diffraction, and gas‐phase structures of 1 and 2 were determined by electron diffraction. The HalC bond lengths in F, Cl, and BrC(NO2)3 in the crystalline state are similar to those in the gas phase. The obtained experimental data are interpreted in terms of Natural Bond Orbitals (NBO), Atoms in Molecules (AIM), and Interacting Quantum Atoms (IQA) theories. All halogenotrinitromethanes show various intra‐ and intermolecular non‐bonded interactions. Intramolecular N⋅⋅⋅O and Hal⋅⋅⋅O (Hal=F (1), Br (2), I (3)) interactions, both competitors in terms of the orientation of the nitro groups by rotation about the CN bonds, lead to a propeller‐type twisting of these groups favoring the mentioned interactions. The origin of the unusually short HalC bonds is discussed in detail. The results of this study are compared to the molecular structure of ClC(NO2)3 and the respective interactions therein.
Twisted theory: A comprehensive spectroscopic and structural study of the halogenotrinitromethanes is presented. The structures were determined by X‐ray diffraction and electron diffraction. Intramolecular N⋅⋅⋅O and Hal⋅⋅⋅O interactions, both competitors in terms of the orientation of the nitro groups by rotation about the CN bonds, lead to a propeller‐type twisting of these groups favoring the mentioned interactions (see figure).
The problem of computation of interatomic distance distributions is considered in the context of gas electron diffraction method. A new theoretical approach has been developed for calculation of mean ...square amplitudes, corrections for interatomic distances and asymmetry parameters on the basis of ab initio molecular dynamics simulations with a posteriori quantum corrections. Several approximations have been evolved, and corresponding algorithms have been coded. Their testing has been performed by calculation of parameters for a set of diatomic molecules, ethane and 9,12-I
2
-1,2-dicarba-
closo
-dodecaborane. Comparison of the obtained amplitudes and distance corrections with those calculated by conventional methods demonstrates the superiority of the new approach. By contrast, asymmetry parameters remain numerically unstable after introduction quantum corrections. The best of the assessed approximations, termed MDC(5), is recommended for routine application to large molecules with small-amplitude vibrations.
The coexistence of two conformers in perfluoropropanoyl fluoride, CF3CF2C(O)F, differing in the CC–CF dihedral angle (gauche 85(10)% and anti 15(10)%), has been determined by means of gas-phase ...electron diffraction (GED). Quantum-chemical calculations performed at the MP2 and B3LYP approximations and cc-pVTZ basis sets reproduce the experimental values with confidence. By contrast, FTIR spectra give no clear evidence for the anti-conformer in the gas phase. Information on this less abundant but stable rotamer is obtained from matrix-isolation/FTIR spectroscopy and liquid Raman spectroscopy. In situ crystallization and single-crystal X-ray diffraction (XRD) data reveal the presence of solely the gauche-conformation in the solid state. A set of intermolecular interactions including CO···CO, C–F···F–C, and F···CO is detected. The nature of bonding and the relative stabilities of gauche- and anti-conformers are explored using natural bond orbitals.
Eine verbesserte Synthese für den einfachsten Salpetersäureester, Methylnitrat, und eine neue Synthese für Fluormethylnitrat benutzen die Salzeliminierung der entsprechenden Iodmethane mit ...Silbernitrat. Beide Verbindungen wurden spektroskopisch und durch Strukturbestimmung im Festkörper von in situ erzeugten Kristallen mittels Röntgenbeugung sowie in der Gasphase mittels Elektronenbeugung identifiziert. Die Fluorierung führt zu Strukturen mit kürzeren C‐O‐ und N‐O‐Bindungen, hat eine energetisch destabilisierende Wirkung und erhöht die Reibungsempfindlichkeit, verringert aber die Detonationsleistung.
Sechs Jahrhunderte nach der Entdeckung des einfachsten Salpetersäureesters, Methylnitrat (H3CONO2): experimentelle Fest‐ und Gasphasenstrukturen wie auch energetische Eigenschaften, verglichen mit denen des neuen monofluorsubstituierten Analogs, Fluormethylnitrat (FH2CONO2).
Abstract
Herein, we report on the synthesis, characterization, and reactivity studies of the first cyclic C
2
As
2
‐diradicaloid {(IPr)CAs}
2
(
6
) (IPr = C{N(Dipp)CH}
2
; Dipp = 2,6‐
i
Pr
2
C
6
H
3
...). Treatment of (IPr)CH
2
(
1
) with AsCl
3
affords the Lewis adduct {(IPr)CH
2
}AsCl
3
(
2
). Compound
2
undergoes stepwise dehydrochlorination to yield {(IPr)CH}AsCl
2
(
3
) and {(IPr)CAsCl}
2
(
5 a
) or {(IPr)CAs}
2
ClOTf (
5 b
). Reduction of
5 a
(or
5 b
) with magnesium turnings gives
6
as a red crystalline solid in 90% yield. Compound
6
featuring a planar C
2
As
2
ring is diamagnetic and exhibits well resolved NMR signals. DFT calculations reveal a singlet ground state for
6
with a small singlet‐triplet energy gap of 8.7 kcal mol
−1
. The diradical character of
6
amounts to 20% (CASSCF, complete active space self consistent field) and 28% (DFT). Treatments of
6
with (PhSe)
2
and Fe
2
(CO)
9
give rise to {(IPr)CAs(SePh)}
2
(
7
) and {(IPr)CAs}
2
Fe(CO)
4
(
8
), respectively.
The Structure and Conformation of (CH3 )3 CSNO Canneva, Antonela; Erben, Mauricio F; Romano, Rosana M ...
Chemistry : a European journal,
2015-Jul-13, Letnik:
21, Številka:
29
Journal Article
Recenzirano
The gas-phase molecular structure of (CH3 )3 CSNO was investigated by using electron diffraction, allowing the first experimental geometrical parameters for an S-nitrosothiol species to be ...elucidated. Depending on the orientation of the -SNO group, two conformers (anti and syn) are identified in the vapor of (CH3 )3 CSNO at room temperature, the syn conformer being less abundant. The conformational landscape is further scrutinized by using vibrational spectroscopy techniques, including gas-phase and matrix-isolation IR spectroscopy, resulting in a contribution of ca. 80:20 for the anti:syn abundance ratio, in good agreement with the computed value at the MP2(full)/cc-pVTZ level of approximation. The UV/Vis and resonance Raman spectra also show the occurrence of the conformational equilibrium in the liquid phase, with a moderate post-resonance Raman signature associated with the 350 nm electronic absorption.
Chlorodifluoroacetyl isothiocyanate, ClF2CC(O)NCS, was synthesized by the reaction of ClF2CC(O)Cl with an excess of AgNCS. The colorless product melts at −85 °C, and its vapor pressure follows the ...equation ln p = −4471.1 (1/T) + 11.35 (p atm, T K) in the range −38 to 22 °C. The compound has been characterized by IR (gas phase, Ar matrix, and matrix photochemistry), by liquid Raman, by 19F and 13C NMR, gas UV–vis, and photoelectron spectroscopy (PES), by photoionization mass spectrometry (PIMS), and by gas electron diffraction (GED). The conformational properties of ClF2CC(O)NCS have been analyzed by joint application of vibrational spectroscopy, GED and quantum chemical calculations. The existence of two conformers has been detected in the gas and liquid phases, in which the C–Cl bond adopts a gauche orientation with respect to the CO group; the CO group is in syn- or anti-position with respect to the NC double bond of the NCS group. The computed ΔG° difference between these two gauche–syn and gauche–anti forms is ΔG° = 0.63 kcal mol–1 in the B3LYP/6-31G(d) approximation. The most significant gas-phase structural parameters for gauche–syn ClF2CC(O)NCS are r e(NCS) 1.559(2) Å, r e(NCS) 1.213(2) Å, r e(NC) 1.399(7) Å, r e(CO) 1.199(2) Å, and ∠ e(CNC) 134.7(13)°. Photolysis of ClF2CC(O)NCS using an ArF excimer laser (193 nm) mainly yields ClF2CNCS, CO, and ClC(O)CF2NCS. The valence electronic properties of the title compound were studied using PES and PIMS. The experimental first vertical ionization energy of 10.43 eV corresponds to the ejection primarily of the sulfur lone-pair electrons of the in-plane nonbonding orbital on the NCS group.
Chlorodifluoroacetyl isocyanate, ClF2CC(O)NCO, was prepared by the reaction of ClF2CC(O)Cl with excess of AgNCO. The colorless compound melts at −83 °C and the vapor pressure follows the equation ln ...p = −3868.3 (1/T) + 10.89 (p Atm, T K) in the range −38 to +22 °C, extrapolated bp ca. 82 °C. It has been characterized by IR (gas phase, Ar matrix), liquid Raman, 19F and 13C NMR, gas UV–vis spectrum, photoelectron spectroscopy (PES), photoionization mass spectrometry (PIMS), and gas electron diffraction (GED). The matrix photochemistry has been studied and the conformational properties of ClF2CC(O)NCO have been analyzed by joint application of vibrational spectroscopy, GED, and quantum chemical calculations. Two conformers were detected in gaseous and liquid phases, in which the C–Cl bond adopts a gauche orientation with respect to the CO group, whereas this group can be in syn or anti orientation with respect to the NC bond of the NCO group. An enthalpy difference ΔH exp ° = 1.3 ± 0.2 kcal mol–1 between the most stable syn–gauche and the less stable anti-gauche form was derived using the van’t Hoff equation, which is in reasonable agreement with the computed difference of ΔH° = 0.8 kcal mol–1 (B3LYP/6-311+G(3df) approximation). The most significant gas phase structural parameters for gauche–syn ClF2CC(O)NCO are r e(NCO) = 1.157(1) Å, r e(NCO) = 1.218(1) Å, r e(N–C) = 1.378(9) Å, r e(CO) = 1.195(1) Å, ∠e(CNC) = 128.6(19)°. Photolysis of ClF2CC(O)NCO using an ArF excimer laser (193 nm) mainly yield ClF2CNCO along with some ClF2CC(O)N nitrene. The valence electronic properties of the title compound were studied using the PES and PIMS. The experimental first vertical ionization energy of 11.54 eV corresponds to the ejection of a carbonylic oxygen lone pair electron.
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