CHC CH Research Articles

Variations of the HCO+, HCN, HNC, N2H+, and NH3 deuterium fractionation in high-mass star-forming regions

ABSTRACT We use spectra and maps of the J = 1 − 0 and J = 2 − 1 DCO+, DCN, DNC, $\rm N_2D^+$ lines, and 111−101 ortho- and para-NH2D lines, obtained with the Institut de Radioastronomie Millimétrique (IRAM)-30 m telescope, as well as observations of their hydrogenated isotopologues to study deuteration processes in five high-mass star-forming regions. The temperature was estimated from CH 3CCH lines, also observed with the IRAM-30 m telescope, and from NH 3 lines, observed with the 100 m radio telescope in Effelsberg, as well as using the integrated intensity ratios of the J = 1 − 0 H13CN and HN13C lines and their main isotopologues. Applying a non-local thermodynamic equilibrium radiative transfer model with radex, the gas density and the molecular column densities were estimated. D/H ratios are 0.001–0.05 for DCO+, 0.001–0.02 for DCN, 0.001–0.05 for DNC, and 0.02–0.4 for NH2D. The D/H ratios decrease with increasing temperature in the range of 20–40 K and slightly vary at densities $n(\rm H_2) \sim 10^4\!-\!10^6$ cm−3. The deuterium fraction of $\rm N_2H^{+}$ is 0.008–0.1 at temperatures in the range of 20–25 K and at a density of ∼105 cm−3. We also estimate relative abundances and find ∼10−11–10−9 for DCO+ and DNC, ∼10−11–10−10 for $\rm N_2D^+$, and ∼10−10–10−8 for NH2D. The relative abundances of these species decrease with increasing temperature. However, the DCN/H2 ratio is almost constant (∼10−10). The observational results agree with the predictions of chemical models (although in some cases there are significant differences).

Solid state luminescence of phosphine-EWO ligands with fluorinated chalcone skeletons and their PdX2 complexes: metal-promoted phosphorescence enhancement.

Complexes trans-[PdX2L2] (X = Cl and Br), where L is 1-(PR2),2-(CHCH-C(O)Ph)-C6F4 (R = Ph, Cy, and iPr), display phosphorescent emission in the solid state, whereas due to their substantially lower lifetimes, the free ligands exhibit fluorescent behaviour. Alternatively, structurally identical derivatives with halide replaced by CN- or Pd replaced by Pt are non-emissive. DFT calculations explain this diverse behaviour, showing that the hybridization of orbitals of the MX2 moiety with those of the chalcone fragment of ligands is significant only for the LUMO of the emissive compounds. In other words, in our complexes, only MLMCT processes (LM = Metal-perturbed Ligand-centered orbital) lead to observable luminescence.

Study on ozonolysis of asymmetric alkenes with matrix isolation and FT-IR spectroscopy

O3 and alkenes are important reactants in the formation of SOA in the atmosphere. The intermediates and reaction mechanism of ozonation of alkene is an important topic in atmospheric chemistry. In this study, the low-temperature matrix isolation was used to capture the intermediates such as Primary ozonides (POZs), Criegee Intermediates (CIs), and Secondary ozonides (SOZs) generated from ozonation of 2-methyl-1-butene (2M1B) and 2-methyl-2-butene (2M2B). The results have been identified by the vacuum infrared spectroscopy and theoretical calculation. Our results show that during the ozonation of asymmetric alkenes, two kinds of CIs and more than two kinds of SOZs were generated due to the different decomposition modes of POZs. The infrared absorption peaks of (CH3)2COO and CH3CH2C(CH3)OO for O–O telescopic vibration was determined to be 889 cm−1 and 913 cm−1, respectively. Using the merged jet method, it was found that a large amount of HCHO was produced during the ozonation of 2M1B, and glyoxal and methylglyoxal were produced in the ozonation of 2M2B. Our findings highlight the importance of asymmetric alkene ozonolysis reactions in producing CIs, further improving the understanding of the generation of CIs from ozonation of alkenes.

Neutral and Anionic Monomeric Zirconium Imides Prepared via Selective C=N Bond Cleavage of a Multidentate and Sterically Demanding β-Diketiminato Ligand.

A sterically encumbering multidentate β-diketiminato ligand, tBu L2 (tBu L2=[ArNC(tBu)CHC(tBu)NCH2 CH2 N(Me)CH2 CH2 NMe2 ]- , Ar=2,6-iPr2 C6 H3 ), is reported in this study along with its coordination chemistry to zirconium(IV). Using the lithio salt of this ligand, Li(tBu L2) (4), the zirconium(IV) precursor (tBu L2)ZrCl3 (6) could be readily prepared in 85 % yield and structurally characterized. Reduction of 6 with 2 equiv of KC8 resulted in formation of the terminal and mononuclear zirconium imide-chloride [C(tBu)CHC(tBu)NCH2 CH2 N(Me)CH2 CH2 NMe2 ]Zr(=NAr)(Cl) (7) as the result of reductive C=N cleavage of the imino fragment in the multidentate ligand tBu L2 by an elusive ZrII species (tBu L2)ZrCl (A). The azabutadienyl ligand in 7 can be further reduced by 2 e- with KC8 to afford the anionic imide [K(THF)2 ]{[CH(tBu)CHC(tBu)NCH2 CH2 N(Me)CH2 CH2 N(Me)CH2 ]Zr=NAr} (8-2THF) in 42 % isolated yield. Complex 8-2THF results from the oxidative addition of an amine C-H bond followed by migration to the vinylic group of the formal [C(tBu)CHC(tBu)NCH2 CH2 N(Me)CH2 CH2 NMe2 ]- ligand in 7. All halides in 6 can be replaced with azides to afford (tBu L2)Zr(N3 )3 (9) which was structurally characterized, and reduction with two equiv of KC8 also results in C=N bond cleavage of tBu L2 to form [C(tBu)CHC(tBu)NCH2 CH2 N(Me)CH2 CH2 NMe2 ]Zr(=NAr)(N3 ) (10), instead of the expected azide disproportionation to N3- and N2 . Solid-state single crystal structural studies confirm the formation of mononuclear and terminal zirconium imido groups in 7, 8-Et2 O, and 10 with Zr=NAr distances being 1.8776(10), 1.9505(15), and 1.881(3) Å, respectively.

Hydrogenating an organometallic carbon chain: buten-yn-diyl (CH[double bond, length as m-dash]CHC[triple bond, length as m-dash]C) as a missing link.

The sequential reaction of [Ru(C[triple bond, length as m-dash]CC[triple bond, length as m-dash]CH)Cl(CO)2(PPh3)2] with [Ru(CO)2(PPh3)3], and N-chlorosuccinimide affords the binuclear tetracarbido complex [Ru2(μ-C[triple bond, length as m-dash]CC[triple bond, length as m-dash]C)Cl2(CO)4(PPh3)4]. This may be compared with the first example of a butenyndiyl bridged bimetallic complex [Ru2(μ-CH[double bond, length as m-dash]CHC[triple bond, length as m-dash]C)Cl2(CO)4(PPh3)4] which is obtained from the reaction of [Ru(C[triple bond, length as m-dash]CC[triple bond, length as m-dash]CH)Cl(CO)2(PPh3)2] with [RuHCl(CO)(PPh3)3] followed by carbonylation. Characterisational data are discussed with reference to constituent model complexes [Ru(C[triple bond, length as m-dash]CH)Cl(CO)2(PPh3)2] and [Ru(CH[double bond, length as m-dash]CH2)Cl(CO)2(PPh3)2] in addition to DFT analysis of the bonding in the complexes [Ru2(μ-L)Cl2(CO)4(PMe3)4] (L = C[triple bond, length as m-dash]C-C[triple bond, length as m-dash]C, CH[double bond, length as m-dash]CHC[triple bond, length as m-dash]C, CH[double bond, length as m-dash]CH-CH[double bond, length as m-dash]CH). A range of other tetracarbido complexes which may be prepared from [RuCl(C[triple bond, length as m-dash]CC[triple bond, length as m-dash]CH)(CO)2(PPh3)2] is also described and includes [RuAu(μ-C4)Cl(CO)3(PPh3)3], [RuIr(μ-C4)Cl(CO)3(PPh3)4], [RuIr(μ-C4)H(NCMe)(CO)3(PPh3)4]BF4, [RuIr(μ-C4)Cl(η2-O2)(CO)3(PPh3)4], [Ru2Hg(μ-C4)2Cl2(CO)4(PPh3)4], [Ru2Pt(μ-C4)2Cl2(CO)4(PPh3)6] and [Ru2(μ-C4)HCl(CO)4(PPh3)4].

Transformation of Tertiary Amines at a Cationic [CCH] Subunit Stabilized by Coordination with a Tetrairon Core

Reaction of [(η5-C5H4Me)4Fe4(HCCH)(HCC–Br)](PF6) with NEt3 in acetonitrile gave the cyanomethylated product [(η5-C5H4Me)4Fe4(HCCH)(HCC–CH2CN)](PF6), while that in dichloromethane gave the [4Fe–4C]-substituted enamine [(η5-C5H4Me)4Fe4(HCCH)(HCC–CH=CHNEt2)](PF6). A possible mechanism starts from the Lewis acid–base interaction between the cationic [CCH] subunit and NEt3 on the tetrairon core.

To kink or not: A search for long-chain cumulenones using microwave spectral taxonomy.

A systematic search for carbon-chain cumulenones beyond H2C4O has been undertaken using microwave spectral taxonomy in combination with a pulsed jet discharge source. No evidence was found for the C2υ isomer of H2C5O or its longer derivatives, but HC(O)C4H, the longer variant of propynal, HC(O)CCH, was identified instead. Its rotational and leading centrifugal distortion constants have been derived to high accuracy from detection of both a- and b-type lines; those below 40 GHz were measured using a Fabry-Perot cavity, while lines between 40 and 72 GHz were recorded by double resonance techniques. Overwhelming evidence for the identification is provided by detection of HC(O)C4D, DC(O)C4H, and HC(18O)C4H at the expected frequencies using isotopically enriched samples. Because HC(18O)C4H is produced with comparable abundance when using either 18O2 or C18O as the source of oxygen, and because H13C(O)C4H is not preferentially formed when starting from 13CO, atomic oxygen appears to be a key reactant in formation, plausibly via O insertion, e.g., H2CC2n+2H + O → HC(O)C2n+2H + H. Under the same experimental conditions, HC(O)CCH is more than 10 times more abundant than H2C3O, regardless of the source of oxygen, and no evidence is found for cyclopropenone, c-C3H2O. Taken together, these observations indicate that propynal and longer chains with an odd number of carbon atoms are either energetically more stable than cumulenones of the same size, are kinetically favored products, or both. On the basis of the HC(O)C4H discovery, searches for the isovalent sulfur species, HC(S)C4H, and HC(O)C6H have been conducted. Guided by new quantum chemical calculations, the rotational spectra of both were observed in the centimeter-wave band with the same spectrometer.

Rate Coefficients for the Reactions of OH Radicals with a Series of Alkyl-Substituted Amines.

Rate coefficients have been determined at (298 ± 2) K and atmospheric pressure for the reaction of OH radicals with two primary monoalkyl-, one secondary dialkyl-, and five tertiary trialkyl-substituted amines in a large volume photoreactor by the relative kinetic technique. The following rate coefficients (in cm3 molecule-1 s-1 units) have been obtained: (1) 1,2-dimethylpropylamine, CH3C(CH3)HC(CH3)H)NH2, (5.08 ± 1.02) × 10-11; (2) tert-amylamine (tert-pentylamine), CH3CH2C(CH3)2NH2, (0.86 ± 0.17) × 10-11; (3) diethylamine, (CH3CH2)2NH, (7.36 ± 1.47) × 10-11; (4) N,N-dimethylethylamine, (CH3)2NCH2CH3, (7.37 ± 1.47) × 10-11; (5) N,N-dimethylpropylamine, (CH3)2NCH2CH2CH3, (10.97 ± 1.78) × 10-11; (6) N,N-dimethylisopropylamine, (CH3)2NCH(CH3)2, (9.79 ± 1.75) × 10-11; (7) N,N-diethylmethylamine, (CH3CH2)2NCH3, (8.92 ± 1.54) × 10-11; (8) triethylamine, (CH3CH2)3N, (10.86 ± 1.88) × 10-11. The quoted errors are the 2σ deviations from least-squares linear analysis of the kinetic data plus a contribution to take into account uncertainties associated with the reference compounds. With the exception of diethylamine, this study represents the first determinations of the rate coefficients for reaction of the compounds with OH radicals. The results are compared with rate coefficients available in the literature for smaller alkyl-substituted amines and also the values predicted for the compounds investigated by using a structure activity relationship (SAR). With the exception of tert-amylamine, the SAR-predicted OH rate coefficients are in good agreement with the experimental values.

Microwave spectral taxonomy: A semi-automated combination of chirped-pulse and cavity Fourier-transform microwave spectroscopy.

Because of its structural specificity, rotational spectroscopy has great potential as an analytical tool for characterizing the chemical composition of complex gas mixtures. However, disentangling the individual molecular constituents of a rotational spectrum, especially if many of the lines are entirely new or unknown, remains challenging. In this paper, we describe an empirical approach that combines the complementary strengths of two techniques, broadband chirped-pulse Fourier transform microwave spectroscopy and narrowband cavity Fourier transform microwave spectroscopy, to characterize and assign lines. This procedure, called microwave spectral taxonomy, involves acquiring a broadband rotational spectrum of a rich mixture, categorizing individual lines based on their relative intensities under series of assays, and finally, linking rotational transitions of individual chemical compounds within each category using double resonance techniques. The power of this procedure is demonstrated for two test cases: a stable molecule with a rich spectrum, 3,4-difluorobenzaldehyde, and products formed in an electrical discharge through a dilute mixture of C2H2 and CS2, in which spectral taxonomy has enabled the identification of propynethial, HC(S)CCH.

Chiral Lithiated Allylic α-Sulfonyl Carbanions: Experimental and Computational Study of Their Structure, Configurational Stability, and Enantioselective Synthesis.

X-ray crystal structure analysis of the lithiated allylic α-sulfonyl carbanions [CH2 CHC(Me)SO2 Ph]Li⋅diglyme, [cC6 H8 SO2 tBu]Li⋅PMDETA and [cC7 H10 SO2 tBu]Li⋅PMDETA showed dimeric and monomeric CIPs, having nearly planar anionic C atoms, only OLi bonds, almost planar allylic units with strong CC bond length alternation and the s-trans conformation around C1C2. They adopt a C1S conformation, which is similar to the one generally found for alkyl and aryl substituted α-sulfonyl carbanions. Cryoscopy of [EtCHCHC(Et)SO2 tBu]Li in THF at 164 K revealed an equilibrium between monomers and dimers in a ratio of 83:17, which is similar to the one found by low temperature NMR spectroscopy. According to NMR spectroscopy the lone-pair orbital at C1 strongly interacts with the CC double bond. Low temperature (6) Li,(1) H NOE experiments of [EtCHCHC(Et)SO2 tBu]Li in THF point to an equilibrium between monomeric CIPs having only OLi bonds and CIPs having both OLi and C1Li bonds. Ab initio calculation of [MeCHCHC(Me)SO2 Me]Li⋅(Me2 O)2 gave three isomeric CIPs having the s-trans conformation and three isomeric CIPs having the s-cis conformation around the C1C2 bond. All s-trans isomers are more stable than the s-cis isomers. At all levels of theory the s-trans isomer having OLi and C1Li bonds is the most stable one followed by the isomer which has two OLi bonds. The allylic unit of the C,O,Li isomer shows strong bond length alternation and the C1 atom is in contrast to the O,Li isomer significantly pyramidalized. According to NBO analysis of the s-trans and s-cis isomers, the interaction of the lone pair at C1 with the π* orbital of the CC double bond is energetically much more favorable than that with the "empty" orbitals at the Li atom. The C1S and C1C2 conformations are determined by the stereoelectronic effects nC -σSR * interaction and allylic conjugation. (1) H DNMR spectroscopy of racemic [EtCHCHC(Et)SO2 tBu]Li, [iPrCHCHC(iPr)SO2 tBu]Li and [EtCHC(Me)C(Et)SO2 tBu]Li in [D8 ]THF gave estimated barriers of enantiomerization of ΔG(≠) =13.2 kcal mol(-1) (270 K), 14.2 kcal mol(-1) (291 K) and 14.2 kcal mol(-1) (295 K), respectively. Deprotonation of sulfone (R)-EtCHCHCH(Et)SO2 tBu (94 % ee) with nBuLi in THF at -105 °C occurred with a calculated enantioselectivity of 93 % ee and gave carbanion (M)-[EtCHCHC(Et)SO2 tBu]Li, the deuteration and alkylation of which with CF3 CO2 D and MeOCH2 I, respectively, proceeded with high enantioselectivities. Time-dependent deuteration of the enantioenriched carbanion (M)-[EtCHCHC(Et)SO2 tBu]Li in THF gave a racemization barrier of ΔG(≠) =12.5 kcal mol(-1) (168 K), which translates to a calculated half-time of racemization of t1/2 =12 min at -105 °C.

Atmospheric reactivity of HCCCH2OH (2-propyn-1-ol) toward OH radicals: experimental determination and theoretical comparison with its alkyne analogue

The rate coefficient for the reaction of propargyl alcohol (2-propyn-1-ol,2P1OL) with OH radicals has been determined using gas chromatography with a flame ionization detector (GC/FID) at 298 K and atmospheric pressure.

On the Photoionization Spectrum of Propyne: A Fully ab Initio Simulation of the Low-Energy Spectrum Including the Jahn–Teller Effect and the Spin–Orbit Interaction

The low energy photoionization spectrum of propyne (CH3-CCH), which reveals the vibronic structure of the propyne cation, is simulated using vibronic coupling theory. The spin-orbit interaction is included using an intensity borrowing approach, enabling determination of the (X̃(2)E1/2,3/2, v = 0) splitting and the relative photoionization intensity of these closely spaced levels. The results are compared with recent experimental studies and misstatements are corrected.

FTIR gas-phase kinetic study on the reactions of OH radicals and Cl atoms with unsaturated esters: Methyl-3,3-dimethyl acrylate, (E)-ethyl tiglate and methyl-3-butenoate

The relative-rate technique has been used to obtain rates coefficients for the reactions of the unsaturated esters methyl-3,3-dimethyl acrylate, (E)-ethyl tiglate and methyl-3-butenoate with OH radicals and chlorine atoms at (298 ± 2) K in synthetic air at a total pressure of (760 ± 10) Torr. The experiments were performed in an environmental chamber using in situ FTIR detection to monitor the decay of the esters relative to different reference compounds. The following room temperature rate coefficients (in units of cm3 molecule−1 s−1) were obtained: k1(OH + (CH3)2CCHC(O)OCH3) = (4.46 ± 1.05) × 10−11, k2(Cl + (CH3)2CCHC(O)OCH3) = (2.78 ± 0.46) × 10−10, k3(OH + CH3CHC(CH3)C(O)OCH2CH3) = (8.32 ± 1.93) × 10−11, k4(Cl + CH3CHC(CH3)C(O)OCH2CH3) = (2.53 ± 0.35) × 10−10, k5(OH + CH2CHCH2C(O)OCH3) = (3.16 ± 0.57) × 10−11, k4(Cl + CH2CHCH2C(O)OCH3) = (2.10 ± 0.35) × 10−10. With the exception of the reaction of Cl with methyl-3,3-dimethyl acrylate (k2), for which one determination exists in the literature, this study is the first kinetic study for these reactions under atmospheric pressure. Reactivity trends are discussed in terms of the effect of the alkyl and ester groups attached to the double bond on the overall rate coefficients towards OH radicals. The atmospheric implications of the reactions were assessed by the estimation of the tropospheric lifetimes of the title reactions.

Addition of diphenylacetylene and methylvinylketone to aluminum complex of redox-active diimine ligand

Diphenylacetylene reacts with aluminum complex (dpp-bian)AlEt(Et2O) (1) (dpp-bian = 1,2-bis[(2,6-diisopropylphenyl)imino]acenaphthene) in the absence of any solvent at 110–130 °C under vacuum to give compound [dpp-bian(PhCCPh)]AlEt (2). The reaction of methylvinylketone with complex 1 easily proceeds at ambient temperature in Et2O and results in the formation of compound [dpp-bian(CH2–CHC(Me)–O)]AlEt (3). Both reactions proceed via addition of unsaturated organic substrate across Al–N–C bond sequence in complex 1. Complexes 2 and 3 have been characterized by IR and 1H NMR spectroscopy. Molecular structures of 2 and 3 have been determined by single-crystal X-ray analysis. Complex 2 was found to be catalyst for the reaction between phenylacetylene and diphenylamine. A full conversion of the reagents was achieved with 5 mol% of complex 2 in benzene in 140 h at 110 °C resulting N-phenyl-2-(1-phenylvinyl)aniline (4a) as the major product (87%).

From Osmium Hydrido Vinylidene to Osmacycles: The Key Role of Osmabutadiene Intermediates

Osmium hydrido vinylidene 1 shows diverse cyclization reactivity with activated terminal alkynes. Treatment of 1 with HC≡CCOR' (R'=OEt and Me) gave osmafurans 3a and 3b via osmium alkenyl/vinylidenes 2a and 2b. In addition, 1 reacted with HC≡CCH(OH)C≡CH to yield osmabenzene 4, in which the alkynol acted as a C(5) fragment to cyclize with 1. Mechanistic analysis indicates that these reactions and the previous formal [3+3] cycloadditions between 1 and HC≡CCH(OH)R (R=Ph, Et, and vinyl) or HC≡CCH(OEt)(2) all go through similar osmabutadiene intermediates. Subsequently, the intermediates either took a "coordination and cyclization" process or a "carbon-carbon coupling" path to cyclization, depending on the coordination ability of substituents on the terminal alkenyl carbon atom.

Thermal decomposition of some silver(I) carboxylates under nitrogen atmosphere

The thermal decomposition reactions of CH3CH2C(CH3)2COOAg (1), (CH3)3SiCH2COOAg (2), CF3COOAg (3), (CH3)3CCOOAg (4), C2H5COOAg (5), C3F7COOAg (6), C6F13COOAg (7) and (CF2)3(COOAg)2 (8) were studied in N2 atmosphere using thermogravimetry (TG), derivative thermogravimetry and differential thermal analysis. Characterized compounds decomposed in one- or multi-step processes with metallic silver formation in the range 215–465 °C. TG-IR studies of gases evolved during thermolysis revealed products of decomposition, such as carboxylic acids, CO2 and recombination reactions.

Stepwise synthesis of a hydrido, N-heterocyclic dicarbene iridium(iii) pincer complex featuring mixed NHC/abnormal NHC ligands

We describe a stepwise synthesis of the hydrido, N-heterocyclic dicarbene iridium(III) pincer complex [Ir(H)I(C(NHC)CC(aNHC))(NCMe)] (3) which features a combination of normal and abnormal NHC ligands. The reaction of the bis(imidazolium) diiodide [(CH(imid)CHCH(imid))]I(2) (1) with [Ir(μ-Cl)(cod)](2) afforded first the mono-NHC Ir(I) complex [IrI(cod)(CH(imid)CHC(NHC))]I (2), which was then reacted with 2 equiv. of Cs(2)CO(3) in acetonitrile at 60 °C for 40 h to yield 3. These observations support our previously proposed mechanism for the formation of hydrido, N-heterocyclic dicarbene iridium(III) pincer complexes from the reaction of bis(imidazolium) salts with weak bases involving a mono-NHC Ir(I) intermediate. We describe the reactivity of the mono-NHC Ir(I) complex 2 under various conditions. By changing the reaction solvent from MeCN to toluene, we observed the cleavage of the imidazol-2-ylidene ring and the formation of an iminoformamide-containing mono-NHC Ir(I) complex [IrI(cod){[NHCH=CHN(Ad)CHO]CHC(NHC)}] (4). Complex 4 was also prepared in high yield from the reaction of 2 with strong bases (potassium tert-butoxide or potassium hexamethyldisilazane), via the initial formation of the complex [IrI(cod)(CH(NHC)CHC(NHC))] (5), which contains a coordinated NHC moiety and a free carbene arm, followed by subsequent hydrolysis of the latter. The bis(imidazolium) salt 1 can be deprotonated by strong bases to form the bis(carbene) ligand C(NHC)CHC(NHC) (6), which readily reacts with [Ir(μ-Cl)(cod)](2) to give the dinuclear complex [{IrI(cod)}(2)(μ-C(NHC)CHC(NHC))] (7), in which the N-heterocyclic bis(carbene) ligand bridges the two metals through the carbene carbon atoms.

Two dimensional self-assembly of bis-acylureas having various functional end groups

We present the synthesis and morphology study of thirteen bis-acylurea molecules with various functional end groups. The bis-acylureas have two acylurea groups, NH CO NH CO , divided by a pentamethylene spacer, (CH 2) 5 , and two symmetric functional end groups, such as, aliphatic, benzyl, mono- and bi-thiophenyl, sulfur-containing, and propargyl (HC CCH 2 ) moieties. The bis-acylureas were synthesized by the coupling reactions of ureas with pimeloyl chloride or pimelic acid. Upon cooling from hot isotropic solutions, the bis-acylureas spontaneously form supermolecules. In the cases of aliphatic, benzyl, mono- and bi-thiophenyl functional groups, two dimensional supramolecular structures with molecularly flat surfaces were formed. Single crystal X-ray diffraction results demonstrate that each bis-acylurea molecule forms biaxial hydrogen bonds with four adjacent molecules forming a grid-like crystalline structure. Among the bis-acylureas with sulfur-containing end groups, those with sulfide ( S ) and disulfide ( SS ) moieties self-organize into two dimensional superstructures, while those with thiol ( SH) and bulky protecting group ( S trityl) precipitate with irregular shapes. The bis-acylurea with propargyl end groups form superstructures of low order possibly due to the steric effect between the rigid moieties. However, the derivatives prepared by click reactions have lamellar molecular packing similar to those of bis-acylureas forming multilayered nanosheet structures.

Theoretical mechanistic study of the reaction of the methylidyne radical with methylacetylene

A detailed doublet potential energy surface for the reaction of CH with CH(3)CCH is investigated at the B3LYP/6-311G(d,p) and G3B3 (single-point) levels. Various possible reaction pathways are probed. It is shown that the reaction is initiated by the addition of CH to the terminal C atom of CH(3)CCH, forming CH(3)CCHCH 1 (1a,1b). Starting from 1 (1a,1b), the most feasible pathway is the ring closure of 1a to CH(3)-cCCHCH 2 followed by dissociation to P ( 3 )(CH(3)-cCCCH+H), or a 2,3 H shift in 1a to form CH(3)CHCCH 3 followed by C-H bond cleavage to form P ( 5 )(CH(2)CHCCH+H), or a 1,2 H-shift in 1 (1a, 1b) to form CH(3)CCCH(2) 4 followed by C-H bond fission to form P ( 6 )(CH(2)CCCH(2)+H). Much less competitively, 1 (1a,1b) can undergo 3,4 H shift to form CH(2)CHCHCH 5. Subsequently, 5 can undergo either C-H bond cleavage to form P ( 5 ) (CH(2)CHCCH+H) or C-C bond cleavage to generate P ( 7 ) (C(2)H(2)+C(2)H(3)). Our calculated results may represent the first mechanistic study of the CH + CH(3)CCH reaction, and may thus lead to a deeper understanding of the title reaction.

Stilbene analogues incorporating the Co(η 4-C 4Ph 4)(η 5-C 5H 4-) end group

A number of organometallic stilbenes of the general type [Co(η 4-C 4Ph 4)(η 5-C 5H 4CH CHR] are reported where R is C 6H 4X-4 (X = H, OMe, Br, NO 2), 1-naphthyl, 9-anthryl, 1-pyrenyl, (η 5-C 5H 4)Co(η 4-C 4Ph 4), and (η 5-C 5H 4)Fe(η 5-C 5H 4Y) {Y = CHO, CH C(CN) 2 and CH CHC 5H 4-η 5)Co(η 4-C 4Ph 4)}. They were prepared by Wittig or Horner–Wadsworth–Emmons reactions which yield both E and Z or only E products respectively. The isomers were separated and all compounds characterised by standard spectroscopic techniques as well as by X-ray diffraction methods in many cases. The electrochemistry of the stilbene analogues in dichloromethane solution is also reported. In most, the (η 5-C 5H 4)Co(η 4-C 4Ph 4) functional group undergoes a reversible one-electron oxidation. For those molecules that also include (η 5-C 5H 4)Fe(η 5-C 5H 4Y), this is preceded by the reversible oxidation of the ferrocenyl group. Spectroscopic and structural data suggests that for most compounds there is little electronic interaction between Co(η 4-C 4Ph 4)(η 5-C 5H 4) and the R end groups which are effectively independent of one another. The only exceptions to this are Z and E-[Co(η 4-C 4Ph 4)(η 5-C 5H 4CH CHC 6H 4NO 2-4], and [Co(η 4-C 4Ph 4)(η 5-C 5H 4CH CHC 5H 4-η 5)Fe{η 5-C 5H 4CH C(CN) 2}] where the electronic spectra are respectively consistent with a significant Co(η 4-C 4Ph 4)(η 5-C 5H 4)/NO 2 donor/acceptor interaction and a less significant Co(η 4-C 4Ph 4)(η 5-C 5H 4)/C(CN) 2 one. However, OTTLE studies show that in the electronic spectra of [Co(η 4-C 4Ph 4)(η 5-C 5H 4CH CHR] + there are low energy absorption bands (950–1800 nm) which are attributed to R → Co(η 4-C 4Ph 4)(η 5-C 5H 4) + or, when R is a ferrocenyl-base group, Co(η 4-C 4Ph 4)(η 5-C 5H 4) → (η 5-C 5H 4)Fe(η 5-C 5H 4Y) + charge transfer transitions. The ferrocenyl compounds undergo cis/trans isomerisation on the OTTLE experiment timescale.