Search

We report the comparison of a series of 2D molecular crystals formed from the intermediates of the dehalogenation reaction of iodoethane versus various fluorinated iodoalkanes on Cu(111). High-resolution scanning tunneling microscopy enables us to distinguish the alkyl groups from the iodine atoms, and we find that the ethyl groups and iodine atoms formed from the dissociation of ethyl iodide are well mixed. However, fluorination of the alkyl tail changes this behavior and leads to local segregation of the two species on the surface. We postulate that the low-polarizability and relatively large dipole moment of the fluorinated species drive the ordered assemblies of the fluorinated alkyl species on the surface and discuss this in the context of how solvophobicity can drive the clustering of fluorinated groups and, hence, phase separation.

1-Benzyl-3-ethylbenzimidazolium iodide (1) and 1-benzyl-3-(2′-nitrilebenzyl)benzimidazolium bromide (2) were prepared by the reaction of 1-benzylbenzimidazole with ethyl iodide or 2-bromomethylbenzonitrile to act as N-heterocyclic carbene (NHC) precursors. Bis-NHC silver(I) complexes having halide (3a and 4a) as well as hexafluorophosphate (3b and 4b) counterions were yielded by the reaction of NHC precursors with silver(I) oxide. Subsequent reactions of the silver(I) halide/hexafluorophosphate complexes with [PdCl2(CNCH3)2] in methanol afforded the NHC palladium(II) complexes (5 and 6) via carbene transfer method. All synthesized compounds were fully characterized by analytical and spectrometric methods. Preliminary catalytic studies evinced that the nitrile-functionalized palladium(II)-NHC complex 6 is highly active in the oxidation of 1-octene as well as styrene in the presence of aqueous hydrogen peroxide as an oxidizing agent. Both the olefins were oxidized to their corresponding oxidized products with 45-52% conversion with moderate selectivity in the presence of NHC palladium complexes, which acted as oxidation catalysts. In order to investigate the suggested structure of the title complexes, density functional theory was used to find the stable structures of the palladium complexes and their isomers. Geometry parameters, molecular orbital energies, electronic energy, band gap, and vibrational frequencies were calculated.

It has been demonstrated that alkylzinc halides efficiently destroy the passivating film on the zinc-copper pair in the course of its alkylation with ethyl bromide to give ethylzinc bromide. The alkylzinc halides efficiency is comparable to that of ethyl iodide and exceeds that of salts of transition or non-transition metals as well as of ultraviolet irradiation. Addition of alkylzinc halides or metal salts as well as ultraviolet irradiation have practically no effect on the developed reaction. The results have demonstrated that the organometallic component of the binary systems is polyfunctional; this permits a generalization of known features of a number of known methods promoting direct synthesis of organometallic compounds.

The photodissociation dynamics of ethyl bromide and ethyl iodide cations (C2H5Br+ and C2H5I+) have been studied. Ethyl halide cations were formed through vacuum ultraviolet (VUV) photoionization of the respective neutral parent molecules at 118.2 nm, and were photolysed at a number of ultraviolet (UV) photolysis wavelengths, including 355 nm and wavelengths in the range from 236 to 266 nm. Time-of-flight mass spectra and velocity-map images have been acquired for all fragment ions and for ground (Br) and spin–orbit excited (Br*) bromine atom products, allowing multiple fragmentation pathways to be investigated. The experimental studies are complemented by spin–orbit resolved ab initio calculations of cuts through the potential energy surfaces (along the RC–Br/I stretch coordinate) for the ground and first few excited states of the respective cations. Analysis of the velocity-map images indicates that photoexcited C2H5Br+ cations undergo prompt C–Br bond fission to form predominantly C2H5+ + Br* products with a near-limiting ‘parallel’ recoil velocity distribution. The observed C2H3+ + H2 + Br product channel is thought to arise via unimolecular decay of highly internally excited C2H5+ products formed following radiationless transfer from the initial excited state populated by photon absorption. Broadly similar behaviour is observed in the case of C2H5I+, along with an additional energetically accessible C–I bond fission channel to form C2H5 + I+ products. HX (X = Br, I) elimination from the highly internally excited C2H5X+ cation is deemed the most probable route to forming the C2H4+ fragment ions observed from both cations. Finally, both ethyl halide cations also show evidence of a minor C–C bond fission process to form CH2X+ + CH3 products.

Direct comparisons of the reactivity and mechanistic pathways for anionic systems in the gas phase and in solution are presented. Rate constants and kinetic isotope effects for the reactions of methyl, ethyl, isopropyl, and tert-butyl iodide with cyanide ion in the gas phase, as well as for the reactions of methyl and ethyl iodide with cyanide ion in several solvents, are reported. In addition to measuring the perdeutero kinetic isotope effect (KIE) for each reaction, the secondary alpha- and beta-deuterium KIEs were determined for the ethyl iodide reaction. Comparisons of experimental results with computational transition states, KIEs, and branching fractions are explored to determine how solvent affects these reactions. The KIEs show that the transition state does not change significantly when the solvent is changed from dimethyl sulfoxide/methanol (a protic solvent) to dimethyl sulfoxide (a strongly polar aprotic solvent) to tetrahydrofuran (a slightly polar aprotic solvent) in the ethyl iodide-cyanide ion S(N)2 reaction in solution, as the "Solvation Rule for S(N)2 Reactions" predicts. However, the Solvation Rule fails the ultimate test of predicting gas phase results, where significantly smaller (more inverse) KIEs indicate the existence of a tighter transition state. This result is primarily attributed to the greater electrostatic forces between the partial negative charges on the iodide and cyanide ions and the partial positive charge on the alpha carbon in the gas phase transition state. Nevertheless, in evaluating the competition between S(N)2 and E2 processes, the mechanistic results for the solution and gas phase reactions are strikingly similar. The reaction of cyanide ion with ethyl iodide occurs exclusively by an S(N)2 mechanism in solution and primarily by an S(N)2 mechanism in the gas phase; only approximately 1% of the gas phase reaction is ascribed to an elimination process.

Low temperature photoisomerization of stilbene and 1,4-diphenyl-1,3-butadiene derivatives was found to vary depending on the organic glass employed in such studies. Examination of the combined results showed that the variation was more likely to arise from the rigidity of the organic glass at the temperature of irradiation rather than the composition of the organic glass; that is, the observed results are consistent with the possible softening of the glass that surrounds the excited substrate in the same manner as detected in the photolysis of ethyl iodide reported by Porter and co-workers. These observations successfully account for the apparent "disagreement" of reports from the Hawaii and the Florida State groups on the mechanism of photoisomerization in low temperature glasses.

The thermal decomposition of ethyl and propyl iodides, along with select isotopomers, up to 1300 K was performed by flash pyrolysis with a 20-100 mus time scale. The pyrolysis was followed by supersonic expansion to isolate the reactive intermediates and initial products, and detection was accomplished by vacuum ultraviolet single photon ionization time-of-flight mass spectrometry (VUV-SPI-TOFMS). The products monitored, such as CH(3), CH(3)I, C(2)H(5), C(2)H(4), HI, I, C(3)H(7), C(3)H(6), and I(2), provide for the simultaneous and direct observation of molecular elimination and bond fission pathways in ethyl and propyl iodides. In the pyrolysis of ethyl iodide, both C-I bond fission and HI molecular elimination pathways are competitive at the elevated temperatures, with C-I bond fission being preferred; at temperaturesor=1000 K, the ethyl radical products further dissociate to ethene + H atoms. In the pyrolysis of isopropyl iodide, both HI molecular elimination and C-I bond fission are observed and the molecular elimination channel is more important at all the elevated temperatures; the isopropyl radicals produced in the C-I fission channel undergo further decomposition to propene + H at temperaturesor=850 K. In contrast, bond fission is found to dominate the n-propyl iodide pyrolysis; at temperaturesor=950 K the n-propyl radicals produced decompose into methyl radical + ethene and propene + H atom. Isotopomer experiments characterize the extent of surface reactions and verify that the HI molecular eliminations in ethyl and propyl iodides proceed by a C1, C2 elimination mechanism (the 1,2 intramolecular elimination).

X-ray photoelectron spectroscopy (XPS) studies revealed that potassium on Mo 2 C/Mo(100) induced cleavage of the C-I bond in adsorbed CH 3 I even at ∼100 K. The temperature of complete C-I bond breaking occurred 60-80 K lower compared to the clean surface. Preadsorbed potassium also influenced the reaction pathway of adsorbed CH 3 formed. It decreased its self-hydrogenation into methane and facilitated the coupling reactions into ethane and ethylene below 200 K. High-resolution electron energy loss spectroscopy (HREELS) confirmed formation of adsorbed CH 3 species and revealed its thermal stability. Potassium exerted a similar influence on the chemistry of C 2 H 5 I on Mo 2 C/Mo(100) surface. Rupture of the C-I bond also occurred more easily on K-covered surface. Ethyl species, the primary product of the dissociation, dehydrogenated into ethylene on one hand and hydrogenated into ethane on the other. Rupture of the C-C bond was not observed even at high potassium coverage. Illumination of coadsorbed layers promoted further dissociation of the C-I bond in both compounds at ∼100 K.

Diacetylplatinum(II) complexes [Pt(COMe)2(N^N)] (N^N = bpy, 3a; 4,4′-t-Bu2-bpy, 3b) were found to undergo oxidative addition reactions with organyl halides. The reaction of 3a with methyl iodide and propargyl bromide led to the formation of the cis addition products (OC-6-34)-[Pt(COMe)2(R)X(bpy)] (R = Me, X = I, 4a; CH2C≡CH, X = Br, 4k). Analogous reactions of 3a with ethyl iodide, benzyl bromide, and substituted benzyl bromides, 3-(bromomethyl)pyridine, 2-(bromomethyl)thiophene, allyl bromide, and cyclohex-2-enyl bromide led to exclusive formation of the trans addition products (OC-6-43)-[Pt(COMe)2(R)X(bpy)] (X = I, R = Et, 4b; X = Br, R = CH2C6H5, 4c; CH2C6H4(o-Br), 4d; CH2C6H4(p-COOH), 4e; CH2-3-py (3-pyridylmethyl), 4f; CH2-2-tp (2-thiophenylmethyl), 4g; CH2CH=CH2, 4h; c-hex-2-enyl (cyclohex-2-enyl), 4i). All complexes 4 were characterized by microanalysis, 1H and 13C NMR and IR spectroscopy. Additionally, complexes 4a, 4f, and 4g were characterized by single-crystal X-ray diffraction analyses. Reactions of 3a and 3b with o-, m- and p-bis(bromomethyl)benzene, respectively, led to the formation of dinuclear platinum(IV) complexes [{Pt(COMe)2Br(N^N)}2-{μ-(CH2)2C6H4}] (5). These complexes were characterized by microanalysis, IR spectroscopy, and depending on their solubility by 1H and 13C NMR spectroscopy, too. A single-crystal X-ray diffraction analysis of complex [{Pt(COMe)2Br(bpy)}2{μ-m-(CH2)2C6H4}] (5b) confirmed its dinuclear composition. The solid-state structures of 4a, 4f, 4g, and 5b are discussed in terms of C–H···O and O–H···O hydrogen bonds as well as π–π stacking between aromatic rings.

The chemistry of ethylene adsorbed on a thin MoAl layer grown in ultrahigh vacuum on a thin alumina film is studied using a combination of temperature-programmed desorption and X-ray, Auger and reflection absorption infrared spectroscopies. Both di-σ-bonded and a small proportion of π-bonded ethylene are found, where the di-σ-bonded ethylene has a σ/π parameter of ∼0.8 and a heat of adsorption of ∼70 kJ/mol. The ethylene self-hydrogenates to yield ethane and a small amount of methane is detected. The surface hydrogenation activation energy of di-σ-bonded ethylene is ∼65 kJ/mol, while the π-bonded species hydrogenates more easily. Adsorbed ethyl species grafted onto the surface by decomposing ethyl iodide predominantly undergo β-hydride elimination to yield ethylene. Ethyl species hydrogenate to ethane at a lower temperature than does di-σ-bonded ethylene implying that addition of hydrogen to adsorbed ethylene is slower than the rate of ethyl hydrogenation.

The VUV photochemistry of the radicals propargyl, C3H3, and ethyl, C2H5, is investigated using synchrotron radiation. The radicals are produced by flash pyrolysis from propargyl bromide and ethyl iodide, respectively. It is shown that dissociative photoionisation of propargyl is associated with loss of a H-atom, leading to formation of c-C3H2+. The process sets in between 12.5 and 13 eV, in agreement with computations. The alternative pathway, leading to C3H+ + H2 is only tentatively observed at energies above 15.5 eV. The onset for dissociative photoionisation of ethyl according to C2H5 → C2H3+ + H2 is observed at 11.6 eV, roughly 1 eV higher than expected from ab initio calculations. In addition we monitor the hitherto unobserved three-body dissociative ionisation of the precursor molecules. The process C2H5I → C2H3+ + H2 + I sets in above 12.7 eV, the dissociative ionisation of C3H3Br → C3H+ + H2 + Br above 15 eV.

We report data from a comprehensive investigation into the photodissociation dynamics of methyl iodide and ethyl iodide at several wavelengths in the range 236-266 nm, within their respective A-bands. The use of non-resonant single-photon ionization at 118.2 nm allows detection and velocity-map imaging of all fragments, regardless of their vibrotational or electronic state. The resulting photofragment kinetic energy and angular distributions and the quantum yields of ground-state and spin-orbit excited iodine fragments are in good agreement with previous studies employing state-selective detection via REMPI. The data are readily rationalised in terms of three competing dissociation mechanisms. The dominant excitation at all wavelengths studied is via a parallel transition to the (3)Q0 state, which either dissociates directly to give an alkyl radical partnered by spin-orbit excited iodine, or undergoes radiationless transfer to the (1)Q1 potential surface, where it dissociates to an alkyl radical partnered by iodine in its electronic ground state. Ground state iodine atoms can also be formed by direct dissociation from the (1)Q1 or (3)Q1 excited states following perpendicular excitation at the shorter and longer wavelength region, respectively, in the current range of interest. The extent of internal excitation of the alkyl fragment varies with dissociation mechanism, and is considerably higher for ethyl fragments from ethyl iodide photolysis than for methyl fragments from methyl iodide photolysis. We discuss the relative advantages and disadvantages of single-photon vacuum-ultraviolet ionization relative to the more widely used REMPI detection schemes, and conclude, in agreement with others, that single-photon ionization is a viable detection method for photofragment imaging studies, particularly when studying large molecules possessing multiple fragmentation channels.

A preliminary study of photophysical and photochemical properties of 9,9′-bianthryl (BA) and 10,10′-dibromo,9,9′-bianthryl (DBrBA) is presented. Dual fluorescence occurring in bianthryl (BA) has been investigated in solvents containing heavy atoms, such as chlorine, bromine and iodine. The presence of heavy atoms reduces strongly the fluorescence lifetimes and the fluorescence quantum yields of BA, the effect is strongest in ethyl iodide, i.e. in the solvent containing the heaviest atom, iodine. On the other hand, it has been found that introduction of two heavy atoms (bromine) into the bianthryl molecule modifies noticeably its fluorescence properties, which indicates existance of an internal heavy atom effect. Again, a reduction of the fluorescence lifetime and the fluorescence quantum yield, compared to the parent molecule, has been observed. On the basis of these observations the mechanism of 1CT ⇒ 3LE intersystem crossing has been discussed. In BA the rate determining process is a reversible spin inversion within the radical pair. In DBrBA where the spin flip is accelerated by the presence of heavy atoms (bromines) the spin-allowed electron transfer 3CT ⇒ 3LE becomes important in the overall intersystem crossing process. It has been found that DBrBA undergoes a photoreduction in the presence of aromatic donors, such as amines, leading finally to BA. Similar reaction seems to be observed in electrochemical measurement. The reduction of DBrBA originates from the primary electron transfer process either photoinduced or electrochemical leading to the free anion radicals of DBrBA.

The hydrogenation of ethylene on Pd(111) is probed using a combination of temperature-programmed desorption (TPD) and reflection−absorption infrared spectroscopy (RAIRS). Ethylene adsorbs on clean Pd(111) in a di-σ configuration but converts to π-bonded species when the surface is presaturated by hydrogen. Ethane is formed with an activation energy of 3.0 ± 0.3 kcal/mol only when Pd(111) is pre-covered by hydrogen and not when ethylene and hydrogen are co-dosed, indicating that ethylene blocks hydrogen adsorption. Experiments performed by grafting ethyl species onto the surface by reaction with ethyl iodide indicate that ethyl species hydrogenate much more rapidly than the overall rate of ethylene hydrogenation, demonstrating that the addition of the first hydrogen atom to adsorbed ethylene to form an ethyl species is the rate-limiting step in the hydrogenation reaction. The adsorption geometry of ethyl iodide is found to depend on dosing conditions. When adsorbed at low exposures at 80 K, the mirror symm...

We studied dehydrogenation reaction of ethylene (C 2 H 4 ) on a Pt(1 1 1) surface using the technique of Cs + reactive ion scattering (RIS). Adsorption of ethyl iodide (C 2 H 5 I) on Pt(1 1 1) was also studied to provide the calibration data. The possible intermediate species in ethylene dehydrogenation to ethylidyne (C–CH 3 ), namely, ethylidene (CH–CH 3 ), vinyl (–CHCH 2 and CCH 2 ), and ethyl species (–CH 2 –CH 3 ), were closely investigated by RIS identification of surface molecules and temperature-programmed kinetic study. The result indicates that the dehydrogenation step occurs through an ethylidene intermediate and that vinyl and ethyl intermediates are not formed.

Perdeuterated ethyl iodide in solid parahydrogen is photolyzed at 4.4 K to find the formation of all deuterated ethylene, ethane, and ethyl radical and deuterium iodide. The temporal change in the ...

At room temperature, a high‐efficiency photochromogenic reaction of destruction of Zn‐tetra(4‐tert‐butylbenzo)porphin molecules in a polyvinylbutyral matrix has been revealed. The linear dependence of the photobleaching rate of porphyrin on the irradiation power density is indicative of a single‐photon character of the reaction. The influence of pyridine and ethyl iodide additives as well as of intermolecular oxygen on the photodissociation rate of pigment molecules has been investigated. The most probable mechanism of transformation of the porphyrin compound is its photodestruction involving free radicals. We suggest using the composition as a photosensitive material, and we have determined its photosensitivity experimentally (S = 0.4·103 cm2/J).

The adsorption, thermal reactions, and photochemistry of C2H5I have been studied on TiO2 by Fourier-transformed infrared spectroscopy. C2H5I is adsorbed on TiO2 and remains intact at 35°C. However, it decomposes to form C2H5O(a) at temperatures below 200°C in vacuum. It is found that this decomposition process is enhanced by the presence of isolated surface hydroxy groups. In the study of the thermal reaction of C2H5I on TiO2 in a closed IR cell without O2, ethylene is the only gas product detected. However in the presence of O2, in addition to ethylene, H2O, CO and CO2 are generated together with surface species probably derived from the adsorption of another product of acetaldehyde. In the photochemistry of C2H5I on TiO2 in forming surface formate and acetate, which are probably produced ia acetaldehyde intermediate, O2 plays an essential role. It is likely that the photoreaction is initiated by O2−, generated from photoelectron capture by adsorbed O2.

We report results on the photodissociation dynamics of the ethyl radical, C2H5. A beam of internally cold radicals is generated by supersonic jet flash pyrolysis of ethyl iodide or n-propylnitrite, respectively. Upon excitation into the A 2A13s Rydberg state ethyl dissociates, presumably on the ground-state surface, into ethylene and a hydrogen atom that is detected by time-resolved photoionization. By varying the excitation energy between 264 and 245 nm, microcanonical rates are obtained as a function of excitation energy. The reaction rates are on the order of 107 s−1, several orders of magnitude slower than expected from simple Rice–Ramsperger–Kassel–Marcus calculations.

The reaction of Li(CH2)4Li with [PtCl2(SEt2)2] yielded an unstable complex, probably [{Pt(CH2CH2CH2CH2)(μ-SEt2)}2], 1. Complex 1 reacts with bis(diphenylphosphino)methane, dppm, and forms [{Pt(CH2CH2CH2CH2)(μ-dppm)}2], 2. Complex 2 has been fully characterized using multinuclear NMR and FAB mass spectroscopies and shown to be fluxional in solution. The bright red platinacyclopentane complex [Pt(CH2CH2CH2CH2)(bpy)], 3, in which bpy=2,2′ bipyridyl, has been prepared by reaction of 1 with bpy. In a comparative kinetic study, it was demonstrated that at different temperatures, EtI reacted 2.2–2.6 times faster with the platina(II)cyclopentane complex 3 than with the dimethyl analogue [PtMe2(bpy)].

This review considers the role of closed-ring intermediates in chemistry, in general, and focuses on recent experimental and theoretical works that provide compelling evidence for a fivemembered ring intermediate in the gas phase. The reactions of oxygen atoms with ethyl iodide and larger alkyl iodides produce HOI and a corresponding ethylenic compound via attack of the oxygen atom at the iodine and closure of the five-membered ring between the oxygen and a hydrogen on the beta-carbon. Detailed results are gathered from infrared chemiluminescence and molecular beam scattering, as well as new kinetics and product yield experiments. The theoretical calculations fully support and characterize the novel reaction mechanism.

The rare (third) example of a triplet-state emission from a transient phototautomer is reported here for the case of the keto form of methyl salicylate. This molecule satisfies two of the three essential criteria predicted for observation of a triplet−singlet emission under conditions of excited-state intramolecular proton transfer: (1) published spectroscopic data confirm a keto tautomer triplet below the stable enol tautomer triplet, and (2) an easily accessible spectroscopic region. The third criterion, (3) noninterfering radiationless transitions, is not satisfied, and the T1‘ → S0‘ transition is not observed. This difficulty is overcome by external heavy-atom perturbation using ethyl iodide matrices at 77 K, with time-resolved spectroscopy. The tautomer phosphorescence is observed at λm = 560 nm, with a lifetime in the microsecond range. Internal heavy-atom perturbation is demonstrated to be effective in 3,5-dibromo and -diiodo methyl salicylates, the enhanced T1‘ → S0‘ emission occurring in the lat...

The photolysis of ethyl iodide in solid parahydrogen leads to the formation of ethyl radical, ethylene, and ethane upon near-UV illumination at about 5 K which are characterized by vibrational spectroscopy. The mechanism of the formation of the products is elucidated consistently. Two kinds of ethylene are discriminated spectroscopically which show distinctly different temporal behaviors during illumination and standing under dark. One of them is attributed to a complex between ethylene and iodine atom. The present work demonstrates that the cage effect is insignificant in the solid parahydrogen matrix, and a variety of elementary reactions of in situ photolysis can be studied in detail in contrast to conventional rare gas matrices.

The relative ligand donor strengths of 10 pyrazole-derived ligands has been determined with great accuracy, making use of the interdependence between the donor strength of the co-ligand and the (13)C NMR chemical shift of the (i)Pr(2)-bimy carbene signal in trans-[PdBr(2)((i)Pr(2)-bimy)L] complexes ((i)Pr(2)-bimy = 1,3-diisopropylbenzimidazolin-2-ylidene; L = pyrazole-derived ligand). Even subtle variations in the substitution pattern of the pyrazole backbone up to three bonds away from the coordinating nitrogen could be detected reliably using this methodology. Alkylation experiments conducted on the pyrazoles using electrophiles of varied reactivity (ethyl bromide, ethyl iodide, and trimethyloxonium tetrafluoroborate) served as a benchmark to rank the pyrazoles in three groups of gradually increasing nucleophilicity, which correlated well with their determined donor strength.

Phosphorescence spectra of nonphosphorescent or very weakly phosphorescent new UV absorbers, 2-methylphenyl cinnamate (MePC), 2-methylphenyl 4-methoxycinnamate (MePMC) and 2-methylphenyl 4-ethoxycinnamate (MePEC) have been observed by using external heavy atom effects of ethyl iodide in ethanol at 77 K. The lowest excited triplet (T(1)) energies of these new UV absorbers are lower than those of a widely used UV-A absorber, 4-tert-butyl-4'-methoxydibenzoylmethane (BM-DBM), in both keto and enol forms. The intermolecular triplet-triplet energy transfer from photolabile BM-DBM to MePMC was observed by measuring the time-resolved phosphorescence spectra. Electron paramagnetic resonance spectra have been observed for the T(1) states of these new UV absorbers in ethanol at 77 K by using benzophenone as a triplet sensitizer. The observed T(1) lifetimes, zero-field splitting (ZFS) parameters and molecular orbital calculations of the ZFS parameters suggest that T(1) states of these new UV absorbers posses mainly (3)ππ* character. The deactivation processes of the lowest excited singlet (S(1)) states are predominantly fluorescence and internal conversion to the ground (G) states in MePMC and MePEC, while the main deactivation process of the S(1) state of MePC is internal conversion to the G state. The molar absorption coefficients of MePMC and MePEC in the UV-A and UV-B regions are larger than that of most widely used UV-B absorber, octyl methoxycinnamate.

The interaction of ethyl iodide with Ni(100) surfaces has been examined by using thermal programmed desorption (TPD), X-ray photoelectron (XPS), and static secondary ion mass (SSIMS) spectroscopies. Ethyl iodide adsorbs molecularly on that surface below 100 K, and dissociates between 100 and 160 K to form ethyl species and iodine atoms. At low coverages the ethyl moieties decompose completely to form surface carbon and hydrogen atoms (which recombine and desorb at slightly above 300 K), but desorption of both ethylene and ethane is also observed at higher coverages. Ethylene forms via the elimination of a hydrogen atom from the beta position, and desorbs between 160 and 210 K depending on the initial coverage of ethyl iodide; ethane, on the other hand, is generated mostly by a direct recombination of ethyl species with hydrogen originating either from adsorption of background gases or from the β-hydride elimination reaction.

The effect of solvent polarity and external heavy atom (ethyl iodide) on the fluorescence properties of 2-tolouidino-6-naphthalene-sulphonate (TNS) and 1-anilino-8-naphthalene-sulphonate (ANS) have been studied. For ANS with rise in polarity, a monotonic decrease of fluorescence yield (α f ) and lifetime (τ f ) is observed while ethyl iodide was found to have negligible effect. For TNS at low polarity α f and τ f are found to increase with rise in polarity, while ethyl iodide causes a decrease in τ f . At high polarity [ E T (30) > 51] behaviour of TNS is more or less similar to that of ANS. It is proposed that polarity-dependent, twisted intramolecular charge transfer is the main non-radiative process for ANS at all polarities [ E T (30) = 36–63] and for TNS only at high polarity. At low polarity intersystem crossing is the main non-radiative pathway for TNS.

The chemistry and kinetics of singlet (pentafluorophenyl)nitrene were studied by chemical trapping and laser flash photolysis techniques. Photolysis of pentafluorophenyl azide in cyclohexane, benzene, diethylamine, pyridine, tetramethylethylene, tetrahydrofuran, dimethyl sulfoxide, and dimethyl sulfide forms adducts in fair to good yeilds. At ambient temperature singlet (pentafluorophenyl) nitrene is intercepted, and intersystem crossing to the lower energy triplet state is unimportant. Triplet nitrene chemistry can be achieved by benzoylbiphenyl photosensitization, the presence of methanol or ethyl iodide, or by lowering the reaction temperature below O°C

The chemisorption and thermal decomposition of ethyl iodide on Pt(111) have been studied by reflection-absorption infrared spectroscopy (RAIRS). At 100 K the chemisorption is molecular, and a change in adsorption geometry occurs from a flat to an upright orientation as the surface coverage is increased. Ethyl, ethylene and ethylidyne were identified at higher temperatures by IR spectrometry as decomposition products. As a consequence of the coverage-dependent orientation of the ethyl iodide molecules on the surface, different reaction mechanisms are operative at low and high coverages. At low coverages, ethyl iodide decomposes quantitatively between 150 and 200 K through a C-I bond breaking step followed by immediate dehydrogenation to ethylene. At saturation coverages, some ethylene formation competes with molecular desorption around 200 K (analogous to the low coverage decomposition), but additional ethylene is produced between 200 and 240 K in a slower, reversible reaction which involves the formation of ethyl species as stable intermediates. Ethylene further decomposes around 300 K to form ethylidyne.

The electron stimulated reactions of methyl iodide (MeI) adsorbed on and suspended within amorphous solid water (ice) were studied using a combination of postirradiation temperature programmed desorption and reflection absorption infrared spectroscopy. For MeI adsorbed on top of amorphous solid water (ice), electron beam irradiation is responsible for both structural and chemical transformations within the overlayer. Electron stimulated reactions of MeI result principally in the formation of methyl radicals and solvated iodide anions. The cross section for electron stimulated decomposition of MeI is comparable to the gas phase value and is only weakly dependent upon the local environment. For both adsorbed MeI and suspended MeI, reactions of methyl radicals within MeI clusters lead to the formation of ethane, ethyl iodide, and diiodomethane. In contrast, reactions between the products of methyl iodide and water dissociation are responsible for the formation of methanol and carbon dioxide. Methane, formed as a result of reactions between methyl radicals and either parent MeI molecules or hydrogen atoms, is also observed. The product distribution is found to depend on the film's initial chemical composition as well as the electron fluence. Results from this study highlight the similarities in the carbon-containing products formed when monohalomethanes coadsorbed withmore » amorphous solid water are irradiated by either electrons or photons.« less

Examination was made of the selectivity of 2-ethylation in the reaction of acetoacetate with ethyl iodide using the nonaqueous phase transfer reaction. Selectivity was high in the reaction using triethylbenzylammonium chloride as the phase transfer catalyst at room temperature. A suitable solvent was shown to be benzene.

The reaction of toluene with hydrogen atoms yielding benzyl and molecular hydrogen, C(6)H(5)CH(3) + H --C(6)H(5)CH(2) + H(2), was investigated using UV laser absorption of benzyl radicals at 266 nm in shock tube experiments. Test gas mixtures of toluene and ethyl iodide, an H-atom source, diluted in argon were heated in reflected shock waves to temperatures ranging from 1256 to 1667 K at total pressures around 1.7 bar. Measurement of laser absorption at 266 nm due to benzyl radicals allowed determination of the rate coefficient of the title reaction, reaction 1. A two-parameter best-fit Arrhenius expression for the rate determinations over the temperature range of these experiments is given by k(1)(T) = 1.33 x 10(15) exp(-14880 [cal/mol]/RT) [cm(3) mol(-1) s(-1)]. With the use of both the high-temperature shock tube measurements reported here and the rate coefficient determination of Ellis et al. (Ellis, C.; Scott, M. S.; Walker, R. W. Combust. Flame 2003, 132, 291) at 773 K the best-fit rate coefficient for reaction 1 can be described using a three-parameter Arrhenius expression by k(1)(T) = 6.47T (3.98) exp(-3384 [cal/mol]/RT) [cm(3) mol(-1) s(-1)].

The lowest triplet state of tris(8-hydroxyquinoline)aluminium(III) (Alq3) has been prepared by pulse radiolysis/energy transfer from appropriate donors in benzene solutions and has an absorption maximum around 510 nm with a lifetime of about 50 mus. It is quenched by molecular oxygen, leading to singlet oxygen formation. From flash photolysis and singlet oxygen formation measurements, a quantum yield of triplet formation of 0.24 was determined for direct photolysis of the complex. A value of 2.10 +/- 0.10 eV was determined for the energy of the lowest triplet state by energy transfer studies and was confirmed by phosphorescence measurements on Alq3, either in the heavy atom solvent ethyl iodide or photosensitized by benzophenone in benzene. Dexter (exchange) energy transfer was observed from triplet Alq3 to platinum(II) octaethylporphyrin.

The solution-phase photodimerization of acephenanthrylene (1) in cyclohexane, chloroform, dibromomethane, and ethyl iodide with visible light (lambda = 419 nm) occurs to form cis (2) and trans (3) photodimers in ratios that vary with the solvent and with the presence or absence of oxygen. The photodimerization exhibits a significant heavy atom effect and also is sensitive to selective quenching by dissolved oxygen, in which only cis stereoisomers are produced. Irradiation of the dimers (lambda = 254 nm) shows that the trans dimers cleave more rapidly than the cis dimers. This is attributed to stabilization of the excited state in the cis dimers.

We have used crossed molecular beams to study the dynamics of chemiionization S N 2 reactions of the type RX+R' 3 -N→RR' 3 N + +X − , where RX is an alkyl halide and R' 3 N is a nucleophile. We have seen reaction between methyl iodide, ethyl iodide, and n-propyl iodide with quinuclidine and between methyl iodide and pyridine and tri-n-propylamine. The reactive cross sections have a threshold between 4.4 and 6.0 eV depending on the system. They rise rapidly above the threshold and then level off at higher energies showing no dependence on the vibrational energy of the nucleophile

The RhIII complex [(PNP)Rh(CN)(CH3)][I] 5, obtained by oxidative addition of methyl iodide to [(PNP)Rh(CN)] 2, reacts selectively in two pathways: In aprotic solvents C-I reductive elimination of methyl iodide followed by its electrophilic attack on the cyano ligand takes place, giving the methyl isonitrile RhI complex [(PNP)Rh(CNCH3)][I] 3, while in protic solvents C-C reductive elimination of acetonitrile takes place forming an iodo RhI complex [(PNP)RhI] 9. Reaction of 2 with ethyl iodide in aprotic solvents gave the corresponding isonitrile complex, while in protic solvents no reactivity was observed. The selectivity of this reaction is likely due to a hydrogen bond between the cyano ligand and the protic solvent, as observed by X-ray diffraction, which retards electrophilic attack on this ligand.

Alkyl radicals play a key role as reaction intermediates for many surface processes such as catalytic hydrocarbon synthesis or the degradation of coatings and lubricants. Their properties and reactivity on surfaces, however, are still poorly understood because simple synthetic routes to prepare them have not yet been developed and their identification among other hydrocarbon fragments requires highly specific and sensitive techniques. Using alkyl halides as precursors, we have prepared alkyl species on single crystal surfaces in an ultrahigh vacuum (UHV) environment and studied their surface chemistry by a combination of different surface science techniques. In this report we present an IR spectroscopic study on the formation of ethyl species from ethyl iodide and their decomposition on a Pt(111) surface.

Through the examination of empirical correlations involving activation parameters for nucleophilic substitution of methyl iodide and of ethyl iodide, nucleophiles have been classified into three series: (1) nucleophiles with two equivalent reaction sites, (2) nucleophiles with a chlorine atom in the para-position, and (3) nucleophiles with a single reaction site. Three types of partial desolvation processes accompanying activation have been deduced on the basis of these classifications. A major factor determining the relative reactivity of methyl iodide to ethyl iodide in the substitution reaction of an anionic nucleophile having a single reaction site in acetonitrile (kMeI/kEtI) is suggested to be partial desolvation around the nucleophilic center on going from reactant to transition-state.

The reaction of hydroxyl radicals with n-alkyl iodides and 1,n-diiodoalkanes (n = 1 to 5) has been studied. Nanosecond pulse radiolysis experiments have been performed to find out the stability constants of the dimer radical cations of the alkyl iodides in acid aqueous solution. The bond enthalpy and entropy for the intermolecular two-centre three-electron bond in ethyl iodide and intramolecular two-centre three-electron bond in 1,4-diiodobutane are determined by means of temperature dependent kinetic studies. Quantum chemical computations have been performed to study the reaction of OH radicals with n-alkyl iodides and 1,n-diiodoalkanes (n = 1 to 5) theoretically. The semiempirical quantum chemical calculation (UHF/AM1) shows that the reaction of hydroxyl radicals (OH) with ethyl iodide (CH3CH2I) and 1,2-diiodoethane (ICH2CH2I) leads to the formation of three electron bonded adducts (RI∴OH) which are bound by ∼10 kcal mol−1. The inter- and intramolecular two-centre three-electron bond strengths in the respective radical cations are also calculated and good correlation is observed between experimental and calculated results.

Benzophenone has been used as a triplet energy donor to sensitize the production of the triplet state of the oxazine, 2,7-bis (diethylamino)-phenazoxonium chloride, in dilute acetonitrile solution. This enabled the spectrum, lifetime (14.5 µs) and absorption coefficient (1.6 × 104 dm3 mol–1 cm–1 at 830 nm) of the triplet oxazine to be determined. The quantum yield of triplet–state production for this oxazine by direct excitation was shown to be < 0.01 but addition of ethyl iodide quenched the oxazine fluorescence by induced intersystem crossing as confirmed in nanosecond laser photolysis experiments in which the oxazine triplet-state transient absorption spectrum was detected in the presence but not in the absence of ethyl iodide. Quenching of triplet benzophenone by oxazine was investigated by means of steady-state luminescence and also transient emission and absorption techniques in deaerated acetonitrile solution at room temperature. A rate constant for triplet-triplet energy transfer of 0.9 ± 0.1 × 1010 dm3 mol–1 s–1 was obtained. Delayed fluorescence was detected, which like the prompt fluorescence exhibits a slight red shift of the maximum owing to increasing reabsorption when the concentration of oxazine increases. The mechanism for this delayed fluorescence is established as involving an interaction between the triplet state of the donor (benzophenone) and the triplet state of the oxazine, i.e. mixed triplet–triplet annihilation.

(E)-β-ionone oximc ethyl ether [(E, E)-4] upon direct irradiation with λ either254or 313 nm yields the geometrical isomer (E, Z)-4 and (Z)-retro-γ-ionone oxime ethyl ether (Z,E)-5 as the sole primary products, illustrating (E)-(Z) isomerization (φ313 =0.49) and a 1, 5-hydrogen shift (φ313 =0.15) respectively. From studies with triplet photosensitizers and with ethyl iodide (to enhance the singlet-triplet intersystem crossing) it is concluded that these two products in the direct irradiation result only from the singlet excited state, and that the inter-system crossing quantum yield is relatively low. Upon prolonged irradiation of (E,E)-4 with λ 313 nm the eventual products are (Z,E)-5 and (Z,Z)-5, whereas with λ 254 nm they are (E,E)-5 and [(Z,E)-5 and/or (E,Z)-5]. Upon triplet photosensitization (E,E)-4 undergoes only (E)-(Z) isomerization, leading to a mixture of all the four geometrical isomers of4. From the dependence of the geometrical isomer distribution in the photostationary state on the triplet energy of the sensitizer the triplet energies of (E,E)-4, (E, Z)-4, (Z, E)-4, and (Z, Z)-4 have been determined to be ca 55, kcal mol respectively.

2- N,N -dimethylamino-1,3-indanedione (DMAI) undergoes demethylation during photolysis (λ > 290 nm), producing 2- N -methylamino-1,3-indanedione (MAI) under conditions of direct or sensitized reaction. Ferrocene successfully quenches demethylation, while ethyl iodide accelerates the reaction rate. The yield and the rate of formation of MAI strongly depend on the reaction conditions, mainly on the solvent, the concentration of DMAI and the presence of an electron acceptor (substituted nitrobenzene). The UV, IR and NMR spectra support the donor—acceptor intramolecular interpretation in the ground state of DMAI and MAI.

Electrophilic attack at both sulphur atoms in the complex Pt(π-CS2)(Ph3P)2 by methyl or ethyl iodide results initially in the formation of a cationic carbene complex [PtI(Ph3P)2(C(SR)2)]11 at 25°C. Subsequent reaction under reflux gives a neutral carbene complex with resultant loss of phosphine ligand.

The triplet state of acenaphthylene has been examined by nanosecond laser flash photolysis using sensitization and heavy atom perturbation techniques. Although acenaphthylene does not form any observable triplet upon direct flash excitation, a transient with microsecond lifetime ({lambda}{sub max} = 315 nm) is observable when a solution of the sample is excited by sensitizers (benzophenone, thioxanthone, benzil). This transient is ascribed to the triplet of acenaphthylene on the basis of its quenching behavior toward oxygen, ferrocene, azulene, and {beta}-carotene. Quantitative data concerning the triplet-triplet absorption and quenching constants are presented. The triplet energy is estimated to lie between 46 and 47 kcal/mol. The triplet can also be produced by direct excitation in solvents containing heavy atoms (ethyl bromide, ethyl iodide). The triplet yield is found to increase with an increase of the amount of the heavy atom containing solvent. No saturation limit is obtained. These facts together with the effect of heavy atoms on the T{sub 1} {yields} S{sub 0} process allow the differing behavior of ethyl bromide and ethyl iodide on the photodimerization process of acenaphthylene to be explained. Triplet-state parameters (extinction coefficient and triplet yield) have been estimated in these solvents by the energy-transfer technique and actinometry.

Addition of singlet quencher molecules like bromobenzene, ethyl iodide, and dimethyl mercury to degassed solutions of anthracene and phenanthrene in EPA at 77°K leads not only to a decrease in fluorescence measured in small glassy samples, but also to an abnormal decrease in the amount of triplet state absorption observed upon flash excitation of these solutions in large volume-containing low temperature cells. It is suggested that great care should be taken in order to be sure of the perfect homogeneity in the distribution of the quencher molecules throughout the sample investigated at low temperature. It is shown that the random distribution can hardly be attained, in view of the high concentration of quenching molecules needed in these experiments, when the cooling process is slow as is the case in a large volume-containing low temperature cell.

The fluorescence decay of trans (2-anthryl)ethylenes containing phenyl, 2-naphthyl, and 2-thienyl groups as the second substituent is biexponential. The decay profiles in benzene are analyzable in terms of two lifetimes in the ranges 6-11 and 17-30 ns, respectively. The complex decay behavior as well as the observation of excitation wavelength dependence of fluorescence spectra, quantum yields, exciplex emission maxima, and fluorescence quenching constants (with oxygen, ethyl iodide (EtI), and N,N-dimethylaniline (DMA) as quenchers) is attributed to the existence of quasi-energetic rotamers in solutions of (2-anthryl)ethylenes. Exciplex lifetimes and transient absorption spectra of radical anions obtained by nanosecond laser flash photolysis in the presence of N,N-dimethylaniline are also presented. 17 references, 6 figures, 6 tables.