Room Temperature In Solvents Research Articles

An NMR and quantum mechanical investigation of solvent effects on conformational equilibria of butanedinitrile.

Vicinal proton-proton NMR couplings and ab initio quantum mechanics have been used to investigate solvent effects on conformational equilibria of butanedinitrile. The trans and gauche conformations are about equally favored at room temperature in solvents of low dielectric constant while the equilibrium is essentially the statistical proportions of one-third trans and two-thirds gauche in water with a high dielectric constant. The coupling assignments were confirmed with the aid of stereospecific deuterium-labeled (R,R or S,S)-1,2-dideuteriobutanedinitrile. The calculations support the observed trends. Similar results were observed for 1,2-dibromo- and dichloroethanes.

High resolution spectroscopic studies of 1-(1-naphthyl)ethylamine in S 0 and S 1: exploring the dependence of circular dichroism on conformational structure

Rotationally resolved spectra of gas-phase samples of 1-(1-naphthyl)-ethylamine (NEA) and amine deuterated forms have been obtained in the microwave and ultraviolet regions, with the isotopomers initially prepared in their zero-point vibrational levels by cooling in pulsed jet and molecular beam supersonic expansions. A single parameter set that includes inertial parameters and 14N nuclear quadrupole constants has accounted for nearly all transitions observed in the Fourier-transform microwave spectrum at 2 K and indicates the presence of only one geometrical isomer in the jet-cooled expansion. The rotational constants, dipole moment orientation, and the amine hydrogen atom positions have been used to identify the conformation of the attached chiral group from among nine possible isomeric forms. The S 1 rotational constants and electronic transition moment orientation have been obtained from high resolution molecular beam data of the band origin at 31771.56(2) cm −1. Excited state “gas phase” predictions from ab initio theory at the CIS/6-31G(d,p) and CIS/6-311 + G(d) levels are compared with the observed S 1 results and with circular dichroism (CD) data obtained for solution phase samples of ( S)-NEA in cyclohexane. Distinguishing spectral features are found in the calculated CD spectra of the three lowest energy conformers arising from rotation about the C–CH(NH 2)CH 3 bond, all of which are thermally populated at room temperature. While the predictions at both levels are in fair agreement with the observed gas phase results, CIS/6-31G(d,p) theory is found to be inadequate to model the condensed phase CD spectrum. In constrast, the calculated spectrum of the equilibrium mixture of conformers at the CIS/6-311 + G(d) level is in good qualitative agreement with the observed CD results and indicates the importance of diffuse functions for the accurate prediction of chiroptical properties of NEA. The most noteworthy exception is the predicted rotatory strength of the S 1 origin, which is overestimated by more than 10-fold. Possible reasons for this discrepancy with experiment include a reversal of S 1(L b) and S 2(L a) states from the absence of electron correlation and/or the neglect of room-temperature solvent effects. These results provide for rigorous benchmark tests of theoretical models and further elucidate the importance of the conformational structure for determinations of absolute stereochemistry from CD spectra.

A Cheap, Catalytic, Scalable, and Environmentally Benign Method for Alkene Epoxidations

A Cheap, Catalytic, Scalable, and Environmentally Benign Method for Alkene Epoxidations

The photochemical reaction of 1,1-dicyano-3-phenylbut-1-ene. Simultaneous occurrence of pi-methane and di-pi-methane rearrangements

The direct photolysis of 1,1-dicyano-3-phenylbut-1-ene (3-MDCN) was investigated at room temperature in solvents of different polarities (hexane, dichloromethane and acetonitrile). Cyclopropanes arising from both the di-p-methane and p-methane (1,2-H migration) processes were obtained as photoproducts. The structures of the products were elucidated by 1H-NMR, GC/MS, IR and chromatography. Relative quantum yield determination and GC analysis of sequential irradiations gave evidence that: i) no secondary reactions occur, even at high conversions; ii) the di-p-methane rearrangement is significantly more affected by the solvent variation than the p-methane reaction. Photosensitization with acetophenone or acetone did not yield any observable products. The existence of the simultaneous mechanisms and the observed effects were considered as evidence of a possible differentiation between localized and delocalized excitation on the excited state surface.

Preparations of Nickel, Cobalt, and Iron Nanoparticles through the Rapid Expansion of Supercritical Fluid Solutions (RESS) and Chemical Reduction

A method based on the rapid expansion of supercritical fluid solutions (RESS) coupled with chemical reduction was developed to produce nickel, cobalt, iron, and iron oxide nanoparticles of reasonably narrow size distributions. Under the protection of a polymer stabilization agent, the largely amorphous metal nanoparticles form stable suspensions in room-temperature solvents.

Solvent dynamics derived from optical Kerr effect, dielectric dispersion, and time-resolved stokes shift measurements: an empirical comparison

Abstract Data from the optical Kerr effect, time-resolved Stokes shift, and dielectric dispersion experiments on 21 common room temperature solvents are collected and compared. The correlation functions of the collective variables (polarizability, solvation energy, and dipole moment fluctations) responsible for each observable are first extracted from the experimental data and compared directly. In any given solvent the decay times of these various correlation functions are often vastly different. Such differences mainly result from the fact that intermolecular correlations affect the collective variables sampled by each technique in a different manner. To compare dynamics at a more basic level, power law relations are applied in an attempt to account for these correlations and to examine the extent to which the collective dynamics in these three experiments can be viewed as arising from the same underlying single-particle motions (primarily rotations). The Stokes shift and dielectric correlation functions can be reasonably inter-related in this manner, but the polarizability anisotropy monitored with Kerr experiments cannot be as simply related to the former two dynamics, probably due to the importance of collision-induced effects in the latter case.

All-Carbon Polymers (Polyfullerenes) from Photochemical Reactions of Fullerene Clusters in Room-Temperature Solvent Mixtures

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTAll-Carbon Polymers (Polyfullerenes) from Photochemical Reactions of Fullerene Clusters in Room-Temperature Solvent MixturesYa-Ping Sun, Bin Ma, Christopher E. Bunker, and Bing LiuCite this: J. Am. Chem. Soc. 1995, 117, 51, 12705–12711Publication Date (Print):December 1, 1995Publication History Published online1 May 2002Published inissue 1 December 1995https://doi.org/10.1021/ja00156a007RIGHTS & PERMISSIONSArticle Views703Altmetric-Citations129LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (832 KB) Get e-Alerts Get e-Alerts

Fluorescence quantum yields of α, ω-diphenylpolyenes

Absolute fluorescence quantum yields of trans-stilbene and all- trans α, ω-diphenylpolyenes with the polyene double-bond number ( n) from two to six have been determined in a room-temperature solvent. The 1 1Bu-fluorescence yield measured as a function of the polyene chain length shows a maximum for n = 2, while the 2 1Ag-fluorescence yield shows a maximum for n = 3, and both yields decrease with further increase of n. The observed quantum yield behavior is discussed briefly.

Formation and Properties of C70 Solidlike Species in Room-Temperature Solutions

Recently, studies of fullerene molecules, especially C{sub 60} and C{sub 70}, have attracted great attention. Many fascinating and sometimes unusual properties, such as formation of complexes between fullerene and solvent molecules in the solid state and significant discrepancies between calculated and experimental electronic transition probabilities in both C{sub 60} and C{sub 70}, have been observed. It was reported that C{sub 70} undergoes anomalous solvatochromic changes in room-temperature solvent mixtures. The characteristic phenomena were attributed to the formation of new absorbing species. In this communication the authors report a spectroscopic study of the characteristic solvatochromic behavior of C{sub 70} in room-temperature mixtures of toluene and acetonitrile. It will be shown that the formation of the new absorbing species of C{sub 70} responsible for the anomalous solvatochromism depends not only on the concentration of C{sub 70} and the composition of the solvent mixtures but also on the way in which the solvent mixtures are prepared. Microstructures of the new absorbing species will be discussed. 11 refs., 2 figs.

OF ASPHALT FRACTIONS OBTAINED BY SUPERCRITICAL AND SOLVENT EXTRACTION

ABSTRACT Supercritical extraction with n-pentane was used to separate asphalt into distinct fractions having different physical and compositional properties. A pilot-scale supercritical unit capable of processing thirty kilograms of asphalt per day was designed and fabricated specifically for asphalt fractionation. The operation and design of the unit is similar to the ROSE (Residuum Oil Supercritical Extraction) process of Keer-McGee. This unit was used to separate asphalt into five different fractions ranging from soft greases to asphaltene-like solids. Supplemental room-temperature solvent fractionation of the hardest of these five using binary pentane/cyclohexane mixtures produces, a total of eight fractions. A variety of analyses provide chemical and physical ctauracterization of the fractions. These include: (1) Corbett Fractionation, (2) FT-IR spectroscopy, (3) size exclusion chromatography, (4) nickel and vanadium atomic absorption, and (5) viscosity

Solvent effect on radiative and non-radiative transitions in all-trans-1,6-diphenylhexatriene

The spectral and luminescent properties of all-rans-1,6-diphenyl-1,3,5-hexatriene (DPH) were studied at room temperature in solvents with various refractive indices (1.33 < n < 1.63) and dielectric constants (1.9 < ϵ < 37.4). The maximum fluorescence quantum yield of DPH (φo = 0.85) was measured in quinoline, and the lowest quantum yield was observed in acetonitrile (φo = 0.17). The experimentally determined values of the fluorescence and non-radiative deactivation probabilities (kf1 and kd) of the lowest singlet excited state S1 are 2.9 × 108 s−1 (quinoline) and 2.0 × 108 s−1 (acetonitrile). The fluorescence from the S1(21A*g) state (the transition to which from the ground state S0(11Ag) is symmetry forbidden) is due to vibronic mixing with a higher S2(11B*u) state, which participates in the strongly allowed electron transition S2 ← S0. The matrix element of the vibronic interaction between the S1 and S2 states (V12) is 840 cm−1.Non-radiative transitions from the S1 state are essentially dependent on the solvent polarity. There is a linear dependence of ln kd on the empirical parameter ET(30), which characterizes the solvent polarity. The polar solvent quenches the fluorescence of DPH by inducing non-radiative transitions through intermediate twisted structures possessing dipole moments of a few debyes.

Thermoreversible gelation of solutions of vinyl polymers

AbstractThe thermoreversible gelation of solutions of isotactic poly(methyl methacrylate) is investigated. Amorphous gels can be prepared in l‐butanol by a combination of a liquid‐liquid demixing with an upper critical demixing temperature and a glass transition. Annealing of the demixed solutions above their glass transition temperature TG, results in the formation of a crystalline gel. In oxylene, crystalline gels are formed by a liquid‐liquid demixing with an lower critical demixing temperature and an annealing at room temperature. Very fast gelation is observed to occur far below room temperature in solvents like 2‐butanone.

Evaluation of the coupling constants between the 2 1A g (S 1) and 1 1B u (S 2) states for diphenylhexatriene and diphenyloctatetraene

The S 1 (2 1A g) and S 2 (1 1B u) fluorescence intensities for diphenylhexatriene and diphenyloctatetraene in room temperature solvents with different polarizabilities have been analyzed quantitatively with a refined treatment. The coupling constants between the S 1 and S 2 states have been evaluated to be 140 and 90 cm −1 for diphenylhexatriene and diphenyloctatetraene, respectively. These values are compared with those obtained from the fluorescence quantum yields and lifetimes.

Geminate recombination and relaxation of molecular iodine

Picosecond absorption kinetics of I2 in several room temperature solvents have been obtained. Probe wavelengths of 500, 580, and 640 nm were used following excitation with 30 ps pulses of 532, 630, or 683 nm light. The results indicate that population of the electronically excited A(3π1u) and A′(3π2u) states occurs rapidly (&amp;lt;30 ps) following dissociation. Analysis of transient absorption intensities indicates that repopulation of the ground electronic state requires about 30–50 ps. We propose that the difference in population times may be understood in terms of trapping in weakly bound electronic states (perhaps 3π0−u) which relax to populate the ground electronic state, or in terms of slow atom recombination into the ground state. The results show that for I2 in CCl4, X state repopulation and vibrational relaxation occur on roughly comparable time scales. The results also show that the recombination dynamics are determined primarily by the nature of dissociative state, not the recoil energy. Vibrational relaxation rates through the ground state mainfold were interpreted in terms of vibration to translation energy transfer as given by the Schwartz, Slawsky, Herzfeld theory. This was found to work quite well for weakly interacting solvents such as CFCl3, C2Cl3F3, and CCl4. This simple theory breaks down for more strongly interacting solvents such as CH2Cl2 and CHCl3.

Electrochemical and spectroscopic studies of neptunium in the aluminum chloride-1-n-butylpyridinium chloride melt at 40.degree.C

The chemistry of neptunium in acidic and basic AlCl/sub 3/-1-n-butylpyridinium chloride melts at 40/sup 0/C has been investigated by means of electrochemical and spectral techniques. In acidic as well as in basic melts, the reduction of Np(IV) to Np(III) at glassy-carbon electrodes is quasi-reversible. Indirect measurements of the formal potential and spectroscopic results on the Np(IV)-Np(III) system as a function of the acidity indicate that Np(III) and Np(IV) exist as NpCl/sub 6//sup 3 -/ and NpCl/sub 6//sup 2 -/ and solvated Np/sup 3 +/ and NpCl/sub x//sup (4-x)+/ (with 3 greater than or equal to x greater than or equal to 1), respectively, in basic and acidic melts. The apparent rate constant K/sup 0/' has been measured on the basic and acidic sites. It depends on the melt acidity only in the latter melts. The Nugent linearization method has been applied to the standard potentials of Np(IV)-Np(III) and U(IV)-U(III) in 2:1 melts. A comparison with the results obtained from other room-temperature solvents shows, as already found with lanthanides, that the acidic melt is a very weak solvating medium.

Definition and use of an Oxoacidity Function ω for the Comparison of Acidity Levels at Iooo K of Some Chloride Melts Involved in Electrometalluric Processes

Abstract Many molten chlorides are used in industry for the electrolytic production of metals. In such processes, the oxoacidity level is crucial with respect to the cost and the yield. The determination and the comparison of the oxoacidic properties of chloride melts then appears to be of practical interest. Such a comaprison is described applying a similar process to that used for pH scales in room temperature solvents. Purification processes of such melts are then explained quantitatively.

A 119Sn Mössbauer study of the thermal degradation of organotin stabilisers in PVC

119mSn Mössbauer studies of the thermal degradation of PVC containing the stabilisers dibutyltinbis (isooctylthioglycollate) (1.2% by weight of the polymer), dioctyltinbis (isooctylthioglycollate (4% by weight of the polymer) and dibutyltinbis (isooctylmaleate) (2% by weight of the polymer) indicate that in each case the stabiliser is converted into the dialkylmonochlorotin ester R2SnCl(X) (X  SCH2CO2C8H17 or O2C.CH  CHCO2C8H17), and not into the dialkyltin dichloride, R2SnCl2, as recently suggested by other workers. Comparison of the Mössbauer data for organotin-stabilised PVC samples prepared by both hot-milling and room temperature solvent casting processes indicates that there is little degradation of the polymer (and stabiliser) during the initial hot-milling process.

TRIARYLMETHANE DYE PHOTOCHROMISM: SPECTROSCOPY AND PHOTOCHEMISTRY OF BRILLIANT GREEN LEUCOCYANIDE

Abstract— The spectroscopy and photochemistry of brilliant green leucocyanide 1a were investigated at room and low temperature, in polar and nonpolar solvents. At 77 K, 1a exhibits solvent independent absorption, fluorescence (φf= 0.1), and phosphorescence (φp= 0.5). Solvent effects become important at room temperature; in polar solvents, φf, decreases and photodissociation yielding brilliant green dye 3 occurs [φdis,(EtOH) ˜0.91. Dye formation and 1a fluorescence can be quenched by 0.1 M crotononitrile. Attempts to sensitize dye formation with triplet sensitizers were unsuccessful. The spectroscopy of 3 was also examined.

Cation Effects on the Fluorescent Solution Spectra of Europium Tetrakis Benzoyltrifluoroacetonate Salts

LASER action in acetonitrile solution has now been reported for a number of salts of europium tetrakis benzoyltrifluoroacetonate (Eu(BTFA)4)− at room temperatures1–3. This communication presents the results of a spectroscopic investigation of several Eu(BTFA)−4 salts at room temperature in solvents of low polarity. Correlations between the spectra and the nature of the cation are also considered.