Liquid alkanes

Gehrke C, Mohrschladt R, Schroeder J, Troe J and Vdhringer P 1991 Photoisomerization dynamics of diphenylbutadiene in compressed liquid alkanes and in solid environment Chem. Phys. 152 45... 

Ryckaert J-P and A Bellemans 1978. Molecular Dynamics of Liquid Alkanes, Faraday Discussions 20 95-10(... 

Extensive discussions have focused on the conformation of the alkyl chains in the interior ". It has been has demonstrated that the alkyl chains of micellised surfactant are not fully extended. Starting from the headgroup, the first two or three carbon-carbon bonds are usually trans, whereas gauche conformations are likely to be encountered near the centre of tlie chain ". As a result, the methyl termini of the surfactant molecules can be located near the surface of the micelle, and have even been suggested to be able to protrude into the aqueous phase "". They are definitely not all gathered in the centre of tire micelle as is often suggested in pictorial representations. NMR studies have indicated that the hydrocarbon chains in a micelle are highly mobile, comparable to the mobility of a liquid alkane ... 

Higher alkanes having unbranched carbon chains are like butane most stable m then-all anti conformations The energy difference between gauche and anti conformations is similar to that of butane and appreciable quantities of the gauche conformation are pres ent m liquid alkanes at 25°C In depicting the conformations of higher alkanes it is often more helpful to look at them from the side rather than end on as m a Newman projec tion Viewed from this perspective the most stable conformations of pentane and hexane... 

Refinery alkylation Liquid alkanes (e.g., isobutane) Gaseous alkenes (e.g., 1-butene) HF or H2SO4... 

However, the assumption of molecule orientation normal to the surface is not convincing enough for this author, and it does not consist well with the results of the molecular d5mamics simulations for the alkane confined between solid walls. An example in Fig. 3 shows that the chain molecules near the wall are found mostly lying parallel, instead of normal, to the wall [6]. This means that the attractions between lubricant molecules and solid wall may readily exceed the inter-molecule forces that are supposed to hold the molecules in the normal direction. Results in Fig. 3 were obtained from simulations for liquid alkane with nonpolar molecules, but similar phenomenon was observed in computer simulations for the functional lubricant PFPE (per-fluoropolyether) adsorbed on a solid substrate [7], confirming that molecules near a solid wall lie parallel to the surface. 

The relationship between Ti and T2 was examined for a number of liquid alkanes and crude oils [15]. It was concluded that there is no difference for light oils, apparently because light oils satisfy the fast-motion condition (the correlation time is less than the Larmor period). However, viscous oils do not satisfy this condition as the departure between Tx and T2 correlates with an increasing viscosity and Larmor frequency. 

The nitroxide radical (from processes 5 and 6 and attack by other radicals on the parent piperidine) is found in photo-oxidizing PPH samples in concentrations of M. x 10 M (initial piperidine level 5 x 10-3M) up to the embrittlement point of the PPH film (7.). Nitroxides are well known to scavenge carbon centered radicals (but not peroxyl radicals) in both polymers and liquid alkanes (reaction 7) (10, 8). In the liquid phase k7 is... 

Liquid alkanes and cycloalkanes are soluble in one another, and they generally dissolve in solvents of low polarity. 

Huber, G. W. Chheda, J. N. Barrett, C. J. Dumesic, J. A., Production of liquid alkanes by aqueous-phase processing of biomass-derived carbohydrates. Science 2005, 308(5727), 1446-1450. 

From the above one might be tempted to attribute ultrasonically enhanced chemical reactivity mainly to the mechanical effects of sonication. However this cannot be the whole reason for the effect of ultrasound on reactivity because there are a variety of homogeneous reactions which are also affected by ultrasonic irradiation. How, for example, can we explain the way in which power ultrasound can cause the emission of light from sonicated water (sonoluminescence), the fragmentation of liquid alkanes, the liberation of iodine from aqueous potassium iodide or the acceleration of homogeneous solvolysis reactions ... 

Alkene Solubility at room temperature/ppm Calculated solubility of liquid alkane at 25 °C/ppm... 

Early pulse radiolysis studies of alkanes at room temperature showed that the solvated electron absorption begins around 1 pm and increases with increasing wavelength to 1.6 pm for -hexane, cyclohexane, and 2-methylbutane [77]. More complete spectra for three liquid alkanes are shown in Fig. 4. The spectrum for methylcyclohexane at 295 K extends to 4 pm and shows a peak at 3.25 pm [78]. At the maximum, the extinction coefScient is 2.8 x 10 cm The spectrum for 3-methyloctane at 127 K, shown in Fig. 4, peaks around 2 pm. The peak for methylcyclohexane is also at 2 pm at lower temperature. Recently, the absorption spectra of solvated electrons in 2-methylpentane, 3-methylpentane, cA-decalin, and methylcyclohexane glasses have been measured accurately at 77 K [80]. For these alkanes, the maxima occur at 1.8 pm, where the extinction coefScient is 2.7 x 10 cm. ... 

Photochemistry and Radiation Chemistry of Liquid Alkanes Formation and Decay of Low-Energy Excited States... 

Most publications dealing with the photodecomposition of alkanes discuss the processes in the gas phase several comprehensive works have already been published in this field [14-17]. In the present work, we summarize the results of liquid phase photolytic studies and compare them with those obtained in radiolysis. An early review on liquid alkane photochemistry was published in Ref. 18, a brief overview of the field was given in Ref. 19. 

According to precise photoconductivity measurements, the ionization onset, which is usually taken as the ionization potential, is ca. 1.5 eV lower in liquid alkanes than in the gas phase [38]. The ionization potentials in liquid and gas phases (7/ and Ig, respectively) are related by the equation ... 

Passing through the threshold energy for ionization of liquid alkanes, the quantum yield of ionization, [Pg.368]

Table 2 Si Lifetimes (nsec) of Selected Liquid Alkanes at Room Temperature Determined in Steady-State Excited State Quenching or in Transient Fluorescence and Absorption Studies...

Table 5 Quantum Yield of Alkane Elimination in the Photolysis of Some Liquid Alkanes...

It would be elegant to finish the part on photophysics and photochemistry of liquid alkanes by giving a picture that unifies the temperature- and energy-dependence results obtained in fluorescence and photodecomposition studies. However, the spectroscopic information available for alkane molecules is not sufficient to identify the exact excited states involved in the radiative and nonradiative processes [55]. Because of the lack of information, there are different views on the positions and identities of excited states involved [52,55,83,121,122]. 

The fluorescence of liquid alkanes is supposed to originate entirely from the relaxed Si state. Walter and Lipsky [154], by measuring the fluorescence yields of alkane solutions irradiated with 165 nm photons or Kr beta particles ( niax = 0-67 MeV) relative to benzene fluorescence, determined the following yields 2.3-dimethylbutane G Si) < 1.3, cyclohexane 1.4-1.7, methylcyclohexane 1.9-2.2, dodecane 3.3-3.9, hexadecane 3.3-3.9, d5-decalin 3.4, and bicyclohexyl 3.5. After reinvestigating the intrinsic quantum yield of cyclohexane fluorescence, Choi et al. published G(5 i) = 1.45 for this alkane in Ref. 155. For tra 5-decalin a G Si) value of 2.8-3.1 has been accepted [65,128,132]. The uncertainties in the values reflect the uncertainties in the intrinsic fluorescence quantum yields. 

Mayer, J., Szadkowska-Nicze, M. Excited states in liquid alkanes and related polymers. In Properties and Reactions of Radiation Induced Transient Species, Selected Topics Mayer, J., Ed. Polish Scientific Publishers Warsawa, 1999 77 pp. 

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