Odd Alkanes Research Articles

PM2.5-bound Inorganic and Nonpolar Organic Compounds in Chuncheon, Korea

In this study, major chemical components of PM2.5 including nitrate, sulfate, organic carbon (OC), and elemental carbon (EC) were measured in Chuncheon, South Korea in May–June, 2021. Average PM2.5 concentration was 16.4±9.7 µg m−3, and OC was the largest contributor of PM2.5 mass concentration. High concentration episodes (HCEs), defined when PM2.5 concentration exceeded 30 µg m−3, were caused by Asian dust, secondary inorganic aerosol (SIA) formation, and primary OC emission. NH4+ was determined to be a limiting factor for SIA formation based on neutralization ratio. There was statistically significant correlation between n-alkanes and PM2.5, and odd alkanes including C27, C29, and C31, which are generally emitted from biogenic sources, were abundant species, suggesting the importance of natural sources over fossil fuel combustion. Polycyclic aromatic hydrocarbons (PAHs) concentrations were significantly lower than those measured at the same sampling site in 2014–2015. Based on the diagnostic ratios of PAHs, vehicular emission, rather than solid fuel emission, were significant for PAHs. Detailed characterization of chemical composition of PM2.5 reported in this study can be of great help in establishing an appropriate abatement policy to reduce PM2.5 concentrations.

Anthropogenic and biogenic hydrocarbons in soils and vegetation from the South Shetland Islands (Antarctica)

Two Antarctic expeditions (in 2009 and 2011) were carried out to assess the local and remote anthropogenic sources of aliphatic and aromatic hydrocarbons, as well as potential biogenic hydrocarbons. Polycyclic aromatic hydrocarbons (PAHs), n-alkanes, biomarkers such as phytane (Ph) and pristane (Pr), and the aliphatic unresolved complex mixture (UCM), were analysed in soil and vegetation samples collected at Deception, Livingston, Barrientos and Penguin Islands (South Shetland Islands, Antarctica). Overall, the patterns of n-alkanes in lichens, mosses and grass were dominated by odd-over-even carbon number alkanes. Mosses and vascular plants showed high abundances of n-C21 to n-C35, while lichens also showed high abundances of n-C17 and n-C19. The lipid content was an important factor controlling the concentrations of n-alkanes in Antarctic vegetation (r2=0.28–0.53, p-level<0.05). n-C12 to n-C35 n-alkanes were analysed in soils with a predominance of odd C number n-alkanes (n-C25, n-C27, n-C29, and n-C31), especially in the background soils not influenced by anthropogenic sources. The large values for the carbon predominance index (CPI) and the correlations between odd alkanes and some PAHs suggest the potential biogenic sources of these hydrocarbons in Antarctica. Unresolved complex mixture and CPI values ~1 detected at soils collected at intertidal areas and within the perimeter of Juan Carlos research station, further supported the evidence that even a small settlement (20 persons during the austral summer) can affect the loading of aliphatic and aromatic hydrocarbons in nearby soils. Nevertheless, the assessment of Pr/n-C17 and Ph/n-C18 ratios showed that hydrocarbon degradation is occurring in these soils.

Studies of biomarkers in the organic matter of the seafloor sediments in the northern and middle Caspian Sea

The present day approach to the investigation and typification of organic matter (OM) in rocks and fossil fuel deposits is based largely on the determination of individual compounds. This approach is the result of significant progress in the studies of the structure and stereochemistry of individual compounds of oil, in which more than 1000 various hydrocarbons (HC) are currently known. It is important to note that this new level of studies was reached through chromatomassspectrometry, which allowed for the opportunity for much finer analysis with a high precision of separation of individual hydrocarbons. Many of these compounds may be considered as chemical fossils that preserved obvious structural relations with initial bioorganic molecules. During diagenesis, initial organic matter is transformed into oil HC, the evidence of which is left in the general composition of the HC systems in the relative concentrations of certain compounds, as well as in their structures. Our studies were focused on seafloor sediment (SFS) sampled from a water area of the northern Caspian Sea, as well as from northern and western parts of the Middle Caspian. We were looking for possible hydrocarbon exhalations of deposits in subsurface conditions relying on the behavior of molecule biomarkers in the northern Caspian sediments. The background distribution of HC and OM in recent sediments was compared with anomalous distributions of HS and OM that had possibly migrated. The geochemical, genetic, and catagenetic features of recent sediments were studied to identify possible sources of migrated organic matter (supposed oil pools). Our interpretation is based on distinguishing between syngenetic OM (immature OM of recent sediments) and migrated OM. Firstly, investigated OM of SFS should manifest features of recent sediments. One of such features, found in the distribution of individual HC, may be the sharp domination of odd alkanes C 25, 27, 29, 31 [1]. Another feature is the domination of biological markers, that is, OM with traces of an insignificant restructuring of biogenic structures that occurred at the beginning of diagenesis. Migrated or redeposited OM may be recognized by high parameters of maturity in HC distribution not particular to recent sediments and by the presence of compounds developed during the catalytic thermal maturation of organic matter that occurred during fossilization when sediment was being transformed into rock. We investigated 40 seafloor sediment samples gathered by the Caspian Fisheries Research Institute (KaspNIRKh) from the water areas of the northern and middle Caspian Sea (its northern and western framing). The samples were analyzed by the method of chromatography using a magnetic chromatomass-spectrometer of high resolution, Thermo Finnigan MAT 900 XP. Chromatomass-spectrometry data is interpreted based on the identification of individual organic compounds.

Thermodynamic properties of (an ester + an alkane). XVIII. Experimental [formula omitted] values for (an alkyl butanoate + an alkane) at T = 318.15 K

This work presents the experimental values of H m E and V m E obtained at a temperature of 318.15 K and atmospheric pressure for a group of 24 binary mixtures comprised of the first four alkyl butanoates (methyl to butyl) with six odd alkanes, from heptane to heptadecane. All the mixtures are endothermic, and present a regular increase in H m E with the molecular weight of the saturated hydrocarbon, while, for a same alkane, the enthalpic effects diminish with increasing alcoholic chain of the butanoate. The variation in V m E occurs in the same direction. In this paper the structural behaviour of these systems and the influence of temperature on excess properties are analysed. Experimental data are correlated with a suitable polynomial equation which is given as a function of concentration and temperature, that permits a simultaneous correlation to be established with other properties of the mixture, such as (vapour + liquid) equilibria; and acceptable results are obtained. Finally, an estimation of H m E is made with two known versions of the UNIFAC model. In the version by Dang and Tassios [J. Dang, D.P. Tassios, Ind. Eng. Chem. Process Des. Dev. 25 (1986) 22–31.], a method is proposed that considers the interaction parameters as a function of the butanoate alkanolic chain. The estimations obtained for H m E are good.

Self‐Assembly of Alkanols on Au(111) Surfaces

Self-assembled monolayers (SAMs) of alkanols (1-C(N)H(2N+1)OH) with varying carbon-chain lengths (N = 10-30) have been systematically studied by means of scanning tunneling microscopy (STM) at the interfaces between alkanol solutions (or liquids) and Au(111) surfaces. The carbon skeletons were found to lie flat on the surfaces. This orientation is consistent with SAMs of alkanols on highly oriented pyrolytic graphite (HOPG) and MoS2 surfaces, and also with alkanes on reconstructed Au(111) surfaces. This result differs from a prior report, which claimed that 1-decanol molecules (N = 10) stood on their ends with the OH polar groups facing the gold substrate. Compared to alkanes, the replacement of one terminal CH3 group with an OH group introduces new bonding features for alkanols owing to the feasibility of forming hydrogen bonds. While SAMs of long-chain alkanols (N > 18) resemble those of alkanes, in which the aliphatic chains make a greater contribution, hydrogen bonding plays a more important role in the formation of SAMs of short-chain alkanols. Thus, in addition to the titled lamellar structure, a herringbone-like structure, seldom seen in SAMs of alkanes, is dominant in alkanol SAMs for values of N < 18. The odd-even effect present in alkane SAMs is also present in alkanol SAMs. Thus, the odd N alkanols (alkanols with an odd number of carbon atoms) adopt perpendicular lamellar structures owing to the favorable interactions of the CH3 terminal groups, similar to the result observed for odd alkanes. In contrast to alkanes on Au(111) surfaces, for which no SAMs on an unreconstructed gold substrate were observed, alkanols are capable of forming SAMs on either the reconstructed or the unreconstructed gold surfaces. Structural models for the packing of alkanol molecules on Au(111) surfaces have been proposed, which successfully explain these experimental observations.

Molecular dynamics in n-alkanes: Premelting phenomena and rotator phases

Molecular dynamics simulations of the n-alkanes C18H38, C19H40, and C20H42 are reported for temperatures just below the melting point. Besides thermodynamic and average structural data for the ordered phase, we discuss the molecular motions initiating the rotator phases observed in spontaneous phase transitions in isothermal, isostress simulations. The RI phase of C19H40 is initiated by particular cork-screw-like jumps combining a quarter turn about the long molecular axis and a half-chain-period translation along the axis. This motion occurs between the minimum-energy conformation of the ordered crystal and a secondary minimum. Transient analogs of the RI and RII phases of the odd alkanes are found on melting C18H38 and C20H42. Collective motions within lamellae of molecules are prominent in the dynamics.

Thermodynamic properties of (an ester + an alkane). XVII. Experimental [formula omitted] and [formula omitted] values for (an alkyl propanoate + an alkane) at 318.15 K

In this article, we record the experimental values of H m E and V m E , obtained at a temperature of T = 318.15 K and atmospheric pressure for a set of 30 binary mixtures comprised of five alkyl propanoates (methyl to pentyl) with six odd alkanes (heptane to heptadecane). The net values obtained for these properties are the result of different effects of the selected compounds on the mixing process. These effects and the variation with temperature are studied. The H m E are positive in all cases and increase with the saturated hydrocarbon chain and diminish with the alkanolic portion of the ester. The variation in V m E is similar to that occurring in the H m E . For the data correlation, a new form of polynomial equation is used in which the variable is the so-called active fraction which, in turn, is a function of the concentration of the mixture, giving acceptable estimations for simultaneous correlations between the values of Gibbs function obtained in the isobaric (liquid + vapour) equilibria and the enthalpies of the mixture, for some of the mixtures studied. The results are explained with the molecular model proposed for (ester + alkane) mixtures. Finally, the application of two versions of the UNIFAC groups contribution method to estimate enthalpies of the mixtures does not give satisfactory results, although the modified UNIFAC gives somewhat better results.

Metastable and Stable Morphologies during Crystallization of Alkanes in Miniemulsion Droplets

Undercooling and crystallization of different alkanes in stable nanodroplets with narrow size distributions were analyzed by using DSC measurements. The crystal structure was determined by X-ray measurements. Alkane droplets with a defined size between 100 and 500 nm in water were prepared by using the miniemulsion process. The required undercooling to obtain crystallization in such droplets is significantly increased compared to that for the bulk material since the nucleation mechanism is shifted from heterogeneous to homogeneous nucleation. For the even alkanes (C18−C24), a structure change from the triclinic in the bulk to orthorhombic structure in small droplets (100 nm) was detected and attributed to confinement effects inside the droplets. An intermediate rotator phase is of less relevance for the nanosized droplets. For odd alkanes, a strong temperature shift of the crystallization point compared to the bulk system was detected, but no structure change was observed. Both in bulk and in miniemulsion...

The crystalline structures of the odd alkanes pentane, heptane, nonane, undecane, tridecane and pentadecane monolayers adsorbed on graphite at submonolayer coverages and from the liquidElectronic supplementary information (ESI) available: Fractional coordinates of single repeat units of some alkanes at sub-monolayer coverage and of the monolayer coexisting with the liquid. See http://www.suppdata/cp/b2/b201988b/

A combination of neutron and X-ray diffraction has been used to structurally characterise the crystalline monolayer structures of all the alkanes with odd number of carbon atoms in their alkyl chains from pentane to pentadecane adsorbed on graphite. The structures of all the molecules investigated at submonolayer coverages are isomorphous with centred rectangular unit cells containing two molecules per cell in a parallel arrangement. This is a completely different structure from the ‘herringbone’ arrangement of molecules found for the shorter ‘even’ alkanes, such as hexane, octane and decane. The monolayers at sub-monolayer coverages are interpreted as uniaxial commensurate with the underlying graphite while those monolayers coexisting with the liquid, while structurally similar, are fully commensurate. The difference between the two structures is a uniaxial compression in the b-direction with the monolayers coexisting with the liquids significantly more dense than at submonolayer coverages. In the low coverage structures the ‘odd’ molecules have an all trans conformation with their extended axes parallel to the surface with the plane of the carbon skeleton also parallel to the graphite surface. At high coverages the carbon skeleton is no longer parallel to the graphite surface but significantly tilted. The longest alkanes, tridecane and pentadecane also show evidence of positional and/or rotational disorder at high coverages.

Thermodynamic properties of (an ethyl ester + and n-alkane). IX. HmEand VmEfor { xCH 3(CH 2) uCOOCH 2CH 3+ (1− x)CH 3(CH 2) 2v + 1CH 3} with u= 0 to 5, and v= 1 to 7

Excess thermodynamic functions H m Eand V m Eare reported in this paper for a set of 42 mixtures formed by six ethyl alkanoates (from ethanoate to heptanoate) and seven odd alkanes (from peptane to heptadecane). The H m Evalues were positive for all mixtures, increasing with the alkane chain length and decreasing with the ester chain-length. The behaviour of V m Eis analogous, with negative values in some mixtures containing pentane. The theoretical estimation of the excess properties considered are also analysed using several models.

Investigation into the structures of some normal alkanes within the homologous series C13H28 to C60H122 using high-resolution synchrotron X-ray powder diffraction

High-resolution X-ray powder diffraction using synchrotron radiation has been used to determine the unit-cell parameters of some of the n-alkanes within the range C13H28–C60H122. These have, in general, been found to conform to the structural patterns predicted by Nyburg and Potworowski (Acta Crystallogr., Sect. B, 1973, 29, 347). Polymorphic behaviour has been observed for the n= even alkanes associated with increasing symmetry from a triclinic structure (space group P1), to a monoclinic structure (space group P21/a) and to an orthorhombic structure (mostly space group Pca21) as the chain length increases. The n-alkanes C38H78,C40H82 and C44H90 were found to crystallize in the polytypic orthorhombic polymorph (space group Pbca) proposed by Boistelle et al.(Acta Crystallogr., Sect. B, 1976, 32, 1240). The n= odd alkanes all conform to an orthorhombic structure (space group Pbcm). A comparative examination of the data, as a function of chain length, suggests the existence of a degree of structural disorder along the crystallographic c-axis for the longer homologues, which implies that incipient chain folding takes place.

Coupled Hartree–Fock dipole polarizabilities of the smaller n-alkanes CnH2n+2(n≤7)

We have calculated the dipole polarizabilities of the ‘‘chain’’ alkanes CnH2n+2 (n ≤7) using the coupled Hartree–Fock method. Our average values are 97%–98% of gas phase experimental values. For the larger alkanes, each CH2 unit adds 12.3 a.u. to the average value (within 2%). The anisotropic polarizability also agrees well with gas phase experimental values, but it continues to increase with the length of the chain. We have also obtained dipole moments for the odd alkanes−propane, pentane, and heptane. For propane, there is a gas phase experimental value with which we agree quite well.

Hydroxyls in polyethylene and in alkanes. A low-temperature dielectric relaxation study

A dielectric relaxation of oxidised polyethylene originally observed by Carson was reproduced both by synthetically introducing hydroxyl groups into the polymer molecules, and by adding long-chain secondary alcohols. By comparing the 4.2 K relaxation strengths and rates of polyethylenes containing these and other additives the crystal structure is shown to be of primary importance only in the case of long-chain secondary alcohols. These also produced weak relaxations when introduced into crystals of odd alkanes, but in even alkanes relaxed strongly, and at a different frequency. 8-aminopentadecane only relaxed strongly in odd alkanes. An attempt is made to correlate these findings with the intermolecular steric hindrances in the respective crystals.

Hydrocarbons in leaf waxes of Saccharum and related genera

The composition of the n-alkanes in the leaf waxes of over 80 clones of Saccharum officinarum, S. edule, S. robustum, S. spontaneum and from a number of related species have been compared by GLC. The waxes contain predominantly odd alkanes, C 27–C 35, the major components being C 29 and C 31. In a number of clones, particularly of S. edule, a homologous series of alkenes was also present. No chemotaxonomic relationship could be derived from the compositions as the intraspecific variation was greater than the interspecific variations.