Temperature dependence of the carbon-13 chemical shifts of paraffinic hydrocarbons

A study of several linear and branched alkanes indicates that the temperature dependence of ¹³C chemical shifts is a complex phenomenon in which several non-additive effects may be operative. The chemical shift temperature coefficients dδ/dT do, however, reveal some systematic trends which could be helpful in the assignments of ¹³C resonances. An empirical equation is proposed (akin to that of Grant and Paul for ¹³C chemical shifts) which accurately correlates all the data obtained near ambient temperatures.     

分子诱导效应指数与链烷烃的沸点

利用基团的诱导效应指数，首次提出了分子的诱导效应指数的概念，并定义了 链烷烃的有效碳链长度NC＝（MIs,N/MIb,N)·N，式中MIs,N,MIb,N分别为直链和支 链异构体的分子诱导效应指数。研究结果表明，链烷烃的沸点Tb(℃）与NC关系是 ：1n(806.5-Tb)=6.9824-0.11431NC^2/3     

Mechanism of dehydrocyclization of paraffinic hydrocarbons on chromium oxide catalysts

Conclusions Dehydrocyclization of normal paraffins to aromatic hydrocarbons on chromium oxide catalysts does not include the stage of the formation of intermediate cyclohexanes or their chemisorbed forms (complexes of the cyclohexanes with the catalyst).Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2561–2562, November, 1969.     

有效碳链长度与链烷烃沸点

对于碳原子数目为N的链烷烃，我们提出其有效碳链长度N~E=(PT~直~,~N/PT~支~,~N)·N。式中PT~直~,~N和PT~支~,~N分别为直链和支链异构体的分子极化指数。研究表明，链烷烃的沸点Tb(K)与N~E有以下关系：log(1076.575-Tb)=3.034649-5.043171×10^-^2N~E^2^/^3。     

On the biosynthesis and optical activity of the flinderoles

A proposed biosynthesis of the flinderoles described herein would produce racemic compounds through nonenzymatic dimerization of borrerine. However, an initial report of optical activity for natural flinderoles is inconsistent with that hypothesis as well as the racemic production of similar natural products. Herein, pure enantiomers of flinderole B were obtained and the specific rotations thereof were found to be significantly different from those in the original report, which were taken at low concentrations. These new data remove the inconsistency arising from the original data.     

On the transition from paraffinic to polymeric behavior: Mechanical properties

An attempt has been made to determine what influence chain folds may have on the α and γ mechanical loss peaks in linear polyethylene. In so doing, one long-chain n-paraffin (C₉₄H₁₉₀) and two low molecular weight polyethylene fractions have been examined with mechanical relaxation, differential scanning calorimetry (DSC), and low-angle x-ray diffraction techniques. The data suggest that chain folds play a prominent role in both the α and γ processes but that other factors such as polydispersity and/or branching are also important.     

On the quantum mechanical theory of natural optical activity

Optical activity due to the coupling of molecular subunits is discussed in its dependence on various electromagnetic tensor properties of the subunits and on geometrical parameters. Certain approximation aspects of the theory are analyzed. Symmetry rules for dynamic-coupling terms are derived. Origin-dependent tensors are eliminated by referring their components to local frequency-dependent polarizability centers. Kirkwood's reduced first order result is revisited.Dedicated to Professor Dr. Günther Ludwig on the occasion of his retirement from the Philipps-Universität in Marburg/Lahn, Germany     

A comparative study of the gas chromatographic behavior of liquid crystals and polyester stationary phases using paraffinic hydrocarbons as standards

Two new categories of stationary phase have been studied: liquid crystals and polyesters. The liquid crystals were p,p′-azoxyphenetol, p(n-hexyloxy)phenyl-p′-methoxy benzoate, and p-pentyloxy-p′-ethoxyazoxybenzene; and the polyester phases 1,4-butanediol succinate (LAC-860), ethylene glycol succinate (LAC-886), diethylene glycol succinate (LAC-738), diethylene glycol adipate (LAC-296), and neopentyl glycol adipate (LAC-769). Abnormal chromatographic behavior, has been observed: an increase in specific retention volumes and an improvement in the separation of normal, branched, and cycloparaffins, depending on their structures, at high temperatures within a specified range. This phenomenon is the opposite of the behavior of traditional stationary phases. From the chromatograms obtained, plots of log v against 1/T, and differential thermal analysis it is concluded that this abnormal behavior may be attributed to the penetration of solutes through the ordered structure of the mesophase and the rod-like molecules of the polyesters. Furthermore, the chromatographic behavior of some of the polyester (LAC-series) stationary phases in respect of temperature changes is similar to that of the nematic mesophases.     

Radiation-thermal conversion of paraffinic oil

Radiation-thermal cracking (RTC) in the high-paraffinic oil from the Kumkol field (Western Kazakhstan) is experimentally studied. It is shown that the high polymerization rate and low olefin contents in products of radiation processing together with relatively low yields of light fractions at low irradiation dose rates and the low level of their isomerization are characteristic for RTC in oil with high contents of heavy paraffins. These observations are attributed to the behavior of heavy alkyl radicals that initiate polymerization and isomerization in heavy paraffin fractions.     

On the classification of polyhex hydrocarbons

A novel classification scheme for polyhex hydrocarbons is proposed.     

On the number of benzenoid hydrocarbons

We present a new algorithm which allows a radical increase in the computer enumeration of benzenoids b(h) with h hexagons. We obtain b(h) up to h = 35. We prove that b(h) approximately const.kappa(h), prove the rigorous bounds 4.789 < or = kappa < or = 5.905, and estimate that kappa = 5.16193016(8). Finally, we provide strong numerical evidence that the generating function summation operator b(h)z(h) approximately A(z) log(1 - kappa z), estimate A(1/kappa) and predict the subleading asymptotic behavior. We also provide compelling arguments that the mean-square radius of gyration (h) of benzenoids of size h grows as h(2 nu), with nu = 0.64115(5).     

Limiting activity coefficients of hydrocarbons in phenol

Temperature dependence of the limiting activity coefficients of saturated (n-hexane, n-heptane, n-octane, and cyclohexane) and aromatic (benzene, toluene, ethylbenzene, o-xylene) hydrocarbons in phenol was studied in the temperature range 308–348 K by the headspace analysis method.     

On dioxo derivatives of benzenoid hydrocarbons

Extending a problem occurring in connection with the stability order of the tautomers of hypericin, we examine the topological factors influencing the stability of the isomeric dioxo derivatives of benzenoid hydrocarbons, in particular the rules determining the number of Kekulé structures in them. Depending on the position of the oxo groups, the pattern of cyclic conjugation varies significantly, as does the Kekulé structure count. Some general regularities along these lines are established.     

On some problems in the theorems of alternant hydrocarbons

A number of theorems of alternant hydrocarbons presented by Dewar are proved to be wrong. A statement of the related theorem instead of Dewar's is presented.     

On the electronic properties of dehydrogenated polycyclic aromatic hydrocarbons

The electronic excited-state properties of a series of dehydrogenated polycyclic aromatic hydrocarbons from phenyl through to decacyl are reported. The radicals were investigated by use of time-dependent density functional theory in conjunction with the B3LYP functional. The pi and n orbitals were seen to converge in energy as the system increased in size, yet all radicals were found to have A' ground states. In addition to the study of the electronic state symmetries, the excited-state transitions and oscillator strengths were investigated with the resulting transitions found within the visible region of the spectrum, placing these radicals in the large group of candidate carriers of the diffuse interstellar bands.