Octane Molecules Research Articles

Alternation of [Ge5O11H]− Inorganic Sheets and Dabconium Cations in a Novel Layered Germanate: Catalytic Properties

Ge5O11H[C6N2H13] has been hydrothermally synthesized. The structure of the material has been determined by single-crystal X-ray diffraction. This novel layered germanate consists of an alternation of [Ge5O11H]− inorganic sheets and monoprotonated 1,4-diazabicyclo-[2,2,2]-octane molecules. It exhibits an arrangement of 4- and 10-ring in infinite layers not observed before. The catalytic activity in Michael reactions has been tested showing that the addition occurs at the amine centers in the interlayer space. Reuse of the catalyst and the persistence of its structure after recovering has been proved.

A study of the microstructure of CTAB/1-butanol/octane/water system by PGSE-NMR, conductivity and cryo-TEM

A quaternary microemulsion system of a cationic surfactant (cetyltrimethylammonium bromide, CTAB), octane, water, and 1-butanol has been investigated using conductivity, pulsed field gradient spin-echo NMR measurements, and electron microscopy (Cryo-TEM and freeze fracture electron microscopy (FFEM)). The conductivity behavior has a distinct percolative phenomenon and a bell-shaped curve as a function of water contents. This indicates that the single-phase microemulsion is changed continuously from oil-in water structure via a bicontinuous structure to water-in oil structure. This result is consistent with those of the PGSE-NMR, Cryo-TEM, and FFEM. In the w/o region, the self-diffusion coefficient of water is relatively high (2–7×10 −10 m 2 s −1) due to the higher solubility of water in the continuous phase which consisted of octane(10 wt.%) and 1-butanol. The penetration of a large amount of octane molecules between surfactant chains results in the self-diffusion coefficient of octane being much lower (1–8×10 −10 m 2 s −1) in the w/o region.

A study of the microstructure of CTAB/1-butanol/octane/ water system by PGSE-NMR and Cryo-TEM

In this work, the effect of octane concentration on the phase behavior of CTAB/water/1-butanol system was studied by using pulsed field gradient spin-echo NMR measurements and freeze fracture electron microscopy (Cryo-TEM and FFEM). When the octane concentration increases, the liquid crystalline phase is destabilized and a continuous single-phase microemulsion region from the water apex to the oil apex is formed. The conductivity behavior has a distinct percolative phenomenon, which indicates that the single-phase microemulsion is changed continuously from oil-in-water (o/w) structure via a bicontinuous structure to water-in-oil (w/o) structure. This result is consistent with those of the PGSE-NMR, Cryo-TEM, and FFEM. In the w/o region, the self-diffusion coefficient of water is relatively high ((1–6)×10−10 m · s−1) due to the higher solubility of water in the continuous phase consisting of octane (10% by weight) and 1-butanol. The penetration of a large amount of octane molecules between surfactant chains results in the much lower self-diffusion coefficient of octane.

Adsorption behaviour of the binary mixtures of octane and nonane at sub-monolayer coverage on graphite

The behaviour of binary mixtures of octane and nonane adsorbed on graphite has been investigated with a combination of adiabatic calorimetry and neutron diffraction. In contrast to the eutectic behaviour of monolayers of these materials at higher coverages, this combination of alkanes is found to form mixed crystals on the surface over an extensive composition range at the sub-monolayer coverages investigated here. In the mixed phase the shorter octane molecules are incorporated into the lattice of the longer nonane molecules. This incorporation occurs despite pure octane and nonane monolayers having different symmetries and is attributed to the expanded nature of the submonolayer phases, relative to higher coverage monolayers, providing room for mixed crystal formation.

On the optimal selection of principal components in QSPR studies

A heuristic method to sort principal components is analysed. The obtained arrangements are property dependent and it is demonstrated how the procedure is equivalent to the called Most Predictive Variable Method. As an application of the new algorithm, a Quantitative Structure–Property Relationships (QSPR) study is performed over the set of the 18 structural isomers of the octane molecule. The original molecular descriptors are obtained from a quantum similarity matrix related to the molecular family. The analysis is based on the use of linear models where distinct sets of principal components act as optimal descriptors for 6 physicochemical molecular properties. The proposed algorithm allows to determine sequences of the first Principal Components which are identified as forming the optimal descriptors set for each of the 6 studied properties. The benefits of the new approach are revealed when comparing the obtained results with classical ones arising from a standard principal component analysis study.

Lipase-Mediated Preparation of A Functionalized Bicyclo[3,2,1]octenone and A Practical Utilization

Both enantiomers of a functionalized bicyclo[3.2.1]octane molecule potentially useful as a versatile chiral building block have been prepared in enantiomerically pure forms from norbornadiene by employing lipase-mediated kinetic resolution. By transforming both enantiomers enantioconvergently into the same chiral lactone serving as the key intermediate for the synthesis of the naturally occurring carbocyclic nucleoside (-)-aristeromycin, the absolute configuration of the resolved products has been established and at the same time their synthetic potential has been demonstrated.

Taylor dispersion and molecular displacements in Poiseuille flow.

We have used pulsed gradient spin echo (PGSE) NMR to measure longitudinal displacements of octane molecules undergoing Poiseuille flow in a 150 microm diameter pipe, accessing time scales which approach the Taylor dispersion limit. We monitor the change in displacement distribution which occurs as molecules undergoing Brownian motion sample an increasing proportion of the ensemble of streamlines, observing the effects of wall collisions and the gradual transition of the propagator from Poiseuille to Taylor-Aris behavior. The further use of a double PGSE sequence allows the direct measurement of the stochastic part of the motion alone.

Enumeration of the Conformers of Unbranched Aliphatic Alkanes

An effective one-electron quantum chemical method was applied to enumerate the conformers of unbranched aliphatic alkanes. The results obtained for butane, pentane, hexane, and heptane were utilized to derive four rules with which the number and sequences of the existing conformers up to undecane could be reproduced. The validity of the rules was confirmed at Hartree−Fock and second-order Moeller−Plesset levels too. Full ab initio conformational analyses were performed for the butane, pentane, hexane, heptane, and octane molecules. The rules demonstrate that the most important factors governing the conformational behavior of unbranched aliphatic alkanes are the nonbonded repulsive−attractive (van der Waals) interactions between the hydrogen atoms attached to the carbon atoms at positions 1,4; 1,5; 1,6; and 1,7. The calculated gas-phase standard heats of formation of the unbranched aliphatic alkanes closely matched the experimental values.

Energetically driven liquid–solid transitions in molecularly thin n-octane films

In this paper we present findings from molecular dynamics simulations that investigated the changes induced in molecularly thin n-octane films, as a result of increasing solid-methylene unit energetic affinity. The solid surfaces were deprived of any topographical features and were modeled as atomically smooth 10-4 Lennard–Jones planes. We observed an abrupt transition in the structural features of the film at a critical value of the characteristic energy that quantified the affinity between solid surfaces and methylene units. The transition was signaled by a discontinuous increase in the degree of intermolecular order and facilitated by a precipitous extension of the octane molecules, which adopted almost fully extended configurations. Furthermore, the transition resulted in the freezing of molecular migration and rotation. The characteristics of the transition showed that it is a mild first order phase transition between a highly ordered liquid and a poorly organized solid. The solid constitutes a phase with order intermediate to that of hydrocarbon ‘‘rotator’’ phases and two-dimensional smectics. These findings demonstrate that solidification of nanoscopically thin films of linear alkanes is a general, energetically driven phenomenon, which does not require the aid of commensurate surface topography. Our simulations provide a natural explanation for the solidlike features exhibited by alkane films studied experimentally.

Structural transitions at solid-liquid interfaces

In this paper we present the findings of our investigations using molecular dynamics, on molecularly thin films of n-octane confined between topographically smooth solid surfaces. We focus on the effect of increasing solid surface-methylene unit energetic affinity and the effect of increasing pressure (normal load) of the film in inducing liquid-solid phase transitions. We observed an abrupt transition in the structural features of the film at a critical value of the characteristic energy that quantified the affinity between solid surfaces and methylene units. This energetically driven transition was evident from the discontinuous increase of intermolecular order, a precipitous extension of the octane molecules and freezing of molecular migration and rotation. Increasing pressure had a similar effect in inducing a liquid-solid phase transition. The characteristics of the transition showed that it is a mild first order transition from a highly ordered liquid to a poorly organized solid. These findings demonstrate that the solidification of nanoscopically thin films of linear alkanes is a general phenomenon (driven either energetically or by increasing pressure), and does not require the aid of commensurate surface topography.

Energetically and pressure driven phase transitions in molecularly thin films of n-alkanes

Molecular dynamics simulations were carried out on molecularly thin films of n-octane confined between topographically smooth solid surfaces. We focused on determining the effect of increasing solid surface-methylene unit energetic affinity and the effect of increasing pressure (normal load) of the film in inducing liquid-solid phase transitions. Simulations of films wide enough to accomodate three segmental layers showed an abrupt transition in the structural features at a critical value of the characteristic energy that quantified the affinity between solid surfaces and methylene units. This energetically driven transition was evident from the discontinuous increase of intermolecular order, a precipitous extension of the octane molecules and freezing of molecular migration and rotation. Increasing pressure had a similar effect in inducing a liquid-solid phase transition. The characteristics of the transition showed that it is a mild first-order transition from a highly ordered liquid to a poorly organized solid. These findings demonstrate that the solidification of nanoscopically thin films of linear alkanes is a general phenomenon (driven either energetically or by increasing pressure), and does not require the aid of commensurate surface topography. Our findings on relatively wider films (5 segmental diameters wide) show that the interfacial layer undergoes a similar first-order phase transition with increasing solid-methylene unit energetic affinity. This energy threshold is significantly higher than the one observed in thin film simulations.

Structural patterns and molecular mobility inside the interface between an fcc solid and liquid n-octane

In this paper we present our results from a molecular dynamics study of n-octane liquids confined between planar 100 fcc solid surfaces. The systems studied were wide enough to develop a bulk-like region throughout the middle portion of the film between two well-separated interfaces. Our work focused on the effects of increasing solid-segment adhesion. For adhesive energies per segment much lower than the thermal energy (weak physisorption) the structure inside the interface and the mobility of octane molecules were found to be liquid-like and quantitatively not very different from the bulk. In strong physisorption cases (adhesive energy of 1–2 kT) we observed the development of qualitatively new structural patterns inside the first interfacial layer. Octane chains lay flat on the surface, adopted very extended almost rod-like conformations and formed two-dimensional liquid crystalline domains with smectic order. The directions of these domains were set by the topography of the underlying solid matrix. For adhesive energies of about 1.5 kT per segment we witnessed a sharp transition from “horizontal” to “tilted” smectic domains. These structural patterns affected profoundly the dynamics of octane molecules. Chain desorption froze for adhesive energies higher than 1.5 kT and rotational relaxation times were at least three orders of magnitude higher than the bulk. However, translational diffusion parallel to the surface remained significant inside the first layer. Surface migration of octane molecules acquired gradually the characteristics of a one-dimensional random walk along the director of the chain's liquid crystalline domain.

Segmental dynamics and relaxation of n-octane at solid–liquid interfaces

In this paper we present our results from a molecular dynamics study of n-octane liquids confined between planar bcc solid surfaces. The systems studied were wide enough to develop a bulklike region throughout the middle portion of the film and two well-separated interfaces. Our work focused on segmental dynamics and relaxation of ‘‘adsorbed’’ octane molecules. In particular, we investigated the role of architectural and dynamical features peculiar to short chain molecules (almost fixed bend angles and restricted torsional rotations) on the dynamics of ‘‘adsorbed’’ chains. We found that the relaxation of octane molecules exhibits the same qualitative trends as those observed in molecular simulations of generic ‘‘bead-spring’’ oligomer films. The most important effect is the dramatic slow down of rotational motions (up to a factor of 1000) for chains adsorbed on strongly physisorbing surfaces (adhesion energy per segment of 1–2 kT). Despite the qualitative similarities with bead-spring chains, the dynamics of realistic short hydrocarbon chains are affected much more strongly by the interfacial environment than their bead-spring counterparts. These stronger effects originate largely from the suppression of torsional angle transitions inside the extremely dense first layer (in cases of strong physisorption). The frequency of torsional transitions was found to be correlated directly with the amount of ‘‘free volume’’ available inside the crowded first layer.

Energetically and Pressure Driven Liquid-Solid Transitions in Molecularly Thin Hydrocarbon Films

ABSTRACTIn this study we used molecular dynamics simulations to investigate the structural changes in nanoscopically thin n-octane films confined between smooth solid surfaces as a result of a) increasing solid-methylene unit affinity and b) increasing pressure. Increasing solid-methylene unit energetic affinity resulted in the solidification of the film at a critical value. A similar transition is observed at a critical value of pressure. Bulk n-octane was a liquid in both cases. The transition was signaled by an abrupt increase in the intermolecular order and was facilitated by a precipitous extension of the octane molecules, which adopted almost fully extended configurations. A discontinuous jump in the film density at the critical values of solid affinity and pressure was evident. The characteristics of the transitions showed that it was a mild first order transition from a highly ordered liquid to a poorly organized solid.

Organic templates in zincophosphate synthesis: Zn5(PO4)2(HPO4)4·H2O·2H2N2C6H12, containing two distinct eight-ring channels and Zn3(PO4)(HPO4)2· HN2C6H12, containing tetrahedral three-rings and Zn–N bonds

The hydrothermal syntheses, single-crystal X-ray structures and some properties of two new microporous, anionic, zinc phosphate frameworks encapsulating organic cations are described. Zn5(PO4)2(HPO4)4·H2O·2H2N2C6H12(ZnPO/dab-C) crystallizes in the triclinic space group P(No. 2) with a= 9.366(1)A, b= 9.882(1)A, c= 19.183(2)A, α= 85.406(3)°, β= 85.029(3)° and γ= 114.485(3)°, V= 1596.51 A3 and Z= 2, with R(F)= 7.11% for 4095 observed reflections [I > 3σ(I)], Zn3(PO4)(HPO4)2·HN2C6H12(ZnPO/dab-D) is orthorhombic, space group P212121(No. 19), a= 11.095(2)A, b= 16.413(2)A, c= 8.263(1)A, V= 1505.61 A3, Z= 4, with R(F)= 5.71% for 1321 observed reflections [I > 3σ(I)].Both of these new materials consist of a three-dimensional network of tetrahedrally coordinted zinc and phosphorus atoms, linked through oxygen atom vertices, to form two different open structures. ZnPO/dab-C contains two distinct one-dimensional eight-ring channels (one regular, one squashed), occupied by extraframework, protonated, 1,4-diazabicyclo[2.2.2]octane (DABCO, [H2N2C6H12]2+) molecules. ZnPO/dab-D is a new framework type containing ‘bridged’ three-rings of tetrahedra. The DABCO molecule coordinates to the framework in this phase via Zn–N links. 31P MAS NMR data for these two materials are presented, and may be interpreted using a simple bond-strength model.

Ligand-induced conformational switching and allosteric effects in macrocyclic porphyrin dimers

Macrocyclic porphyrin dimers linked by biphenyl or pyromellitimide bridges show major conformational changes on protonation or on binding a single 1,4-diazabicyclo[2.2.2]octane (DABCO) molecule within the cavity; the binding of a second DABCO molecule leads to a further conformational switch.

ChemInform Abstract: Vicinal Heteroatom‐13C Spin‐Spin Coupling Constants in the Apical Positions of Cage Complexes: Inorganic Analogues of Heteroatomic Bicyclo(2.2.2)octane Molecules

ChemInformVolume 18, Issue 20 Physical Organic Chemistry ChemInform Abstract: Vicinal Heteroatom-13C Spin-Spin Coupling Constants in the Apical Positions of Cage Complexes: Inorganic Analogues of Heteroatomic Bicyclo(2.2.2)octane Molecules P. A. LAY, P. A. LAY Res. Sch. Chem., Aust. Natl. Univ., Canberra, ACT 2601, Aust.Search for more papers by this authorA. M. SARGESON, A. M. SARGESON Res. Sch. Chem., Aust. Natl. Univ., Canberra, ACT 2601, Aust.Search for more papers by this author P. A. LAY, P. A. LAY Res. Sch. Chem., Aust. Natl. Univ., Canberra, ACT 2601, Aust.Search for more papers by this authorA. M. SARGESON, A. M. SARGESON Res. Sch. Chem., Aust. Natl. Univ., Canberra, ACT 2601, Aust.Search for more papers by this author First published: May 19, 1987 https://doi.org/10.1002/chin.198720044Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume18, Issue20May 19, 1987 RelatedInformation

Esr studies of the ring opening of cyclopropane radical cations in freon matrices

The radical cations of cyclopropane and several of its methyl derivatives have been characterized by ESR spectroscopy following their generation by γ irradiation of dilute solutions of the parent compounds in Freon matrices at 77 K. In the CFCl 3, CF 3CCl 3, and CF 2ClCCl 3, matrices, only the ring-closed species is usually observed in the accessible temperature range up to ca 160 K. In the CFCl 2CF 2Cl matrix, however, the ring-closed radical cations initially formed at 77 K undergo ring opening between 83 and 110 K, the more highly substituted radical cations requiring a higher temperature for this transformation. The ring-closed radical cations are 2A 1 species for C 2v symmetry, the most substituted cyclopropane C-C bond being elongated with the spin density largely confined to the basal carbons in a face-to-face (90°, 90°) structure. In the ring-opened radical cations, the radical center is localized on the most substituted carbon atom following the breaking of the weakened C-C bond of the ring-closed species. The radical conformations of the ring-opened species have been determined, the RCH 2CH 2· center produced from cyclopropane having a bisected conformation while the RCH 2CMe 2· center obtained from 1,1,2,2-tetramethylcyclopropane is eclipsed, as expected for the presence of α-methyl substituents at the radical site. The nature of the putative carbocation center in the ring-opened radical cations is discussed with reference to recent proposals that this center is strongly coordinated to an electrophile (Cl - or RCl) thereby negating the requirement for an orthogonal structure. Consideration of the strong matrix dependence of the ring-opening reaction suggests a possible solvation effect, however, in which the CFCl 2CF 2Cl matrix assists the twisting of one of the CR 1R 2 groups at the most substituted bond, leading to the rupture of this one-electron σ bond. A strong solvation effect also explains why ring-opening can occur in a suitable polar solvent despite theoretical calculations of unfavourable energetics for a similar gas-phase reaction. Experiments are also described on spiro[2.5]octane, the cyclopropane ring undergoing scission at the CH 2-CH 2 bond of this radical cation to give an RCH 2· radical center. this radical then undergoes a H-atom abstraction with a neutral spiro[2.5]octane molecule in the CFCl 2CF 2Cl matrix at higher temperature to give the spiro[2.5]oct-6-yl radical.

An electron diffraction study of the structure of the bicyclo[3,2,1]octane molecule in a gaseous medium

An electron diffraction study of the structure of the bicyclo[3,2,1]octane molecule in a gaseous medium

ChemInform Abstract: A DOUBLE‐MINIMUM SKELETAL TORSION IN 1‐SILABICYCLO(2.2.2)OCTANE BY MICROWAVE SPECTROSCOPY

Abstract The 1-silabicyclo[2.2.2]octane molecule HSi(CH 2 CH 2 ) 3 CH was investigated by microwave spectroscopy. The observed spectra followed the symmetric-rotor pattern with the unresolved K structures, but were accompanied by many strong vibrational satellites. A series of the prominent satellites was assigned to the excited states of the skeletal torsion. The transition frequencies and the relative intensities which were measured for the satellites were used to determine the double-minimum potential function to the skeletal torsion. The height of the potential hump and the equilibrium torsional angle, which was defined as the SiCCC dihedral angle, were determined to be 606 ± 40 cal/mole and 21.3° ± 1.0°, respectively. The results that the double-minimum nature of the potential function is more pronounced in 1-silabicyclo[2.2.2]octane than in other bicyclo[2.2.2]octane derivatives studied previously are discussed in detail in terms of the internal-rotation potential around the CC and CSi bonds and the strains in the valence angles of the C and Si atoms.