Linear Alkynes Research Articles

Zirconocene-mediated, high-yielding macrocyclizations of silyl-terminated diynes.

A series of silyl-terminated diynes of varying lengths and substitution patterns have been prepared. These diynes undergo zirconocene coupling with selective formation of trimeric macrocycles from linear alkynes, while nonlinear diynes give cyclodimeric products. The length of the linear diynes can be increased for the preparation of macrocycles with large nanoscale cavities. Reaction of the zirconium-containing macrocycles with acid results in the synthesis of metal-free cyclophanes. All of these macrocycles were prepared in multigram quantities, in the absence of high-dilution conditions, to give products in > 75% yield that are easily purified as crystalline solids.

Polymerization of aliphatic disubstituted acetylenes by MoOCl4-n-Bu4Sn-EtOH catalyst: Formation of polymers with narrow MWDs and confirmation of the living character

The polymerization of aliphatic disubstituted acetylenes was examined with MoOCl 4 -n-Bu 4 Sn-EtOH (1/1/2) ternary catalyst in anisole at 0 °C. Various linear aliphatic disubstituted acetylenes such as 2-nonyne provided polymers with narrow molecular weight distributions (weight-average molecular weight/number-average molecular weight = 1.05-1.20). The living character of the polymerization was proven by both the time profile of the polymerization and the multistage polymerization of 2-nonyne. The initiation efficiency was about 3%, which is rather low. Although 5-dodecyne, which has a triple bond in a more inner part, polymerized more slowly than 2-nonyne, their living characters were hardly different. Diblock copolymers were synthesized by the sequential living polymerization of internal linear alkynes.

Auger spectra of linear alkynes and alkenes. Experiment and theory

The Auger spectra of molecules in the two sequences 1-propyne, 1-butyne, 1-pentyne and 1-propene, 1-butene, 1-pentene have been studied in a comparative way. Experimental Auger spectra are reported for 1-propene, 1-butene and 1-pentyne. Two-particle Green's function calculations interpret these spectra and make predictions for the other members of the studied sequences. The calculated Auger spectra are related to ionization spectra by a renormalization technique. The ionization potentials display the formation of the 2s bands of the alkyl chain in both sequences which is confirmed by the experimental valence XPS spectra. The 2p regions show influence of hyperconjugation between the multiple bond and the alkyl group. From atomwise decomposed theoretical Auger spectra it is observed that the sp 2 pattern of the double bonds appears for both terminal carbon atoms of the alkenes, but that the sp pattern of the triple bond appears only for one terminal carbon atom, the second one already having a distorted lineshape. The sp 3 patterns of the methyl and methylene units in the alkyl group are distorted throughout the chain with some oscillations of maxima with the atomic position.

Gas-chromatographic study of the thermodynamic properties of systems containing linear alkenes and alkynes

The selectivity of silicone phases OV-101, OV-17 and OV-225 with respect to the retention indices and thermodynamic functions of solution (relative molar enthalpies, entropies and free energies) of n-alkene and n-alkyne isomers and homologs was investigated and correlated with the molecular structure of the isomers.

ChemInform Abstract: Mn(I)‐Induced 1,6‐Demethanation Across the CC Triple Bond of Linear Alkynes in the Gas Phase. A Case for the Generation of Manganese Cycloalkynes?

AbstractComplexes of Mn(alkynes)+, generated in the gas phase, are found to exhibit a reactivity which is even richer than that of analogous Fe species.

Manganese(I)-induced 1,6-demethanation across the carbon-carbon triple bond of linear alkynes in the gas phase. A case for the generation of manganese cycloalkynes?

Manganese(I)-induced 1,6-demethanation across the carbon-carbon triple bond of linear alkynes in the gas phase. A case for the generation of manganese cycloalkynes?

Center of mass displacement and relaxation times of linear alkynes

The carbon-13 chemical shifts and relaxation times of various linear alkynes have been measured. Complexation of these compounds with dicobalt octacarbonyl induces changes in δ's and T 1's. Unambiguous assignments were obtained from deuterium labelled octynes. The T 1 variations result from the displacement of the center of mass of the aliphatic chain. They are systematic and can thus be used for assignment purposes.

Gaseous alkyne ions

AbstractUsing the relative abundance of metastable ions, collisional activation spectra, field ionization kinetic measurements, isotopic labelling, appearance energy and kinetic energy release data, it is shown that linear alkyne radical cations with more than six carbon atoms do not isomerize to equilibrating structures prior to decomposition. At the shortest ion lifetimes the molecular ions of linear alkynes decompose mainly by simple β‐bond fission which allows an unequivocal localization of the triple bond. At medium ion lifetimes fragmentation occurs predominantly via a McLafferty rearrangement, while at long ion lifetimes competing alkyl losses prevail. These alkyl losses occur via cyclic intermediates leading to thermochemically stable cycloalkenyl ions. All these reactions occur with a high specificity with respect to the carbon and hydrogen atoms involved and are preceded by little or no hydrogen exchange reactions.

Heats of hydrogenation and formation of linear alkynes and a molecular mechanics interpretation

Heats of hydrogenation and formation of linear alkynes and a molecular mechanics interpretation

ChemInform Abstract: LINEAR ALKYNES AND THE EFFECT ON BOND LENGTHS OF CHAIN LENGTHENING AND MONO‐ AND DI‐SUBSTITUTION BY LITHIUM AND CYANIDE

Abstract Ab initio calculations have been applied to a series of linear alkynes and their lithioand cyano-derivatives. The calculations predict that the C-C and CC internuclear distances will depend on the length of the molecule, the position of the particular bond in the molecule, and the presence or absence of substituents. Although small changes in the σ-overlap population are observed, the variations in bond lengths call be attributed primarily to alterations in the π-overlap population. The HOMO and LUMO energies for the various related molecules are compared, and the total electronic energies are partitioned into bond contributions.

Linear alkynes and the effect on bond lengths of chain lengthening and mono- and di-substitution by lithium and cyanide

Ab initio calculations have been applied to a series of linear alkynes and their lithioand cyano-derivatives. The calculations predict that the C-C and CC internuclear distances will depend on the length of the molecule, the position of the particular bond in the molecule, and the presence or absence of substituents. Although small changes in the σ-overlap population are observed, the variations in bond lengths call be attributed primarily to alterations in the π-overlap population. The HOMO and LUMO energies for the various related molecules are compared, and the total electronic energies are partitioned into bond contributions.

Carbon-13 nuclear magnetic resonance spectroscopy. Spectra of the linear alkynes

The ^(13)C chemical shifts of a selection of linear alkynes are collected and correlated with structure. A system of empirical rules by which the ^(13)C nuclear magnetic resonance spectra of such compounds can be predicted is derived. The failure of the current point-dipole approximation to predict correctly the shifts due to the anisotropy of the triple bond is discussed.