Tertiary Carbon Hydrogen Bond Research Articles

Switching up stereocenters

Small stereochemical changes can bring big distinctions to molecules like drugs, fragrances, and propellants. Switching the stereochemistry of a single substituent can change a rose-scented substance into a molecule with a mildly minty odor, for example. But depending on the surrounding substituents, changing a single stereocenter can require complex, multistep synthesis—essentially making the molecule from scratch. Chemists at the Massachusetts Institute of Technology led by Alison E. Wendlandt now report a stereochemical editing method that can switch unactivated tertiary carbon-hydrogen bonds, which are typically tough to invert (or epimerize, in chemical parlance), in a single step using a light-catalyzed process with a decatungstate polyanion and disulfide cocatalyst ( Science 2022, DOI: 10.1126/science.add6852 ). “We basically found a tool that allows us to invert these kinds of stereocenters, and what that really let us do was reenvision how we might construct molecules as a result,” Wendlandt says. The reaction proceeds via

How formaldehyde affects the thermo-oxidative and photo-oxidative mechanism of polypropylene: A DFT/TD-DFT study

• The effect mechanism of formaldehyde on the thermo-oxidative and photo-oxidative aging of PP is studied by DFT/TD-DFT. • Energies required for elementary reactions in conversion of tertiary carbon radical to carbonyl group are calculated. Previous studies have shown that formaldehyde significantly accelerates the thermo-oxidative and photooxidative ageing of polypropylene (PP). However, the related mechanisms have not yet been clarified. Computational simulation can compensate for the limitations of experimental methods to help investigate reaction mechanisms and has been widely applied to study thermal and thermal-oxidative ageing processes. However, there has been no systematic methodology for investigating photooxidative ageing processes by simulation. In this paper, density functional theory (DFT) and time-dependent density functional theory (TD-DFT) are applied to investigate how formaldehyde affects the thermo-oxidative and photooxidative ageing mechanism of PP. Formaldehyde can promote the generation of tertiary carbon radicals by reacting with tertiary hydrogen, causing a significant decrease in the bond energy of the tertiary C-H bond. The relaxed scan shows that when the oxygen atom of formaldehyde approaches the tertiary hydrogen up to 1.20 Å, the transition energy from the HOMO to the LUMO will decrease to 324 kJ/mol, which is equivalent to photons of 361 nm. The charge density difference (CDD) shows that the transfer of electrons from the tertiary carbon‒hydrogen bond to the formaldehyde molecule is followed by photoexcitation, which causes the breaking of the tertiary carbon bond and the formation of hydroxymethyl radicals. The TD-DFT simulation further confirms the above conclusions from the geometry of the molecules. The energy required for each elementary reaction to the formation of the carbonyl group is also calculated.

Insights into the Role of Framework and Nonframework Aluminum in the Protolytic Reaction of Carbon–Carbon and Tertiary Carbon–Hydrogen Bonds of Isobutane

Insights into the Role of Framework and Nonframework Aluminum in the Protolytic Reaction of Carbon–Carbon and Tertiary Carbon–Hydrogen Bonds of Isobutane

Stabilization of Palladium Nanoparticles by Polyoxometalates Appended with Alkylthiol Tethers and their Use as Binary Catalysts for Liquid Phase Aerobic Oxydehydrogenation

A polyoxometalate with two alkyl thiol appendages, Q4[SiW11O40(SiCH2CH2CH2SH)2] (Q=ammonium salt) stabilized the formation of palladium nanoparticles. This tethered polyoxometalate–palladium binary catalyst was effective for the aerobic oxydehydrogenation of vinylcyclohexene and vinylcyclohexane to styrene as the major product via activation of the allylic, tertiary carbon-hydrogen bond.

Selective catalysis of μ-oxo-bismetalloporphyrins for 2-methylbutane oxidation with PhIO under mild conditions

Fourteen μ-oxo-bisironporphyrins and nine μ-oxo-bismanganeseporphyrins were synthesized, and their selective catalysis for the oxidation of the secondary and tertiary carbon–hydrogen bonds of 2-methylbutane with PhIO were also studied. The ratio of the relative reaction selectivity of tertiary carbon–hydrogen bonds to secondary carbon–hydrogen bonds was 3:1 when ironporphyrins were used as catalysts, and 4:1 when manganeseporphyrins were used as catalysts. The research showed that the substituents on the porphyrin rings influenced the catalytic selectivity of metalloporphyrins for the oxidation of the secondary and tertiary carbon–hydrogen bonds as well as the reaction rate. Whether ironporphyrins or manganeseporphyrins, the electron-attracting groups on porphyrin rings increased the catalytic selectivity of metalloporphyrins for the tertiary carbon–hydrogen bonds and the reaction rates, however, the electron-releasing groups increased the catalytic selectivity of metalloporphyrins for secondary carbon–hydrogen bonds, but reduced the reaction rates.

Study of the selective catalysis of metalloporphyrins for 2-methyl-butane oxidation with PhIO under mild conditions

Abstract Nine ironporphyrins and eight manganeseporphyrins were synthesized, and their selective catalysis for the oxidation of the secondary and tertiary carbon–hydrogen bonds of 2-methyl-butane with PhIO was studied. The proportion of the oxidation product of tertiary carbon–hydrogen bond to the one of secondary carbon–hydrogen bond was 3:1 when ironporphyrins were used as catalysts, and 2.3:1 when manganeseporphyrins were used as catalysts. The research showed that the substituting groups on the porphyrin rings influenced the catalytic selectivity of metalloporphyrins for the oxidation of the secondary and tertiary carbon–hydrogen bonds as well as the reaction yields. The electron-attracting groups on benzene rings of ironporphyrins increased the catalytic selectivity of ironporphyrins for the tertiary carbon–hydrogen bond oxidation and the reaction speeds, and the electron-releasing groups increased the catalytic selectivity for secondary carbon–hydrogen bond oxidation and reduced the reaction speeds. Both electron-attracting and -releasing groups on benzene rings of manganeseporphyrins enhanced the catalytic selectivity of manganeseporphyrins for the secondary carbon–hydrogen bond oxidation.

The carbon-hydrogen insertion reaction of dichlorocarbene with polycyclic hydrocarbons.

The factors influencing the carbon-hydrogen insertion reaction of dichlorocarbene into tertiary carbon-hydrogen bonds are discussed.

The controversial heat of formation of the tert-C4H9 radical and the tertiary carbon-hydrogen bond energy

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTThe controversial heat of formation of the tert-C4H9 radical and the tertiary carbon-hydrogen bond energyDavid GutmanCite this: Acc. Chem. Res. 1990, 23, 11, 375–380Publication Date (Print):November 1, 1990Publication History Published online1 May 2002Published inissue 1 November 1990https://doi.org/10.1021/ar00179a005RIGHTS & PERMISSIONSArticle Views154Altmetric-Citations52LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (793 KB) Get e-Alerts Get e-Alerts

Radical ions in photochemistry. 21. The photosensitized (electron transfer) tautomerization of alkenes; the phenyl alkene system

Alkenes, conjugated with a phenyl group, can be converted to nonconjugated tautomers by sensitized (electron transfer) irradiation. For example, irradiation of an acetonitrile solution of the conjugated alkene 1-phenylpropene, the electron accepting photosensitizer 1,4-dicyanobenzene, the cosensitizer biphenyl, and the base 2,4,6-trimethylpyridine gave the nonconjugated tautomer 3-phenylpropene in good yield. Similarly, 2-methyl-1-phenylpropene gave 2-methyl-3-phenylpropene, and 1-phenyl-1-butene gaveE- and Z-1-phenyl-2-butene. The reaction also works well with cyclic alkenes. For example, 1-phenylcyclohexene gave 3-phenylcyclohexene, and 1-(phenylmethylene)cyclohexane gave 1-(phenylmethyl)cyclohexene. The proposed mechanism involves the initial formation of the alkene radical cation and the sensitizer radical anion, induced by irradiation of the sensitizer and mediated by the cosensitizer. Deprotonation of the radical cation assisted by the base gives the ambident radical, which is then reduced to the anion by the sensitizer radical anion. Protonation of the ambident anion at the benzylic position completes the sequence. Reprotonation at the original position is an energy wasting step. Tautomerization is driven toward the isomer with the higher oxidation potential, which is, in the cases studied, the less thermodynamically stable isomer. The regioselectivity of the deprotonation step is dependent upon the conformation of the allylic carbon–hydrogen bond. The tautomerization of 2-methyl- 1-phenylbutene gave both 2-phenylmethyl-1-butène and 2-methyl-1-phenyl-2-butene (E and Z isomers), while 2,3-dimethyl- 1-phenylbutene gave only 3-methyl-2-phenylmethyl-1 -butene. In the latter case, steric interaction of the methyls on the isopropyl group prevents effective overlap of the tertiary carbon–hydrogen bond with the singly occupied molecular orbital, thus inhibiting deprotonation from this site. Keywords: photosensitized, electron transfer, alkene, tautomerization, radical cation.

ESR study of the effect of ferric chloride on the photodegradation of model compound for polypropylene

AbstractIn our previous article on the photodegradation of polypropyle (PP), the effect of ferric chloride (FeCl3) accelerating the formation of peroxy radical and depressing the formation of alkyl radical were reported. In the present article, the influence of FeCl3 on model compounds of PP was examined using electron spin resonance (ESR) spectrometry. The following compounds were employed as models of PP, including its irregular structures: 2‐methylpentane (2‐MP), 2,4‐dimethylpentane (2,4‐DMP), 2‐methyl‐4‐pentanone (2‐M4P), 2,6‐dimethyl‐4‐heptanone (2,6‐DM4H), 2‐methyl‐1‐pentene (2‐M1P), and tert‐butylhydroperoxide (t‐BuO2H). FeCl3 accelerated the formation of alkyl radicals for 2‐MP and 2,4‐DMP, alkyl and acyl radicals for 2‐M4P and 2,6‐DM4H, and alkyl radicals for 2‐M1P. As no definite effect of FeCl3 was observed for n‐pentane and 2‐octanone, FeCl3 was assumed to attack saturated hydrocarbons, ketones at a tertiary carbon‐hydrogen bond, and hydrocabons at an allylic hydroge, leading to easier photodegradations. FeCl3 was also effective for the photodegradation of t‐BuO2H using λ >300 nm, so that FeCl3 is believed to contribute also to the photodegradation of PP under the same irradation conditions. The catalytic effect of FeCl3 in photodegradation seems to origirate in a redox reaction.

Mechanism of oxidation of saturated hydrocarbons by cobalt(III), manganese(III), and lead(IV) trifluoroacetates

Oxidation of adamantane with lead tetra-acetate or manganese triacetate in acetic acid gives poor yields of primary products (based on the oxidant). However, oxidation of adamantane by manganese(III), cobalt(III), or lead(IV) acetates in trifluoroacetic acid gives high yields of 1-adamantyl trifluoroacetate as primary product. Other hydrocarbons are also oxidised by attack at a bridgehead carbon–hydrogen bond. Thus bicyclo[3.3.1]nonane with Pb4+ gives the trifluoroacetate of bicyclo[3.3.1 ]nonan-1-ol in 74% yield and similarly diamantane gives the two bridgehead trifluoroacetates in 93% yield. The generality of these oxidations is discussed. A product analysis shows that in contrast to anodic oxidation which gives products of fragmentation with substituted adamantanes, oxidation by PbIV, CoIII, or MnIII leads only to products by attack at a bridgehead tertiary carbon–hydrogen bond. In further contrast, anodic oxidation of 1,3,5-trimethyl-7-t-butyladamantane (30) leads to fragmentation products in high yield, but oxidation of tetrasubstituted adamantanes such as (30) by metal salts is very sluggish and gives, in low yield, complex product mixtures. Comparison of the electrochemical oxidations with those by CoIII. MnIII, and PbIV suggests that, in contrast to current views, oxidation of saturated hydrocarbons by metal salts does not proceed via cation radical intermediates. A mechanism proceeding by localised attack at a carbon–hydrogen bond is suggested. Adamantane with potassium permanganate in trifluoroacetic acid gives protoadamantanone (37) in 30% yield based on hydrocarbon consumed. A novel mechanism for this oxidation is tentatively proposed.

Synthesis of bicyclobutanes: exclusive insertion of a cyclopropylidene into primary rather than tertiary carbon-hydrogen bonds.

Das Dibromcyclopropan (I) erhalt man aus 2,3,4-Trimethyl-penten-(2) und Bromoform/Kalium-tert-butylat in Pentan, es liefert bei der Behandlung mit Methyllithium bei -40°C, 10°C oder 36°C die Bicyclobutane (II)-(IV).

Heterogeneity and mechanism in hydrocarbon oxidation

The distribution of the intermediate products of the oxidation of low-molecular-weight hydrocarbons, such as isobutane, n -butane, and n -pentane, is often dependent on the nature of the reactor surface, while that obtained from higher-molecular-weight hydrocarbons is little affected by surface conditions. Extensive kinetic and analytical investigations of the oxidation of n -butane, isobutane, n -pentane, and 2-methylpentane, in the temperature range 250°–400°C, show that this variation of heterogeneity with molecular structure may be explained in terms of the ability of the alkylperoxy radicals derived from these fuels to isomerize. Under initial conditions of temperature and pressure, where cool flames propagate, heterogeneous reactions are important only for those fuels whose alkylperoxy radicals cannot isomerize by 1:5 H-transfer involving a secondary or tertiary carbon-hydrogen bond.

Trichloromethylsilane derivatives as dichloromethylene transfer agents; kinetic evidence for free dichlorocarbene

The trichloromethylsilane derivatives CCl3·SiXYZ (I; X = Y = Z = Cl; II; X = Y = Cl, Z = OEt; III; X = Cl, Y = Z = OEt; IV; X = Y = Z = OEt; V; X = Y = Cl, Z = Me; VI; X = Y = Cl, Z = CCl3) give good yields of 1,1-dichloro-2-n-alkylcyclopropane when heated (ca. 175–240 °C) with dodec-1-ene and hexadec-1-ene. Insertion of the dichloromethylene group into the tertiary carbon–hydrogen bond of p-cymene occurs when (I) or (IV) is heated (ca. 175 °C) with p-cymene. Kinetic evidence is presented for the intermediacy of free dichlorocarbene in the dichloromethylene transfer reactions of (I) and (IV). The activation energies for the reactions of compounds (I), (IV), and trichloromethyltrifluorosilane with olefins are compared.

Kinetics and Mechanism of the Gas Phase Reaction between Iodine and Isopropyl Alcohol and the Tertiary Carbon-Hydrogen Bond Strength in Isopropyl Alcohol1a

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTKinetics and Mechanism of the Gas Phase Reaction between Iodine and Isopropyl Alcohol and the Tertiary Carbon-Hydrogen Bond Strength in Isopropyl Alcohol1aR. Walsh and S. W. BensonCite this: J. Am. Chem. Soc. 1966, 88, 15, 3480–3485Publication Date (Print):August 1, 1966Publication History Published online1 May 2002Published inissue 1 August 1966https://doi.org/10.1021/ja00967a003RIGHTS & PERMISSIONSArticle Views122Altmetric-Citations24LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (647 KB) Get e-Alerts Get e-Alerts

α-Eliminierung an verzweigten halogen-und dihalogenalkanen

The α-elimination of hydrogen chloride from 1-chloroalkanes, and the α-elimination of iodine from 1,1-diiodoalkanes have been studied with particular emphasis on the formation of isomeric cyclopropanes. The product ratios are compared to those obtained by the pyrolysis of diazoalkanes. The intermediates produced by the α-eliminations are found to insert more selectively into secondary and tertiary carbon-hydrogen bonds. Treatment of 1,1-diiodoneoalkanes with Na, Li and Mg affords predominantly cyclopropanes whereas Zn and Cu produce olefins via rearrangements of the Wagner-Meerwein type. Die α-Eliminierung von Chlorwasserstoff aus 1-Chloralkanen und die α-Eliminierung von Jod aus 1,1-Dijodalkanen wurden untersucht, besonders in Hinblick auf die Bildung isomerer Cyclopropane. Die Produktverhältnisse werden mit denen der Diazoalkan-Pyrolyse verglichen. Man findet, daβ sich die Zwischenstufen der α-Eliminierung selektiver in sekundäre und tertiäre CH-Bindungen einschieben. Einwirkung von Na, Li und Mg auf 1,1-Dijodneoalkane führt überwiegend zu Cyclopropanen, während Zn und Cu unter Wagner-Meerwein-Umlagerung Olefine liefern.

Stability of tertiary carbon–hydrogen bonds in polyacrylonitrile

Stability of tertiary carbon–hydrogen bonds in polyacrylonitrile

Examination of the oxidative degradation of polyacrylonitrile using infrared spectroscopy

AbstractThe oxidative thermal degradation of polyacrylonitrile has been examined using infrared spectroscopy. It was found that the generally accepted mechanism for the thermal degradation of polyacrylonitrile in air, which involves direct interaction of neighboring nitrile groups, and alternate proposals, involving azomethine crosslinks through reaction of the nitrile group and a neighboring tertiary hydrogen atom, do not satisfactorily represent an initial degradation scheme accounting for the observed infrared spectral changes. Rather, it must be concluded that these reactions take place after the initial degradation, to produce highly complex pyridinoid systems, and are not observable under the experimental conditions employed here. By detailed interpretation of the spectral changes using, in part, a difference spectral examination technique, an alternate route for the oxidative degradation involving the introduction of double bonds in the polymer chain could be formulated. This reaction can best be visualized as occurring via the attack of molecular oxygen at the activated tertiary carbon–hydrogen bond adjacent to the electron‐withdrawing nitrile group. The nitrile group was shown to remain unreacted during the course of the initial oxidation. After the introduction of the double bond, a number of secondary degradative reactions, of which the previously proposed routes of degradation are representative, take place; these include degradation reactions of the nitrile groups to form acid and amide groups. It was observed that the accumulation of oxygenated intermediates on the surface of the polymer film is a rapid reaction and that the initial degradation process is controlled by the concentration of these species.

A SYSTEM OF MOLECULAR THERMOCHEMISTRY FOR ORGANIC GASES AND LIQUIDS

An analysis has been made of the heats of formation and combustion of organic gases and liquids, and of the heats of vaporization of liquids. The work has been done as far as possible with homologous series, in order to discover systematic effects. The data are converted into heats of atomization, i.e., the heats required to convert the gases or liquids into their constituent atoms. It is shown that the heats of atomization of the gaseous aliphatic hydrocarbons (paraffins, olefins, and acetylenes) can be accurately represented by a scheme in which a distinction is made between primary, secondary, and tertiary carbon–hydrogen bonds, and between bonds that are next to, and next but one to, multiple bonds. For aromatic molecules an appropriate correction for resonance is proposed. For other types of compound it is found that suitable values for the various bonds (e.g., C–CHO, C–OH) will give rise to good agreement with experiment.It is shown that to a reliable approximation heats of vaporization are also amenable to the same treatment. Since this is so it is possible to assign bond values on the basis of which it is possible to make predictions about heats of formation of liquids.A system of coefficients is worked out by means of which the numbers of atoms of various kinds in a molecule can be expressed in terms of the numbers of the different kinds of bonds. On the basis of these it is shown how bond contributions to heats of formation and heats of combustion can be calculated. A table (Table X) gives the contributions proposed for the heats of atomization, heats of formation, and heats of combustion for both gases and liquids.