The Influence of Heteroatom-substituted Methyl Groups and of Vinyl Groups (CR2=CR—) Attached to C-2 of 1,3-Dioxolanes on the Ease and Direction of Hydrogenolysis of the 1,3-Dioxolanes by AlH2Cl, AlH3, or LiAlH4

1971 ◽  
Vol 49 (15) ◽  
pp. 2563-2577 ◽  
Author(s):  
H. A. Davis ◽  
R. K. Brown
Keyword(s):  
Diethyl Ether ◽  
Ring Opening ◽  
Room Temperature ◽  
Methyl Groups ◽  
Double Bond Migration ◽  
Methyl Group ◽  
Hydride Ion ◽  
Vinyl Group ◽  
Dialkyl Ethers ◽  
Reflux Temperature

Heteroatom substituents on the methyl group of 2-methyl-1,3-dioxolane retard the rate of hydrogenolysis by AlH2Cl of ether solutions of the 2-substituted 1,3-dioxolanes. The effectiveness of the heteroatoms in decreasing the ease of hydrogenolysis is H < S < O < Br < NR2. This retardation is thought to be due to the destabilization of the transition state leading to the intermediate oxocarbonium ion, caused by the electronegativity of the heteroatom and/or coordination of some of the AlH2Cl with the heteroatom.AlH2Cl or AlH3 in diethyl ether at room temperature reduces 2-vinyl- or 2-[alkyl (or aryl) substituted vinyl]-1,3-dioxolanes to only the β,γ-unsaturated alkyl β-hydroxyethyl ether, the product expected from hydride ion addition to C-2 of the 1,3-dioxolane. The ease of hydrogenolysis increases with increasing alkyl (or aryl) substitution on the 2-vinyl group.LiAlH4 in diethyl ether at room temperature, or in di-n-propyl ether or 1,2-dimethoxyethane (DME) at room temperature or reflux temperature, reduces 2-vinyl-l,3-dioxolane only to α-propenyl β-hydroxyethyl ether. This product is the result of hydride addition to the β-carbon of the vinyl group accompanied by ring opening and double bond migration. Alkyl substituents attached to the vinyl group of 2-vinyl-1,3-dioxolane markedly retard the rate of hydrogenolysis by LiAlH4 in the dialkyl ethers at room temperature, but at the reflux temperature (90°) of di-n-propyl ether the 2-alkylated vinyl-1,3-dioxolanes are hydrogenolyzed, but only to the β,γ-unsaturated alkyl β-hydroxyethyl ether. In refluxing DME (80°) the 2-alkylated vinyl-1,3-dioxolanes give primarily, if not exclusively, the α,β-unsaturated alkyl β-hydroxyethyl ether. A rationale is suggested to account for these results.

HINDERED CONFORMATIONAL ISOMERIZATION OF 9,10-DIHYDRO-9,9-DIMETHYL-10-METHYLENEANTHRACENES

1964 ◽  
Vol 42 (3) ◽  
pp. 565-571 ◽  
Author(s):  
D. Y. Curtin ◽  
C. G. Carlson ◽  
C. G. McCarty
Keyword(s):  
Room Temperature ◽  
Methyl Groups ◽  
Conformational Isomerization ◽  
Methylene Carbon ◽  
Methyl Group ◽  
First Order ◽  
Methylene Carbon Atom ◽  
Center Ring ◽  
Bromo Compound ◽  
Dibromo Derivative

While the n.m.r. spectrum of 10,10-dimethyl-9-methylene-9,10-dihydroanthracene (I) shows the geminal methyl group absorption as a sharp singlet the spectrum of the dibromo derivative, 10,10-dimethyl-9-dibromomethylene-9,10-dihydroanthracene (II) shows the methyl absorptions as two sharp well-separated peaks at room temperature which coalesce at 91°. 10,10-Dimethyl-9-phenylbromomethylene-9,10-dihydroanthracene (III), and the methyl ester (V) of IV show a broad geminal methyl spectrum at room temperature which separates to a doublet at lower temperatures and sharpens to a singlet at higher temperatures. Rate constants for the first-order processes responsible for the change in spectrum of II, III, and V have been calculated at the coalescence temperatures to be 57 (364 °K), 35 (305 °K), and 61 (300 °K) sec−1, respectively. The ΔH≠'s were used to extrapolate the rates to 305° to give values of 1, 40, and 100 sec−1, respectively. The process being studied is inferred to be the equilibrium between two boat conformations of the center ring in the dihydroanthracene system, rapid interconversion leading to identical environments for the two methyl groups. A comparison with the geometrically similar o,o′-disubstituted biphenyl racemization gives support for this explanation. A number of compounds with a proton and one substituent on the methylene carbon atom of I (substituents: bromine, chlorine, phenyl, carboxy, carbomethoxy, phenylmercapto) and also 10,10-dimethyl-9-phenylcarbomethoxymethylene-9,10-dihydroanthracene (XII) showed a single methyl absorption at room temperature. The methyl spectrum of the mono bromo compound VI did not broaden at temperatures down to 246 °K.

Melting Gel Films for Low Temperature Seals

2013 ◽  
Vol 1547 ◽  
pp. 81-86 ◽  
Author(s):  
Mihaela Jitianu ◽  
Andrei Jitianu ◽  
Michael Stamper ◽  
Doreen Aboagye ◽  
Lisa C. Klein
Keyword(s):  
Room Temperature ◽  
Viscous Fluids ◽  
Methyl Groups ◽  
Scanning Calorimetry ◽  
Hybrid Gels ◽  
Methyl Group ◽  
Oscillatory Rheometry ◽  
Melting Gels ◽  
Viscous Modulus ◽  
Insight Into

ABSTRACTMelting gels are silica-based hybrid gels with the curious behavior that they are rigid at room temperature, but soften around 110°C. A typical melting gel is prepared by mixing methyltriethoxysilane (MTES) and dimethyldiethoxysilane (DMDES). MTES has one methyl group substituted for an ethoxy, and DMDES has two substitutions. The methyl groups do not hydrolyze, which limits the network-forming capability of the precursors. To gain insight into the molecular structure of the melting gels, differential scanning calorimetry and oscillatory rheometry studies were performed on melting gels before consolidation. According to oscillatory rheometry, at room temperature, the gels behave as viscous fluids, with a viscous modulus, G″(t,ω0) that is larger than the elastic modulus, G′(t,ω0). As the temperature is decreased, gels continue to behave as viscous fluids, with both moduli increasing with decreasing temperature. At some point, the moduli cross over, and this temperature is recorded as the glass transition temperature Tg. The Tg values obtained from both methods are in excellent agreement. The Tg decreases from -0.3oC to -56oC with an increase in the amount of di-substituted siloxane (DMDES) from 30 to 50 mole %. A decrease of the Tg follows an increase of the number of hydrolytically stable groups, meaning a decrease in the number of oxygen bridges between siloxane chains.

X+ transfer from the halonium ions of adamantylideneadamantane to acceptor olefins. The possibility of chiral induction in the transfer process

1997 ◽  
Vol 75 (12) ◽  
pp. 1844-1850 ◽  
Author(s):  
Alexei A. Neverov ◽  
Theresa L. Muise ◽  
R.S. Brown
Keyword(s):  
Nmr Spectra ◽  
Room Temperature ◽  
Reaction Rate ◽  
Methyl Groups ◽  
Kinetic Behavior ◽  
Methyl Group ◽  
Chiral Induction ◽  
H Nmr ◽  
Group 12 ◽  
Kinetics Of

The bromonium ion of adamantylideneadamantane (Ad=Ad-Br+) has been used to induce the bromocyclization of a 4-pentenyl glycoside (10) and a 5-hexenyl glycoside (11) in dichloroethane. The kinetics of these processes have been studied at 25 °C in the presence of varying [Ad=Ad] and, in the case of the transfer to 10, in the presence of pentanol. The second-order rate constants for bromocyclization of these two alkenes are (1.04 ± 0.06) × 10−1 M−1 s−1 and (5.34 ± 0.2) × 10−1 M−1 s−1, respectively, and in no case does added Ad=Ad or pentanol alter the reaction rate. The kinetic behavior is interpreted in terms of cyclization occurring directly from a 1:1 complex of Ad=Ad-Br+ and 10 or 11. The chiral induction for the bromocyclization of 10 promoted by AdAd-Br+ was measured at 20% e.e., the (−)-(S)-tetrahydrofurfuryl bromide being the dominant stereoisomer. Ad=Ad molecules substituted at one of the homoallylic carbons by an axial methyl group (12), or by two methyl groups (axial and equatorial), were synthesized and the 1H NMR spectra of their bromonium ions is given. These materials are not stable for prolonged times at room temperature. A limited kinetic study of the reaction of 12-Br+ and 4-pentenol indicated that the Br+ transfer is 500 times faster than the comparable transfer from Ad=Ad-Br+ to 4-pentenol. The possibility of using these materials to induce chiral bromocyclization is discussed. Keywords: bromonium ion, halonium, transfer, chiral, adamantylideneadamantane.

Reactions of neopentane and 1, 1-dimethylcyclopropane with deuterium over metal films

1972 ◽  
Vol 329 (1579) ◽  
pp. 391-403 ◽  
Keyword(s):  
Ring Opening ◽  
Exchange Process ◽  
Major Product ◽  
Bond Rupture ◽  
Methyl Groups ◽  
Carbon Bond ◽  
Methyl Group ◽  
Nickel Films ◽  
Carbon Carbon Bond ◽  
Cobalt And Nickel

The simultaneous exchange and hydrogenolysis of neopentane have been examined over cobalt and nickel films by using a combined gas chromatographic-mass spectrometric technique. Exchange was mostly limited to one methyl group, yielding (CH 3 ) 3 (CH 2 D)C and (CH 3 ) 3 (CD 3 )C as the major products. With cobalt the multiply exchanged species predominated but nickel was selective towards the mono-deuterated product. Some of the initial exchanged neopentanes had more than three deuteriums and therefore were due to an αγ -exchange process. Methane was the major product from hydrogenolysis; nickel yielded more of the in termediate hydrocarbons (isobutane, propane and ethane) than cobalt. All of the hydrogenolysis products were completely exchanged. With cobalt, hydrogenolysis and exchange are comparable in rate but over nickel exchange occurs 6.5 times faster than hydrogenolysis. The hydrogenolysis of 1,1-dimethylcyclopropane was examined over iron, cobalt and nickel films at the same temperatures as were used for the neopentane reactions. Ring opening was favoured at the carbon-carbon bond opposite the substituent methyl groups to form neopentane. Considerable multiple carbon–carbon bond rupture occurred; over cobalt, methane was the major product but with nickel the reaction was specific to isobutane and methane. Iron was intermediate in behaviour. All the hydrogenolysis products were fully exchanged except neopentane, the major isotopes of which were (CH 3 ) 2 (CH 2 D ) 2 C and (CH 3 ) 2 (CH 2 D)(CD 3 )C. These products are analogous to those formed from neopentane exchange. The relative amounts of singly and multiply deuterated methyl groups formed from the two processes show a linear relation for the three metals, suggesting that ring opening occurs via a neopentane species which is adsorbed at only one methyl group. No exchanged 1,1-dimethylcyclopropanes were observed.

A Reinvestigation of the Deceptively Simple Reaction of Toluene with ●OH, and the Fate of the Benzyl Radical. I. a Combined Thermodynamic and Kinetic Study on the Competition Between ●OH Addition and Hydrogen Abstraction Reactions.

2019 ◽  
Author(s):  
Zoi Salta ◽  
Agnie M. Kosmas ◽  
Marc E. Segovia ◽  
Martina Kieninger ◽  
Oscar Ventura ◽  
...  
Keyword(s):  
Density Functional ◽  
Room Temperature ◽  
Hydrogen Abstraction ◽  
Reaction Rates ◽  
Composite Model ◽  
Alternative Mechanism ◽  
Radical Intermediate ◽  
Experimental Conditions ◽  
Methyl Group ◽  
Benzyl Radical

This work reports density functional and composite model chemistry calculations performed on the reactions of toluene with the hydroxyl radical. Both experimentally observed H-abstraction from the methyl group and possible additions to the phenyl ring were investigated. Reaction enthalpies and heights of the barriers suggest that H-abstraction is more favorable than ●OH addition to the ring. The calculated reaction rates at room temperature and the radical-intermediate product fractions support this view. This is somehow contradictory with the fact that, under most experimental conditions, cresols are observed in a larger concentration than benzaldehyde. Since the accepted mechanism for benzaldehyde formation involves H-abstraction, a contradiction arises that begs for an explanation. In this first part of our work we give the evidences that support the preference of hydrogen abstraction over ●OH addition and suggest an alternative mechanism which shows that cresols can actually arise also from the former reaction and not only from the latter.

A Reinvestigation of the Deceptively Simple Reaction of Toluene with ●OH, and the Fate of the Benzyl Radical. I. a Combined Thermodynamic and Kinetic Study on the Competition Between ●OH Addition and Hydrogen Abstraction Reactions.

2019 ◽  
Author(s):  
Zoi Salta ◽  
Agnie M. Kosmas ◽  
Marc E. Segovia ◽  
Martina Kieninger ◽  
Oscar Ventura ◽  
...  
Keyword(s):  
Density Functional ◽  
Room Temperature ◽  
Hydrogen Abstraction ◽  
Reaction Rates ◽  
Composite Model ◽  
Alternative Mechanism ◽  
Radical Intermediate ◽  
Experimental Conditions ◽  
Methyl Group ◽  
Benzyl Radical

This work reports density functional and composite model chemistry calculations performed on the reactions of toluene with the hydroxyl radical. Both experimentally observed H-abstraction from the methyl group and possible additions to the phenyl ring were investigated. Reaction enthalpies and heights of the barriers suggest that H-abstraction is more favorable than ●OH addition to the ring. The calculated reaction rates at room temperature and the radical-intermediate product fractions support this view. This is somehow contradictory with the fact that, under most experimental conditions, cresols are observed in a larger concentration than benzaldehyde. Since the accepted mechanism for benzaldehyde formation involves H-abstraction, a contradiction arises that begs for an explanation. In this first part of our work we give the evidences that support the preference of hydrogen abstraction over ●OH addition and suggest an alternative mechanism which shows that cresols can actually arise also from the former reaction and not only from the latter.

Kinetics of the Imidazolium Ring-Opening of mRNA 5'-cap Analogs in Aqueous Alkali

2006 ◽  
Vol 71 (4) ◽  
pp. 567-578 ◽  
Author(s):  
Alicja Stachelska ◽  
Zbigniew J. Wieczorek ◽  
Janusz Stępiński ◽  
Marzena Jankowska-Anyszka ◽  
Harri Lönnberg ◽  
...  
Keyword(s):  
Electrostatic Interaction ◽  
Ring Opening ◽  
Nucleophilic Attack ◽  
Amino Groups ◽  
Hydroxide Ion ◽  
Methyl Group ◽  
Structural Modifications ◽  
Alkyl Groups ◽  
Imidazolium Ring ◽  
Kinetics Of

Second-order rate constants for the hydroxide-ion-catalyzed imidazolium ring-opening of several mono- and dinucleosidic analogs of mRNA 5'-cap have been determined. Intramolecular stacking of the two nucleobases in the dinucleosidic analogs, m7GpppN (m7G = 7-methylguanosine, N = 5'-linked nucleoside), and electrostatic interaction between the N-alkylated imidazolium ring and phosphate moiety have been shown to shield the m7G moiety against the nucleophilic attack of hydroxide ion. In addition, the effect of methylation of the nucleobase amino groups and replacement of the 7-methyl group with other alkyl groups have been studied. The influence of all the structural modifications studied turned out to be modest, the cleavage rates of the most and least reactive analogs (with the exception of non-phosphorylated nucleosides) differing only by a factor of 5.

scholarly journals Synthesis and Characterization of Polyphosphazenes Modified with Hydroxyethyl Methacrylate and Lactic Acid

2013 ◽  
Vol 2013 ◽  
pp. 1-7 ◽  
Author(s):  
Evelyn Carolina Martínez Ceballos ◽  
Ricardo Vera Graziano ◽  
Gonzalo Martínez Barrera ◽  
Oscar Olea Mejía
Keyword(s):  
Lactic Acid ◽  
Ring Opening ◽  
Room Temperature ◽  
Block Structure ◽  
Ring Opening Polymerization ◽  
Synthesis And Characterization ◽  
Poly Lactic Acid ◽  
Hydroxyethyl Methacrylate ◽  
H Nmr

Poly(dichlorophosphazene) was prepared by melt ring-opening polymerization of the hexachlorocyclotriphosphazene. Poly[bis(2-hydroxyethyl-methacrylate)-phosphazene] and poly[(2-hydroxyethyl-methacrylate)-graft-poly(lactic-acid)-phosphazene] were obtained by nucleophilic condensation reactions at different concentrations of the substituents. The properties of the synthesized copolymers were assessed by FTIR,1H-NMR and31P-NMR, thermal analysis (DSC-TGA), and electron microscopy (SEM). The copolymers have a block structure and show twoTg's below room temperature. They are stable up to a temperature of 100°C. The type of the substituents attached to the PZ backbone determines the morphology of the polymers.

Sign in / Sign up

Export Citation Format

Share Document