Effect Of Methyl Substituents Research Articles

Photochemistry of ring substituted polystyrenes—Part IV: Photolyses of poly( o-, m-, p-methylstyrenes)

The photodegradations of films (2 × 10 −4 cm thick) of poly( o-, m- and p-methylstyrenes) with 254 nm radiation under high vacuum at 25°C are studied. In all cases the principal gaseous product is hydrogen but smaller quantities of methane, and very small amounts of ethane, are also formed, indicating that fission of bonds between the ring and the methyl groups is also involved. Ultraviolet and visible spectra of degraded films indicate the presence of unsaturated groups and of coloured species. Solubility data indicate that crosslinking and chain scission occur simultaneously. Rates of crosslinking are greater than those for polystyrene and this is attributable to the participation of the substituted phenyl radicals (formed by phenyl-CH 3fission) in addition reactions. However, crosslinking is inhibited sterically to some extent in the poly( o-methylstyrene). Quantum yields for gaseous product formation and probabilities of chain scission and crosslinking are determined. Mechanisms are advanced that correlate the rate of product formation and chain scission with the effect of the particular methyl substituent on the stabilities of the radical intermediates.

Stereochemistry of the photoinduced and Michael addition of methanol to seven- and eight-membered 2-cycloalkenones. The effect of methyl substituents

Stereochemistry of the photoinduced and Michael addition of methanol to seven- and eight-membered 2-cycloalkenones. The effect of methyl substituents

The stereochemistry of the reduction of 3-ketopiperidines: The effect of e- and ?-C(2)-methyl groups on the ratio of epimeric alcohols

The cis and trans isomers of 1,2-dimethyl-5-tert-butyl-3-piperidone were synthesized and their interconversion and reduction stereochemistry were studied. The effect of the equatorial and axial vicinal methyl substituents on the stereochemistry of the hydride and catalytic reduction of the ketone function was shown.

SOLVENT AND METHYL SUBSTITUENT EFFECT ON PHOTOTAUTOMERISM AND IONIZATION OF ALLOXAZINES

Abstract— The absorption and emission spectra of alloxazine and its methyl derivatives have been measured in solvents of different polarity. From roughly linear correlation between two long wavelength absorption maxima and the emission maxima positions vs solvent polarities. systematic deviations have been observed for alloxazines in pyridine, acetic acid and water. The deviations depend on the methylation site of alloxazine in a way suggesting formation of hydrogen bond in the ground state and phototautomerism in the excited state. As phototautomerism of alloxazines in the presence of pyridine and water may involve ionic equilibria, the pKa values of alloxazines have been measured (8.11–8.58) and the pKB* estimated from the Förster cycle (2.3–6.6 for N‐1 monoanion and 7.4–7.8 for N‐3 monoanion). The phototautomeric efficiency of alloxazines in pyridine, acetic acid and water depend on the acidity of the N‐1 proton and on the steric effects of methyl substituents, mainly at C‐9. The anionic forms of alloxazines differ from the phototautomeric species in emission maxima positions, radiative lifetimes and they are dissimilarly influenced by the methylation site and medium viscosity.

Electrophilic aromatic substitution. Part 22. The effect of methyl substituents on detritiation of the 9-position of phenanthrene; tritium migration during exchange

Rates of protiodetritiation in trifluoroacetic acid at 70 °C have been measured for 9-tritiated phenanthrenes containing a methyl substituent in each of the positions 1–8. The activating effects of these substituents are as follows (positions in parentheses): 4.24(1); 2.77(2); 17.4(3); 2.96(4); 2.37(5); 3.16(6); 3.05(7); 2.67(8). The methyl substituent effects (with the exception of 6-methyl) closely parallel those obtained for the corresponding interactions in naphthalene, such differences as do exist being predicted by empirical calculations which simply consider the change in bond orders on going from ground state to transition state; calculations of the effect of a CH2– substituent on localization energies are also satisfactory models. The reactivity of the 6-methyl compound is anomalously high and is believed to be due to migration of tritium across the 9,10-bond accompanying the exchange, thereby giving a small amount of the more reactive 3-methyl[9-3H]phenanthrene. Likewise, detritiation of 3-methyl[9-3H]phenanthrene gave a curved kinetic plot indicating the presence of an isomer, less reactive towards exchange, i.e. from tritium migration to give 6-methyl[9-3H]phenanthrene. This, the first example of a 1,2-migration of hydrogen in non-super acid media is calculated to occur to the extent of 6–10% during the time of the kinetic runs. σ+-Constants for all but the 3-methyl compound are closely similar and in the range –(0.415–0.44); the high reactivity of the 3-methyl compound for which σ+ is –0.51 derives from the strong conjugative interaction leading to a p-quinonoid-like transition state.

Stereochemical aspects of proton chemical shifts. VII. The γ effects of hydroxyl, methoxyl and methyl substituents

AbstractThe 1H NMR chemical shifts of some hydroxy, methoxy or methyl substituted trans‐decalins, trans‐1, 3‐dioxadecalins and cyclohexanes are reported. It is concluded that the replacement in a g+g+ HCCCH fragment of one hydrogen by hydroxy, methoxy or methyl results in a modest (0.1 ppm) upfield shift of the other hydrogen atom. Experimental limitations to the transferability of shift increments from one molecular environment to another are demonstrated. The syntheses of 1α,5β‐dimethoxy‐ and 1β,5α‐dimethoxy‐trans‐decalin are given.

ChemInform Abstract: CARBON‐13 CHEMICAL SHIFTS OF SOME PYRIDINES, 2,2′‐BIPYRIDYLS AND 1,10‐PHENANTHROLINES

ChemInform Abstract: CARBON‐13 CHEMICAL SHIFTS OF SOME PYRIDINES, 2,2′‐BIPYRIDYLS AND 1,10‐PHENANTHROLINES

Carbon‐13 nuclear magnetic resonance spectroscopy of methyl‐substituted piperidines and their hydrochloride salts

AbstractCarbon‐13 chemical shifts and 1J(CH) coupling constants of piperidine, 4‐t‐butylpiperidine, five C‐methyl substituted piperidines and of the corresponding N‐methyl compounds have been measured. These NMR parameters have also been determined for the fourteen corresponding hydrochlorides. The N‐methyl‐C‐methyl piperidinium salts showed two stereoisomers on the positive nitrogen atom. The effect of protonation is discussed in relation to charge and steric effects and the methyl substituent effects are compared with those of methyl‐substituted cyclohexanes. Deviations from the general tendencies in the series are correlated with changes in ring conformations around the highly crowded substituted carbons.

Methyl substituent effects in the 13C spectra of cyclohexanone O‐methyl oximes and N,N‐dimethylhydrazones

AbstractThe 13C NMR spectra of a series of 4‐t‐butylcyclohexane‐O‐methyl oximes and N,N‐dimethylhydrazones containing α‐methyl substituents have been measured. The effects of α‐methyl substitution (syn‐axial, anti‐axial and anti‐equatorial) on the carbons α, β and γ to the substitution site are similar to those previously found in cyclohexanones. Use has been made of these substituent parameters to determine the conformational equilibria of the mobile 2‐methylcyclohexanone derivatives.

Theoretical studies of the K + affinities of bases: a comparison of K + and Li + affinities

We have carried out ab initio calculations on interactions of K + affinities of some amines, alcohols, ethers, cyanides and amides to try to understand substituent effects on K + affinities as well as the differences between K + and Li + affinities. The calculated methyl substituent effect on K + affinities is in disagreement with experiment, in contrast to the Li + affinities. The Likely source of this disagreement is either the inadequacy of “double zeta” basis to correctly represent the polarization energy or to the fact that these SCF calculations do not include dispersion attraction.

Cationic polymerization of methyl substituted 1,3‐dioxepanes

AbstractThe polymerization of 4‐methyl‐1,3‐dioxepane (1a), 2,4‐dimethyl‐1,3‐dioxepane (1b), and 4,4‐dimethyl‐1,3‐dioxepane (1c) was investigated in 1,2‐dichloroethane at different temperatures ranging from −60 to 0°C by using boron trifluoride etherate as initiator. The polymerization of 1a involves an equilibrium between monomer and polymer, and gives a viscous polymer along with some cyclic oligomers of different sizes. 1H NMR and 13C NMR analysis of the polymer revealed that the bond cleavage of the unsymmetrical 1,3‐dioxepane ring in the polymerization occurred nearly randomly at the two acetal CO bonds. The thermodynamic parameters for the polymerization were determined from the temperature dependence of the equilibrium monomer concentrations: ΔH=−9,3±1,3 kJ · mol−1 and ΔS=−38,8±7,8J · mol−1 · K−1. Dimethyl substituted 1,3‐dioxepanes were found to be very reluctant to polymerize: Only a liquid oligomer was formed in very low yield from 1b, and even oligomer was not obtained from 1c. The effect of methyl substituents on the cationic polymerizability of 1,3‐dioxepanes is discussed from the thermodynamic point of view.

Molecular orbital theory of the hydrogen bond. 18. Methyl substituent effects on amide hydrogen bonding

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTMolecular orbital theory of the hydrogen bond. 18. Methyl substituent effects on amide hydrogen bondingJanet E. Del BeneCite this: J. Am. Chem. Soc. 1978, 100, 5, 1387–1394Publication Date (Print):March 1, 1978Publication History Published online1 May 2002Published inissue 1 March 1978https://doi.org/10.1021/ja00473a011RIGHTS & PERMISSIONSArticle Views101Altmetric-Citations38LEARN 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 (997 KB) Get e-Alerts Get e-Alerts

Structure and properties of poly(2,5‐dimethylterephthalamides)

AbstractSix methyl‐substituted wholly aromatic polyamides were synthesized from the reaction of 2,5‐dimethylterephthaloyl chloride with p‐phenylenediamine, its 2,5‐dimethyl and 2‐methyl derivatives, m‐phenylenediamine, or its 2‐methyl and 4‐methyl derivatives by solution polycondensation at low temperature. The x‐ray diffraction diagrams of the polyamides obtained exhibit crystal patterns. Density values range from 1.26 to 1.37 g/cm3. NMR spectra determined in concentrated H2SO4 solution are reported. Poly(2,5‐dimethylterephthalamides) have lower thermal stability than the corresponding polyterephthalamides. The increase in solubility of polyamide by the introduction of the 2,5‐dimethylterephthaloyl linkage is accompanied by a decrease in thermal stability. The effect of methyl substituents on thermal properties and solubility is discussed in terms of the packing of polymeric molecules and the extent of hydrogen bonding of the amide groups.

The baeyer-villiger reaction of strained cage compounds, 1,3-bishomocubanones, via carbocations

The Baeyer-Villiger oxidation of 1,3-bishomocubanone 1a in chloroform with m-chloroperbenzoic acid (m-CPBA) at room temperature proceeds quite rapidly and gives the ordinary lactone, 10-oxapentacy-clo[5.4.0.0 2.5.0 3.9.0 4.8]undecan-11-one 2a and the skeletal rearrangement product, 11-oxapentacy-clo[6.3.0.0 2.4.0 3.7.0 5.9]undecan-10-one 4a. Methyl substituted homologs ( 1d, 1e, 1f) of 1a give the corresponding ordinary and rearranged lactones ( 2d, 2e, 2f, 4d, 4e, 4f). In these oxidations, the mechanism via carbocations, cyclobutyl 18 and cyclopropylcarbinyl cations 19, plays a major role different from the ordinary concerted migration mechanism. Solvent effects, kinetic treatments, and methyl substituent effects on product ratios support this carbocation mechanism. The adduct formation process between a ketone and m-CPBA must be rate-determining.

Benzoquinone imines. Part 14. The kinetics and mechanism of the coupling of p-benzoquinone monoimines with m-aminophenols

The coupling of p-benzoquinone monoimines with m-aminophenols involves rate-controlling electrophilic attack of the p-benzoquinone imine and/or its conjugate acid on the 4-carbon atom of the m-aminophenolate ion to give the corresponding aminodihydroxydiphenylamine. The latter undergoes rapid oxidation to afford the 2-aminoindo-phenol [2-amino-N-(4-hydroxyphenyl)-p-benzoquinone monoimine]. In concentrated solution, if the 2-amino-indophenol has no substituent in the 5-position, addition of p-aminophenols to give a trinuclear species occurs. The effect of methyl and chloro substituents on the reactivity of the imine and m-aminophenol, and on the spectrum of the 2-aminoindophenol are discussed.

Organoiron complexes in organic synthesis. Part 2. Conformational and steric effects of methyl substituents in tricarbonyliron derivatives of bicyclo[4.4.0]decadienes

The reactions of cyanide and dimethyl sodiomalonate with 7- and 10-methyl-substituted derivatives of tricarbonyl-[1,3–6-η-4-methoxybicyclo[4.4.0]deca-3,5-dienylium]iron hexafluorophosphate have been studied. The presence of exo-methyl groups suppresses the addition of nucleophile to the angular terminus, C-1, and endo-methyl groups cause the formation of mixtures of angularly and non-angularly substituted products.

The noncumulative effect of methyl substituents on the rate of addition of benzeneselenenyl chloride to olefins

The rates and products of addition of benzeneselenenyl chloride to ethylene and its six Me substituted derivatives have been determined in methylene chloride at 25°. Unlike the addition of 4-chlorobenzenesulfenyl chloride to this same series of compounds, the effect of Me groups on the rates of addition is not cumulative. Also the regiochemistry of the product is different. For arenesulfenyl chloride additions, products of anti-Markownikoff orientation are formed preferentially under conditions of kinetic control. Under similar conditions regiospecific formation of the Markownikoff adduct is observed for the addition of benzeneselenenyl chloride to methylpropene and 2-methyl-2-butene. These data indicate a difference in both rate and product determining transition states between additions of arenesulfenyl and selenenyl chlorides to alkenes.

Binding of lithium(1+) ion to Lewis bases in the gas phase. Reversals in methyl substituent effects for different reference acids

Binding of lithium(1+) ion to Lewis bases in the gas phase. Reversals in methyl substituent effects for different reference acids

Gas phase basicities and relative proton affinities of compounds between water and ammonia from pulsed ion cyclotron resonance thermal equilibriums measurements

The pulsed ion cyclotron resonance method for precise determinations of proton transfer equilibrium constants has been applied to 46 carbon, nitrogen, oxygen, phosphorus, sulfur, arsenic, and selenium bases, with duplicating overlapping sequences, to obtain the relative proton affinities of water and ammonia. Where comparison is possible, the results are in generally good accord with those obtained by high-pressure mass spectroscopy. The results provide important new insights into the intrinsic effects of molecular structure on base strengths. Applications of these results to derive other gaseous ion thermochemical data are illustrated. In particular, methyl substituent effects on proton affinities have been extensively evaluated and interpretations are made of the comparisons with corresponding effects of homolytic bond dissociation energies of the conjugate acids of n-bases and with the hydride affinities of substituted methyl cations. Comparisons of the effects of n-alkyl substituents on the proton affinities of water and alcohols with carboxylic acids and their esters indicate that protonation is thermodynamically favored in the gas phase at the carbonyl oxygen of the latter. Large effects of polar electronegative substituents have been observed for various oxygen and nitrogen bases. An evaluation of entropy effects in gas phase proton transfer equilibria shows such effects to bemore » generally small for simple bases and approximately equal to entropy effects expected for changes in molecular rotational symmetry numbers. Finally, the present result provides the basis for evaluations of absolute proton affinities and of relative ion solvation energies.« less

A comparison of the role of charge transfer, hyperconjugation, inductive and field interactions in substitutd methyl and silyl substituent effects on benzene π vertical ionization energies

The first two vertical π-ionization energies of MX3 substituted benzenes as determined by photoelectron spectroscopy are compared with the results of modified CNDO/2 calculations, where M is Si or C and X is H, F, Cl and OCH3. The major substituent interaction mechanisms of MX3 are described within the CNDO/2 model. The results for methylorthobenzoate support intramolecular charge transfer stabilization of the benzene radical cation ground state by oxygen lone pair electrons, whereas the dominant interaction of the Si(OCH3)3 group is a positive charge stabilising field effect. The first vertical ionization energies of PhSiCl3 and PhCCl3 are unexpectedly assigned to ionization from the a′ π orbital rather than the a″ orbital nodal at the substituent site. Carbon-chlorine hyperconjugation is a suggested stabilizing interaction in the PhCCl32A′ cation. The shape of the first band in the PE spectrum of phenylsilane is described as a possible example of a pseudo Jahn—Teller effect. Unlike CX3, SiX3 substituents except, where X is methoxy, exhibit calculated opposing field and σ-inductive effects.