Adjacent Methyl Research Articles

Reinvestigation of the substituent effects of fluorine on the 1H NMR chemical shifts of the adjacent methylene group in fluorinated [2.2]paracyclophanes

Reinvestigation of the substituent effects of fluorine on the 1H NMR chemical shifts of the adjacent methylene group in fluorinated [2.2]paracyclophanes

Regio- and Stereochemistry of Alkene Expulsion from Ionized sec-Alkyl Phenyl Ethers

Photoionization mass spectrometry of isotopically substituted 2-phenoxypropane (iPrOPh), 2-phenoxybutane (sBuOPh), and 3-phenoxypentane (3AmOPh) permits the analysis of branching ratios for competing pathways by which the radical cations expel neutral alkene to yield ionized phenol. Ionization energies (IEs) of 2-phenoxyalkanes do not differ significantly between 2-phenoxypropane and 2-phenoxyoctane and are unaffected by deuterium substitution. IEs for 3-phenoxyalkanes are 0.04 eV lower than for the 2-phenoxyalkanes. Measurements of PhOD•+:PhOH•+ ratios from deuterated analogues as a function of photon energy lead to a dissection of two mechanisms: direct syn elimination via four-member transition states (which differentiates between stereochemically distinct positions on an adjacent methylene group) and formation of ion−neutral complexes (which affords hydrogen transfer from all positions of the side chain). Syn elimination from ionized sBuOPh partitions among trans-2-butene, cis-2-butene, and 1-butene in a ratio of approximately 6:5:4, exhibiting no systematic variation with internal energy. The proportion of ion−neutral complex formation for sBuOPh increases with energy, from virtually nil at 9.6 eV to about 20% at 9.81 eV to slightly more than one-half at 11.92 eV. Ion−neutral complexes from sBuOPh yield nearly equal proportions of 1-butene and 2-butenes, with little variation as a function of internal energy, while those from 3AmOPh yield about 80−90% 2-pentenes. DFT calculations confirm the preference for syn elimination from ionized iPrOPh at low internal energies. The computed energy of that transition state agrees with published experimental determinations. Analysis of the electron density using the atoms-in-molecules approach shows that the transition state does not possess cyclic topology, unlike vicinal eliminations from neutral molecules (which pass through bona fide cyclic transition states). Cyclic topology is seen for a structure that precedes the potential energy maximum, but that ring disappears at the top of the barrier. Both syn elimination and ion−neutral complex formation from the radical cation proceed far along the pathway for bond heterolysis before arriving at a point at which the two types of mechanism diverge from one another.

New Methylene Specific Experiments for the Measurement of Scalar Spin–Spin Coupling Constants between Protons Attached to13C

New two- and three-dimensional NMR methods are proposed for the measurement of3J(H, H) coupling constants between two adjacent methylene moieties. The new experiment, which is based on a combination of the E.COSY principle and double/zero quantum heteronuclear spectroscopy, has been applied to diaceton-glucose and to the protein rhodniin. The coupling constants of CH-CH2groups have been compared with those obtained from a HCCH-E.COSY experiment to check the reliability of the results. An analysis of the coupling constants derived by comparison between experimental and simulated spectra is presented. Simulations were done with the program wtest considering fully correlated dipolar relaxation. Side-chain conformations in amino acids with adjacent methylene groups can be determined by the new experiment.

Racemic Ethyl 4-(2-Fluorophenyl)-2,6,6-trimethyl-5-oxo-1,4,5,6,7,8-hexahydroquinoline-3-carboxylate

The title compound, C21H24FNO3, has potential calcium modulatory properties. The 1,4-dihydropyridine ring has a shallow boat conformation with the 2-fluorophenyl substituent in an axial synperiplanar orientation. The quinoline ring has a half-chair conformation. Steric interactions between the adjacent methyl and ethoxycarbonyl substituents cause local bond-angle distortions. The molecules are linked into chains by intermolecular N—H⋯O hydrogen bonds.

Highly stereoselective epoxidation of a 4-methyl-5-(triethylsilyl)oxyallyl alcohol system with m-chloroperoxybenzoic acid

Epoxidation of 4-methyl-5-(triethylsilyl)oxyallyl alcohol system with m-chloroperoxybenzoic acid (MCPBA) has been found to occur highly stereoselectively and in high yields from the opposite side of the C 5 triethylsiloxy group regardless of the stereochemistry of an adjacent methyl group.

Synthesis, Spectral Studies and C-S, C-N Bond Fissions of Some Novel N-[Alkyl (4′- Substituted Phenylthio)] Phthalimides

N-[(4'-Substituted phenylthio)ethyl] phthalimide la-g and their corresponding n-propyl 2a-g, n-butyl 3a-g derivatives have been synthesised. The structure of these compounds were proved by UV,IR, 1H NMR, 13CMR and mass spectra. The 1H and 13C chemical shifts of the adjacent methylene protons and carbons of both the sulfur atom and phthalimido nitrogen group were reasonably correlated using σ° values. The carbon-nitrogen and the carbon-sulfur bond fissions in alkaline and acidic media were discussed.

(N-Methylthiocarbamoyl)tetrathiafulvalene derivatives and their radical cations: synthetic and X-ray structural studies

Lithiation of 4,5-bis(methylsulfanyl)-TTF 9, 4,5-(ethylenedisulfanyl)-TTF 10, 4,5-dimethyl-TTF 11 and 4,5,5′-trimethyl-TTF 12 (TTF=tetrathiafulvalene) followed by reaction with methyl isothiocyanate affords the corresponding (N-methylthio-carbamoyl)-TTF derivatives 14–17, respectively, in 54–70% yields. These new TTF derivatives display a broad intramolecular charge-transfer band in their UV–VIS spectra arising from conjugation between the donor TTF ring and the acceptor N-methylthiocarbamoyl moiety. Steric hindrance between the adjacent N-methylthiocarbamoyl and methyl substituents in 17 causes a marked hyposchromic shift in this band (λmax 395 nm) compared to compounds 14–16 (lambda;max 435–467 nm). Consistent with the electron-withdrawing properties of the N-methylthiocarbamoyl substituent, its attachment to the TTF ring raises slightly the oxidation potential of the system. Charge transfer complexes of these donors and (N-methylthiocarbamoyl)-TTF 2 with 7,7,8,8-tetracyano-p-quinodimethane (TCNQ) and salts with bromide anions are reported, some of which have high room temperature conductivity values. The X-ray crystal structures are presented for 16, 17 and the salts 2·Br, 14·TCNQ and (17)2·20. The structure of 16 comprises orthogonal dimers (kappa packing) while in the structure of 17 individual molecules are orthogonal to each other. There is weak intermolecular hydrogen bonding in both 16 and 17. In the structure of 2·Br, the radical cations 2+· are almost planar and they form an infinite stair-like stack of dimers, with bromide anions situated between the stacks, and linked with the cation by a strong N–H‥Br bond. The structure of 14·TCNQ comprises mixed ‥DDAADD‥ stacks; the N-methylthiocarbamoyl group engages in an interstack N–H‥N bond with a TCNQ anion. Analysis of the bond lengths in the structure suggests that there is partial charge transfer from 14 to TCNQ. In the structure of (17)2·20 molecules form mixed ‥DDADDA‥ stacks and analysis of bond lengths suggests that there is only a small degree of charge transfer from donor to acceptor. The geometries of compounds 2, 14, 16, 17 were optimised using the PM3 semi-empirical method and the results compare favourably with the X-ray structural data.

ω-Alkenyl-α-Methoxy-Benzyllithiums : Original Synthesis and Reactivity

1-Methoxy-benzyllithiums bearing suitably positioned C,C double bonds possess a high propensity to produce a five or a six membered cycle by carbocyclisation reaction. The reaction proceeds completely stereoselectively and produces a five membered cycle possessing the cis-stereochemistry between the methoxy and the adjacent methyl group. © 1997 Published by Elsevier Science Ltd.

Synthesis and nuclear magnetic resonance spectroscopic properties of some acetylenic tellura fatty acid esters

Five positional isomers of acetylenic tellura stearate ( 1– 5) have been synthesized by three different routes. The number of methylene groups located between the acetylenic system and the tellurium metal varies from 0 to 4. The 1H and 13C NMR spectroscopic properties have been studied. The tellurium atom induces strong deshielding effects on the adjacent methylene protons, which in combination with the deshielding effects of the acetylenic system allows most of the methylene groups between the tellurium and the triple bond to be identified by 1H NMR spectroscopic analysis. The tellurium causes a very strong shielding effect (ca. −27.1 ppm) on the carbon shift of the adjacent α-methylene carbon atom, but weak deshielding effects on the β-(ca. +2.6 ppm) and γ-(ca. +2.3 ppm) methylene carbon atoms. Carbon shifts of methylene carbon atoms, especially those which are located between the tellurium atom and the triple bond, are found very much upfield ( δ C 0.65–4.81) and in one case in the negative region ( δ C−17.95) of the 13C NMR spectrum. Most of the signals of the carbon nuclei of these analogue have been identified and from the results of these analyses the number of methylene groups between the acetylenic system and the tellurium atom can be determined.

Zirconocene-Mediated Cyclization of 2-Bromo α,ω-Dienes

When it is first treated with n-butyllithium at −78 °C, zirconocene dichloride is an effective reagent for the cyclization of some 2-bromo α,ω-dienes at 25 °C. The products are carbo- and heterocyclic five-membered rings with adjacent methylene and methyl substituents. Reductive cyclization to form zirconacyclopentanes, followed by β-bromo elimination, is indicated as the order of steps in the reaction mechanism. Use of catalytic zirconocene dichloride with excess butylmagnesium chloride in diethyl ether at 25 °C is effective only for cyclization of 2-bromo-1,6-heptadiene.

Intramolecularly Stabilized Phenylsilyl and Anthrylsilyl Cations

Phenyl-substituted silylium cations with two −CH2Z substituents in the ortho positions (R2SiC6H3(CH2Z)2+, I) first synthesized by Corriu and co-workers provide useful model systems to investigate solvent coordination of silylium cations R2HSi+ (H is equivalent to the C6H5 group) in solution. By rotation of the side chains, group Z can be positioned in such a way that Si+−Z interactions lead to an internal solvation of the silylium cation thus competing for or even preventing external solvation of −R2Si+ in solution. For Z = NR2, the properties of type I cations resemble those of the strongly coordinated silylium cation−solvent complexes R‘2HSi(NR3)2+ as is reflected by complexation energies, interaction distances, and δ29Si NMR chemical shift values typical of pentacoordinated Si. Weakly coordinating solvents such as alkanes can be mimicked by using for type I cations the side chain −C(CH3)3. A −SiH2+ group interacts with the closest H atoms of the two adjacent methyl groups and, despite the fact that interactions are just electrostatic, I largely loses its silylium cation character as indicated by the calculated δ29Si value. More silylium cation character is retained when a 1,8-dimethyl-substituted anthryl ring rather than the phenyl ring is used as a template for simulating solvent coordination of silylium cations in solution. The silyl cation Me2SiC14H7(CH3)2+ (18) with the −SiMe2+ group at position 9 framed between the two methyl substituents has a δ29Si IGLO value of 187 ppm, which is just 150 ppm upfield from the corresponding value for Me2HSi+ in the gas phase (334 ppm). The synthesis of 18 and related cations should be an interesting target for experimental work on silylium cations in solution.

Evidence for lateral chain conformation change in the solid phase of substituted nematogens

Abstract A new homologous series of 4-(4-chlorobenzoyloxy)-2-alkoxy-3-methyl-4′-(4-trans-pentyl-cyclohexanoyloxy) azobenzenes has been synthesized. These compounds contain four rings in the main core, a lateral alkoxy branch and an adjacent lateral methyl group on one inner ring. They present a large nematic range and a solid-solid phase transition for the first members of the series. The crystal structures of two similar compounds containing a lateral butoxy chain have been solved. The HM4 compound (C31H33N2O5Cl) is derived from the series, but does not have the terminal pentyl chain while the PM4 compound (C36H43N2O5Cl) possesses this terminal chain. HM4 and PM4 crystallize, respectively, in P21/c (Z = 4) and P1 (Z = 2) space groups. The final reliability factors are R = 0.138 for HM4 (the terminal cyclohexyl ring is largely disordered) and R = 0.041 for PM4, for 2204 and 1963 observed reflections, respectively. The four ring central core is linear and rigid for both compounds. The conformation of the b...

Molecular association, chelate conformation and reactivity correlations in substituted o-phenylenebis(salicylidenato)copper( II) complexes: UV-visible, EPR and X-ray structural investigations

Substituted o-phenylenesbis(salicylidenaminato) complexes of copper(II), Cu(5-X-saloph), where X = H ( 1), CH 3O ( 2) and Cl ( 3) have been synthesized and characterized. Complex 1, C 20H 14N 2O 2Cu, crystallizes in the orthorhombic space group P2 12 12 1 with two molecules (A and B) in the assymetric unit related by a non-crystallographic centre of inversion and the nitrogen atom of A coming closer to the metal ion of B and vice versa. The geometry around copper is essentially square planar in both A and B with average CuN and CuO bond distances being 1.89(2) and 1.95(2) →ing chelate conformation is also planar with a moderate “twist” at the “sal” groups. EPR spectra of the complexes are characterized by axial or rhombic g and A Cu tensors and indicate the occupancy of an unpaired electron in a “formal” d xy orbital. Solutions at 298 K showed superhyperfine features due to interaction of transferred unpaired spin with the nuclear spin of two magnetically equivalent 14N nuclei and the protons attached to adjacent methylene carbon atoms. The complexes exhibit solvatochromism. Substitution and δ-donor solvents show marked effects on the UV-visible and EPR spectra. MO calculations reveal that the in-plane δ and π bondings are covalent in nature. The correlation between conformational flexibility and reactivity is discussed.

(Trimethoxysilyl)carbene: Photochemistry, Oxidation, and Carbonylation of a Silylcarbene

Photolysis (λ > 345 nm) of matrix-isolated (trimethoxysilyl)diazomethane (1e) leads to the formation of (trimethoxysilyl)carbene (2e), which was characterized by IR and UV−vis spectroscopy. The photochemistry, reaction with molecular oxygen, and carbonylation of 2e were studied in argon matrices at cryogenic temperatures. These experiments demonstrate that 2e is a triplet ground state carbene. Photolysis at 280 nm results in the formation of 1,1-dimethoxy-1,2-silaoxetane by insertion of the carbene center into one of the adjacent methyl groups.

Foiled Conjugation in α-Oximino Carbocations

The 4-CHNOCH3 group is a cation-stabilizing group when placed in the para-position of a cumyl cation. The effect of this group on cumyl cations when flanked by adjacent methyl groups has now been determined. Solvolysis rates of 3,5-(CH3)2-4-(CHNOCH3)cumyl trifluoroacetates are somewhat slower than that of 3,5-dimethylcumyl trifluoroacetate. This is attributed to steric inhibition of the cation-stabilizing resonance effect of the p-oximino group. In a 1-adamantyl system, where an α-oximino group has been placed directly adjacent to a developing cationic center, solvolysis rates relative to 1-adamantyl mesylate are slowed by a factor of 108. This is attributed a cation-destabilizing inductive effect where geometric constraints prevent stabilizing orbital overlap of the cationic center with the adjacent α-oximino group. This cation-destabilizing effect fades in the homoadamantyl and the bicyclo[3.3.1]nonyl systems, where rate-retarding effects are 1.6 × 104 and 1.5 × 102, respectively. The behavior of geomet...

Reactions of fused and unfused α-pyrones with magnesium alkoxide, sodium alkoxide and water as the nucleophile: effects of chelation

The reactions between a series of α-pyrones (two mono- and three fused) and the non-chelating base sodium alkoxide, the chelating base magnesium alkoxide and water as the nucleophile, have been studied. Aromatic and other products formed reflect the points of attack on the pyrone systems and when sodium methoxide is used the ensuing cyclisation is preferentially by aldol mechanisms. The employment of excess magnesium methoxide or ethoxide gives magnesium-chelated precursors and the nature of products now depends on these intermediates, and the protection afforded by such magnesium chelation to the reaction products. In the case of structures containing chelated β-keto ester features the chelates are screened from attack as aldol acceptors, but are effective Claisen acceptors. In such chelates an adjacent methylene is activated by further magnesium alkoxide to act as an aldol or Claisen donor. These contrasting aldol/Claisen reactivities, as between a non-chelating and a chelating base, are illustrated in the ensuing chemistry of the pyrones. Treatment with water releases the main carbon chain with decarboxylation, from which new products may form.

Nuclear magnetic resonance properties of tellurium dichloride derivatives of methyl telluralaurate isomers

Reaction of methyl 2- to 6-telluralaurate with sulfuryl chloride gives the corresponding tellurium dichloride (TeCl 2) derivatives quantitatively. The TeCl, group induces a strong de-shielding effect on the adjacent methylene groups. The 2-, 3- and 4-positional isomers are identified by 1H-NMR spectroscopic analysis, and 13C-NMR spectroscopic analysis allows all five positional isomers to be characterized.

Synthetic studies on development of a novel macrolide ionophore: Configurational requirement of 16-membered macrodiolide for binding ability

Twelve synthetic 16-membered macrodiolides were prepared from racemic homononactic acid. The compounds which have an anti-relationship between the ether linkage of THF and the adjacent methyl showed the cation-binding ability. Macrodiolide 12 exhibited the ion selectivity for Li +.

ChemInform Abstract: Eclipsed Ground‐State Conformations for Methoxycyclohexenes such as (I) ‐(IV) with Adjacent Methyl Group Substitution. An NMR Criterion and Molecular Mechanics Calculations.

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Conformational investigation of gaseous 1,5-hexadiene by electron diffraction and molecular mechanics

The molecular structure of gaseous 1,5-hexadiene has been studied by electron diffraction. The following bond lengths ( r g) and bond angles were obtained (CH) mean, 1.087 ± 0.002 A ̊ ; CC, 1.340 ± 0.003 A ̊ ; C(H 2)C(H), 1.508 ± 0.012 A ̊ ; C(H 2)C(H 2), 1.538 ± 0.027 A ̊ ; C(H 2)C(H 2)C(H), 11.5 ± 0.9°; C(H 2)C(H)C(H 2), 124.6 ± 1.0°; C(H)C(H 2)H, 128.9 ± 1.5°; C(H 2)C(H)H, 116.8 ± 2.3°; HC(H 2)H, 112.0 ± 2.6°. The electron diffraction data are compatible with the presence of anti and gauche conformers with respect to the central CC bond, as predicted by molecular mechanics (MM2) calculations, the anti form being the most stable. Each of the CC bonds eclipses one of the CH bonds of the adjacent methylene group, as suggested by a gas-phase overtone spectroscopic investigation. The electron diffraction bond lengths and bond angles are generally in good agreement with the results of the MM2 calculations. The energy difference between the gauche and anti conformers estimated from the electron diffraction analysis (1.0 ± 0.5 kJ mol −1) has the same sign but considerably smaller magnitude than the difference obtained by MM2 calculations. One of the gauche conformers of the free molecule is remarkably similar to the hexadiene ligand of crystalline (1,5-hexadiene)copper(I) trifluoromethanesulfonate. Apparently, the chelating interaction stabilizes the rotational form whose geometry is the easiest to adapt in the complex although it is not the most favorable energetically for the free molecule.