Methyl Carbon Resonances Research Articles

Configurational sequence determination of poly(isobornyl acrylate) by NMR spectroscopy

Poly(isobornyl acrylate) (PiBA) was prepared by atom transfer radical polymerization (ATRP). Complete characterization of microstructure of PiBA was carried out using one-dimensional [ 1H, 13C{ 1H}] and two-dimensional (HSQC, TOCSY and HMBC) NMR spectra. The methyl, methylene, methine, quaternary and carbonyl carbon resonance signals were found to be sensitive to various configurational sequences. The methine carbon (C 12) was assigned up to triad configurational sequences in 13C{ 1H} NMR spectrum whereas β-methylene carbon resonances were assigned up to diad configurational sequences. The quaternary carbon in 13C{ 1H} NMR spectrum were resolved completely with the help of HMBC NMR spectrum. The stereoregularity of PiBA was found to be random with mm = 20%, mr = 53%, and rr = 27%.

Synthesis and structure elucidation of 25,26,27,28-tetramethylcalix[4]arene tetraketone using 1D and 2D NMR spectroscopies

The 1H and 13C NMR spectra of the new calix[4]arene-based tetraketone were completely assigned by one- and two-dimensional homo- and heteronuclear experiments ( 1H– 1H COSY, 1H– 13C HMQC, and HMBC) at 400 and 100 MHz, respectively, at 25 °C standard pulse sequence. 1H and 13C spectra were measured at room temperature for 25,26,27,28-tetramethylcalix[4]arene tetraketone ( 1). 13C{ 1H}, DEPT and NMR techniques were used to distinguish the methyl, methylene and methine carbon resonance signals of calix[4]arene 1. Correlation of 1D ( 1H, 13C{ 1H}, DEPT) and 2D (HMQC and HMBC) NMR data was used to completely assign various overlapping and broad signals of calix[4]arene 1. Heteronuclear multibond correlation (HMBC) studies were used to completely assign various carbon resonances. Our results show that the conformation of calix[4]arene 1 in the solution is very similar to the cone conformation reported in the literature.

One- and two-dimensional NMR studies of methyl acrylate/vinyl acetate/ N-vinyl carbazole terpolymers

Terpolymers of methyl acrylate/vinyl acetate/ N-vinyl carbazole (M/A/C) with different compositions were synthesized by solution polymerization using AIBN as an initiator. Composition of terpolymers was determined from quantitative 13C{ 1H} NMR spectrum. Two-dimensional heteronuclear single quantum correlation (HSQC) and total correlated spectroscopy (TOCSY) were used to assign the methylene and methine carbon resonances by analyzing two and three bond order couplings. Various resonance signals were assigned to different compositional and configurational sequences with the help of one- and two-dimensional NMR spectra. Three and four bond order coupling between carbonyl carbon and other neighboring protons have been investigated with the help of 2D heteronuclear multiple bond correlation (HMBC) spectra. The complex and overlapped 1H NMR spectrum of terpolymer was analyzed completely with the help of 2D HSQC and TOCSY spectra.

Microstructure determination of poly(acrylonitrile-co-methyl methacrylate-co-methyl acrylate) terpolymers by 2D HMBC

A compositional and configurational sequence analysis from two-dimensional heteronuclear multiple bond correlation (HMBC) spectra of acrylonitrile/methyl methacrylate/methyl acrylate (A/B/M) terpolymer is being reported here. The methylene and methine carbon resonances assigned from 2D HSQC spectra were established by analyzing two and three bond order couplings with methyl, methylene and methine protons. α-Methyl carbon resonance of B-unit and methine carbon resonances of A- and M-unit were assigned up to triad compositional and configurational sequences while methylene carbon resonances were assigned up to tetrad compositional and configurational sequences. The assignments of carbonyl carbon resonances based on analysis of three bond couplings with methyl and methylene protons are reported. Quaternary carbon resonance of B-unit was assigned completely with the help of two bond order couplings with methyl and methylene protons. Both carbonyl and quaternary carbon resonances were found to be sensitive up to triad compositional and configurational sequences. Complete spectral assignment of quaternary and carbonyl carbon resonances showing the critical contribution of 2D HMBC spectra is indirect analysis of carbon resonances.

The Identification and Location of Succinyl Residues and the Characterization of the Interior Arabinan Region Allow for a Model of the Complete Primary Structure of Mycobacterium tuberculosis Mycolyl Arabinogalactan

The complex cell wall of Mycobacterium tuberculosis is the hallmark of acid fast bacteria and is responsible for much of its physiological characteristics. Hence, much effort has been made to determine its primary structure. Such studies have been hampered by its extreme complexity. Also, its insolubility leads to difficulties determining the presence or absence of base labile groups. We have used an endogenous arabinase to solubilize the arabinan region of the cell wall and have shown using mass spectrometry and NMR that succinyl esters are present on O2 of the inner-branched 1,3,5-alpha-d-arabinofuranosyl residues. In addition, an inner arabinan region of 14 linear alpha-1,5 arabinofuranosyl residues has been identified. These and earlier results now allow the presentation of a model of the entire primary structure of the mycobacterial mycolyl arabinogalactan highlighted by three arabinan chains of 31 residues each.

Microstructure determination and thermal studies ofn‐acryloylcarbazole/vinyl acetate copolymers

AbstractCopolymers ofN‐acryloylcarbazole (A) and vinyl acetate (V) were synthesized by bulk polymerization using benzoyl peroxide (BPO) as free‐radical initiator at 65°C in different in‐feed ratios. The composition of the copolymer was determined by1H‐NMR spectrum. The comonomer reactivity ratios, determined by Kelen–Tudos (KT) and nonlinear error‐in‐variables (EVM) methods, wererA= 16.75 ± 1.38,rV= 0.015 ± 0.002, andrA= 16.36,rV= 0.015, respectively. Complete spectral assignments of the1H and13C{1H} NMR spectra of the copolymers were done by the help of distortionless enhancement by polarization transfer (DEPT) and two‐dimensional NMR techniques such as heteronuclear single quantum coherence (HSQC) and total correlation spectroscopy (TOCSY). The methine and methylene carbon resonances were found to be compositional as well as configurational sensitive. The signals obtained were broad pertaining to the restricted rotation of bulky carbazole group. The thermal stability and glass‐transition temperatures (Tg) of the copolymers were found to be dependant on polymer composition and characteristic of rotational rigidity of the polymer chain. Variation in the values ofTgwith the copolymer composition was found to be in good agreement with theoretical values obtained from Johnston and Barton equations. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 2720–2733, 2007

Microstructure determination of 9-ethyl-3-hydroxymethylcarbazolyl acrylate/methacrylonitrile using two-dimensional NMR spectroscopy

Solution polymerization was carried out using AIBN as initiator at 60 °C and varying the molar infeed ratio to get different composition of 9-ethyl-3-hydroxymethylcarbazolyl acrylate-co-methacrylonitrile (C/N). The molecular weight was determined using gel-permeation chromatography (GPC). Differential scanning calorimetry (DSC) was used to determine the glass transition temperature ( T g). 13C{ 1H}, DEPT-45, 90 and 135 NMR techniques were used to distinguish the α-methyl, methine, backbone methylene and quaternary carbon resonance signals of C/N copolymers. Correlation of 1D ( 1H, 13C{ 1H}, DEPT) and 2D (HSQC, TOCSY, HMBC) NMR data were used to completely assign various overlapping and broad signals of C/N copolymers. Heteronuclear multi bond correlation (HMBC) studies were used to completely assign various nitrile resonances. The reactivity ratios calculated by Kelen–Tudos (KT) method were found to be r C = 0.31 ± 0.03 and r N = 0.80 ± 0.02 whereas those calculated from RREVM method were found to be r C = 0.35 and r N = 0.83, respectively.

Structural investigations of (9-ethyl-carbazol-6-yl) methyl methacrylate/methyl acrylate copolymers using two-dimensional NMR spectroscopy

(9-Ethyl-carbazol-6-yl) methyl methacrylate/methyl acrylate (E/A) copolymers of different compositions were prepared by solution polymerization by varying the molar infeed ratio, using AIBN as initiator at 60°C. The reactivity ratios calculated by Kelen–Tudos (KT) method were found to be rE = 1.16 ± 0.02 and rA = 0.69 ± 0.01 whereas those calculated from RREVM method were found to be rE = 1.18 and rA = 0.68. The molecular weights (Mw) and polydispersity index (PDI, Mw/Mn) were determined using gel permeation chromatography (GPC). Glass transition temperatures (Tg) for different compositions of E/A copolymers were determined using differential scanning calorimetry (DSC). Copolymer molar outfeed ratio (FE) was calculated from 1H NMR spectra. The α-methyl, methine, backbone methylene, and quaternary carbon resonance signals of the copolymers were distinguished using 13C{1H}, DEPT-45, -90, and -135 NMR techniques. The α-methyl and β-methylene showed compositional and configurational sensitivity up to pentad and tetrad level, respectively, whereas methine showed only compositional sensitivity up to pentad level. Unambiguous assignments for 1H and 13C{1H} NMR spectra were done by correlating 1D (1H, 13C{1H}, DEPT) and 2D (HSQC, TOCSY) NMR data. The spectral assignments for carbonyl region were done by studying higher bond order couplings by heteronuclear multibond correlation (HMBC) spectra. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 5595–5606, 2006

Microstructure analysis of methyl acrylate/methyl methacrylate copolymers by two‐dimensional NMR spectroscopy. II

AbstractIn the present article, a comprehensive two‐dimensional heteronuclear multi bond correlation (HMBC) spectral analysis of methyl acrylate (A)/methyl methacrylate (B) copolymers is reported. The methylene carbon and methine carbon resonances assigned from the 2D HSQC spectroscopy were established by analyzing the two and three bond order couplings with α‐methyl protons, methylene protons, and methine protons. Quaternary carbon resonances of the B unit were assigned by investigating the two bond order couplings with α‐methyl protons and methylene protons. Assignments of carbonyl carbon resonances based on the analysis of three bond couplings with α‐methyl protons and methylene protons are reported. The analyses present comprehensive assignments of the carbonyl carbon resonances showing the critical contribution of 2D HMBC spectroscopy in the indirect analysis of carbon resonances. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci, 2006

Microstructure analysis of methyl acrylate/methyl methacrylate copolymers by two‐dimensional NMR spectroscopy

AbstractMethyl acrylate (A)/methyl methacrylate (B) copolymers of different compositions were synthesized in bulk at 50°C and the compositions were determined from 1H NMR spectra. Reactivity ratios were optimized using the least square methodology. Compositional and configurational assignments were done using two‐dimensional (2D) Heteronuclear Single Quantum Correlation (HSQC) and Total Correlation Spectroscopy (TOCSY) experiments. Methylene proton and carbon resonances were assigned for compositional and configurational sensitivity at tetrad level. Carbon resonances of methine group of methyl acrylate were assigned for compositional sensitivity up to triad level with the help of 2D HSQC spectra. α‐Methyl group of methyl methacrylate was assigned up to triad level of compositional and configurational placements for carbon and proton resonances by 2D HSQC spectroscopy. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 1437–1445, 2006

Comprehensive analysis of stereoregularity and sequence distribution in 2- N-carbazolylethyl acrylate and methyl methacrylate copolymers by 2D NMR spectroscopy and their thermal studies

A series of 2- N-carbazolylethyl acrylate (C) and methyl methacrylate (M) copolymers with varying compositions were prepared in toluene at 60 °C using AIBN as an initiator. The molar outfeed ratio ( F C) for various compositions was determined from 1H NMR spectra. Reactivity ratios calculated using Kelen–Tudos (KT) and non-linear error in variable (RREVM) methods were found to be r C=0.43±0.8 and r M=2.78±0.52. Molecular weight distribution was determined by gel permeation chromatography (GPC). The methine carbon of C unit showed splitting up to the pentad level in 13C{ 1H} NMR spectra and was found to be sensitive to the variation in C/M copolymer compositions. The backbone methylene and carbonyl carbons of both M and C unit along with α-methyl carbon of the M unit showed both compositional and configurational sensitivity. Distortionless enhancement by polarization transfer (DEPT) helped in differentiating the methylene carbon signals from the methine and methyl carbon resonances. 2D heteronuclear single quantum coherence (HSQC) and 2D total correlation spectroscopy (TOCSY) were used in tandem to deduce all spectral assignments. 2D heteronuclear multiple bond coherence (HMBC) played an important role in studying the stereoregularity of the carbonyl carbon. The trend in variation of glass transition temperature ( T g) of various C/M copolymer compositions was also studied.

Investigation on conformational order and mobility of DiamondBond-C18 and C18-alkyl modified silica gels by Fourier transform infrared and solid-state NMR spectroscopy

The effect of surface coverage and solid supports on the conformational order of alkyl chains of commercially available carbon clad zirconia based supports and synthesised C18-alkyl modified silica based supports are probed in the dry state for the first time using variable temperature Fourier transform infrared (FT-IR) and solid-state 13C NMR spectroscopy. From FT-IR spectroscopy, the conformational order of alkyl chains tethered to the substrates is examined by the analysis of CH 2 symmetric and anti-symmetric stretching bands. Through solid-state 13C NMR spectroscopy, the order is inferred from the relative intensity of the main methylene carbon resonance assigned to trans and trans-gauche conformations. It is found that molecules tethered to the graphite layer experience a strongly diamagnetic component of the highly anisotropic magnetic susceptibility of the graphite lattice, which reflects upfield shift in the 13C NMR spectra of commercially available octadecyl-modified carbon clad zirconia based column materials. The present results prove that temperature, surface coverage and solid supports have an influence on the conformational order and mobility of alkyl chains tethered to the carbon clad inorganic metal oxides.

Atom transfer radical copolymerizationof acrylonitrile/n‐butyl acrylate: Microstructure determination by two‐dimensional nuclearmagnetic resonance spectroscopy

AbstractAtom transfer radical polymerization conditions were optimized and standardized with different initiator and catalyst systems. Acrylonitrile/n‐butyl acrylate copolymers were synthesized with 2‐bromopropionitrile as the initiator and CuCl/Cu(0)/2,2′‐bipyridine as the catalyst system. Variations of the feed composition led to copolymers with different compositions. The number‐average molecular weight and the polydispersity index were determined by gel permeation chromatography. Quantitative 13C{1H} NMR was employed to determine the copolymer composition. The reactivity ratios calculated with a methodology based on the Mao–Huglin terminal model were rA = 1.30 and rB = 0.68 for acrylonitrile and n‐butyl acrylate, respectively. The reactivity ratios determined by the modified Kelen–Tudos method were rA = 1.29 ± 0.01 and rB = 0.67 ± 0.01. 13C{1H} NMR and distortionless enhancement by polarization transfer (DEPT‐45, 90, and 135) were used to distinguish methyl, methylene, methine, and quaternary carbon resonance signals. The overlapping and broad signals of the copolymers were assigned completely to various compositional and configurational sequences by the correlation of one‐dimensional (1H, 13C{1H}, and DEPT) and two‐dimensional (heteronuclear single quantum coherence, total correlation spectroscopy, and heteronuclear multibond correlation) NMR spectral data. The complete spectral assignments of carbonyl and nitrile carbons were performed with the help of heteronuclear multibond correlation spectra. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2810–2825, 2005

Investigation of microstructure of the acrylonitrile‐styrene‐glycidyl methacrylate terpolymers by 1D and 2D NMR spectroscopy

AbstractAcrylonitrile‐styrene‐glycidyl methacrylate (N/S/G) terpolymers were prepared by bulk polymerization by using benzoyl peroxide as initiator and analyzed by NMR spectroscopy. The compositions of terpolymers were determined by quantitative 13C{1H}‐NMR spectra and compared with those calculated by Goldfinger's equation by using comonomer reactivity ratios: rNS = 0.04, rSN = 0.40; rNG = 0.22, rGN = 1.37; rSG = 0.44, rGS = 0.53. The 13C{1H}‐ and 1H‐NMR spectra were overlapping and complex. The spectral assignments were done with the help of distortionless enhancement by polarization transfer and two‐dimensional 13C‐1H heteronuclear single quantum correlation experiments. 2D total correlated spectroscopy was used to ascertain the various coupling between the protons. The methyl, methine, methylene, and oxymethylene carbon resonances showed compositional sensitivity. 2D nuclear Overhauser enhancement spectroscopy (NOESY) experiment was used to ascertain the spatial proton–proton couplings. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1779–1790, 2003

Carbon-13 lineshapes in solid-state NMR of labeled compounds. Effects of coherent CSA–dipolar cross-correlation

The experimental lineshapes of the carboxyl and methyl carbon resonances of fully 13C enriched l-Alanine are studied in detail at different MAS frequencies and decoupling field strengths. Complex lineshapes at intermediate spinning speeds were explained by the joint effect of off rotational resonance and coherent CSA–dipolar cross-correlation. Whereas off rotational-resonance effects lead to complex lineshapes due to a splitting of some energy levels, coherent CSA–dipolar cross-correlation introduces either a differential intensity and/or a differential broadening of the lines of the J-multiplet. The conditions which lead to such effects are explained and experimentally verified. Additional simulations show that these effects can be expected over a wide range of static magnetic fields and are not restricted to l-Alanine.

N-vinyl-2-pyrrolidone and methacrylonitrile copolymers: nuclear magnetic resonance characterization

The copolymers of N-vinyl-2-pyrrolidone and methacrylonitrile ( V/ N) were prepared by free radical bulk polymerisation. The copolymer composition was determined from the quantitative 13C{ 1H} NMR spectrum. The reactivity ratios for N-vinyl-2-pyrrolidone ( V) and methacrylonitrile ( N) were found to be r V =0.04, r N =1.56. The complete spectral assignment of the overlapped and complex carbon and proton NMR spectra were done with the help of two dimensional 13C– 1H Heteronuclear Single Quantum Correlation Spectroscopy (HSQC) and Total Correlation Spectroscopy (TOCSY). Distortionless Enhancement by Polarization Transfer (DEPT) was used to differentiate between the methylene, the methine and the methyl carbon resonance signals of the copolymers.

Miscibility and intermolecular specific interactions in blends of poly(hydroxyether of bisphenol A) and poly(4-vinyl pyridine)

The blends of poly(hydroxyether of bisphenol A) (phenoxy) with poly(4-vinyl pyridine) (P4VPy) were investigated by differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR) and high-resolution solid-state nuclear magnetic resonance (NMR) spectroscopy. The single, composition-dependent glass transition temperature ( T g) was observed for each blend, indicating that the system is completely miscible. The sigmoid T g-composition relationship is characteristic of the presence of the strong intermolecular specific interactions in the blend system. FTIR studies revealed that there was intermolecular hydrogen bonding in the blends and the intermolecular hydrogen bonding between the pendant hydroxyl groups of phenoxy and nitrogen atoms of pyridine ring is much stronger than that of self-association in phenoxy. To examine the miscibility of the system at the molecular level, the high resolution 13C cross-polarization (CP)/magic angle spinning (MAS) together with the high-power dipolar decoupling (DD) NMR technique was employed. Upon adding P4VPy to the system, the chemical shift of the hydroxyl-substituted methylene carbon resonance of phenoxy was observed to shift downfield in the 13C CP/MAS spectra. The proton spin–lattice relaxation time T 1(H) and the proton spin–lattice relaxation time in the rotating frame T 1ρ(H) were measured as a function of the blend composition. In light of the proton spin–lattice relaxation parameters, it is concluded that the phenoxy and P4VPy chains are intimately mixed on the scale of 20–30 Å.

Analysis of sequence distribution in methyl methacrylate–methyl acrylate copolymers by 13C NMR spectroscopy

Methyl methacrylate (MMA)–methyl acrylate (MA) copolymers, prepared in bulk at 50°C using AIBN as initiator, were characterized by 150MHz 13C NMR spectroscopy, including use of the Distortionless Enhancement by Polarization Transfer (DEPT) experiment to obtain methylene and methine carbon resonances as subspectra. Dyad, triad, tetrad and partial pentad distributions were measured from the α-methyl, methine and methylene carbon resonances. These were in good agreement with distributions calculated for the copolymers based on monomer feed compositions, conversions and reactivity ratios of 2.60 and 0.27 for methyl methacrylate and methyl acrylate, respectively.

Microstructure of glycidylmethacrylate/vinyl acetate copolymers by two‐dimensional nuclear magnetic resonance spectroscopy

AbstractGlycidylmethacrylate/vinyl acetate copolymers were prepared by solution polymerization with benzene as a solvent and benzoyl peroxide as an initiator. Copolymer compositions were determined from 1H NMR spectra, and comonomer reactivity ratios were determined by the Kelen–Tudos (KT) method and the nonlinear least‐squares error‐in‐variable method (EVM). The reactivity ratios obtained from KT and EVM were rG = 37.4 ± 12.0 and rV = 0.036 ± 0.019 and rG = 35.2 and rV = 0.03, respectively. Complete spectral assignments of 13C and 1H NMR spectra were done with the help of distortionless enhancement by polarization transfer and two‐dimensional 13C–1H heteronuclear single quantum coherence and total correlation spectroscopy. The methyl, methine, and methylene carbon resonance showed both stereochemical and compositional sensitivity. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 4051–4060, 2001

C30 Self-Assembled Monolayers on Silica, Titania, and Zirconia: HPLC Performance, Atomic Force Microscopy, Ellipsometry, and NMR Studies of Molecular Dynamics and Uniformity of Coverage

C30 self-assembled monolayers (SAMs) have been prepared on zirconia, titania, and two different silica gels by reacting C30 trichlorosilane with the humidified surfaces. 13C solid-state NMR spectroscopy indicated higher alkyl chain order on titania and zirconia materials than on the silica C30 phases. Order is inferred from the relative intensity of the main methylene carbon resonance assigned to an all-trans conformation. Carbon longitudinal relaxation time (T1C) data reveal that these ordered alkyl chains still have large-amplitude motions on submicrosecond time scales at ambient temperature. Since fast diffusional rotation about the chain axis is compatible with an all-trans conformation, T1C, carbon chemical shift, and proton line width data for the alkane rotator phase (C19) and the C30 phases were compared. Proton spin diffusion experiments were also conducted using an initial polarization gradient based on mobility differences. These experiments indicated both a higher mobility for the free end of ...