Low-Frequency Modes in Molecular Crystals. IX. Methyl Torsions and Barriers to Internal Rotation of Some Three-Top Molecules

Durig, J. R.; Craven, S. M.; Bragin, J.

doi:10.1063/1.1673792

Cited by 86 publications

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“…All geometries were optimized using the B3LYP/cc-pVQZ method. The geometrical parameters, in general, are in good agreement with previous experimental 24,26,27 and theoretical results. 29,30 The IRC paths using the B3LYP/ cc-pVTZ method for the rotation motion were calculated by changing the dihedral angle d (H-C-N-lone pair) and the relative energy from the ground state structure (d = ± 60°), which are presented in Figure 3.…”

Section: Resultssupporting

confidence: 79%

“…24,25,27,28 The inclusion of core correlation is more important for the inversion barrier, as already discussed for the methylamine and dimethylamine. The calculated barrier height results for the torsion of one methyl group are consistent with the experimental and previous theoretical results.…”

Section: Resultsmentioning

confidence: 80%

“…[20][21][22][23] The trimethylamine molecule has also received various experimental and theoretical studies. [24][25][26][27][28][29][30][31] The experimental data of the geometry, vibrational frequencies and internalinversion and rotational barriers were obtained using microwave, 24,26 infrared and Raman, 25,27 techniques and employing analysis of the ultraviolet absorption and fluorescence spectra. 28 Theoretical results were also obtained using ab initio methods up to MP4 level.…”

Section: Introductionmentioning

confidence: 99%

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A theoretical study of the inversion and rotation barriers in Methyl-substituted Amines

Nascimento¹,

Pelegrini²,

Ferrão³

et al. 2011

J. Braz. Chem. Soc.

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Barreiras de energia para os movimentos de inversão e rotação das moléculas metilamina, dimetilamina e trimetilamina foram calculadas usando a metodologia CCSD(T)//B3LYP com os conjuntos de funções de base de Dunning, cc-pVTZ, cc-pVQZ e cc-pCVTZ. O procedimento de extrapolação para o conjunto de base completa (complete basis set, CBS) e os efeitos da correlação dos elétrons do caroço também foram incluídos nos cálculos das barreiras de energia. Nossos melhores resultados estão em excelente concordâncias com os dados experimentais, indicando que a metodologia utilizada é recomendada para a predição exata de propriedades estruturais e de barreiras de energia de outros sistemas moleculares.Barrier heights of the internal rotation and inversion motions of methylamine, dimethylamine and trimethylamine molecules were calculated with the CCSD(T)//B3LYP methodology in combination with the cc-pVTZ, cc-pVQZ, and cc-pCVTZ basis sets of Dunning. The complete basis set (CBS) extrapolation procedure and core-valence (CV) correlation effects are also examined to the barrier heights. Our best estimate results (CCSD(T)/CBS+CV//B3LYP/cc-pVQZ) are in very good agreement with the experimental data, indicating the use of this methodology to provide accurate predictions of structures and barrier heights for other systems. Keywords: energy barriers, methylamine, dimethylamine, trimethylamine, CCSD//B3LYP IntroductionThe methyl-substituted amines, methylamine (CH 3 NH 2 ), dimethylamine [(CH 3 ) 2 NH], and trimethylamine [(CH 3 ) 3 N] form an interesting group of molecules which are important in organic syntheses and biological processes, as well as they are efficient corrosion inhibitors of aluminum. Beyond their technological importance, these species are rich in structural features presenting large amplitude internal motions, rotation of the methyl groups and internal inversion of the amino group.Methylamine has been extensively studied by experimentalists in which its internal rotation and inversion barrier heights were determined using microwave (MW), infrared (IR) and electron diffraction (ED) experiments. [1][2][3][4][5][6][7] Methylamine is considered a small molecule from the theoretical point of view, therefore it is appropriate to be studied using high level theoretical quantum chemical methodologies, having received many contributions. [7][8][9][10][11][12][13][14] Lee et al. 8 investigated the origin of the structural stability of methylamine concluding that the stereo electronic effect is the major interaction force affecting its stability. Csonka and Sztraka 9 using density functional and post-HartreeFock methodologies showed that the density functional BP86/6-311G(d) method provides reliable results for geometry and vibrational frequencies, as compared with the experimental results. Smeyers and Villa 10 discussed the influence of the zero-point energy correction to the rotation and inversion motions based on the MP2 results, and During and Zheng 7 calculated these motions barriers using B3LYP and MP2 methods. Recently,...

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Section: Resultssupporting

confidence: 79%

Section: Resultsmentioning

confidence: 80%

Section: Introductionmentioning

confidence: 99%

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A theoretical study of the inversion and rotation barriers in Methyl-substituted Amines

Nascimento¹,

Pelegrini²,

Ferrão³

et al. 2011

J. Braz. Chem. Soc.

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“…',2z and 3.38 lrcal/mol for solid (CH3j31'. 17 Since the values of many more barriers to rotation about the 1 ' 4 bond arc necessary before the nature of the substituent effects can be reasonably predicated, it was decided to record the far-infrared spectra of the series CH31'CI2, CH31'OClz, CHJ'OCIF', CH31'OI',, and CHsl'SCIz for the purpose of determining the frequencies of the torsional oscillations. Raman spectra of the c-orrcspondirig cwmpourids in the solid state were also recorded when feasible.…”

Section: Introductionmentioning

confidence: 99%

Vibrational spectra and structure of organophosphorus compounds. X. Methyl torsional frequencies and barriers to internal rotation of some CH3PXY2 compounds

Durig¹,

Casper²

1971

J. Phys. Chem.

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The present investigation has eliminated the possibility of the presence of a cis isomer in the solid phnse, and there is no indication of a second isomer in the liquid or vapor phase. Bloom and Sutton encountered some difficulty in purification of their sample and at least two of their runs produced erratic results. They suggested that the work should be rechecked using a sample purified by a different technique but were not able to continue the project because of the war. In light of the spectroscopic evidence and the element of doubt in the dipole moment measurements, the conclusion that biacetyl exists in only the trans, configuration in all phases seems justified. ConclusionsVibrational assignments have satisfactorily been made for solid biacetyl according to Cth symmetry. Spectra of the liquid :md vapor phascs show no indicntion of : L second isomeric form, and it is concluded that the nonbonded forces betwoen hnlogcns which stabilize the cis isomer of the oxnlyl hdides are not present hctwoen bhe methyls of biacetyl. Thc mulunl exclusion between infrared :md Raman spectra of crystalline biacetyl necessitates :I centrosymmetric structure and the space group is probably C2A or D2,,. The splitting of tlhe Raman-active librational modes :wid the :rppcar:mce of translational bands in the far-infrared spectrum indicate that there are at least two and possibly four molecules per unit cell. The barrier to methyl rotation has been calculated to be 2.65 ltcal/mol, considerably higher than those found for other acetyl compounds.The far-infrared spectra of CHaPC1,, CHsPOCI,, CHaPOFCl, CHIPOF,, and CHaPSClr in the solid and gaseous states have been recorded from 33 to 350 cm-1. Methyl torsional modes were observed in the aolid state for all compounds except CHaPOFCl. The Raman spectra of CH3PC12, CHaPOF2, and CH31'SCl, in the solid state were recorded and torsional frequencies were observed for CH3PC12 and CH3PS('l,. The wave numbers for these internal rotations were 228, 264, 240, and 221 cni-1 for the CH3PC12, CH3POC12, CH8POF2, and CH&'SClt molecules, respectively. The threefold barriers calculated from these assignments arc 3.4, 4.4, 3.6, and 3.2 kcal/mol, respectively. These barrier values are compared with those previously reported for other organophosphorus compounds. TJattice modes were observed in the wave number range 65-1 20 cin-' in the far-infrared spectra for all compounds.

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“…CH3 Torsions Torsional vibrations of methyl groups have been observed over a wide range of frequencies (270 to 100 cm-') in a variety of compounds (18,19). For the CH3AsX2 molecules (4) it was concluded that the torsions should lie in the range 185-135 cm-', but a definite assignment was only made in one case, namely 134 cm-' for CH,AsBr,.…”

Section: As-i Stretchingmentioning

confidence: 99%

The Infrared and Raman Spectra of Dimethyliodoarsine

Shurvell¹,

Gold²,

Norris³

1972

Can. J. Chem.

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Low-Frequency Modes in Molecular Crystals. IX. Methyl Torsions and Barriers to Internal Rotation of Some Three-Top Molecules

Abstract: Articles you may be interested inLow frequency modes in molecular crystals. XIX. Methyl torsions and barriers to internal rotation of some three top molecules with C 3 symmetry

Cited by 86 publications

References 50 publications

A theoretical study of the inversion and rotation barriers in Methyl-substituted Amines

A theoretical study of the inversion and rotation barriers in Methyl-substituted Amines

Vibrational spectra and structure of organophosphorus compounds. X. Methyl torsional frequencies and barriers to internal rotation of some CH3PXY2 compounds

The Infrared and Raman Spectra of Dimethyliodoarsine

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