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1.
G. A. Crowder 《光谱学快报》2013,46(9):1039-1048
Abstract

Infrared and Raman spectra were obtained for 4,4-dimethylheptane and were interpreted with the aid of normal coordinate calculations. It was shown that this compound exists in three conformations. Force constant values transferred from dimethylpentanes resulted in an overall average difference between observed and calculated wavenumbers of 4.5 cm?1 for the three conformers.  相似文献   

2.
Abstract

Infrared and Raman spectra were obtained for 3,3-dimethylhexane and were interpreted with the aid of normal coordinate calculations. It was shown that this compound exists in more than one molecular conformation. Two of those conformations were identified. Transferred force constant values resulted in an overall average difference between observed and calculated wavenumbers of 4.6 cm?1 for the two conformers.  相似文献   

3.
Abstract

Infrared spectra were obtained for 2-methylhexane and 3-methylhexane, and were interpreted with the aid of normal coordinate calculations. It was shown that 2-methylhexane exists in three conformations. Evidence for the presence of three conformations of 3-methylhexane is presented, but a fourth conformer probably exists. Transferred force constant values resulted in an overall average difference between observed and calculated wavenumbers of 4.3 cm?1, or 0.5%, for seven conformers of these two compounds.  相似文献   

4.
Abstract

Infrared spectra were obtained for 1,2-dibromopropane-d6 in the liquid and in the unannealed and annealed solid states. Vibrational assignments were made for the three conformers of 1,2-dibromopropane and the three conformers of 1,2-dibromopropane-d6 with the aid of normal coordinate calculations. All three possible conformers of CD2BrCDBrCD3 were found to be present in the liquid and unannealed solid, but the PHSHH conformer was absent in the annealed solid.  相似文献   

5.
Recently we studied NQR 35Cl and NMR 31P spectra of a series of substituted phosphapyrimidines, PhP, (1,2,6-phosphadiazines) and reported some peculiarities of the phosphadiazine ring structure1. Continuing the investigation of this class of compounds, we have obtained in this work infrared and Raman spectra of some PhP and have calculated in-plane normal vibrations. Normal coordinate calculations have been made in order to aid in the assignment of the PhP fundamental frequencies and to obtain values for force constants of the phosphadiazine cycle to transfer to other phosphacyclic compounds.  相似文献   

6.
FT‐IR and FT‐Raman spectra of p‐bromonitrobenzene (p‐BNB) have been recorded in the region 4000–400 cm−1 and 4000–50 cm−1, respectively. The molecular structure, geometry optimization, vibrational wavenumbers have been investigated. The spectra were interpreted with the aid of normal coordinate analysis based on the density functional theory (DFT) using the standard B3LYP/6‐31G method and basis set combination and was scaled using multiple scale factors yielding good agreement between observed and calculated wavenumbers. The results of the calculations are applied to simulate infrared and Raman spectra of the title compound which showed reasonable agreement with the observed spectra. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

7.
Infrared and Raman spectra were obtained for 5- methyl-2-hexyne and wereinterpreted with the aid of normal coordinate calculations. The spectra and molecular mechanics calculations show the compound to exist in two spectroscopically distinguishable stable conformations, with the C1 conformer being only a little more stable than the Cs, conformer. Vibrational assignments were made for both conformers.  相似文献   

8.
Abstract

Normal coordinate calculations were made for 1-butyne, propionitrile, and the two conformers each of 1-pentyne and butyronitrile, using a thirty-one parameter modified valence force field. Only the triple bond stretching force constant was assumed to be different in the two families of compounds. Twenty force constants were refined to fit 117 frequencies of the six molecules, with the average error being 5.1 cm?1, or 0.65%.  相似文献   

9.
Vibrational spectra have been published and normal coordinate calculations have been made for 1,2-dichlorobutane.1,2 Those calculations were limited to the three conformers that had all four carbon atoms coplanar. Molecular mechanics calculations have now shown a conformer that was omitted to be the second most abundant conformer. Therefore, normal coordinate calculations have been made for this conformer and molecular mechanics calculations have been made for all possible conformers.  相似文献   

10.
Abstract

Normal coordinate analysis was carried out on the vapor phase Raman and i.r. spectral data of methanol and its deuterated species to determine a vibrational force field. Based on the results of calculations, the 25-parameter molecular force field was analyzed and compared with the earlier studies and the vibrational band assignments were discussed in terms of the vibrational mode mixings, particularly, in the wavenumber region below 1500 cm?1.  相似文献   

11.
Abstract

In order to aid assignment of Co-C bond stretching vibrational frequency of CH3Co(DH)2H2O (DH=dimethylgIyoximato monanion) in IR and Raman spectra, its isotopic substitution CD3Co(DH)2H2O has been synthesized and normal coordinate analyses on the two complex have been made. The bands were assigned in terms of potential energy distribution. The results provide definitive band assignment of the Co-C bond and Co-N bond stretching modes which are coupling at 511 cm?1.  相似文献   

12.
The liquid phase FTIR and FT‐Raman spectra of 1,3‐dibromo‐2,4,5,6‐tetrafluoro benzene (DTB) and 1,2,3,4,5‐pentafluoro benzene (PB) were recorded in the regions 4000–400 cm−1 and 4000–50 cm−1, respectively. The spectra were interpreted with the aid of normal coordinate analysis following full structure opti1mization and force field calculations based on the density functional theory using the standard B3LYP/6‐31G* method and basis set combination. The scaled force field reproduced the experimental wavenumbers of the molecule for DTFB and PFB, respectively. The effects of halogen substituents on the structure and vibrational wavenumbers have been investigated. Assignments of fundamental modes were made based on the comparison between calculated and experimental results. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

13.
The internal coordinate path Hamiltonian is introduced for the study of the vibrations of molecules which have one large amplitude motion. The Hamiltonian is represented in terms of a one path coordinate and 3N—7 normal coordinates. The variational method is used to solve the Schrödinger equation. The molecules studied are methanol and malonaldehyde. For methanol the internal coordinate is a dihedral angle, for malonaldehyde it is the difference in the distances between the migrating hydrogen and the neighbouring oxygen atoms. For methanol there is little coupling between the path and the normal coordinates and so no complications were encountered in the calculations which used harmonic surfaces generated by density functional and M?ller—Plesset theory. Fundamental frequencies were predicted. Malonaldehyde is a different story. There is substantial coupling between the path coordinate and several of the normal coordinates. This introduces many complications: an anharmonic surface is essential and large variational configuration interaction calculations are essential for convergence. Furthermore, because the Coriolis terms require the evaluation of derivatives of both the nuclear coordinates and the normal coordinate eigenvectors along the path, great care must be taken with these numerical procedures. B3LYP predicts too low a transition state which overemphasizes the large Coriolis terms near the transition state. This may be one of the reasons why our fundamental vibrations are in poor agreement with observation. It is most encouraging that the tunnelling splitting is 58 cm?1 (obs. 21.56 cm?1), obtained with our quartic density functional surface.  相似文献   

14.
Abstract

Mid-infrared, far-infrared, and Raman vibrational spectroscopic studies were combined with density functional theory (DFT) calculations and normal coordinate force field analyses for N,N′-dimethylurea (DMU), N,N,N′,N′-tetramethylurea (TMU), and N,N′-dimethylpropyleneurea (DMPU: IUPAC name 1,3-dimethyltetrahydropyrimidin-2(1H)-one). The equilibrium molecular geometry of DMU (all three conformers), TMU, and DMPU and the frequencies, intensities, and depolarization ratios of their fundamental infrared (IR) and Raman vibrational transitions were obtained by DFT calculations. The vibrational spectra were fully analyzed by normal coordinate methods as well. A starting force field for DMPU was obtained by adapting corresponding force constants for DMU and TMU, resulting after refinements in the stretching force constants C=O (7.69, 7.30, 7.68 N·cm?1), C–N (5.16, 5.55, 5.05 N·cm?1), and C-Me (5.93, 4.00, 4.22 N·cm?1) for DMU, TMU, and DMPU, respectively. The dominating conformer of liquid DMU was identified as trans-trans, strong intermolecular hydrogen bonding was verified in solid DMU, and weak dipole–dipole association was found in liquid TMU and in DMPU. Special attention was paid to analyzing the methyl group frequencies, which revealed deviations from local C3v symmetry. A linear correlation was found between the CH stretching force constants and the inverse of the CH bond lengths (1/r 2). The averaged NH stretching frequencies of gaseous, dissolved, and solid urea and of DMU, with variations for hydrogen bonding of different strength, are linearly correlated to the NH stretching force constants. Characteristic skeletal vibrations were assigned for a broad variety of urea derivatives and also for pyrimidine derivatives, which all contain the N2C=O entity. The very strong IR bands of C=O stretching (1,676 ± 40 cm?1) and asymmetric CN2 stretching (1,478 ± 60 cm?1), and the very intense Raman feature of symmetric CN2 stretching or ring breathing (757 ± 80 cm?1), can be recognized as fingerprint bands also for the pyrimidine derivatives cytosine, thymine, and uracil, which all are nucleobases in DNA and RNA nucleotides.  相似文献   

15.
FTIR and FT Raman spectra of 2‐bromo‐4‐chloro phenol (BCP) and 2‐chloro‐4‐nitro phenol (CNP) were recorded in the region 4000–400 and 4000–50 cm−1, respectively. The molecular structure, geometry optimization, and vibrational wavenumbers were investigated. The spectra were interpreted with the aid of normal coordinate analysis based on density functional theory (DFT) using the standard B3LYP/6‐31G** method and basis set combination and was scaled using multiple scale factors, which yield good agreement between the observed and calculated wavenumbers. The results of the calculations are applied to simulate the infrared and Raman spectra of the title compounds, which showed excellent agreement with the observed spectra. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

16.
FT‐IR and FT‐Raman spectra of benzoic acid (BA) and 3,5‐dichloro salicylic acid (SA) have been recorded in the regions of 4000–400 and 4000–50 cm−1 respectively. The spectra were interpreted with the aid of normal coordinate analysis following the full structure optimizations and force field calculations based on density functional theory (DFT) using standard B3LYP6‐31G** method and basis set combinations. The DFT force field transformed to natural internal coordinates was corrected by a well‐established set of scale factors that were found to be transferable to the title compounds. The infrared and Raman spectra were also predicted from the calculated intensities. Comparison of the simulated spectra with the experimental spectra provides important information about the ability of the computational method to describe the vibrational modes. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

17.
In a previous paper1 the infrared spectra of some chelates of the type N,N′-ethylenebis(acetylacetoneiminato)-metal(II) were reported and the vibrational assignments were made on a correlative basis and with the aid of the results of a normal coordinate treatment. In order to provide further data for a more reliable assignment of the vibrational spectra of this class of metal chelates an investigation was carried out on the infrared pleochroism of the single crystals of N,N′-ethylenebis(acetylacetoneiminato)-copper(II) (CuBae.1/2H20 in the following).  相似文献   

18.
19.
Abstract

A complete normal coordinate analysis has been performed for the tricyanomethanide ion C(CN)? 3 for which a planar structure of symmetry D3h was assumed. The symmetric Fand internal f valence force constant matrices were derived in the general case by using a GVFF and the results are applied to C(CN)? 3.  相似文献   

20.
G. A. Crowder 《光谱学快报》2013,46(10):1923-1938
Normal coordinate calculations were made for 2-methyl-1-butene to aid in making vibrational assignments for both conformers. A partial solid-state IR spectrum was obtained that showed the presence of only the trans (Cs) conformer. Molecular mechanics and semi-empirical molecular orbital calculations were also made for both conformers.  相似文献   

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