Scaled quantum mechanical (SQM) force field and vibrational assignment for styrene

Hargitai, Richard; Szalay, Péter G.; Pongor, Gábor; Fogarasi, Géza

doi:10.1016/0166-1280(94)80049-9

Cited by 32 publications

(39 citation statements)

References 35 publications

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“…The ground state was invariably found to be bent, with an equilibrium torsional angle of 15°-20°. 24,25,30 Head-Gordon and Pople 24 found that the torsion barrier is very small ͑0.04 kcal/mol͒ at the HF/6-31G* level of theory, and increased to 0.21 kcal/ mol at a higher level ͑MP2/6-311G**//HF/6-31G*͒. All calculations agree that the torsional potential is very flat, 25 and that the molecule is essentially planar in the ground state.…”

Section: Introductionmentioning

confidence: 64%

“…24,25,30 Head-Gordon and Pople 24 found that the torsion barrier is very small ͑0.04 kcal/mol͒ at the HF/6-31G* level of theory, and increased to 0.21 kcal/ mol at a higher level ͑MP2/6-311G**//HF/6-31G*͒. All calculations agree that the torsional potential is very flat, 25 and that the molecule is essentially planar in the ground state. In the excited state, the molecule was found to be strictly planar by both semiempirical 22,23 and ab initio calculations 31,32 with a fairly deep well in the torsional degree of freedom.…”

Section: Introductionmentioning

confidence: 64%

“…14,15 The low lying electronic states of styrene, which is the simplest molecule containing both an aromatic ring and a double bond, have been extensively studied experimentally 16 -20 and theoretically. [21][22][23][24][25] Experimental data based primarily on UV spectroscopy indicate that the molecule is planar in both the ground and the first electronically excited singlet states. The small dipole moment of styrene made the measurement of the microwave spectrum extremely difficult.…”

Section: Introductionmentioning

confidence: 99%

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Ab initio study of styrene and β-methyl styrene in the ground and in the two lowest excited singlet states

Zilberg

Haas

1995

The Journal of Chemical Physics

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The structure and vibrational frequencies of styrene and trans-β-methyl styrene in the lowest three singlet states (S0, S1, and S2) have been calculated using ab initio quantum chemical methods. The frequencies are compared with experimental data obtained in the bulk and in a supersonic jet. The calculation shows that in the ground state the molecules have a broad shallow potential as a function of the torsional angle, are essentially planar, but may be slightly bent. In the S1 and S2 states, the molecules are planar; In S1, the main structural change is in the aromatic ring, that is somewhat expanded. In S2, the C=C vinyl double bond elongates, while the C1—Cα single bond becomes shorter, bringing these two bonds to almost equal length. Correlation diagrams connecting ground state vibrational modes with ones belonging to electronically excited states are given; they show that for many out-of-plane modes the vibrational frequencies decrease upon electronic excitation. This is accounted for in terms of the changes in the π electron distribution taking place upon optical excitation that result in decreasing the force constants characterizing these vibrations. The frequencies of most in-plane modes change very little, but mixing between S0 modes is indicated in some cases, and a few vibrations, among them a Kekulé-type mode, undergo considerable change. The relation to the spectroscopy of the corresponding transitions in benzene is briefly discussed.

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Section: Introductionmentioning

confidence: 64%

Section: Introductionmentioning

confidence: 64%

Section: Introductionmentioning

confidence: 99%

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Ab initio study of styrene and β-methyl styrene in the ground and in the two lowest excited singlet states

Zilberg

Haas

1995

The Journal of Chemical Physics

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“…6 (from 100 to 1750 cm −1 ), along with the spectra of their synthetic precursors 3,4-methylene-dioxybenzaldehyde (piperonal) and 3,4-methylenedioxy-␤-methyl-␤-nitrostyrene. The corresponding vibrational wavenumbers were assigned in the light of the theoretical results presently carried out (Table 2) and the spectroscopic data previously reported for ␤-methyl-␤-nitrostyrene derivatives [42][43][44][45] and similar compounds [46][47][48][49][50][51][52].…”

Section: Raman Spectroscopymentioning

confidence: 99%

Electrochemical and spectroscopic characterisation of amphetamine-like drugs: Application to the screening of 3,4-methylenedioxymethamphetamine (MDMA) and its synthetic precursors

Milhazes

Martins

Uriarte

et al. 2007

Analytica Chimica Acta

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A complete physicochemical characterisation of MDMA and its synthetic precursors MDA, 3,4-methylenedioxybenzaldehyde (piperonal) and 3,4-methylenedioxy-␤-methyl-␤-nitrostyrene was carried out through voltammetric assays and Raman spectroscopy combined with theoretical (DFT) calculations. The former provided important analytical redox data, concluding that the oxidative mechanism of the N-demethylation of MDMA involves the removal of an electron from the amino-nitrogen atom, leading to the formation of a primary amine and an aldehyde. The vibrational spectroscopic experiments enable to afford a rapid and reliable detection of this type of compounds, since they yield characteristic spectral patterns that lead to an unequivocal identification.Moreover, the rational synthesis of the drug of abuse 3,4-methylenedioxymethamphetamine (MDMA or "ecstasy") from one of its most relevant precursors 3,4-methylene-dioxyamphetamine (MDA), is reported. In addition, several approaches for the N-methylation of MDA, a limiting synthetic step, were attempted and the overall yields compared.

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“…Whether, in fact, there exists a (small) barrier to planarity in 2 is a matter of disagreement (1)(2)(3)(4)(5)(6)(7)(8) between experimental and theoretical data. The P-CH bond is absent in 1, while I3c nmr chemical shifts indicate (9) rather similar n conjugational energies in the two molecules.…”

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confidence: 99%

¹H and¹³C nuclear magnetic resonance and molecular orbital studies of the internal rotational potential and of spin–spin coupling transmission in phenylallene

Schaefer¹,

Kroeker²,

McKinnon³

1995

Can. J. Chem.

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The 'H nuclear magnetic resonance spectra of phenylallene, diluted in acetone-d6 and benzene-d6, yield long-range coupling constants over as many as eight formal bonds between the ring and side-chain protons. These are discussed in terms of o-and IT-electron spin-spin coupling mechanisms, which are sensitive to the torsion angle between the allenyl and phenyl fragments. The torsion angle is assessed by means of molecular orbital computations of the internal rotational potential, whose height is calculated as 16.0 kJ1mol at the MP216-31G* level of correlation-gradient theory. Comparison with experimental and theoretical internal rotational potentials for styrene suggests that steric repulsions in the planar form of styrene amount to about 4 Idlmol. In a field of 7.0 T, phenylallene is partially aligned, entailing a positive dipolar coupling constant between the methylene protons, from which absolute signs of the spin-spin coupling constants involving these protons can be inferred. Such coupling constants over seven and eight bonds, to the mefa and para protons, are taken as being mediated by the extended a-electron system, providing a measure of IT-electron contributions to coupling constants between mefa protons and those in side chains (spin correlation). Some coupling constants between protons and I3c nuclei in the side chain, as well as between ring protons and these I3c nuclei, are also discussed in terms of spin coupling mechanisms. Solvent perturbations of one-bond proton~arbon coupling constants in the allenyl group do not follow the usual pattern in which an increase in polarity of the solvent is associated with an increase in the magnitude of the coupling constant.

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Scaled quantum mechanical (SQM) force field and vibrational assignment for styrene

Cited by 32 publications

References 35 publications

Ab initio study of styrene and β-methyl styrene in the ground and in the two lowest excited singlet states

Ab initio study of styrene and β-methyl styrene in the ground and in the two lowest excited singlet states

Electrochemical and spectroscopic characterisation of amphetamine-like drugs: Application to the screening of 3,4-methylenedioxymethamphetamine (MDMA) and its synthetic precursors

¹H and¹³C nuclear magnetic resonance and molecular orbital studies of the internal rotational potential and of spin–spin coupling transmission in phenylallene

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Scaled quantum mechanical (SQM) force field and vibrational assignment for styrene

Cited by 32 publications

References 35 publications

Ab initio study of styrene and β-methyl styrene in the ground and in the two lowest excited singlet states

Ab initio study of styrene and β-methyl styrene in the ground and in the two lowest excited singlet states

Electrochemical and spectroscopic characterisation of amphetamine-like drugs: Application to the screening of 3,4-methylenedioxymethamphetamine (MDMA) and its synthetic precursors

1H and13C nuclear magnetic resonance and molecular orbital studies of the internal rotational potential and of spin–spin coupling transmission in phenylallene

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¹H and¹³C nuclear magnetic resonance and molecular orbital studies of the internal rotational potential and of spin–spin coupling transmission in phenylallene