Theory and application of photoelectron spectroscopy. Part 91. Conformational study of 1,2-dimethylhexahydropyridazine by variable-temperature photoelectron spectroscopy

Schweig, Armin; Thon, N.; Nelsen, Stephen F.; Grezzo, Loretta A.

doi:10.1021/ja00545a006

Cited by 16 publications

(5 citation statements)

References 7 publications

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“…The available data are not sufficient for parametrization of the MM3 calculation in the usual way. 27,29,33 We have reported the evaluation of heats of formation by ab initio homodesmotic methods. , On the basis of homodesmotic reactions 1−7, the H ° f values for hydrazine, trimethylhydrazine, tetramethylhydrazine, ethylhydrazine, isopropylhydrazine, and t ert -butylhydrazine are readily evaluated as follows: 25 …”

Section: Resultsmentioning

confidence: 99%

“…A difficult computational problem with hydrazines has been to get the relative energies of diequatorial and equatorial, axial dimethylhexahydropyridazine (structures 10 and 11, Figure 4) correct. Experimental data indicated 26 that the ee conformation is more stable than the ae conformation by ∆E ) 0.8 kcal/mol, and the axial, axial conformer (structure 12, Figure 4) was not observed. Note that there are no adjustable parameters to fit here.…”

Section: å]mentioning

confidence: 99%

“…27,29,33 We have reported the evaluation of heats of formation by ab initio homodesmotic methods. 25,26 On the basis of homodesmotic reactions 1-7, the H°f values for hydrazine, trimethylhydrazine, tetramethylhydrazine, ethylhydrazine, isopropylhydrazine, and tert-butylhydrazine are readily evaluated as follows: 25 The H°f values obtained this way at the 6-31G** MP2 level are given in Table 8.…”

Section: å]mentioning

confidence: 99%

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Quantum Mechanical and Molecular Mechanics (MM3) Studies of Hydrazines

Lii

Chen

et al. 1996

J. Phys. Chem.

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The structures, conformational energies, and vibrational frequencies of hydrazines have been studied at 6-31G** MP2 and 6-31G** B3LYP levels. Our theoretical structures generally agree with the available experimental data. However, our theoretical NsN bond length for tetramethylhydrazine is 1.436 Å at the 6-31G** MP2 level, indicating that the experimental NsN distance (1.401 Å) is too short. We confirm that the ab initio NsN bond length strongly depends on the torsional angle even at the correlated levels. The NsN bond lengths are much longer in the syn and anti conformations of 1,1-dimethylhydrazine than that in the gauche conformation. MM3 parameters for hydrazines have been optimized to reproduce experimental or quantum mechanical structures, energies, and vibrational frequencies. The bond lengthening resulting from lone-pair repulsion was accounted for with a torsion-stretch interaction. The heats of formation for hydrazines were calculated via both MP2 and MM3 methods. The optimized MM3 force field was applied to several cyclic hydrazines, and good agreement with experiments was noted. We found that diequatorial dimethylhexahydropyridazine is 0.9 kcal/mol more stable than the axial, equatorial conformer, in agreement with the experimental value of 1.2 kcal/mol.

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Section: Resultsmentioning

confidence: 99%

Section: å]mentioning

confidence: 99%

Section: å]mentioning

confidence: 99%

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Quantum Mechanical and Molecular Mechanics (MM3) Studies of Hydrazines

Lii

Chen

et al. 1996

J. Phys. Chem.

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“…Former studies, including a number of experimental conformational analysis works − and theoretical studies for N−CH 2 −N and N−N containing systems, , targeted the neutral form of structures ( 1 )−( 3 ) and related systems. Predicted p K a values for structures ( 2 ) and ( 3 ) are 10.04 ± 0.20 and 11.21 ± 0.20, respectively .…”

Section: Introductionmentioning

confidence: 99%

Theoretical Studies of the In-Solution Isomeric Protonation of Non-Aromatic Six-Member Rings with Two Nitrogens

Messer

2011

J. Phys. Chem. B

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For exploring the preferred site for hydrogen bond formation, theoretical calculations have been performed for a number of six-member, non-aromatic rings allowing for alternative protonation on the ring nitrogens. Gas-phase protonation studies for test molecules indicate that the B3LYP/aug-cc-pvtz and QCISD(T)CBS calculations approach the experimental values within about 1 kcal/mol with considerable improvement for relative enthalpies and free energies. Relative free energies calculated at the IEF-PCM/B3LYP/aug-cc-pvtz level predict favorable protonation on the tertiary rather than on the secondary nitrogen both in aqueous solution and in a dichloromethane solvent for saturated rings. Protonation on a nitrogen atom next to a C=C bond is disfavored due to a large increase in internal energy. Monte Carlo simulations considering a counterion and Ewald summation for the long-range electrostatic effects for a 0.1 molar model system predict ΔG(solv)/MC values generally less negative than from the IEF-PCM calculations. These results make the protonation on the tertiary nitrogen even more favored. The solute-solvent pair-energy distribution depends sensitively on the applied model. In conclusion, the freely moving anion has been considered as the most relevant model with overall neutrality for the system and applying the least restrictions.

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“…The most interesting difference in behavior between the phases occurs for [u6]Me 2 relative [6]Me 2 , which switch in relative reactivity between the gas phase and solution. The nearly zero dipole moment diequatorial (ee) form of [6]Me 2 predominates more in the gas phase than in solution (∆∆G Њ is 1.2 kcal mol Ϫ1 in the gas phase, about 1 kcal mol Ϫ1 larger than in solution), 7 which would have led us to expect even larger reactivity of [6]Me 2 compared to [u6]Me 2 in the gas phase than in solution. As indicated in Scheme 2, the lone pair-lone pair twist angle θ = 180Њ ee form has a significantly smaller vertical vibrational reorganization energy (λ v ), which should make it undergo faster ET than the ae form.…”

Section: Discussionmentioning

confidence: 99%