Rotational Isomerism and Thermodynamic Functions of 2-Methylbutane and 2,3-Dimethylbutane. Vapor Heat Capacity and Heat of Vaporization of 2-Methylbutane

Scott, D. W.; McCullough, J. P.; Williamson, K.D.; Waddington, Guy

doi:10.1021/ja01148a083

Cited by 46 publications

(14 citation statements)

References 4 publications

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“…As listed in Table , heat capacities for nine selected alkanes ranging in size from C5 to C8 were calculated with HO hf , UM-N, and UM-VT. The benchmarks chosen are the ideal gas heat capacities obtained by measuring heat capacities at two or more pressures and extrapolating linearly to zero pressure. − As shown in Figure , because of the absence of anharmonic effects, all of the heat capacities calculated with the HO hf model are underestimated. The UM-N heat capacities are slightly more accurate than those of the HO hf model since the UM-N model takes local anharmonicities into account.…”

Section: Resultsmentioning

confidence: 99%

“…The benchmarks chosen are the ideal gas heat capacities obtained by measuring heat capacities at two or more pressures and extrapolating linearly to zero pressure. [53][54][55][56][57] As shown in Fig. 4, because of the absence of anharmonic effects, all of the heat capacities calculated with the HO hf model are underestimated.…”

Section: Heat Capacities Entropies and Enthalpiesmentioning

confidence: 94%

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Thermodynamics of Anharmonic Systems: Uncoupled Mode Approximations for Molecules

Bell

Head‐Gordon

2016

J. Chem. Theory Comput.

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Abstract:The partition functions, heat capacities, entropies, and enthalpies of selected molecules were calculated using uncoupled mode (UM) approximations, where the full-dimensional potential energy surface for internal motions was modeled as a sum of independent one-dimensional potentials for each mode. The computational cost of such approaches scales the same with molecular size as standard harmonic oscillator vibrational analysis using harmonic frequencies (HO hf ).To compute thermodynamic properties, a computational protocol for obtaining the energy levels of each mode was However, the accuracies in entropy calculations differ significantly between these three models. For the same test set, the RMS error of the standard entropies calculated by UM-VT is 2.

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Section: Resultsmentioning

confidence: 99%

Section: Heat Capacities Entropies and Enthalpiesmentioning

confidence: 94%

Thermodynamics of Anharmonic Systems: Uncoupled Mode Approximations for Molecules

Bell

Head‐Gordon

2016

J. Chem. Theory Comput.

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“…At five temperatures, nmr spectra were determined with audio side bands from Hc, and provided values for Jcc and /c,i,c• For each of these five temperatures, Jcc was "In °C; accurate to ±1°. 6 In hertz. Chemical shift assignments are based on the work of Hobgood and Goldstein,80 where va appears at lower field than rB.…”

Section: Resultsmentioning

confidence: 99%

Conformational analysis of 1,3-butadiene

Lipnick¹,

Garbisch²

1973

J. Am. Chem. Soc.

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The conformational analysis of 1,3-butadiene has been accomplished using the temperature dependences of two nuclear magnetic resonance spectral parameters, SAB and Jcc, obtained from 2,3-dideuterio-l,3-butadiene (2) and 1,1,4,4-tetradeuterio-l,3-butadiene (3), respectively. These parameters have been correlated with the trans cis conformational equilibrium (eq 1). The magnitude of the derived vicinal 2,3 proton-proton coupling of the minor conformer indicates that it is nonplanar (skew). The enthalpy difference for the trans ^skew equilibrium (la ^lc, Id) was found to be +2105 ± 44 cal/mol at AS = +1.376 eu. The compound 1,3-butadiene is generally represented as a mixture of two planar conformers, la (s-trans) and lb (s-cis), in mobile equilibrium.3 Hiickel, using theoretical considerations, suggested the possibility of two such forms as early as 1932.4

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“…The selected liquid volumes of Table III are considered accurate to a maximum of ±0.3% from the NBP to 360 K, 0.4% from 360 to 440 K, and 0.2 % from 440 to 460 K. The error limits of vapor volume at the NBP are ±23 cm3 mol-1, providing the measurement of enthalpy of vaporization of Scott et al (25) is correct. The accuracy of enthalpy of vaporization values in Table III depends on that of the vapor pressure slope and the vapor volume with error limits of 1.4% for dP/df.…”

Section: Accuracy Of Saturated Propertiesmentioning

confidence: 98%