1992
DOI: 10.1021/j100202a030
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Barriers to internal rotation in CF3CFCl2, CF3CHCl2, CF3CF2Br, CF3CF2Cl, CF3CH2Br, and CF3CH2Cl: fluorine-19 and proton dynamic NMR studies; ab initio molecular orbital barrier calculations

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Cited by 16 publications
(13 citation statements)
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“…In comparison to the value obtained for ethane at the same level of theory (MP2/aug-cc-pVTZ level), 47 the rotational barrier in HCFC-133a (18.4 kJ mol −1 ) increases by ∼6 kJ mol −1 , mostly due to the increased electrostatic hindrance between the negatively charged F and Cl atoms in the transition state. 48 The obtained value for the rotational barrier is lower than the previously reported theoretical data (within the 21.7-28.4 kJ mol −1 range), 46,48,49 but agrees well with the experimentally determined value (19.1 kJ mol −1 ), estimated from the observed Raman torsional frequency. 50 The obtained optimized geometrical parameters for both the minimum energy structure and transition state are shown in Table I.…”
Section: A Structural Results For the Ground Statesupporting
confidence: 89%
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“…In comparison to the value obtained for ethane at the same level of theory (MP2/aug-cc-pVTZ level), 47 the rotational barrier in HCFC-133a (18.4 kJ mol −1 ) increases by ∼6 kJ mol −1 , mostly due to the increased electrostatic hindrance between the negatively charged F and Cl atoms in the transition state. 48 The obtained value for the rotational barrier is lower than the previously reported theoretical data (within the 21.7-28.4 kJ mol −1 range), 46,48,49 but agrees well with the experimentally determined value (19.1 kJ mol −1 ), estimated from the observed Raman torsional frequency. 50 The obtained optimized geometrical parameters for both the minimum energy structure and transition state are shown in Table I.…”
Section: A Structural Results For the Ground Statesupporting
confidence: 89%
“…The ground state structure of HCFC-133a has been investigated before both experimentally (by microwave spectroscopy) 44 and theoretically (at the MP2/6-311G * * and HF/3-21G levels of approximation). 45,46 In this molecule, the conformationally relevant degree of freedom is associated with the internal rotation about the C-C bond. As expected, the staggered structure (with 3 equivalent-bysymmetry forms) is the minimum energy structure, while the eclipsed structures correspond to the transition states separating two symmetry-equivalent minima.…”
Section: A Structural Results For the Ground Statementioning
confidence: 99%
“…Although it is generally assumed that 3 J FF is very small in perfluorinated groups, the results in this study and the low temperature analysis of CF 3 CFCl 2 [7] indicate that the actual values are much larger. Magnetic inequivalence should be observed for geminal fluorines in CF 2 groups and determination of the vicinal coupling constants then requires a non-first-order analysis.…”
Section: Resultsmentioning
confidence: 52%
“…Magnetic inequivalence should be observed for geminal fluorines in CF 2 groups and determination of the vicinal coupling constants then requires a non-first-order analysis. At present there is no way to observe the individual gauche and trans 3 J FF between CF 2 groups except from very low temperature ($100 K) spectra at which rotation between the three rotamers is slow [7]. But if steric effects are important in the relative populations of the rotamers such that the population of the gauche rotamer is nil, then the difference between the observed 3 J(AX) and 3 J(AX 0 ) coupling constants equals the difference between the gauche and trans coupling constants in the trans rotamer I.…”
Section: Resultsmentioning
confidence: 94%
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