Conformational analysis. 7. 1,2-Difluoroethane. An electron-diffraction investigation of the molecular structure, composition, trans-gauche energy and entropy differences, and potential hindering internal rotation

Friesen, Dwayne T.; Hedberg, Kenneth

doi:10.1021/ja00532a001

Cited by 80 publications

(48 citation statements)

References 5 publications

(6 reference statements)

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“…55 Electron diffraction yields 71.3Њ for the dihedral angle and 1.503 Å and 1.389 Å for the C-C and C-F bond lengths of DFE. 26 The F-C-C-Cl dihedral angle in CFE has been experimentally determined as 68Њ, 51 in excellent accord with the calculated value of 67.5Њ. Microwave spectroscopy has also been used to study FP, 57 and the experimentally determined C-C-C-F dihedral angle for the gauche conformer of 62.6Њ is in excellent accord with our calculated value of 62.3Њ.…”

Section: Resultssupporting

confidence: 73%

“…Many previous experimental and computational studies have addressed the conformational behavior of DFE. [24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][47][48][49][50] The numerous calculations all concur that the gauche conformer is preferred to the anti in the gas phase by 0.5-1.0 kcal mol Ϫ1 . 24,30- 38 The highest level of calculation previously applied is probably the G2(MP2) study by Wiberg and coworkers.…”

Section: Resultsmentioning

confidence: 86%

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Is hyperconjugation responsible for the “gauche effect” in 1-fluoropropane and other 2-substituted-1-fluoroethanes? †

Rablen¹,

Hoffmann²,

Hrovat³

et al. 1999

J. Chem. Soc., Perkin Trans. 2

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Section: Resultssupporting

confidence: 73%

Section: Resultsmentioning

confidence: 86%

Is hyperconjugation responsible for the “gauche effect” in 1-fluoropropane and other 2-substituted-1-fluoroethanes? †

Rablen¹,

Hoffmann²,

Hrovat³

et al. 1999

J. Chem. Soc., Perkin Trans. 2

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“…30,31 1,2-difluoroethane has received much attention because the expected anti conformation is not the minimum energy structure; it instead adopts a gauche configuration of the two C-F bonds. [32][33][34][35][36][37][38][39][40][41][42][43][44] The usual steric arguments cannot explain this preference -hyperconjugative effects and electrostatics must be taken into consideration as well. 11 Although the gauche effect in difluoroethane is well studied, analogous effects in larger systems, such as cyclohexanes, are not well understood.…”

Section: Introductionmentioning

confidence: 99%

Easy chairs: the conformational preferences of polyfluorocyclohexanes

2013

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Polyfluorocyclohexanes present an interesting challenge to our current understanding of fundamental organic chemistry. In part to improve molecular mechanics methods and facilitate drug design, a systematic survey of cyclohexanes with up to six fluorine substituents has been carried out, using theoretical methods. The preferred conformers are determined by delocalization effects, such as hyperconjugation, and do not necessarily follow the common assumption that substituents prefer the equatorial position. Thus, accurate ab intio results, which can capture electronic effects, are required. The lowest energy conformations of fluorocyclohexane, difluorocyclohexanes (six structural isomers), trifluorocyclohexanes (nine structural isomers), tetrafluorocyclohexanes (seventeen structural isomers), pentafluorocyclohexane (ten structural isomers), and hexafluorocyclohexanes (seven structural isomers) have been determined; relative energies, geometries, dipole moments, and population distributions are reported. We present a model for predicting the relative energies of polyfluorocyclohexane conformers based on the number of 1,2; 1,3; and 1,4 interactions present. The model is based on the energies from the difluorocyclohexanes; the correlation coefficient (R 2 ) between computed relative energies and model relative energies is 0.967.

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“…h Experimental value from (Durig et al, 1992). There are other two population data obtained from electron diffraction experiment that differ considerably from the more recent reported value in (Durig et al, 1992) based on the vibrational spectroscopy analysis: 9% of the anti form from (Fernholt & Kveseth, 1980) at room temperature and 4.0±1.8% at 22 ºC from (Friesen & Hedberg, 1980). Table 2.…”

Section: Conformational Analysis Of 12-substituted Alkanesmentioning

confidence: 55%