1,1-Difluoroethane

Reactions with Organic Compounds. Tetrafluoroethylene and OF2 react spontaneously to form C2F and COF2. Ethylene and OF2 may react explosively, but under controlled conditions monofluoroethane and 1,2-difluoroethane can be recovered (33). Benzene is oxidized to quinone and hydroquinone by OF2. Methanol and ethanol are oxidized at room temperature (4). Organic amines are extensively degraded by OF2 at room temperature, but primary aHphatic amines in a fluorocarbon solvent at —42°C are smoothly oxidized to the corresponding nitroso compounds (34). 

Try your hand at constructing Z-matrices for these three isomers of 1,2-Dichloro-1,2-Difluoroethane ... 

In the case of a number of vicinal difluoro systems, such as 2,3-difluoro-2,3-diphenylethane or 2,3-difluorosuccinic acid derivatives, the coupling systems are AA XX, which means that they will produce second-order spectra (see Chapter 2, Section 2.3.5). A case in point is the fluorine and proton spectra of 1,2-difluoroethane, which have been... 

Figure 3.63 illustrates the gauche effect for vicinal lone pairs and polar C—F bonds with the examples of (a) hydrazine and (b) 1,2-difluoroethane, respectively. As seen in Fig. 3.63(a), the

lone pairs are anti to one another (thus squandering their powerful donor strength on vicinal moieties with no acceptor capacity) is disfavored by 3.2 kcal mol-1 relative to the preferred = 93.9° conformer in which each nN hyperconjugates effectively with... 

Figure 3.63 Rotation-barrier profiles illustrating the gauche effect for (a) lone pairs in hydrazine and (b) polar bonds in 1,2-difluoroethane. (The angle 4> = 0°, as

Our approach will be illustrated by using 1,2-difluoroethane as the model system. This molecule can be dissected as shown below. The sigma nonbonded interaction of the fluorine 2px lone pairs and its impact upon conformational preference can be... 

Fig. 17. Sigma type stabilizing orbital interactions in syn and anti 1,2-difluoroethane...

Good quality ab initio calculations have not yet been carried out in order to test whether lone pair nonbonded attraction obtains in 1,2-difluoroethane. Results of INDO calculations shown below indicate the presence of a nonbonded attractive interaction on the basis of the partial bond order p (F2px, F2px). By contrast, the presence of a nonbonded repulsive interaction favoring the anti conformation is indicated on the basis of the bond order p(F2px, F2px). 

Fig. 18. Pi type stabilizing orbital interactions in syn and anti 1,2-difluoroethane. The symmetry labels are assigned with respect to a mirror plane (syn conformer) or a rotational axis (anti con-former)...

The sigma nonbonded interaction between the two substituents fall into pattern d of Scheme 1. Here, unlike the case of 1,2-difluoroethane, we conclude that there will be a preference for the syn conformation due to the sigma nonbonded interaction of the pi systems of the substituents. This will be counteracted by the inherent preference of any ethane molecule for the staggered geometry and a compromise is expected to be reached in the gauche conformation, barring adverse steric effects. 

The results of INDO calculations of planar and distorted difluorobenzene in which the C—F bonds have been displaced a few degrees above and below the mean plane, are shown above. As can be seen, the planar geometry maintains pi nonbonded attractive interaction. Sigma lone pair interactions will be similar to those which obtain in 1,2-difluoroethane and appear to be repulsive in nature. 

Sigma lone pair nonbonded interaction in 1,2-difluorocyclopropane presents a similar situation to that observed in 1,2-difluoroethane (see Pattern b Scheme 1). Specifically, sigma nonbonded attraction may favor the trans isomer. This can be seen in the results of CNDO/2 calculations shown above where it appears that the sigma nonbonded interaction is repulsive in the cis isomer. 

Consider the model systems 1,1- and 1,2-difluoroethane shown below. 

Fig. 55. Configuration interaction diagram for (a) 1,1 difluoroethane and (b) 1,2 difluoroethane. nj and ft2 are charge resonance configurations, i.e.

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