Hydrogen compared with fluorine

It will become apparent that fluorine not directly attached to the carbanionic carbon 1.18B is strongly stabUising but, when directly attached as in 1.18A and 1.19A, it has either a moderate stabilising effect compared with hydrogen, or it definitely destabilises, depending on the stereochemistry of the carbanion. 

The physical properties of hydrofluorocarbons reflect their polar character, and possibly the importance of intermolecular hydrogen bonding (3). Hydrofluorocarbons often bod higher than either their PFC or hydrocarbon counterparts. For example, l-C H F bods at 91.5°C compared with 58°C for n-Q and 69°C for Within the series of fluorinated methanes, the boiling point reaches a maximum for CH2F2, which contains an equal... 

Eveiy bond has a characteristic length and strength. Example compares molecular hydrogen with molecular fluorine. 

The amount of heat required to raise the temperature of a material is related to the vibrational and rotational motions thermally excited within the sample. Polymers typically have relatively (compared with metals) large specific heats, with most falling within the range of 1 to 2 kJ kg-1 K . Replacement of hydrogen atoms by heavier atoms such as fluorine or chlorine leads to lower Cp values. The Cp values change as materials undergo phase changes (such as that at the T ) but remain constant between such transitions. 

It is of particular interest to compare fluorine with other halogens or alkyl groups in order to confirm that fluorine mimics hydrogen. Comparison of the fluorine atom with the methyl group clearly indicates that the difference in van der Waals radii is an important factor in this lipase system. 

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