C-H bond enthelpy of halogenated hydrocarbons

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In summary, the trend of C-H bond enthalpies in this case is CH3I > CH3F > CH3Br > CH3Cl, with CH3Cl having the lowest C-H bond enthalpy. The properties of fluorine, including its high electron affinity and dissociation energy, as well as the repulsion between nonbonding electron pairs, contribute to the weakness of the F-F bond and its relatively low C-H bond enthalpy compared to the other halogens. This behavior is unique to fluorine and sets it apart from the other halogens.
  • #1
Homework Statement
Hi, so based on data collected from databases, I found a trend in the C-H bond enthalpy of halogenated hydrocarbons such as those with the formula CH3X



In this case, the C-H bond enthalpy increases following this order: CH3I (greatest C-H bond enthalpy)> CH3F > CH3BR >CH3CL (lowest C-H bond enthalpy)



It can be seen that the CH bond enthalpy generally increases further down the halogens group, but fluorine is an exception to this trend, does anyone know why?
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In this case, the C-H bond enthalpy increases following this order: CH3I (greatest C-H bond enthalpy)> CH3F > CH3BR >CH3CL (lowest C-H bond enthalpy)
 
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  • #2
I don't know the definitive answer, but there are some properties that may help you explain the case with F. The following data taken from Inorganic Chemistry by Miessler.Halogen, electron affinity, ##\Delta## H of dissociation
F, 328, 158
Cl, 349, 242
Br, 325, 192
I, 295, 151
At, 270A few notes about F from text:

it is likely that the weakness of the F-F bond is largely a consequence of the repulsions between the nonbonding electron pairs. the small size of the fluorine atom brings these pairs into close proximity when F-F bonds are formed. Electrostatic repulsions between these pairs on neighboring atoms result in weaker bonding and an equilibrium bond distance significantly greater than would be expected in the absence of such repulsions.
 
  • #3
In general fluorine is notorious for being "different" from its heavier cousins.
 

1. What is the C-H bond enthalpy of halogenated hydrocarbons?

The C-H bond enthalpy of halogenated hydrocarbons refers to the amount of energy required to break the bond between a carbon atom and a hydrogen atom in a halogenated hydrocarbon molecule. It is a measure of the strength of this bond.

2. How is the C-H bond enthalpy of halogenated hydrocarbons determined?

The C-H bond enthalpy of halogenated hydrocarbons is determined experimentally using techniques such as calorimetry or spectroscopy. These methods involve measuring the amount of energy released or absorbed during a chemical reaction involving the breaking of C-H bonds.

3. Why is the C-H bond enthalpy of halogenated hydrocarbons important?

The C-H bond enthalpy of halogenated hydrocarbons is important because it affects the reactivity and stability of these molecules. It also plays a role in determining the products of chemical reactions involving halogenated hydrocarbons.

4. How does the C-H bond enthalpy of halogenated hydrocarbons vary with different halogens?

The C-H bond enthalpy of halogenated hydrocarbons generally increases with the size and electronegativity of the halogen atom. This is because larger and more electronegative halogens exert a stronger pull on the shared electrons in the C-H bond, making it harder to break.

5. Can the C-H bond enthalpy of halogenated hydrocarbons be used to predict their toxicity?

No, the C-H bond enthalpy of halogenated hydrocarbons cannot be used as a sole predictor of their toxicity. While there is a general trend of increasing toxicity with increasing C-H bond enthalpy, other factors such as the type and position of the halogen atom, as well as the overall structure of the molecule, also play a significant role in determining toxicity.

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