How Can the Energy Stored in Functional Groups be Determined?

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Discussion Overview

The discussion revolves around determining the energy stored in specific functional groups in chemistry, focusing on various types of functional groups such as Azide, Nitro, Alkynyl, and Cyanides. The scope includes theoretical considerations and the implications of energy measurements in chemical contexts.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • One participant inquires about methods to quantify the energy stored in functional groups, mentioning specific examples that are known to store significant energy.
  • Another participant suggests that the energy could be estimated by summing the bond energies within the functional group.
  • A third participant questions the type of energy being referenced, highlighting distinctions between total energy, energy relative to free atoms, and heat of formation, indicating that these measures can lead to different interpretations.
  • This participant also notes that energy values are not uniform across similar functional groups, using the example of differing pKa values in carboxylic acids to illustrate that small differences in energy can be chemically significant.
  • A later reply clarifies that the energy in question refers specifically to the energy released or absorbed during bond dissociation.

Areas of Agreement / Disagreement

Participants express differing views on how to define and measure the energy associated with functional groups, indicating that multiple competing perspectives exist without a consensus on a single approach.

Contextual Notes

Limitations include the ambiguity in defining the type of energy being discussed and the potential variability in energy values across similar functional groups, which may depend on specific conditions or definitions.

samblohm
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How would I find the amount of energy that is stored in a particular functional group? I know things like Azide, Nitro, Alkynyl, Cyanides, etc. would all store a lot of energy.
 
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It would (approximately) just be the sum over all of the bond energies in the group.
 
What kind of energy? The total energy (which chemists never use)? The energy relative free atoms? The heat of formation (energy relative pure compounds)?

It's also only approximately the same for various functional groups. Otherwise, for instance, every carboxylic acid would have the same pKa. (whereas, say, the side-chain pKa's of aspartic and glutamic acid differ by 0.2 pH units, despite being about as similar as they could get) The difference in energy is small relative any number for the total energy, but it's a chemically relevant difference.
 
By energy I meant the amount of energy that is released (or absorbed) during the dissociation of the bond.
 

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