Energy of Functional Groups

[samblohm]

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.

[zhermes]

It would (approximately) just be the sum over all of the bond energies in the group.

[alxm]

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.

[samblohm]

By energy I meant the amount of energy that is released (or absorbed) during the dissociation of the bond.