[galpinj]

Hi everyone,

Quick question about BDE; normally BDE for double and triple bonds is higher for single bonds. My question, which may be dumb, is if enough BDE is given to break a double bond, does this mean that only the double bond has been broken and the single bond is still present or that both bonds have been broken?

For example, C=C has a BDE of 144 kcal/mol. If 144 kcal/mol were added to break the bond, would the product be C. + .C or would the result be C-C (double bond broken)

Thank you!

[AWK]

Data show the whole energy needed to disconect atoms.

[j.k.11]

Bond dissociation energy gives the energy required for homolytic bond cleavage.

For a single bond that's sigma bond cleavage; for double bonds sigma + pi; for triple bonds sigma + 2 pi.

[Enthalpy]

As a sidenote, I suggest that you use joules instead of calories for your own use. But you must know calories too because useful docs use them.

[galpinj]

Really, eh? I was pretty confident the answer would be that it only breaks one bond - go figure! So, in a weird way, it's more efficient to break a C=C double bond than it would be to break two C-C single bonds. That seems a little off to me, but I guess that's the way it is!

[Mitch]

Really, eh? I was pretty confident the answer would be that it only breaks one bond - go figure! So, in a weird way, it's more efficient to break a C=C double bond than it would be to break two C-C single bonds. That seems a little off to me, but I guess that's the way it is!

A single bond uses stronger sigma bonding. A double bond uses a weaker pi bond plus a strong sigma bond. So, yes a double bond does not simply mean two times the strength of a single bond.

[galpinj]

Really, eh? I was pretty confident the answer would be that it only breaks one bond - go figure! So, in a weird way, it's more efficient to break a C=C double bond than it would be to break two C-C single bonds. That seems a little off to me, but I guess that's the way it is!

A single bond uses stronger sigma bonding. A double bond uses a weaker pi bond plus a strong sigma bond. So, yes a double bond does not simply mean two times the strength of a single bond.

Thanks Mitch! Any reason why the pi bond would not be as strong as a sigma bond? Is it because sigma bonds contain more "s" character?

Appreciate the *delete me*

[Mitch]

Because sigma orbitals have more overlap, bonding, than pi orbitals. More overlap, the stronger the bond.

[mjc123]

But consider
O-O 146 kJ/mol; O=O 495
N-N 163; N=N 418; N≡N 941
Attributed to the effects of lone pair repulsion

[galpinj]

But consider
O-O 146 kJ/mol; O=O 495
N-N 163; N=N 418; N≡N 941
Attributed to the effects of lone pair repulsion

How does lone-pair repulsion influence our BDE in your examples? I can't see how the lone pairs are influencing the BDE between two atoms