bond stability

[NonTraditional3]

---

Members do not see this ad.

Bond Strength:

Alkyne > Alkene > Alkane

Bond Length:

Alkane>Alkene>Alkyne.

Bond Stability?
TBR says that the most stable (strongest) bond has the highest bond dissociation energy, because the lower the energy of the bond, the more energy is required to cleave that bond. So, more energy is require to break alkyne than alkene, and more energy for the alkene than the alkane. Is this increased strength/stability conferred because there is increased electron density in the triple bond than the double bond, and more electron density in the double bond than the single bond?

 

[NuttyEngDude]

Yes, extra pi bonds in a double or triple bond means each bond has to be individually broken so more energy required right? if it needs more energy it's more stable.

 

[NonTraditional3]

Yes, extra pi bonds in a double or triple bond means each bond has to be individually broken so more energy required right? if it needs more energy it's more stable.

but, even though the increased electron density confers stability, the bonds are also more reactive? I thought stability meant less reactive...but everything seems to say that alkyne more reactive than alkene, alkene more reactive than alkane....

 

[NuttyEngDude]

Different types of stable. The stability of the triple bond is against outside forces that would pull the atom away, so the measurement of what it takes to pull it away is the Bond Dissociation Energy (BDE).

The alkyne is in a higher energy state than alkene or alkane but not as a high as a lone pair, so it would react to get to a lower energy state. Lower energy states are less reactive and more stable but would take less energy to break those bonds from outside source than a triple bond.

So in the first paragraph stability is used in the sense to mean how "strong" the bonds are and how much energy it would take to break that bond and in the second paragraph, stability is used in the sense of how much the bond will spontaneously react with another molecule if given the chance.