Hybridization, Substitution and BDE

[Ginger Ale]

Hey all, I was doing passage 1, test one in BKR's orgo workbook and I was looking at the table they provided trying to find a trend between BDE and hybridization. Is there such a trend? Would a sp3-sp3 bond have a lower BDE than an sp-sp3 bond between carbons? If so, why?

Also, does a tertiary carbon bonded to a primary carbon have a lower BDE than a secondary carbon bonded to a primary carbon? If so, does this explain why heat of combustion for a branched alkane is lower than that of a straight chain alkane (i.e 2-methlyhexane versus propane) ?

Thank you! I appreciate your help

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[PiBond]

Hey all, I was doing passage 1, test one in BKR's orgo workbook and I was looking at the table they provided trying to find a trend between BDE and hybridization. Is there such a trend? Would a sp3-sp3 bond have a lower BDE than an sp-sp3 bond between carbons? If so, why?

Also, does a tertiary carbon bonded to a primary carbon have a lower BDE than a secondary carbon bonded to a primary carbon? If so, does this explain why heat of combustion for a branched alkane is lower than that of a straight chain alkane (i.e 2-methlyhexane versus propane) ?

Thank you! I appreciate your help

For the trend to work we need to compare bonds with the same atoms (ie carbon-carbon). The more s-character the shorter the bond. Shorter bonds are stronger bonds--therefore, they have higher BDE's. A sp3-sp3 bond would have a lower BDE than an sp-sp3 bond due to the fact that it has more p-character (thus longer and weaker). Remember that BDE is a measurement of how much energy it takes a break a bond homolytically.

A tertiary carbon bonded to a primary carbon should have a lower BDE than a secondary bonded to a primary. This is due to the stability of the radical products. For heats of combustion, we have to look at the stability of the initial compounds if we are making a comparison. The more stable compound will have a lower heat of combustion than the less stable compound. The equation: delta H = energy of bonds broken - energy of bonds formed, explains it best in my opinion

hope that helps.

 

[TwoPaddles]

Hey all, I was doing passage 1, test one in BKR's orgo workbook and I was looking at the table they provided trying to find a trend between BDE and hybridization. Is there such a trend? Would a sp3-sp3 bond have a lower BDE than an sp-sp3 bond between carbons? If so, why?

Also, does a tertiary carbon bonded to a primary carbon have a lower BDE than a secondary carbon bonded to a primary carbon? If so, does this explain why heat of combustion for a branched alkane is lower than that of a straight chain alkane (i.e 2-methlyhexane versus propane) ?

Thank you! I appreciate your help

sp-sp3 will have a higher BDE than a sp3-sp3 bond because it is shorter in length (and thus, stronger bond) than the sp3-sp3 bond. The shorter = the stronger = the higher BDE (meaning it takes a lot more energy to break that bond)

 

[Ginger Ale]

Thanks, I appreciate your help!