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Topic: CO + BF3  (Read 8097 times)

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Offline Dolphinsiu

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CO + BF3
« on: May 01, 2008, 02:47:56 AM »
Describe the change in stretching frequency for CO upon the reaction with BF3. Given v (free CO) = 2143 cm-1

I truly know it is adduct formation, CO contains one sigma bond, one pi bond and one dative covalent bond from O to C, leaving both a lone pair in C and O. BF3 has low lying vacant 2p orbital. They truly reacts via adduct formation

However, it seems the probability of CO: --> BF3 and OC: --> BF3 are the same. The problem is the energy required to break B - F p(pi) - p(pi) interaction. Is the above adduct reaction still feasible? If yes, does the stretching frequency increase due to steric crowding (sp2 to sp3)? Thank you!

My Attempt Answer:
OC: + BF3 --> OCBF3
CO: + BF3 --> COBF3

B in BF3, +3 oxidation state, sp2 hybrid.
B – F is covalent and multiple bond in nature due to p(pi) –p (pi) interaction. B in BF3 is 6 valence electrons which is incomplete octet.
C – O involves one sigma bond, one pi bond and one dative covalent bond from O to C, leaving a lone pair electrons on both C and O atom.
As B in BF3 is electron deficient and has low lying vacant pz orbital. The reaction proceeds via adduct formation.
CO can form stable octet configuration with BF3 with the breakage of p(pi) –p (pi) interaction due to strong sigma bonding is formed in B – C bond and B – O bond which makes the product more stable. Steric hindrance of 3F’s gives frontal strain on CO. Weakening of CO bond means decrease in CO stretching frequency.
« Last Edit: May 01, 2008, 03:04:20 AM by Dolphinsiu »

Offline nj_bartel

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Re: CO + BF3
« Reply #1 on: May 01, 2008, 03:53:23 AM »
OC + BF3 seems much more probably to me on a precursory glance simply because the carbon in carbon monoxide is strongly nucleophilic and I would assume the B in BF3 is pretty strongly electrophilic, so OCBF3 seems much more probable.

My knowledge level of the chemistry you're doing is far lower than yours, so take that with a grain of salt, but it just makes sense to me  ;D

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