Journal
JOURNAL OF ORGANIC CHEMISTRY
Volume 65, Issue 11, Pages 3303-3309Publisher
AMER CHEMICAL SOC
DOI: 10.1021/jo991592a
Keywords
-
Categories
Ask authors/readers for more resources
The problem of the absolute proton affinity (APA) of some polyguanides is addressed by the MP2(fc)/G-311+G**//HF/6-31G* theoretical model. It is shown that the linear chain polyguanides exhibit increased basicity as a function of the number of guanide subunits. However, the saturation effect yields an asymptotic APA value of 254 kcal/mol. Branched polyguanides on the other hand have higher APAs than their linear counterparts. The largest proton affinity is found in a doubly bifurcated heptaguanide, being as high as 285 kcal/mol, thus potentially representing one of the strongest organic bases. Finally, it is found that all polyguanides protonate at imino nitrogen atoms, since they are apparently susceptible the most to the proton attack. The origin of their very high intrinsic basicity is traced down to a dramatic increase in the resonance interaction of the corresponding conjugate bases. For instance, the increase in the resonance energy in the protonated guanidine is estimated to be in a range of 24-27 kcal/mol, which is higher than the aromatic stabilization in benzene. The proton affinity of some polycyclic guanides including Schwesinger proton sponge and porphine is briefly discussed.
Authors
I am an author on this paper
Click your name to claim this paper and add it to your profile.
Reviews
Recommended
No Data Available