I know that fluorine is more electronegative than bromine. However, because of the size of bromine, it is more stable with a negative charge. In the case of HF vs. HBr, to me, HBr is without a doubt the stronger acid. When it comes to comparing CHFX3 with CHBrX3, we are supposed to compare the stability of their conjugate bases.
In CFX3X−, the fluorine can hold the electronegative charge quite well. It also exerts a strong inductive effect.
In CBrX3X−, the bromine is less electronegative than the fluorine but is more polarizable, so I think it can hold the negative charge more efficiently.
With this understanding, I am concluding that CBrX3X− is more stable which would mean CHBrX3 is the stronger acid. However, I've been told otherwise.
I'm aware that the C−Br bond length is longer than the C−F bond length. I'm wondering if that short bond length causes CFX3X− to be more stable than CBrX3X−. If this is true, is it okay for me to think about CFX3X− dissociating vs. CBrX3X− dissociating? In that scenario, I believe CBrX3X− dissociates more easily than CFX3X−, meaning CFX3X− is more stable.
Note: This logic wouldn't apply to the instance of HOX− vs. HSX− because HSX− is more stable than HOX− (even though H−O bond length is shorter than H−S bond length).
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