Chemistry Stack Exchange is a question and answer site for scientists, academics, teachers, and students in the field of chemistry. It only takes a minute to sign up.
Sign up to join this community
Hunsdiecker reaction follows free radical mechanism but it is given that rate of reaction with different alkyl groups (R) attached to silver salts of carboxylic acid follows the order as follows
Primary > Secondary > Tertiary (Rate)
But free radical stability is exactly opposite!
Primary < Secondary < Tertiary (Stability Free Radicals)
What can be the reason for this kind of trend in this reaction?
I'm attaching the reaction mechanism for reference
.
If the free radical is less stable, it will react faster. So once the system is started, the propagation (step 4) will proceed faster for primary radicals. That means that it is the limiting step and that step 3 is faster than 4 for any type of R.
The reason behind this is that in the 3rd step the electron of the C -R bond is breaking and electron is going to each of them but if the R is tertiary then due to the positive inductive effect the electron density gets high in the R and as a result of this it becomes difficult for the new electron to hold by R. In case of primary there is no such a type of situation get creates.so that's why reactivity is in the order of primary then secondary and then tertiary .
