For Q 15),you can just compare higher stretching frequency by back bonding that higher is the stretching frequency,lower is the back bonding.
So,PF3 has back bonding ,so it has lower stretching frequency.
Hence,option b) must be correct.
No bro,I have also done surfing on the internet but I couldn't reach to the solution.
If you can then please @Aniket_1
This is from wiki i dont know if you checked this or not but this might help
It came in wrong order its 1,3,2 read in this manner
But in this table,there is no data regarding the carbonyl complex of Ni and Co. So how can we compare these with carbonyl complex of Fe.
In Some facts there are the rules especially the first one i guess which says frequncy decreases by 100 when charge is added to metal centre.
By this fe>co>ni
Also here is the answer of q.14 not a proper solution but you can say this might be the reason for answer to be
Ya,that may be the correct answer.
But I still not sure.
I went through some theories the first thing is at many places the word stretching frequency is used.
Is that kind of question ever asked in exam by now so we can conclude using that solution too if possible.
Ya,I also have not gone through these type of questions before,so what did you conclude from this solution? As we will try your conclusion as a concept for these type of questions, also please write the answer in the summarized form.
For 15 ans should be A
As PMe3 is electron donating group it increases electron density on the metal nd so backbonding increases therefore CO stretching frequency decreases
Bt in case of PF3 group decreases electron density on metal so there is no backbonding and CO stretching frequency increases.