I would like to know what the answer for question number 11

I would like to know what the answer for question number 11 and why. thanks!

molecular sieves 8) C3 Compound L Compound M Assuming Reaction #5 is intramolecular compound L is the major organic product Assuming Reaction #5 is intramolecular compound M is the major organic product None of the above O Question 11 [1.6 pts] Which one of the following statements about the compound shown in Figure #1 is correct? Figure #1 (C 1 HT HT O O O The chemical shift of protons Hr should be downfield from the TMS signal The chemical shift of protons Hr should be upfield from the TMS signal None of the above

Solution

The Chemical shift of protons H_T for Al(CH₃)₃ should be upfield from the TMS signal. Reason:

In NMR instrument, probe molecules are generally Lewis bases, Trimethyl aluminum reversibly binds with Lewis base to form adducts as shown below:

Al(CH₃)3 + Base = Base-Al(CH₃)₃

In the proton NMR spectrum of Trimethylaluminum, addition of excess base narrows the Trimethylaluminum resonance significantly and shifts the TMA resonance upfield by about 0.5 ppm. This exchange of Trimethylaluminum between the free and complexed state is fast and a sharp single peak upfield to TMS is observed.