Greetings!
I'm new here so, I'll introduce myself: I'm Ray, a graduate student, who is studying Science of Materials in a university in Mexico. Almost 25 years old, and I love chemistry, physics and math!
So much about myself. Now, the question is... I'm doing research about molecular recognition of anions, and I'm trying to obtain the calculate spectrum of my molecule, but I'm having problems with the tables... A table (1) given by my professor, shows me a value of chemical shifts to certain proton (e.g., -I = 1.82), but another table (2) I found in books, shows me another value (e.g., -I = 1.94). When I try to calculate the chemical shifts of the proton of CH
2 in CH
3CH2I, the calculated values using both tables are:
(1): 0.23 + 0.47 (-C(R/H)
3) + 1.82 (-I) = 2.52 ppm
(2): (0.23 + 0.62 (-R
α) + 1.94 (-I
α))*0.90
a =
2.511 ppmHere, the difference isn't significative but... When I try to calculate the chemical shifts of the methyl proton in the same molecule, the calculated values are:
(1): 0.23 + 0.47 (-C(R/H)
3) = 0.70 ppm
(2): (0.23 + 0.62 (-R
α) + 0.90 (-I
β)) =
1.575 ppmFor the methyl proton, the chemical shifts are different!! I'm doing exactly what the professor teach us, and what the table says in the reference (for methylene proton, multiply by 0.90 after the addition, and for all protons, add the chemical shifts from α and β substituents). Am I doing something wrong? I'm attaching the table the professor gives and the table I extract from a book D:
The formula I used with professor's table was: δ = 0.23 (base value) + δ
X + δ
Y, and for book's table: δ = 0.23 (base value) + δ
α + δ
βProfessor's TableBook's Table