[megarushan]

why is that chemical shift of no 1 carbon (NH2 group) is greater than no 2 carbon (NO2 group)...and no 3 carbon greater than  no 4 carbon....what are the reasons....
thank you....

[Irlanur]

what are the physical reasons for carbon chemical shift?

[Babcock_Hall]

According to Forum rules, you must show an attempt first.  I suggest giving some thought to resonance.

[megarushan]

According to Forum rules, you must show an attempt first.  I suggest giving some thought to resonance.

i think nh2 is higher than no2 because in C1 their is a pi withdrawing effect due to no2 group in para position...am i correct...
sorry about my english....

[OrgXemProf]

Two suggestions:

1. The 1,4-substituents in p-nitroanaline exert opposite resonance interactions with the adjacent benzene ring (i. e., NH2 donates electrons by resonance, whereas NO2 withdraws electrons by resonance) and are directly conjugated with one another. Consider the effect of these substituents at C(1) and C(4) by looking at the canonical form that results from direct conjugation between NH2 and NO2.

Evidence that this canonical form is an important contributor to the resonance hybrid is provided by the fact that p-nitroanline diplays a dipole moment (6.10 D) greater than the sum of the dipole moments of nitrobenzene (3.95 D) and aniline (1.53 D).

2. Then, by considering the electronic (resonance) effects of NH2 and NO2, can you explain why the carbon-13 NMR chemical shift of C(4) occurs upfield of that which corresponds to C(3)?