Final answer:
The amide N-H protons in a hydrogen NMR spectrum of a double-stranded amidine dimer would exhibit downfield shifts due to deshielding effects, which occur because of the resonance delocalization of electrons within the amide group.
Step-by-step explanation:
If a hydrogen NMR spectrum were obtained for a double-stranded amidine dimer, the amide N-H proton resonances would experience deshielding effects. This means the answer to the question is B. Yes, they would exhibit downfield shifts due to deshielding effects. In NMR spectroscopy, shielding refers to the reduction of the local magnetic field experienced by a nucleus because of the surrounding electron density. However, the amide group is involved in resonance where the nitrogen’s lone pair electrons partially delocalize to the carbonyl group. This creates partial double bond character between the nitrogen and the carbonyl carbon, reducing the electron density around the N-H proton. As a result, amide protons in hydrogen NMR spectra tend to resonate downfield as compared to amines due to this deshielding.