Final answer:
The incorrect statement about NOE experiments is that signals are restricted to spins of covalently bonded nuclei. NOE can occur between any spatially close spins, not just those that are covalently bonded. The correct answer is option: c. are restricted to spins associated with covalently bonded nuclei.
Step-by-step explanation:
The statement that is NOT true about NOE (Nuclear Overhauser Effect) experiments is that signals are restricted to spins associated with covalently bonded nuclei. In reality, NOE can be detected between spins of nuclei that are spatially close, but not necessarily covalently bonded. This effect is utilized in nuclear magnetic resonance (NMR) spectroscopy where signals detected result from dipolar couplings between spatially close spins regardless of whether they are covalently bonded or not.
Further, the strength of the NOE signals have amplitudes related to the distance between the involved spins, which provides valuable spatial information about the positions of atoms in a molecule. In practice, NOE can often be observed between atoms separated by up to 5 Ångströms (Å), which corresponds to several bonds apart in a molecular structure.