Final answer:
A 2D NMR spectrum is an advanced nuclear magnetic resonance spectroscopy technique where dots on the graph represent correlations between nuclear spins, providing detailed structural information of complex molecules.
Step-by-step explanation:
A 2D NMR spectrum is a two-dimensional Nuclear Magnetic Resonance spectroscopy graph that provides detailed information about the molecular structure. In a 2D NMR spectrum, the dots or peaks represent correlations between nuclear spins that are close in space or through bonding relationships. This technique is vital for elucidating the structure of complex molecules by providing insights into the scalar couplings and through-space interactions of the atoms within a molecule. The x and y axes of a 2D NMR spectrum typically represent the frequencies of two different NMR-active nuclei, such as 1H,13C, or 15N. When an NMR-active nucleus interacts with another through a bond or space, it gives rise to a cross-peak represented by a dot on the spectrum. These cross-peaks allow for the identification of how atoms within a molecule are related spatially or through a bonding network, thereby giving valuable structural information that is difficult to garner from a traditional one-dimensional NMR.