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Two-dimensional nuclear magnetic resonance spectroscopy (2D NMR) is a general term that encompasses a set of techniques based upon common basic principles (Bruch 145). The multi-pulse method employed by 2D NMR allows complex spectra to be interpreted more quickly and accurately (Skoog, Holler, & Nieman 484). One of the problems involved with traditional one-dimensional NMR spectroscopy is the overlapping of peaks that can occur in a multi-spin system. Because of this overlap, assigning coupling constants and chemical shifts to particular nuclei can be difficult (Atta-ur-Rahman 240).
In traditional 1D NMR, a "single pulse is applied and the resultant free-induction decay (FID) is detected as a function of a single time variable" (Bruch 146). 2D NMR uses a pulse sequence rather than the single pulse, and the FID is detected as a function of two variables: t1, which is related to the time spacing between pulses, and t2, a second time variable (Bruch 146).
All 2D NMR experiments are composed of three periods: preparation, evolution, and detection. The purpose of the preparation time is to allow the nuclei in the sample to reach equilibrium with the static external magnetic field environment. During the evolution period, the spin system is disturbed with a pulse sequence (Bruch 147). The NMR receiver is inactive during the evolution stage (Atta-ur-Rahman 241). The spin system's response to the pulse sequence is detected during the detection period (Bruch 147).
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