Multiple FID acquisition

The practical aspects of some NMR experiments designed for the simultaneous acquisition of 2D COSY and 2D TOCSY spectra are presented and discussed. Several techniques involving afterglow‐based, coherence transfer pathway (CTP)‐based, and NMR by Ordered Acquisition using ¹H‐detection (NOAH)‐based strategies for the collection of different free‐induction signal decays (FIDs) within the same scan are evaluated and compared. These methods offer a faster recording of these spectra in small‐molecule NMR when sensitivity is not a limiting factor, with a reduction in spectrometer time about 45–60% when compared with the conventional sequential acquisition of the parent experiments. It is also shown how the optimized design of an extended three‐FID approach yields one COSY and two TOCSY spectra simultaneously by combining CTP and NOAH principles in the same experiment, affording substantial sensitivity enhancements per time unit.

A time-efficient NMR strategy that involves the interleaved acquisition of two 2D HSQC spectra having different spectral widths in the indirect ¹³C dimension is presented. We show how the two equivalent coherence transfer pathways involved in sensitivity-enhanced HSQC experiments are managed selectively and detected separately in different FID periods within the same scan. The feasibility of this new SADA-HSQC ( Spectral Aliasing in Dually Acquired HSQC ) technique is demonstrated by recording simultaneously two complementary datasets, conventional and highly-resolved spectral-aliased 2D HSQC spectra, in a single NMR experiment. Combining the information from both datasets, accurate chemical shift determination and excellent signal dispersion is achieved in a unique measurement using only few t₁ increments.

A dual NMR data acquisition strategy to handle and detect two active equivalent transfer pathways is presented and discussed. We illustrate the power of this time‐efficient approach by collecting two different 2D spectra simultaneously in a single experiment: i) TOCSY or HSQC‐TOCSY spectra with different mixing times, ii) F2‐¹³C‐coupled and decoupled HSQC spectra, iii) conventional and pure‐shift HSQC spectra, or iv) complementary HSQC and HSQC‐TOCSY spectra.

Multiple-FID acquisition (MFA) within the same scan is applied to acquire simultaneously multiple 2D spectra from a single NMR experiment. A discussion on the incorporation of the MFA strategy in several homonuclear and heteronuclear 2D pulse sequences is presented. As a proof of concept, a set of novel COSY, TOCSY and HMBC experiments are reported as a time-efficient solution in small-molecule NMR spectroscopy.

One experiment, four NMR spectra: By combining the principles of time‐sharing evolution and multiple FID acquisition within the same scan, several fully complementary NMR spectra can be obtained in a single‐shot acquisition. Four different HMBC and HMBC‐relayed experiments (see spectra) can be carried out simultaneously for ¹³C and ¹⁵N at natural abundance, with a saving in measuring time of up to 75 %.