¹J_CH NMR Profile: Identification of Key Structural Features and Functionalities by Visual Observation and Direct Measurement of One-Bond Proton-Carbon Coupling Constants

Abstract

A user-friendly NMR interface for the visual and accurate determination of experimental one-bond proton-carbon coupling constants (J) in small molecules is presented. This intuitive J profile correlates directly to δ(H), and J facilitates the rapid identification and assignment of H signals belonging to key structural elements and functional groups. Illustrative examples are provided for some target molecules, including terminal alkynes, strained rings, electronegative substituents, or lone-pair-bearing heteronuclei.

Multiplicity‐edited 1H‐1H TOCSY experiment

“…In order to achieve full homodecoupling for all 1 H signals, a perfect BIRD element can be implemented as shown in Figure c. It consists of a double BIRD‐based perfect‐echo separated by a central 90° ( 1 H) pulse . The first echo is a BIRD d element for the exclusive evolution of 2 J HH , and the second echo is a BIRD r,X element for the evolution of both δ( 1 H) and 2 J HH .…”

“…In this work, we propose extensions of the regular TOCSY and HD‐TOCSY experiments by introducing ME, referred to as ME‐TOCSY. Additionally, it will be shown how the experiment can offer a superior spectral resolution thanks to the broadband homodecoupling feature implemented in the indirect F1 dimension by the application of a perfect BIRD element . To the best of our knowledge, this perfect BIRD block is for the first time implemented during the proton chemical shift evolution period in a 2D NMR experiment.…”

Current developments in homonuclear and heteronuclear J‐resolved NMR experiments

“…The J res format was already incorporated in older heteronuclear 13 C‐detected J ‐resolved experiments to visualize carbon multiplicities and measure 1 J CH . More sensitive proton‐detected J ‐resolved HMQC and HSQC schemes are now available to measure heteronuclear couplings along F 1 . Figure summarizes several heteronuclear spin‐echo building blocks, including 1 H‐selective, isotope‐filtered BIRD and perfect BIRD refocusing elements, which can be incorporated in either the central 13 C‐evolution period or the initial and final 1 H‐evolution INEPT periods in HSQC experiments.…”

“…J evolution can also be monitored during the two different 1 H‐evolution INEPT periods involved in the regular HSQC scheme . Figure a shows a versatile general pulse scheme to obtain several heteronuclear J ‐resolved spectra.…”

“…The resulting 2 J HH ‐resolved HSQC spectrum displays singlets at F 1 = 0 for CH/CH 3 signals, whereas doublets due to 2 J HH are clearly visualized for diastereotopic CH 2 protons. Finally, the use of an incremented perfectBIRD element affords exclusive monitoring of 1 J CH (doublets in F 1 ) for all proton signals, independent of any CH n ( n = 1,2,3) multiplicity (Figure d) . This perfectBIRD element is based on the perfect‐echo concept, consisting of a double echo building block, t 1 /2‐BIRD d ‐ t 1 /2‐90 y ( 1 H)‐ t 1 /2‐BIRD d,X ‐ t 1 /2, in order to let 2 J HAHB evolve during both echoes, whereas 1 J CHA only evolves during the second one.…”