Determination of long-range proton-carbon 13 coupling constants with selective two-dimensional INEPT

Pyrazolo[4′,3′:5,6]pyrano[2,3‐b]quinoxalin‐4(1H)‐one: Synthesis and characterization of a novel tetracyclic ring system

“…Full and unambiguous assignment for all proton, carbon, and nitrogen resonances Synthesis of the tetracyclic title compounds 13 C NMR spectra, APT, HMQC and HMBC spectra as well as experiments with selective excitation such as 1D-TOCSY [11], 1D-HETCOR [12] and selective long-range INEPT [13,14]. The 15 N NMR spectra were mainly recorded using the gradient selected, sensitivity enhanced HMBC sequence [15].…”

Derivatives of pyrazinecarboxylic acid: 1H, 13C and 15N NMR spectroscopic investigations

“…[36] The 1 H NMR and 13 C NMR spectra were recorded either on a Varian UnityPlus NMR spectrometer (300 MHz for 1 13 C-NMR spectra (gated decoupling), gs-HSQC [37] (1024 × 256 data matrix, 10 ppm for 1 H, 160 ppm for 13 C, four transients accumulated per t 1 increment; optimized for J = 160 Hz, qsine multiplication in both dimensions) and gs-HMBC [38] (1024 × 256 data matrix, 10 ppm for 1 H, 180 ppm for 13 C, 16 transients accumulated per t 1 increment; optimized for J = 8 Hz, sine multiplication in both dimensions) techniques to all compounds. The unequivocal mapping of 13 C, 1 H coupling constants was performed via 2D long-range INEPT (δ,J) spectra with selective excitation (DANTE) [11] of pyrazine-H resonances (12 Hz excitation width, optimized for J = 8 Hz, 64 increments for 20 Hz width in F1, 128 transients accumulated per t 1 increment; zero-filling to 128 data points in the F1 dimension, shifted sine multiplication in F1). The 15 N-NMR spectra were obtained on a Bruker Avance 500 instrument (50.69 MHz) equipped with a 5 mm broadband observe probe at 25…”

“…Whereas the signals of C-3 and C-6 in each case exhibit one larger and one smaller long-range coupling (for instance, C-3 in 1 gives a 10.2 Hz and a 1.4 Hz splitting, the C-6 signal is split with 10.8 and 1.3 Hz), the C-5 resonance shows two larger splittings [1: 2 J(C5,H6) = 10.8 Hz and 3 J(C5,H3) = 9.6 Hz]. The latter couplings can be unequivocally discriminated employing 2D (δ,J) long-range INEPT spectra with selective excitation [11] of the resonances due to H-6 and H-3, respectively. Besides, unequivocal assignment of C-3 and C-6 in 1-4 can also be easily achieved by consulting the 1 J(C-H) correlations from the HSQC spectra, as H-3 and H-6 can be easily identified as described above.…”

A Convenient Approach to Heterocyclic Building Blocks: Synthesis of Novel Ring Systems Containing a [5,6]Pyrano[2,3-c]pyrazol-4(1H)-one Moiety

“…This lack of high quality data provided the motivation for us to perform detailed NMR spectroscopic investigations of all novel compounds prepared and also their precursors. 13 C, 1 H spin coupling constants were also determined and unequivocally assigned by two-dimensional (δ, J) long-range INEPT spectra with selective excitation [24]. The 15 N-NMR spectra were mainly recorded using the gradient selected, sensitivity enhanced HMBC sequence [25].…”