Since the 1 JC3H3 coupling breaks the frequency degeneracy of H3 and H5, the 12 C-bound H5 proton can be inverted separately from H3 using the WS-selective 180° pulse (Figure ). The resulting pure shifted SERFBIRD experiment is shown in Figure , revealing the 4 JH3H5 coupling. This coupling is not accessible from SERF, G-SERF or PSYCHEDELIC experiments that focus on the all-12 C isotopomer signals. Pulse sequences. The SERFBIRD and SATASERF sequences are shown in Figure . Each first apply a 13 C-isotopomer filter, whose primary purpose is to suppress the 12 C-bound 1 H signals via pulse field gradient (PFG) enforced coherence transfer pathway selection, followed by a selective 2DJ sequence with optional pure shift acquisition. SERFBIRD (Figure ) uses an INEPT-ST2PT sequence as 13 C-isotopomer filter. The single transition to single transition polarization transfer (ST2PT) delivers either the 13 C a or 13 C b satellite in one scan, avoiding a doubling of responses relative to the regular 1 H spectrum. It also provides optimal sensitivity by applying the principle of sensitivity improvement and by using both the 1 H and 13 C steady-state polarizations. As SERFBIRD does not tolerate geminal 1 H-1 H couplings (vide infra), the 13 C to 1 H polarization transfer is optimized for methine ( 13 CH) groups only. Optionally, residual signals from methylene protons ( 13 CH2) can be suppressed further using difference spectroscopy by alternating the ∆a and ∆b delays between transients. It is also possible to co-sample 13 C chemical shift evolution with a weighting factor k relative to the JHH sampling in a similar way as in the 2 JHH-resolved HSQC by Parella and coworkers (vide infra). Alternatively, a 13 C selective pulse can be used for spectral editing (see supporting information). The selective 2DJ part of SERFBIRD follows the general scheme proposed for such experiments. 5b At natural isotope abundance, the central BIRD element ensures active spin refocusing for the observed protons experiencing a 1 JCH coupling, except if they experience a geminal 1 H-1 H coupling. 14a Its combination with the two frequency-selective 180° inversion pulses set to a chosen proton S at offset WS ensures only a net evolution during t1 of 1 H-1 H couplings involving this proton. Double absorption mode line shapes are obtained using the Pell-Keeler method and making good use of the frequency selective pulses. For this, experiments with normal (N) and reversed (R) sense coupling evolution are recorded by alternating the positions of the t1 evolution periods in the sequence. When co-sampling 13 C chemical shift evolution, this is done in conjunction with echo/anti-echo encoding. To increase sensitivity and spectral resolution in F2, real-time BIRD pure shift acquisition can be used. The homonuclear decoupling scheme is similar to the one used by except that no 13 C composite pulse decoupling is applied, preserving the spin-state of the 13 C nucleus. This also avoids sample heating, allowing for longer acquisition times and higher digital resolution along F2. Alternatively, interferogram pure shift acquisition is possible which under specific circumstances may be preferred (see supporting information). The combination of 2DJ and pure shift acquisitions have been shown to lead to enhanced chunking artifacts that are anti-phase in F1. Except when 13 C chemical shift is co-sampled in t1, this can be mitigated thanks to the Pell-Keeler method since symmetric spectra along F1 are expected. The SATASERF pulse sequence (Figure ) is similar to SERFBIRD, but with two main differences. Firstly, a frequency selective 180° pulse set to a particular 13 C satellite of the observed proton at offset WI is used instead of BIRD, just as in SERF. Secondly, instead of ST2PT, 13 C anti-phase magnetization is simply converted to 1 H anti-phase magnetization without refocusing it to in-phase magnetization. This is because SATASERF's main use is the observation of protons from 13 CH2 groups, and sensitivity improvement and 13 C spin-state selective excitation schemes work far less well in such cases. This does make SATASERF inherently less sensitive than SERFBIRD (see Figure ). Retaining the anti-phase mode of the 1 H-13 C doublet avoids complications with JCH phase-modulations, while generating both 13 C satellites is not an issue given the WI-selective 180° pulse usually already selects for just one of them. When using pure shift acquisition, typically the interferogram approach will be preferred in this case (see supporting information). 9 The delays da and db serve to refocus 13 C chemical shift (except for kt1) and 1 JCH coupling evolution. For real-time pure shift acquisition, taq is the total acquisition time and N is the number of data chunks. For interferogram acquisition, tch is the duration of the chunk of time domain data. Echo/anti-echo processing is performed using two separate datasets that either use the N-type t1 delays and +g1 gradient, or the R-type t1 delays and -g1 gradient. PFG amplitudes and phase cycles are listed in Tables . In SERFBIRD, the phase f5 controls the choice of 13 C satellite.