Figure 1.

(A) 2D ¹³C-¹³C CORD sequences: (1) basic CORD; (2) CORD_xix; (3) CORD_xy4. These irradiation schemes are composites of rotor-synchronized R2_n^v- symmetry sequences, R2₁¹ (ω_rf= ω_r), R2₁² (ω_rf= ω_r), R2₂¹ (ω_rf= ½ ω_r), and R2₂² (ω_rf= ½ ω_r). Each R2_n^v element consists of two π pulses per n rotor periods. (B) 2D ¹³C-¹³C CORD_xy4 spectra of U-¹³C,¹⁵N-LC8 (ω_r=40 kHz). Polarization transfer is uniformly efficient in both aliphatic and carbonyl regions of the spectrum.¹¹