Inverse-HETCOR spectrum

Figure I. The methylene region of the inverse-HETCOR spectrum of A/M copolymer.

FIGURE 6.18. The 300-MHz (F2) HMQC (also called inverse detected HETCOR ) spectrum of caryophyllene oxide. 

ID ll spectrum, and crosspeaks are arranged symmetrically around the diagonal. There is only one radio frequency channel in a homonuclear experiment, the H channel, so the center of the spectral window (set by the exact frequency of pulses and of the reference frequency in the receiver) is the same in If and F (Varian tof, Bruker ol). The spectral widths should be set to the same value in both dimensions, leading to a square data matrix. Heteronuclear experiments have no diagonal, and two separate radio frequency channels are used (transmitter for F2, decoupler for F ) with two independently set spectral windows (Varian tof and dof, sw, and swl, Bruker ol and o2, sw(If), and sw(I )). Heteronuclear experiments can be further subdivided into direct (HETCOR) and inverse (HSQC, HMQC, HMBC) experiments. Direct experiments detect the X nucleus (e.g., 13C) in the directly detected dimension (Ff) using a direct probe (13C coil on the inside, closest to the sample, H coil on the outside), and inverse experiments detect XH in the To dimension using an inverse probe (XH coil on the inside, 13C coil outside). 

The HMQC spectrum is a proton-detected (inverse detection) HETCOR (Chapter 6) it shows lJ CH coupling. Table 5.9 in Chapter 5 allows us to arrange the aromatic unsubstituled carbon atoms as C-6, C-4, C-3 from left to right. The HMQC spectrum confirms the same sequence for H-6, H-4, H-3. The aromatic, unsubstituted carbon atoms can now be correlated with the firmly assigned aliphatic protons. The substituted aromatic carbon atoms cannot yet be assigned. 

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