Carbon attached proton test

APT, you will perhaps remember, stands for Attached Proton Test, meaning that this spectrum tells you the multiphcity of the signals (Me, CH2, CH or quaternary C). These two spectra tell you how many magnetically non-equivalent types of carbon are present in the molecule, but (for the reasons we discussed earlier) we do not use integration to try to find out relative numbers. We shall present APT spectra as follows CH, CH3 in negative phase (down), CH2 and quaternary C in positive phase (up). 

The J-MODulated (JMOD) C experiment, also known as Attached Proton Test (APT) was the first and simplest way to determine "C multiplicities. In contrast to DEPT no polarization transfer is included in the pulse sequence (Fig. 3.16) and as a consequence the signals of quaternary carbons are visible in the spectrum, but the sequence is far less sensitive than DEPT or INEPT. The value of D2 is used to differentiate between the different carbon multiplicities. The signal intensities of quaternary carbons are not influenced by the value of D2 for D2 equal to 1 CH and CH, groups have maximum negative intensity and CHj has maximum positive intensity. For D2 equal to 1 /C2 J, ) only the signals of quaternary carbons are visible. 

The other experiment worth mentioning, which, by the way, is also obsolete, is the attached proton test or APT. This experiment is based on the different magnitudes of Tl—13C coupling for methine, methylene, and methyl groups. By adjusting certain delays in the pulse sequence (not given), quaternary and methylene carbons could be phased up, and methine and methyl carbons could be phased down. Since phase is arbitrary, this order could be reversed. This ability of distinguishing... 

Figure 5-17 illustrates the result of the complete editing experiment for cholesteryl acetate, which gives negative peaks for CH and CH3 resonances and positive peaks for C and CH2. Proton irradiation during acquisition provides decoupling. This experiment affords a visual identification of the substitution pattern of all carbons, and has been called 7 modulation or the Attached Proton Test (APT). It exists in many variants. 

Figure 5-17 Lower The normal proton-decoupled spectrum of cholesteryl acetate. Upper The attached proton test (APT), phased so that CHt and quaternary carbons are positive and CH and CH3 carbons are negative. (Reproduced with permission from A. E. Derome, Modern NMR Techniques for Chemical Research Pergamon Press, Oxford, UK, 1987,...

C-NMR spectra (10) of salicylic acid in DMSO-de (Figs. 4-6) was recorded on a Varian XL-200 NMR spectrometer. The multiplicity of the resoanance was obtained from APT (Attached Proton Test) program. The 13C-NMR spectrum displayed all the seven carbons resonances. The carbon chemical shifts assignments are presented in Table 4. 

APT (attached proton test) Spin echo based selection of multiplicities of signals. Quaternary C and CH2 carbon atoms give positive signals (Peak UP), while CH and CH3 give negative signals (Peak DOWN). 

S. L. Patt and J. N. Shoolery, Attached Proton Test for Carbon-13 NMR, Journal of Magnetic Resonance 46 535-539 (1982). 

Due to the great complexity of this class of molecules, nuclear magnetic resonance (NMR) and mass spectroscopy (MS) are the tools most widely used to identify cucurbitacins. Both one- and two-dimensional NMR techniques have been employed for the structural elucidation of new compounds 2D NMR, 1H-NMR, 13C-NMR, correlated spectroscopy (COSY), heteronuclear chemical shift correlation (HETCOR), attached proton test (APT), distortionless enhancement by polarization transfer (DEPT), and nuclear Overhauser effect spectroscopy (NOESY) are common techniques for determining the proton and carbon chemical shifts, constants, connectivity, stereochemistry, and chirality of these compounds [1,38,45-47]. 

C-NMR spectrum (12) of clonidine hydrochloride Fig. (7-9) was recorded in DMSO-de by Varian XL-200 MHz NMR spectrometer. The multiplicity of the resonances was obtained from DEPT (Distortionless enhancement by polarization transfer) and APT (attached proton test). The carbon chemical shifts are presented in Table (7). 

The l C-NMR spectmm (22.5 MHz) of naphazoline hydrochloride has been reported and the chemical shifts have been assigned for the methylene and imidazoline carbons. The 13C-NMR spectmm (75 MHz) of naphazoline hydrochloride (143 mg/mL DMSO-d at 100°C) was obtained using a Varian VXR 300 spectrometer (Figure 5) and the assignments are listed in Table m. The Attached Proton Test (A (Figure 5) and extensive 2-D studies were performed in order to assign aromatic carbons. 

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