Attached proton test experiment

APT Attached proton test, a modification of the J-modulated spin-echo experiment to determine C//multiplicities, a less sensitive alternative to DEPT... 

Figure 2.4 (A) Pulse sequence for the gated spin-echo (GASPE) or attached proton test (APT) experiment. (B) Effect of the pulse sequence on the C magnetization vectors of a CH group.

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. 

A solution of Cp2TiCl [52] (0.43 g, 2 mmol) in THF was added dropwise to a solution of the epoxide (1.0 mmol) in 20 mL of THF at room temperature. A solution of 1A HC1 in ether (4 mL) was added, and the mixture was stirred for 10 min. The precipitated solid was removed and the filtrate was added to excess (5 mL) of aqueous saturated sodium di-hydrogenphosphate. The organic layer was separated and the aqueous layer was extracted with ether. The product was isolated as a mixture of exo- and endo-Me isomers in 70% yield. The structures were confirmed by l3C-NMR, H-NMR, chemical shift correlation mapping, nOe measurements, and attached proton test (APT) experiments. No [a]D was recorded because the product was isolated as a mixture. 

Figure F1.4.2 The aromatic region of the 1-D 1H NMR of cyanidin gives rise to a characteristic splitting pattern (upper spectrum). The lower spectrum shows the aromatic region of the 1-D 13C compensated attached proton test (CAPT) NMR spectrum of cyanidin. This spectrum contains all the fifteen 13C resonances of the aglycone in addition to solvent signals (labeled S) and the anomeric sugar proton labeled 1". In this spectrum, the 13C nuclei which have a proton attached are represented with resonances pointing downwards, while the quaternary 13C nuclei are pointing upwards. The 1H NMR experiment was obtained within 25 sec, while the CAPT experiment was obtained within 1 hr 46 min.

Several experiments are suitable for recording anthocyanin 1-D 13C NMR spectra. For example, in Fig. FI.4.2 the authors have used a compensated attached proton test (CAPT Torres et al., 1993 Braun et al., 1998). 

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. 

There are a number of reports on the synthesis of the saturated ring system, and NMR spectra were used to determine the structure. In some cases, the stereochemistry has been established by spectroscopic analysis <90JOC2254>. Some 0x0 derivatives, such as (97), have been studied by attached proton test (APT) and heteronuclear shift correlation (HETCOR) experiments <9lJOC858>. Pyrrolidine ring conformation in two 2,3-dioxoperhydropyrrolo[l,2-c]imidazoles were analyzed from H NMR data using a generalized Karplus equation <85BSB187>. 

The DEPT experiment is a modification of a basic NMR experiment called the attached proton test (APT) experiment. Although a detailed explanation of the theory underlying the DEPT experiment is beyond the scope of this book, an examination of a much simpler experiment (APT) should give you sufficient insight into the DEPT experiment so that you will understand how its results are determined. 

In practice, however, we rarely collect a H-coupled spectrum because of the poor sensitivity associated with this experiment. More elegant experiments that require less instrument time are available to provide similar information. These experiments include the attached proton test (APT) [1] and the distortionless enhancement through polarization transfer (DEPT) [2] experiments. Careful examination of data generated by the heteronuclear multiple quantum... 

Two important 1-D experiments that make use of J-couplings are the attached proton test (AIT) and the distortionless enhancement through polarization transfer (DEPT) experiment. Both the APT and DEPT experiments provide information about whefber or not the observed nucleus—virtually always —is protonated, and if so,... 

MHz frequency as shown. A proton spectrum occurs over a chemical shift range of 10 ppm, which corresponds to 2.5 kHz at 500 MHz. As seen in Figure 3.22, all of the protons in the sample would see 98%-100% of the power of the 500 MHz radiation delivered and all would be excited simultaneously. A pulse programmer is used to control the timing and shape of the RF pulses used to excite the sample. Square wave pulses are commonly used, but multipulse experiments and 2D NMR experiments with other pulse shapes are performed. There are hundreds of pulse sequences and 2D experiments that have been developed, with curious names like attached proton test (APT), DEPT, INEPT, INADEQUATE, COSY, and many more, some of which will be discussed later in the chapter. Each pulse sequence provides specific and unique NMR responses that enable the analyst to sort out the NMR spectrum and deduce the chemical structure of a molecule. 

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