Methine resonances

ACCORD-ADEQUATE spectrum using a 500-MHz spectrometer equipped with a 5-mm cryoprobe. The data were acquired as 180 hypercomplex points in the second frequency domain using 256 transients/fi increment. The broad 14-vinyl methylene resonance was located in the structure based on correlations in the ACCORD-ADEQUATE spectrum from H14 to C13 and from H12 to both Cll and C13. The C18 aromatic methine resonance afforded ADEQUATE correlations to the flanking C17 and C19 non-protonated carbons and, finally, the C23 methine provided a correlation to the C22 non-protonated carbon. 

As will be noted from even a cursory look at the structures of the two acylation products shown in Scheme 1, there is but a single aromatic methine resonance, that, regardless of which substitution product... 

An n,l-ADEQUATE spectrum of strychnine (1) recorded using a /CH delay optimized for 8 Hz and a 1JCC delay optimized for 50 Hz is shown in Figure 11.77 The spectrum was recorded with the F1 frequency range set for 350 ppm with the transmitter located at 175 ppm just downfield of the CIO carbonyl resonance. To illustrate the interpretation of an n, 1-ADEQUATE spectrum, correlations for the C14 methine resonance will be considered. Obviously, based on the structure of strychnine (1), there are three carbon-carbon correlations possible from C14 to the C13 methine, the C15 methylene, and C21 quaternary vinyl carbons. 

The point just made about HSQC-1,1-ADEQUATE s/n versus data acquisition time requirements is illustrated very dramatically by the curves shown in Figure 16 for several resonances for strychnine (l).50 Despite the relatively low s/n for the Cl2 methine resonance in the... 

C NMR of linear cross-linked PS. The proton decoupled 13C NMR spectra of linear and 1% cross-linked PS at 75 MHz in chloroform are illustrated in Figure 3. These spectra are similar to those for linear and cross-linked chloromethylated PS previously reported at lower field (14), although we have been able to resolve more structure in tHe" aliphatic and aromatic regions here. The quarternary and methylene carbon resonances at about 146 ppm and between 40 and 50 ppm respectively, are the most strongly affected by stereochemistry (20). The ortho and meta resonances at 128.4 ppm show partially resolved structure in the linear PS, as does the para carbon at 126.1 ppm. The methine resonance at... 

Note 1 - small signals 8 = 5.41 and 4.62 correspond to methine H atoms on tartrate branch points the ratio of these intensities to the total intensity of all tartrate methine resonances allows estimation of the percentage branching. 

Fig. 10.16. (A) GHSQC spectrum of strychnine (1) using the pulse sequence shown in Fig. 10.15 without multiplicity editing. (B) Multiplicity-edited GHSQC spectrum of strychinine showing methylene resonances (red contours) inverted with methine resonances (black contours) with positive phase. (Strychnine has no methyl resonances.) Multiplicity-editing does have some cost in sensitivity, estimated to be 20% by the authors. For this reason, when severely sample limited, it is preferable to record an HSQC spectrum without multiplicity editing. Likewise, there is a sensitivity cost associated with the use of gradient based pulse sequences. For extremely small quantities of sample, non-gradient experiments are preferable.

Hydrochlorinated 1,4-po1ydimethylbutadiene. Figure 8 shows the 22.6 MHz C NMR spectrum of the hydrochlorinated 1,4-polydimethyl butadiene sample. Identification of methyl, methylene, methine, and quaternary carbon resonances was made by off-resonance decoupling experiments. It can be seen that all resonances but the methyl resonance at 15.1 ppm, and the methine resonance at... 

Exceptions do exist as shown in the spectrum of polyacrylonitrile in Figure 6. The methine resonances show a distinct triplet with very little splitting exhibited by the methylene resonances. The greatest sensitivity toward configuration occurs for the nitrile resonances where an almost ideal Bemoulllan distribution is observed. ... 

At 55 kHz field, where relaxation times should indicate molecular motion, the relaxation times of the methyl groups showed a temperature dependence between —30 °C and 50 °C. An unresolved peak containing methylene and methine resonances showed a very weak temperature variation. Garroway et al. 62) concluded that the observed C-13 Tle values for fields above 40 kHz were not dominated by spin-spin effects for the DGEBA-PIP system. 

An introduction of branching, either long or short, will create additional resonances to those described above. For long chain branches, these will be an a, B, (and sometimes y) and a methine resonance as depicted structurally below ... 

The olefinic methylene group (protons and carbon) and the three methyl groups (protons and carbons) are trivial assignments, and they correspond with our previous discussion. Of more interest and of greater utility, we assign the three methine protons the doublet of doublets at 2.86 ppm (correlates with the carbon resonance at 63.0 ppm), the apparent quartet at 2.60 ppm (correlates with the carbon resonance at 48.0 ppm), and an apparent triplet at 1.76 ppm (correlates with the carbon resonance at 50.1 ppm). From the COSY and from the known structure, we now are now able to assign all three methine resonances and feed this information back into the COSY to establish other correlations. 

In the full editing APT spectrum [t = (7) ] shown in Figure 5-17, carbons with an odd number of attached protons (CH and CH3) are easily distinguished from those with an even number (CH2 and quaternary, as zero is considered to be an even number). If it is necessary to differentiate carbons within either of these two groups, the APT experiment can be rerun with different values of t. For t = (27)methylene and quaternary carbons can be distinguished, because the former are nulled while the latter have full intensity. Differentiating between methyl and methine carbons is less definitive. For t = 2/37, methyl signals have approximately one-third of the intensity of the methine resonances. 

Table I shows by means of a SFORD experiment that the peaks at 31.3 and 35.2 ppm appear as triplets and are due to methylene carbons. The rest of the aliphatic carbons are all doublets or methine carbons. We find also from suppressed NOE experiments (Table I) that the peak areas are as follows the methylene resonance at 31.3 ppm represents 3 carbons the methylene resonance at 35.2 ppm corresponds to one carbon the methine resonance at 44.7 ppm represents 5 carbons the peak appearing at about 50.5 ppm accounts for 3 carbons and the methine resonance at about 77 ppm represents 4 carbons. The number of carbons present can be assigned either by assuming that the resonance at...

Figure 3.54. Calibration of indirect proton pulses using the DEPT sequence. When the proton editing pulse in the sequence is exactly 90, only methine resonances are apparent (see Chapter 4 also). The sample is menthol in CDCI3.

If the methyl, methylene and methine resonance bands are sufficiently well separated, a comparison of the integration values can be used to advantage in determining the relative number of the various types of carbon atoms present (methyl, methylene, methine). 

The Amino Acids, and especially the alpha amino acid s, are distinguished by their high degree of solubility in water (D20) and that many of these compounds contain a methine resonance band at relatively low field (3.3-4.5 ppm). 

INEPT spectrum for LDPE, which was obtained with the delay time of A=3/4J(6 ms) and 6000 FID accumulations and (b) the spectrum obtained by the common method, which is shown for comparison. In this figure one can easily distinguish methine resonances(upward peaks) fran methylene resonances(downward peaks). Combined with the INEPT spectrum with the delay time A=1/2J, all methyl, methylene, and methine resonances can be identified. 

Figure 4 shows the methine region of the INEPT spectrum observed with the delay time of A= 3/4 J (a). Three thousand accumulations were stored on 32 K memory locations. The common spectrum(b) is also depicted in this figure. We can easily separate methine resonances(upward) from methylene... 

Bovey et al.(3) also observed both H-links and Y branches in an NMR study of a normal alkane irradiated in vacuum in the molten state. The long chain Y branch was easy to recognize in the present study because of the presence of a methine resonance at 38.19 ppm, an a methylene resonance at 34.55 ppm and a P methylene resonance at 27.30 ppm. These assignments are in excellent agreement with those of Bovey et al. (3) and correspond closely to the methine and a, p methylene resonances observed for an ethylene-l-octene copolymer as shown below ... 

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