Methine carbon resonance

KINETIC RESULTS FOR DCP AND TCH. The portion of the 50.13 MHz 13C NMR spectra containing the methylene and methine carbon resonances of DCP and the resultant products of its (n-Bu)3SnH reduction are presented in Figure 2 at several degrees of reduction. Comparison of the intensities of resonances possessing similar T, relaxation times (see above) permits a quantitative accounting of the amounts of each species (D,M,P) present at any degree of reduction. 

The COSY spectrum for caryophyllene oxide can be understood more clearly when interpreted in conjunction with the information from an HMQC spectrum (Figure 5.17). From the DEPT spectrum (see Figure 5.15), we already know that caryophyllene oxide has three methyl carbon resonances (16.4, 22.6, and 29.3 ppm), six methylene carbon resonances (26.6,29.2, 29.5, 38.4, 39.1, and 112.0 ppm), three methine carbon resonances (48.1, 50.1, and 63.0 ppm) and three quaternary carbon resonances (33.3,59.1, and 151.0 ppm)... 

Triad, pentad and heptad assignments were developed for the aromatic C-l carbon resonance patterns and triad assignments previously proposed for the methine carbon resonances of polystyrene were verified. Based on the assignments developed, the 13C-NMR spectrum of polystyrene indicates it to be almost atactic, P(m)=0.45. 

Before the real sample is examined, the methylene and methine carbons (resonating in the range 43-44 ppm) in the spectrum of camphor must be clearly resolved [5]. 

Poly(vinyl alcohol) prepared by the basic hydrolysis of poly(vinyl acetate) was characterized by two-dimensional NMR spectroscopy. The methylene and methine carbon resonances were assigned to tetrad and pentad configurational sequences. These assignments were justified with the help of 2D HSQC-TOCSY NMR experiment. 

Figure 5.13 Expansion of the aliphatic region of the 40 Hz HSQC-1,1-ADEQUATE spectrum of Dinaciclib 10. A convenient starting point is provided by the piperidine methine carbon resonance at 47 ppm enclosed in the black box. Two correlation pathways can be traced beginning from the resonance. One coupling pathway defines the pendant p-hydroxy ethyl moiety (C26, C27). The other connectivity pathway sequences and assigns the resonances of the remainder of the piperidine (C16-C13). Responses enclosed in red boxes are artefacts that arise due to resonance overlaps proton spectrum in the multiplicity-edited HSQC and 1,1-ADEQUATE spectra used in the GIC calculation of the HSQC-1,1-ADEQUATE spectrum. Reprinted from Martin et al. [96]. Copyright 2011, with permission from Elsevier.

In the present study ethylene-vinyl alcohol copolymers (E-VOH) with an increasing content of ethylene were synthesized and investigated using high-resolution solid state C NMR. A splitting of the methine carbon resonance into three peaks could be observed. This splitting could be explained taking into account tacticity and sequence effects. 

The complete assignment of the chemical shifts together with the relative area intensities for the methine carbon resonances are given in Table 1 and will be discussed now in some detail. 

The low field region shows three methine carbon resonances, peaks 1-3. Referring to Terao [2], and concentrating for the moment only at PV(, peaks 1-3 in the solid state cannot simply be assigned to the tacticity induced splitting of the mm, mr and rr triads respectively the relative area intensities of the three peaks in the solid state are not consistent with the triad tacticity observed in solution [2]. Moreover a significant downfield shift of the resonances 1 and 2 occurs compared with the observed chemical shifts for mm and mr triad resonances in solution, which results in much larger mutual chemical shift differences between the methine carbon resonances in the solid. 

It is thus seen that the carbonyl-, quaternary aromatic-, CF-, methine- and methylene-carbon resonances of aFS-MA copolymers can provide information about their structures. In particular, the methine carbon resonances seem to be the most useful for sequence distribution measurement. 

Table V. Comparison of Methine Carbon Resonance Areas to Triad Fractions Calculated for the Copolymers.

Mole % aFS in Copolymer Relative Methine Carbon Resonance Areas MA-Centered Triad Fractions ... 

Four yegs ago, Morris and Freeman(31) reported a method for enhancing C NMR signals by using polarization transfer from protons(INEPT). Subsequently, Doddrell and Pegg(32) showed that this INEPT method could be used to identify methine, methylene, and methyl groups of a complex molecule v en combined with appropriate delay time (A) prior to data acquisition and broad- d decou ing. If A=1/2J (J is the coupling constant between C and ), only methine carbon resonances appear in the... 

The best results are obtained using methane resonances 4 and 5 (Table 4.5) to determine copolymer composition. This is because the methine carbon resonance is the least sensitive towards configurational differences and also the least affected by overlap from neighbouring resonances. Similar results are obtained peak heights or peak areas are used. 

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