MHz H NMR Spectra of Toluene

If you are wondering why there are more lines for the ring hydrogen signals than the three we expected on the basis of symmetry, you will find out in Chapter 8  

The nuclear Overhauser effect is the enhancement of intensity of an NMR signal generated by one nucleus when it is near another nonequivalent nucleus being simultaneously irradiated. We will discuss this effect in more detail later 

Although the signal positions will spread out (when measured in hertz), the chemical shifts (8) should remain unaffected. Relative intensities might vary a little because of different pulse parameters. But, by and large, the spectra should not change significantly, since there are no accidental equivalencies to resolve. 

There is another very significant difference between the H spectra we saw previously and this - C spectrum. Did you notice it The H signals of toluene differ in chemical shift by only about 5 ppm, which would correspond to 1(X) Hz at 20 MHz. The C signals, on the other hand, occupy a span of nearly 120 ppm (24(X) Hz) In fact, the H signals of most known compounds show up in a fairly narrow range of chemical shift, about 8 -5-15 ppm (5000 Hz at 250 MHz), while C signals span a range of 250 ppm (15715 Hz at 62.9 MHz). These spans, in fact, determine the spectral width discussed in Section 3.4. For this reason, the chance of accidental equivalence is far smaller in the case of - C spectra than with H spectra. 

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Fig. 16. 270-MHz H NMR spectra of poly(ethyl methacrylate) in CDC13 at 55°C. (A) Normal spectrum. (B) Spectrum obtained with a pulse sequence of (180° 0.8 s 90°-20s). (C) Normal spectrum measured in toluene-<78 at 110°C.

The respective 400 MHz H NMR spectra of (4) and (5) in CDCI3 at room temperature (298 K) display two broad doublets for the methylenes of (4) and (5) typical of an AB system, two singlets for the t-butyl groups, two metallocene signals and two aromatic absorptions. On warming to 55 C (328 K) the two doublets sharpen and at 100 °C (373 K) in toluene the respective AB systems are still observed. These NMR data are similar to those shown by the dimethyl derivative of p-tert-butylcalix[4]arene [12] and by the crowned p-tert-butylcalix[4]arenes [3, 13]. These compounds are all... 

The thermal polymerization of -MeOSt has already been mentioned by Staudinger and Dreher [239]. Heating a bulk sample to 90 °C for several days yielded a polymer with a DP = 390 (by viscosity measurements). Later, Russian authors [269] polymerized thermally all three isomers at 100 to 125 °C and found the p and m isomers to polymerize less rapidly than styrene, but the o isomer more rapidly. The stereoregularity of poly(/ -MeOSt) prepared by thermal polymerization in bulk at 60 °C was examined by Yuki et al. [270]. 100-MHz H-NMR spectra showed a rather split signal for the methoxy group and was interpreted in terms of pentad sequences. The analysis of the thermally polymerized sample showed a rather low content of syndiotactic triads. Kawamura et al. [244] studied the C-NMR spectra of o- and -MeOSt polymers prepared with BPO in toluene at 80 °C. They found both polymers to be rich in syndiotactic sequences [o derivative,, = 0.80 p derivative, P = 0.1 (P, = probability of racemic addition of monomer to the growing chain)]. 

The structure and chiral properties of the enolate intermediate were then investigated. Treatment of 40 with KHMDS (1.1 equiv) in toluene-THF (4 1) at —78°C for 30 minutes followed by t-butyldimethylsilyl (TBS) triflate gave Z-enol silyl ether 54 and its -isomer 55 in respective isolated yields of 57% and 27%.30 In the lH NMR spectra of both 54 and 55, methylene protons of the MOM groups appeared as AB quartets, which indicates restricted rotation of the C(l)-N bonds. The rotational barrier of the C(l)-N bond of the major Z-isomer 54 was determined to be 16.8 kcal/mol at 92°C by variable-temperature NMR measurements in toluene- (400 MHz 1 H... 

F. 1. 186.5 MHz Sn NMR spectra (recorded by the refocused INEPT pulse sequence with CPD H decoupling) of tris(trunethyl)stannylamine in, (MejSn)3N, toluene, labelled partially ( 13%) with N (sample by courtesy of W. Storch, M. Vosteen, University of Munich). The broad lines originate from the Sn- N and Sn- N- Sn isotopomers. All sharp lines arise from the Sn- N and " Sn- N- Sn isotopomers. Note the isotope induced chemical shift i i4/isN(ii9sn) = -38.4ppb and the resolved C satellites of the sharp lines due to V( Sn,N,Sn, C) in the isotopomers containing N. 

Fig. 11. H and 2H NMR spectra of PMMA (PMMA-23K) prepared with f-butylmagnesium-d6 bromide in toluene at —78°C. (a) 500-MHz H NMR spectrum measured in nitrobenzene- at 110°C (b) 61.3-MHz 2H NMR spectrum measured in nitrobenzene/nitrobenzene-<75 (95/5) at 110°C. (From Ref. 73.)...

Figure 5.9. Variable temperature H NMR spectra (300 MHz, toluene-tig) of OsClfHjXNH=C(Ph)- )2. Reprinted with permission from Barea et al.42 Copyright 1998 American Chemical Society.

Methyl acrylamidoglycolate methylether (MAGME) (American Cyan-amid) was filtered while warm and recrystallized from xylene (mp 70 73 C). All other monomers were freed from inhibitor on an aluminium oxide column. p-Trimethylsilylstyrene was synthesized from p-chlorostyrene using a Grignard reaction and chlorotrimethylsilane. Azobisisobutyronitrile (AIBN) was used as free-radical initiator in all polymerizations and carbon tetrabromide as chain-transfer agent. Polymerizations were carried out at 60 C in a 50 50 mixture of toluene and butanol under a nitrogen atmosphere. The reaction was carried out for 3,5 h and the formed polymer precipitated in cold diethylether. It was then redissolved and repreciptated prior to further use. once more IR spectra were recorded on a Perkin Elmer 1710 FTIR and NMR on a 200 MHz Bruker WP 200. FTIR was used to determine the co-polymer composition. 

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