NMR splitting pattern

The H NMR splitting patterns of the cations of 1- and 3-methyl-/rans-2-amino-3,4,4a,5,6,7,8,8a-octahydroquinazoline are similar to those of the unmethylated amine [71JCS(C)238] and are consistent with the anancom-eric chair-chair conformation. The c -2-aminooctahydroquinazolinium cations behaved like the di-perhydroquinazolinium cations and the cis-perhydroquinazolin-2-ones in solution [74JCS(P2)2313]. The 3-methyl derivative assumes only the N-in form, whereas the preferred conformation of the Tmethyl and 1,3-dimethyl derivatives is the N-out form. 

H-NMR splitting patterns peak split by spin-spin ... 

The NMR-splitting pattern characteristic of conkurchine-type alkaloids 74a) disclosed the presence of an 18(iV)-double bond and the structure of holonamine was thus ascertained 89) to be CLX. 

The H-NMR splitting patterns of methylene signals of these heterocalixarenes reveal their variable flexibility depending on the nature of the cyclic ureas and on moving from benzimidazolone to uracil to quinazolone the rigidity of respective calixarenes increases (2000JCS(P1)1037). 

The c/s-fused diaziridines (31a) and (31b) are also an equilibrium system, interchanging exo and endo positions of methyl and ethyl groups. The NMR spectrum shows two methyl peaks at 0 °C, coalescing to a single sharp peak at 75 °C. The ethyl group shows the sharp characteristic quartet-triplet splitting pattern at 75 °C (74JOC3187). 

Two features that aie fundfflnental to H NMR spectroscopy—integrated areas and splitting patterns—aie not very important in NMR. 

Anethole, C H O, a major constituent of the oil of anise, has the lH NMR spectrum shown. On oxidation with Na2Cr207, anethole yields p-methoxy-benzoic acid. What is the structure of anethole Assign all peaks in the NMR spectrum, and account for the observed splitting patterns. 

Tree diagram (Section 13.12) A diagram used in NMR to sort out the complicated splitting patterns that can arise from multiple couplings. 

Triplet (Section 13.1 I) A symmetrical three-line splitting pattern observed in the 11 NMR spectrum when a proton has two equivalent neighbor protons. 

Fig. 15. Splitting pattern with the assignment of the 13C-NMR shifts of meso-4,5-dimethyloctane at 100.6 MHz within the slow exchange regime of the CH—CH bond rotation. Chemical shifts refer to TMS = 0 ppm. (Ref. 30>)...

Something of scientific interest (among numerous other applications, Pascal s triangle is used to predict nuclear magnetic resonance [NMR] multiplet splitting patterns) has been created from the repeated application of a simple rule. 

Another important point can be deduced from the splitting pattern of the methylene protons in the H-nmr spectrum of the dianion salt [5]2-/2Li +. It appears from the equivalence of, for example, H-9,11 and the nonequivalence of H-9, 11 that the charged ring is planar, while the uncharged ring is tub-shaped (Fig. 6) (Krummel et al, 1987). The latter... 

Have you wondered about those funny curves drawn over the NMR peaks They re electronic integrations and they can tell you how many protons there are at each chemical shift. Measure the distances between the horizontal lines just before and just after each group. With a cheap plastic ruler I get 52 mm for the benzene ring protons, 21 mm for the —CH2— protons, and about 30 mm for the —CH3 protons. Now you divide all the values by the smallest one. Well, 21 mm is the smallest, and without a calculator I get 2.47 1 1.43. Not even close. And how do you get that 0.47 or 0.43 proton Try for the simplest whole number ratio. Multiply everything by 2, and you ll have 4.94 2 2.86. This is very close to 5 2 3, the actual number of protons in ethylbenzene. Use other whole numbers the results are not as good and you can t justify the splitting pattern—3 split BY 2 and 2 split BY 3—with other ratios. Don t use each piece of information in a vacuum. 

The NMR spectrum also provides information about the number of nuclei within each distinct environment. This is given by the area under each resonant peak representing the relative number of nuclei of each type. Furthermore, the surrounding nuclei also cause a splitting pattern. For example, one H surrounded by n other H neighbors will have its resonance peak split into n + 1 peaks. 

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