Multiplets carbon-proton

Organic compounds contain four types of carbon atom methyl, methylene, methine and quaternary. And so if we simply record the spectrum as we would a proton spectrum, the result will be a series of quartets, triplets, doublets and singlets, each associated with a carbon-proton one-bond coupling constant of between 125 and 250 Hz. If we are dealing with a complex molecule, these multiplets will overlap and give us spectra which are almost impossible to analyse. In addition, coupling interactions over two or more bonds complicate the picture still further. 

It is the coupling constant JCH which modulates the signal amplitude (Fig. 2.41). Thus, in order to recover the carbon-proton multiplets as the spectra of modulation frequencies JCH. a second Fourier transformation in the time domain t, has to be performed. 

Fig. 2.51 (d)). As a result, only the vector sum of all multiplet components will he detected, and the signal amplitudes will be. /-modulated by carbon-proton coupling as t, is varied. 

The data in Fig. 5 illustrate very nicely a less well known feature of 2D C/H shift correlation. The cross-sections of C-2 and C-3 (Fig. 6) show first order multiplets for protons which are strongly coupled in the ID spectrum. This is because the 2D spectrum is dealing with the satellites in the spectrum (one carbon at a time) and whereas H-2 is strongly coupled to H-3, the satellites of H-2 are not strongly coupled to H-3 and vice yersa. As a corollary of this one must also be aware that it is possible for the 2D experiment to give second order multiplets when the ID spectrum is first order. 

Carbon-proton connectivities can be determined using several methods. The number of protons directly attached to the carbon in question will split the carbon resonance according to the 2nl + 1 rule seen in proton NMR. There tends to be, however, much overlap of the multiplets in fully proton-coupled carbon spectra, sometimes such that it is very difficult to distinguish between the various multiplets. Routine carbon spectra are therefore measured fully proton decoupled for simplicity. Information regarding the exact number of protons attached to the carbons can be acquired from APT, DEPT or INEPT experiments. In APT spectra, the carbons bearing an odd number of protons (CH, CH3) can be distinguished from carbons with no or two attached protons (quaternary C, CH2). DEPT and INEPT experiments can distinguish between all four types of carbons (primary, secondary, tertiary and quaternary). Heteronuclear 2D /-resolved spectroscopy can also be used to obtain the multiplicities of the carbons, as well as Vc-h ... 

The purity of cyclobutanone was checked by gas chromatography on a 3.6-m. column containing 20% silicone SE 30 on chromosorb W at 65°. The infrared spectrum (neat) shows carbonyl absorption at 1779 cm. - the proton magnetic resonance spectrum (carbon tetrachloride) shows a multiplet at 8 2.00 and a triplet at S 3.05 in the ratio 1 2. 

Proton magnetic resonance (carbon tetrachloride) S 3.75 (singlet with fine structure) infrared (neat) cm. 2985, 2273, 1667, 1527, 1515 fluorine magnetic resonance (carbon tetrachloride) p.p.m. (CFCI3 internal standard) 142.4 (symmetrical multiplet, 2 ortho F), 153.8 (triplet with flne structure, 1 para P, J = 20 Hz), 161.7 (multiplet, 2 meta F). 

The spectral properties of the product are as follows infrared (neat) cm.-1 3268, 1377, 1037 proton magnetic resonance (carbon tetrachloride) d, multiplicity, number of protons 0.88 (multiplet, 6), 1.38 (multiplet, 7), 3.33 (unresolved doublet, 2), 5.14 (broad singlet, 1). 

The checkers found that a fraction, b.p. 45-71° (18 mm.), had the following spectral properties infrared (carbon tetrachloride) no absorption in the 3300-1600 cm.-1 region attributable to OH, C=0, or C=C vibrations proton magnetic resonance (chloroform-d) <5, multiplicity, number of protons, assignment 3.1-4.2 (multiplet, 4, CH—Cl, CH—O, and C//2—O), 1.0-2.5 (multiplet, 7, GH3 and 2 x C//2)-Thin layer chromatographic analysis of this fraction on silica gel plates using chloroform as eluent indicated the presence of a major component (the cis- and fraus-isomers), Rf = 0.60, and a minor unidentified component, Rf = 0.14. 

The first example of chemically induced multiplet polarization was observed on treatment of a solution of n-butyl bromide and n-butyl lithium in hexane with a little ether to initiate reaction by depolymerizing the organometallic compound (Ward and Lawler, 1967). Polarization (E/A) of the protons on carbon atoms 1 and 2 in the 1-butene produced was observed and taken as evidence of the correctness of an earlier suggestion (Bryce-Smith, 1956) that radical intermediates are involved in this elimination. Similar observations were made in the reaction of t-butyl lithium with n-butyl bromide when both 1-butene and isobutene were found to be polarized. The observations were particularly significant because multiplet polarization could not be explained by the electron-nuclear cross-relaxation theory of CIDNP then being advanced to explain net polarization (Lawler, 1967 Bargon and Fischer, 1967). 

The submitters obtained 59.6-64.1 g. (65-70%) of product melting at 36-37° after recrystallization from ethanol. Reported melting points for bis(phenylthio)methane are 34-35°, 38-40°, and 39.5-40.5°." The proton magnetic resonance spectrum of the product in carbon tetrachloride exhibits a two-proton singlet at 8 4.30 and a 10-proton multiplet at 8 7.10-7.56. 

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