THE PROTON MAGNETIC RESONANCE SPECTRUM OF CYCLOPROPYLAMINE, THE A2A2′X CASE WITH STRONG CROSS-COUPLING: A PSEUDO FIRST-ORDER SPECTRUM WITH COMBINATION LINES

By means of the anisotropic solvent effect of benzene on the ring protons of cyclopropylamine the proton spectrum is converted to A2A2′X. Since the cross-coupling from the A2 to the A2′ protons is large the spectrum does not approximate to a pseudo first-order AX4 spectrum. Instead, it is one which may be described as pseudo first-order with combination lines. The presence of the latter allows a fairly complete set of coupling constants to be derived in a simpler way than by a computer attack on the general A2B2X spectrum. Conversely, the approach developed here, when applicable, allows the derivation of reliable input parameters for a computer program. From the temperature dependence of the A2A2′X case the A2 and A2′ protons can be distinguished and it is found that the protons trans to the amino group are preferentially shifted to high field by the benzene molecules.

PROTON MAGNETIC RESONANCE SPECTRUM OF 1-PHENYLCYCLOPROPYLCARBOXYLIC ACID: A2B2 SPECTRA OF CYCLOPROPANES

A2B2 spectra of 1,1 -disubstituted cyclopropanes have been calculated over a range of values of the spectral parameters. The sign of the geminal coupling is opposite to that of the vicinal couplings. Since this is also the case with other saturated ring systems the theoretical spectra should be useful in studies of other saturated ring systems.The shifts and coupling constants are given for the protons in 1-phenylcyclopropylcarboxylic acid in solution in carbon disulphide, chloroform, and benzene as an example of the A2B2 analysis. The ring protons in 1-phenylcyclopropylcarbinol were found to be equivalent in different solvents, with insignificant coupling to the protons in the methylene and phenyl groups. A qualitative discussion of the shifts of the various protons in various solvents is given.

RING-PROTON CHEMICAL SHIFTS OF SOME SUBSTITUTED ANILINES IN CARBON TETRACHLORIDE AND TRIFLUOROACETIC ACID

The chemical shifts of the ring-proton spectra of a series of substituted anilines are reported relative to internal benzene in the solvents carbon tetrachloride and trifluoroacetic acid. The substituent parameters in cyclohexane derived by Martin can be used together with our parameters for the para-fluoro and -ammonio (NH3+) groups to demonstrate additivity of the substituent effects in both carbon tetrachloride and trifluoroacetic acid. The somewhat puzzling ring-proton shifts in the latter solvent are attributed to counterion effects arising from a juxtaposition of the two centers of charge. Steric hindrance to π-overlap of the amino group with the ring is demonstrated in certain cases and a parallel behavior is found between the ring-proton shifts and the electronic spectra of these molecules.

TEMPERATURE AND SOLVENT EFFECTS ON THE PROTON MAGNETIC RESONANCE SPECTRUM OF BIS(2,2-DICHLOROCYCLOPROPYL) ETHER

The proton magnetic resonance spectrum of bis(2,2-dichlorocyclopropyl) ether consists of two partially overlapping ABX spectra due to the meso and d,l isomers. A study of the temperature dependence of the spectra in different solvents demonstrates the existence of complex formation with benzene. It is found that for the most abundant isomer the heat of formation of the complex is −1700 ± 100 cal/mole, entropy of formation is −6.2 ± 0.3 e.u. The association shifts are 52 ± 2 c.p.s., 64 ± 5 c.p.s., and 88 ± 5 c.p.s. at 60 Mc/s for the three protons situated at different points in the molecule.

SYMMETRIZATION OF SPIN FUNCTIONS FOR THREE EQUIVALENT SPIN 1/2 NUCLEI BY MEANS OF THE POINT GROUP C3

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RELATIVE SIGNS OF PROTON COUPLING CONSTANTS IN 1-CHLORO-2,2-DIMETHYLCYCLOPROPANE

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PROTON MAGNETIC RESONANCE SHIFTS AND THE ELECTRON DENSITY DISTRIBUTION IN AROMATIC SYSTEMS

The quantitative nature of the empirical linear correlation between the proton resonance shifts in aromatic molecules and the local electron density on the carbon atom to which the proton is bonded has been investigated. The application of this relationship to the determination of the electron density distribution of a variety of aromatic molecules, as well as the main limitations inherent in this application, are discussed. Electron density distributions have been derived for aniline, anisole, azulene, acepleiadylene, pyridine, pyridinium ion, and for the aromatic ions pentalenyl, indenyl, fluorenyl, triphenylmethyl cation, and azulene dianion, and are compared with those calculated by molecular orbital methods. In general there is a fairly good correspondence between the experimental and calculated density values, although for the aromatic ions the excess charge tends to be somewhat more uniformly distributed over the molecule than would be indicated by simple MO calculations.

PROTON COUPLING CONSTANTS IN SUBSTITUTED CYCLOPROPANES

Coupling constants between geminal protons are reported for a number of cyclopropane derivatives. They are compared with results from previous work and other values in the literature. It is suggested that the geminal couplings are of opposite sign to the vicinal couplings and therefore negative. Comparison of the H—C—H angles with the former are therefore no longer valid. It is also suggested that the geminal couplings are zero in ethylene sulphides and positive in epoxides and that there is a change in sign in going from carbon through sulphur to oxygen as the third atom in the ring. The vicinal coupling constants depend on the dihedral angle as predicted by theory but the substituent effects do not appear to follow a simple dependence on the electronegativity as they do in substituted ethanes.

EXCHANGE RATE AND ACTIVATION ENERGY OF EXCHANGE FOR N,N-DIMETHYLANILINE IN TRIFLUORACETIC ACID

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C13 SPLITTINGS IN SOME SUBSTITUTED BENZENES

C13 sidebands in the proton spectra of some symmetrically substituted benzenes have been used to obtain carbon–hydrogen coupling constants as well as proton coupling constants.A long-range carbon–hydrogen coupling constant has also been found. Substituents which act as electron acceptors in an inductive manner are found to increase the C13H coupling constants by as much as 20 c.p.s. The patterns of the sidebands are discussed and possible errors in first-order analyses are indicated.

THE PROTON RESONANCE SPECTRUM OF 2-FURANACROLEIN

The proton resonance spectrum of 2-furanacrolein consists of two effectively independent ABX spectra, that due to the ring protons and that due to the side-chain protons. The solvent effects are such that the latter reduces to an AA1X case. The ABX and AA1X cases are discussed as deviations from the A2X case. The difference is simply that forbidden singlet–triplet transitions in the A2X case become allowed in the ABX case because the singlet and triplet states are uncoupled as the A2 nuclei become nonequivalent. Energy level diagrams are given to illustrate this situation.

THE PROTON MAGNETIC RESONANCE SPECTRA OF CHRYSANTHEMUM ETHYL ESTER AND THE RELATED cis- AND trans-CHRYSANTHEMUMIC ACIDS

The high-resolution proton magnetic resonance spectra of a mixture of the cis and trans isomers of chrysanthemum monocarboxylic acid ethyl ester have been studied. The cis-chrysanthemumic and trans-chrysanthemumic acids spectra were obtained to facilitate the interpretation of the complex spectra of the ester. The percentage of the trans isomer in the chrysanthemum ester was measured to be 62.0 ± 1.1%. The cyclopropane proton spin coupling constants were found to be Jcis = 8.7 c.p.s. and Jtrans = 5.4 c.p.s., in reasonable agreement with Karplus' calculations of the dependence of coupling constants on the dihedral angle.

THE PROTON MAGNETIC RESONANCE SPECTRUM OF 1-FLUORO-2,4-DINITROBENZENE

A reliable analysis of the proton resonance spectrum of 1-fluoro-2,4-dinitrobenzene is described. Solvent effects were used to obtain this analysis and a possible source of error in a previous analysis is indicated. Spectra parameters are also derived for 1,5-difluoro-2,4-dinitrobenzene. The spectrum of the latter compound confirms the assignment of peaks in the spectrum of the former.

CORRELATIONS OF ETHYLENIC PROTON COUPLING CONSTANTS WITH ELECTRONEGATIVITY

A strong correlation is found between the electronegativity, Ex, and the three proton coupling constant of the vinyl group in over a hundred compounds of the type CH2 = CHX. This correlation extends over the range Ex = 4 to 1 and over the range Jgem + Jcis + Jtrans = 14 to 50 c.p.s. Simple implications and some useful applications of this correlation are discussed.

SOLVENT EFFECTS ON THE RING PROTON MAGNETIC RESONANCE SPECTRA OF SOME SUBSTITUTED QUINOLINES

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SOLVENT EFFECTS AS AN AID IN THE ANALYSIS OF THE PROTON MAGNETIC RESONANCE SPECTRUM OF VINYL BROMIDE

By making use of specific solvent effects it has been possible to vary the relative chemical shift between the geminal protons of vinyl bromide from about +10 cycles/sec to −4 cycles/sec (at 60 Mc/sec) and to study the resultant changes in the proton resonance spectrum in the limiting region of zero chemical shift. Of particular interest is the growth and displacement of the combination lines, which appear in the resonance signals of the proton bonded to the same carbon atom as the bromine. From the variation of the six possible lines in this region it was confirmed that the cis and trans proton coupling constants must have the same sign. The intensity distribution of the lines in the geminal proton region require the geminal coupling constant to be of opposite sign to the other two.

ON THE COUPLING BETWEEN H1 AND F19 NUCLEI IN p-FLUOROTOLUENE. II

By making use of specific solvent interaction effects it has been found possible to vary the relative chemical shift between ortho and meta protons in p-fluorotoluene continuously from about 0.2 p.p.m. to zero. The values of the HF coupling constants were found to be [Formula: see text] and [Formula: see text]. As the internal chemical shift goes to zero the ring proton spectrum collapses to two lines with a separation of 7.3 c/s. This splitting is interpreted as equal to [Formula: see text]. Corresponding changes observed in the CH3 proton spectrum are consistent with this interpretation.

ON THE COUPLING BETWEEN F19 AND H1 NUCLEI IN p-FLUOROTOLUENE

The proton and fluorine high resolution nuclear magnetic resonance spectra of p-fluorotoluene are discussed in terms of the case A2A2′X. The 4 × 4 submatrices are diagonalized in analytical form and therefore explicit values for all energy levels can be obtained. The spectra are consistent with [Formula: see text] which may be of theoretical interest.