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The nuclear magnetic resonance spectra of dl -valine, dl -threonine, and dl - allo threonine have been recorded in neutral, acidic, and alkaline medium at 60 and 100 MHz. The chemical shifts and coupling constants obtained from first-order analysis are discussed with special reference to a paper by Aruldhas on the NMR spectra of dl -valine and dl -threonine [Spectrochim. Acta 23A, 1345 (1967)].

This paper describes the preparation and a PMR investigation of a series of deuterium derivatives of 1,1-dimethylcyclohexane, cis- and trans-1,3- and 1,4-di-t-butylcyclohexane, and cis,cis-1,3,5-tri-t-butylcyclohexane. Accurate PMR parameters are obtained by the application of deuterium decoupling and computer simulation and iteration of the spectra. The coupling constants in trans-1,4-di-t-butylcyclohexane show that the t-butyl sides of the ring are puckered to the same extent as in t-butylcyclohexane. In cis-1,3-di-t-butylcyclohexane and cis,cis-1,3,5-tri-t-butylcyclohexane the axial protons at the carbon atoms between the t-butyl groups are also bent towards the centre of the ring. The axial methyl group in 1,1-dimethylcyclohexane is shown to cause a flattening of the ring. The chemical shifts of the ring protons provide further insight into the “anomalous” shift of 2-axial protons in methylcyclohexane(s). The vicinal coupling constants of trans-1,3-di-t-butylcyclohexane confirm that this compound exists for the greater part in a twist conformation.

A new component of the crude phosphatides of Zea Mays Linn. has been identified as sitosteryl-β-D-(6-O-fattyacyl)-glucopyranoside (I). Its gross structure, as a monoester of sitosteryl-β-D-glucoside, was derived from a study of the products formed on methanolysis and on acid hydrolysis. The location of the fatty ester was established by comparison of the proton chemical shift for H 2 C-6 in its tribenzoyl derivative with the chemical shifts for the corresponding protons in model benzoyl, acetyl and mixed benzoyl-acetyl derivatives of sitosteryl-β-D-glucopyranoside. The structure was confirmed by comparison, especially of optical rotation data, with a sample of sitosteryl-β-D-(6-O-stearoyl)-glucopyranoside prepared by synthesis. The [α] D values for the natural (−45°) and the synthetic sample (−46.5°) are practically identical. Further there is good agreement between the molar rotation difference ( ΔM D ) between (I) and its parent sitosterylglucoside and between the synthetic pair of glucoside and its ester. The approach to structure followed, in particular the use of ΔM D comparisons, and the optical rotation data recorded in this paper, provide simple and convenient means for establishing the structure of other natural esterified sterol glycosides.

The energies of the LMM Auger transitions show, for certain elements, a far greater dependence on chemical state than do the binding energies of the individual electrons involved in the transitions. This behaviour is not predicted by the existing models for the energy of an Auger transition but is of considerable practical importance in the examination of surface films by X. p. s. It permits, for example, the separation of the photo-excited spectrum due to a surface oxide from that of an underlying metal where this would be impossible by using photoelectrons alone. In this paper we describe the determination of such chemical shifts by the in situ oxidation of evaporated metals in the range iron to selenium. The self-consistency of the body of data thus obtained was checked by the determination of the energies of the excited 3d and 3p states occurring during the LMM transitions. This form of examination also permitted determination of the ‘effective incremental charge’, as postulated in the model of Bergström & Hill (1954), for both the metals and their oxides. This parameter depended very strongly and in a nonlinear way on chemical state. The nonlinearity is accounted for by use of a new model which retains the simplicity of that due to Bergström & Hill but allows the inclusion of polarization and ionic charge effects. In such a sequence of oxides, which have known oxygen densities, the O 1s peak provides an excellent standard against which the intensities of the Auger signals can be compared: it is found that the relative intensity increases linearly from nickel through to arsenic.

The physical foundations and the applications of a new method in nuclear magnetic resonance spectroscopy — the simplification of spectra by means of paramagnetic shift reagents, complexes of lanthanides with diketones — are examined, and data given on the properties of the most widely used reagents. The discussion covers the mechanism of interaction of the shift reagent with the organic compound (substrate), the dependence of the displacement of the signals on the concentration of the components and the temperature, the equilibrium in the reagent–substrate system, the effect of the nature of functional groups in the substrate, of the lanthanide ion, and of the ligand in the reagent on the magnitude of the shift in the n.m.r. spectra, the dependence of the shift and the line width on geometrical factors, and the effect of the shift reagent on spin–spin coupling constants. The use of shift reagents in the nuclear magnetic resonance of protons and other nuclei is considered briefly. The paper includes a summary of compounds whose spectra have been studied in the presence of shift reagents and also 348 references.

Nous presentons dans ce travail l'etude conformationnelle de divers ethanes di- ou trisubstitues par des groupements N-dialkyle, thioalkyl, alcoxy, N-pyrrolidino, N-benzyl, nitrile ou methoxycarbonyle. Les spectres ont ete analyses par une methode basee sur les deplacements chimiques. La stabilite relative des isomeres de rotation est discutee en fonction des parametres structuraux accessibles (geometriques et electroniques). In this paper we report the conformational analysis of several di- or trisubstituted ethanes substituted by the following groups: N-dialkly, thioalkyl, alkoxy, N-pyrrolidino, N-benzyl, nitrile or carbomethoxy. Spectra were calculated by a method based on chemical shifts. Relative stabilities of rotamers were discussed in relation to structural parameters (geometrical and electronic).

The interactions of organic cations, such as alkylamine hydrochlorides, RNH+3Cl-(R=CH3, C2H5, C3H7, C4H9) and tetraalkylammonium bromides, R4N+Br- (R=C2H5, C3H7, C4H9) with an organic anion, 2, 7-naphthalenedisulfonic acid (NDS) in aqueous solutions have been studied by using nmr spectroscopy. For comparison, the interactions of aliphatic alcohols (ROH, R=C2H5, C3H7, C4H9) with NDS were studied.The chemical shifts of aliphatic protons of such compounds in the presence of NDS were displaced to higher field (relative to external TMS). The large upfield shifts can be explained by the proximity of the aliphatic moieties to the anisotropic aromatic in aqueous solutions. In this paper were listed the shifts, Δδ, observed for alcohols, alkylamine hydrochlorides and tetraalkylammonium bromides (1 mol/l) when the medium was changed from pure water to NDS aqueous solutions (1 and 1.5 mol/l).The results obtained are as follows:(1) Alcohols. The shifts, Δδ, increased with increasing the length of the alkyl chains. Methyl and methylene proton signals were shifted to about the same extent.(2) Alkylamine hydrochlorides. The shifts increased with increasing the length of the alkyl chains. The methyl proton singals were shifted more than the methylene protons.(3) Tetraalkylammonium bromides. The shifts decreased with increasing the length of the alkyl chains. The methylene proton signals were shifted more than the methyl protons.From the above results the spatial mode of the interaction between the organic ions in aqueous solutions was discussed.

On binding a paramagnetic broadening probe at the end of a random coil polypeptide chain, one obtains sequential broadening of the -CH resonances along the chain and, hence, can determine the sequence of the peptide. The method has been applied to tripeptides (0.25 mg of material being used), tetrapeptides and a hexapeptide under conditions such that gadolinium ions bind at the C-terminus or cupric ions at the N-terminus. Dimethylation of the lysine residues of lysozyrne and observation of the chemical shifts of the six dimethyl proton resonances as a function of pH allows the determination of their pK. From studies of selective broadening of the methyl resonances on addition of gadolinium ions and the known structure of the lysozyme—ion complex, it is possible to obtain the pK values of the lysine residues of lysozyme. Approaches to the determination of the structure in solution of proteins using paramagnetic broadening and shifting probes is discussed. Problems concerning the site of ion binding and the assignment of p.m.r. resonances arise when the crystal structure is unknown. The amount by which a proton magnetic resonance (p.m.r.) line is broadened by a paramagnetic probe with a long electronic relaxation time —e.g. gadolinium(III)—is dependent on the inverse sixth power of the distance between the nucleus giving rise to the resonance and the paramagnetic probe. Furthermore, if the paramagnetic probe is an ion which binds rapidly and reversibly at a specific site, then the width of the resonance line will progressively increase as the concentration of paramagnetic ion is increased until such time as the site is saturated. after which no further broadening will occur. On the binding of gadolinium ions at low concentration to lysozyme. there is preferential broadening of p.m.r. resonances that arise from protons which are closest to the binding 2 The binding site has been shown by x-ray studies3 to be located between glutamic acid 35 and aspartic acid 52. By the use of difference spectroscopy46, in this case the subtraction of a paramagnetically broadened spectrum from the spectrum of native lysozyme, it has been possible to observe the resonances from the side chains of valine 83 J. H. BRADBURY ET AL. 109 and alanine 11012. In addition, distance information has been obtained from these studies with broadening probes and also from the use of lanthanide ions with short electronic relaxation times (europium(III). praseodymium(HI)). which cause shifts of resonances2' . In this paper three applications are given of the use of paramagnetic ions in peptide and protein chemistry. 1. DETERMINATION OF PRIMARY STRUCTURE (SEQUENCE) OF PEPTIDES If a peptide is present as a random coil in aqueous solution (which can be achieved by use of a denaturant such as urea or guanidine hydrochloride). then the average distance from one end of the molecule to successive cx-CH groups along the peptide chain increases as one proceeds along the chain. Thus, addition of a small amount of a suitable paramagnetic ion which is bound at one end causes most broadening of the ct-CH resonance of the nearest amino acid residue, less of the second residue and very little of the third residue8. This effect is shown in Figure 1. for addition of gadolinium

Chemical shift reagents (CSR) can substantially increase the amount of structural information obtainable from NMR studies of saturated and unsaturated lipid derivatives. It is theoretically possible to obtain even more information from CSR studies of unsaturated lipid derivatives by introducing additional CSR-active functional groups into those molecules through derivatization of their double bonds. However additional CSR coordination sites complicate spectral interpretation, because they increase the number of signals that overlap. Therefore two model compounds were investigated to test the feasibility of attempting other CSR analyses of polyfunctional molecules of unknown structure. This paper describes successful CSR studies of methyl ricinoleate and methyl 12-hydroxystearate. A series of complementary interpretive techniques was used to assign proton signals in spectra obtained during incremental Eu(fod)3 addition studies with these compounds. Individual proton signals can be observed and assigned for all the protons in methyl ricinoleate, except those on carbons 5, 6 and 7. Information obtained for methyl 12-hydroxystearate is less specific. Signals are observed for all protons in methyl 12-hydroxystearate, although in some cases several proton signals overlap.

High resolution hydrogen NMR spectra of amorphous, stereoblock, and isotactic fractions of polypropylene show distinct differences. The spectra are complex but those of polypropene-2-d1 and polypropene-2,3,3,3-d4 are simple and easily interpreted. The differences in the spectra of the amorphous, stereoblock and isotactic fractions of the polymers is the result of a difference in the chemical shifts of isotactic and syndiotactic type methylenes. The ratio of the types of methylenes can be estimated from the spectra of polypropene-2,3,3,3-d4. In isotactic polymer the concentration of syndiotactic type methylenes is below the limit of detection. Assuming that the inversions in stereochemical configuration are randomly distributed along the polymer chain, the average length of sterically identical segments in stereoblock polymer is about fifteen monomer units. In amorphous polymer the ratio of isotactic to syndiotactic type sequences is approximately one. The spectra of the deuterated polymers show no detectable rearrangement of hydrogen and deuterium atoms in the polymerization.

The compounds obtained from the reactions of phenyl salicylate and 2-hydroxybenzo-phenone with phosphorus pentachloride have been shown to have structures I A and II A, respectively, rather than alternative heterocyclic structures on the basis of the comparison of the P31 chemical shifts with appropriate reference compounds and additional chemical evidence. Compound I reacts with two equivalents of phenol in the presence of two equivalents of triethylamine to form mainly compound VIII (substitution on phosphorus). Structure VIII is confirmed via P31 n.m.r. and IR spectra and the fact that partial hydrolysis forms the same compound (VII) that is obtained from the reaction of compound III with phenol (only phosphorus substitution possible). A mechanism with initial reaction of phosphorus pentachloride (as tetrachlorophosphonium ion) on the phenolic hydroxyl is postulated on the basis of the available evidence. The P31 chemical shifts for compounds XIV A and XV A confirm these structures as heterocyclic in accord with previous chemical evidence. Structure XIV A is of historical importance as one of the first three cyclic structures ever published in the classical paper in which Couper announced his structural theory of organic chemistry.

This paper presents an analytical method to investigate some acidic phosphate esters (mono-, di-, tri-alkyl phosphates) by a nuclear magnetic resonance spectroscopy on 31P nuclei.These alkyl phosphates in the experiment have shown their chemical shifts to be very close to each other and the sensitivity of 31P is generally low. We have solved the former problem by adding two volumes of di-(2-ethyl hexyl)-amine to one volume of sample of alkyl phosphate mixtures. For the latter, time averaging S/N improvement by a digital computer was carried out.The subject of processing includes a multi-scan averaging or CAT (computer of average transients), smoothing of accumulated data and off-line data processings which cover the print out of peak positions, peak areas and their percent ratios, chemical shifts, and spin-coupling constants.The communication with the system is supported by a teletype and an operator unit which facilitates the spectrometer. The performance of the system has proved to be very satisfactory.

The pi interactions within molecules containing the pentafluorophenyl group are examined using the coupling constant-chemical shift relationship as proposed in the preceding paper. The following series, selected from the 73 pentafluorophenyl compounds studied, are discussed: pentafluorophenylphosphines and some of their complexes including metal carbonyl derivates: compounds of the type C6F5XMR3, where X = O or S,M = Si,Ge,Sn, or Pb, and R = Ch3 or C6H5; and of the type C6H5NHR where R = B(C6H5)2,CH3,H,Si(CH3)3. Estimates of (p to d) pi bonding between group IV elements and oxygen, sulfur, and nitrogen are given. The influence of a sigma-bond polarity upon back donation by halogens is considered. (Author)

The chemical shifts of nuclear magnetic resonance frequencies are determined by the secondary magnetic field due to the electronic current induced by the applied field. This paper is concerned with the general problem of finding the current density vector field. An approximate orbital theory is developed which enables this to be divided up, under certain conditions, into local diamagnetic and paramagnetic circulations about individual atoms. The method is applied to the acetylene molecule as an example.

This paper reports the synthesis, analytical data, melting points, and phosphorus chemical shifts of over seventy quaternary phosphonium salts. Most of these data have not been reported.

Currently there is great interest in the precise conformation of complicated natural products in solution. Nuclear magnetic resonance (NiVIR) has great promise in this connection and has made possible a high degree of sophistication in the conformational analysis of the steroids. However, less progress has been made with peptides. In this paper, we wish to report our analysis of 100and 220-AMc N1\MIR spectra of the cyclic antibiotic decapeptide gramicidin S-A in solution. Methods.-Proton magnetic resonance spectra were obtained on Varian Associates high-resolution spectrometers operating at 100 and 220 Mc. The internal reference was tetramethylsilane (TMS), which appears at 0 ppm in all spectra. Sample colncentrations were 3-6%o (gm/100 ml). The normal operating temperature was 320. Gramicidin S-A was isolated from a crude preparation by countercurrent distributionib and lyophilized in glacial acetic acid. Deuterated dimethylsulfoxide (DMS0) and deuterated methanol (CD30D) were purchased from NMR specialties. DMSO-d6 was dried when necessary over calcium hydride. Results and Discussion. A twofold axis of molecular symmetry in the crystal has been demonstrated for gramicidin-S by X-ray crystallography.2 From the known amino acid sequence,3' 4 it seemed likely that this conformation would hold in solution; this is confirmed by the NMIR results reported here. Ten amino acid residues, two of each kind, are present. The strong single resonance band at 7.3 ppm in CD30D (and in DMSO if the partially interfering amide signal is subtracted, see later) must result from the ten aromatic protons of the two phernylalanines. With this as a basic inference, integration under the peak areas assigned to amide bands then corresponds to two protons for each of four regions, although these areas are not all clearly separated by a single solvent and temperature condition. Their assignment to a particular amino acid residue is made possible by decoupling and deuterium exchange experiments as outlined below. The assignments of the proton chemical shifts in the gramicidin S-A spectra are based on the following: (a) comparison with NMVIR spectra of constituent amino acids and known peptides; (b) spectra taken on instruments of varying field strengths (60, 100, and 220 Mc); (c) spectra taken in solvents that promote and solvents that prohibit proton exchange; (d) double resonance experiments; and (e) variable temperature spectra. Decoupling experiments were necessary in order (a) to show that the splitting of the amide proton peaks was due to spin-spin interaction and not to chemical shifts (a fact also proved by the invariability of the amide coupling constants in both the 100and 220-Mic spectra) and (b) to determine which Ca, C:, and NH protons are coupled together. The coupling constants between these types of protons will be designated Ja,3 and JNC. A knowledge of these should define the stereochemistry around the C -C and N-C" bonds.

Theoretical values of the nuclear magnetic shielding constant σvJ for each of the molecules H2, HD, HT, D2, DT and T2 in their lower vibrational and rotational levels have been obtained from the results of the preceding paper. Values of the shielding constants of these compounds at temperatures in the range 0–700 K are predicted. Over the range -100 K to +200 K the shielding constant of H2 gas (at low densities) falls by 0·038 p.p.m., an amount that should be measurable. For H2, D2 and T2 there is a significant difference between the shielding constants of the ortho and para modifications at low temperatures. However, only for D2 is it possible for the N.M.R. method, in principle, to obtain a doublet splitting. For hydrogen gas the shielding constant at 300 K is calculated to be 26·297 p.p.m. This is in satisfactory agreement with the experimental value of 26·51 (±0·33) p.p.m. The isotope shift σ(HD)-σ(H2) is calculated to be 0·042 p.p.m. at 300 K. This agrees well with the three independent experimental ...

The proton spectrum of poly(vinyl chloride) prepared by free-radical polymerization has been studied at 220 MHz and interpreted in terms of pentads for the x-protons and tetrads for the n-protons. The chemical shifts are in good agreement with those reported elsewhere using selectively deuterated polymers. The magnitudes of the vicinal coupling constants indicate that in the solvents employed, the isotactic dyads are in approximate equilibrium between the conformations which, if repeated, result in a helix, whereas syndiotactic dyads are probably in the conformation with the backbone in a planar zigzag structure. The tetrad and pentad relative intensities are consistent with Bernoullian chain propagation statistics, with a value m(the probability of isotactic placement) of 0.43. Radiolysis of poly(vinyl chloride) (PVC) was studied by ultraviolet and visible spectroscopy following post-irradiation storage at selected temperatures in a cryostatic cell. A sequence of alkyl, allyl and polyenyl radicals followed by chain transfer to PVC leads to polyene formation. Allyl, dienyl and trienyl radicals were associated with absorption bands at 2520, 2910, and 3300 A, respectively. Radical intermediates react readily with oxygen. INTRODUCTION In this paper, I wish to report on recent work carried out at the Bell Telephone Laboratories on the structure and chemical reactivity of polyvinyl chloride. Although many techniques and types of spectroscopy have been applied to this polymer in this and other laboratories, our principal tools in this work have been high resolution nmr for the study of its configuration and conformation and esr and uv spectroscopy for the study of its chemical behaviour, in particular the dehydrochlorination reaction which is initiated by high energy radiation. STEREOCHEMICAL CONFIGURATIONf Interpretation of the nmr data for polyvinyl chloride has been protracted and controversial, in part because of ambiguities in the spectra and in part t In the following discussion, familiarity with the basic concepts used in interpreting the nmr spectra of vinyl polymers will be assumed. For those needing it, a review of these concepts can be found in Acc. Chem. Res. 1, 175 (1968).

The procedures developed in previous papers of this series have been extended to aromatic fluorides, using 19F NMR chemical shifts as a guide to the selection of parameters for fluorine. Attempts to correlate chemical shifts with the local π‐electron density on fluorine proved unsatisfactory, the correlation depending on the number of atoms ortho to fluorine that carry p or π electrons. Similar results followed for charge densities calculated by a recently developed semiempirical SCF MO treatment in which all the valence electrons are included. Analysis of the Karplus–Das–Prosser–Goodman treatment of chemical shifts suggested that this “ortho effect” arose from neglected long‐range interactions. A treatment including these was developed and shown to account well for the 19F chemical shifts of nearly 100 aryl fluorides.

The nuclear magnetic resonances of N 14 in ammonia and related compounds have been studied in a field H 0 = 10,730 gauss. Shifts of the resonances relative to the peak associated with N 14 in the NH 4 + ions in a saturated aqueous solution of NH 4 NO 3 have been measured for the following compounds: NH 4 Cl, NH 4 Br, NH 4 I, NH 4 H 2 PO 4 , (NH 4 ) 2 S, NH 4 SO 4 · ZnSO 4 · 6H 2 O, NH 4 SCN, ammonium hydroxide, NH 3 liquid, NH 3 dissolved in ethanol, Ag(NH 3 ) 2 NO 3 , Zn(NH 3 ) 5 Cl, Ca(NH 3 ) 8 Cl 2 , N(CH 3 ) 4 Cl, N(CH 3 ) 4 Br, and NH(CH 3 ) 2 . Mixtures of ammonium salt solutions with ammonium hydroxide have also been studied. The relative widths of the resonance peaks have been determined. Experimental details are given in the paper. The structure of ammonium hydroxide is discussed in the light of the data presented.

The regularities of the changes of the chemical shift in the F19 NMR of trifluorovinyl compounds are discussed in this paper. It has been shown that the conditions $$\delta _{F_1 }< \delta _{F2}< \delta _F^0< \delta _{F3} $$ , where δ F 0 is the shift of F19 in tetrafluorethylene (X=F) are satisfied for the chemical shifts of fluorine in compounds. An increase in the electronegativity of X leads to a decrease in the ionic nature of the C-F3 bond and to a shift toward weak fields. The effect of X on the $$\delta _{F_1 } $$ and $$\delta _{F_2 } $$ shifts is not linked in a specific way to the electronegativity of the X group and is probably determined by the effect of the electric fields on the shielding of the F19 nucleus. Increments were calculated from the data obtained on the shifts in trifluorovinyl compounds. The method of increments was used for the assignment of the lines in 1, 2-difluoro olefins. This method for the assignment is confirmed by known data. Several cases for the application of the increment method are proposed. The results of spectral measurements of the F19 NMR in some trifluorovinyl compounds are given in the experimental part.

A systematic procedure is developed for the analysis of the spin‐spin multiplets that are observed in the high‐resolution NMR (nuclear magnetic resonance) spectra of liquids. It is shown how the symmetry properties of nuclear spin functions can be used to simplify the interpretation of NMR multiplets in terms of the empirical quantities, chemical shifts, and spin‐spin coupling constants. It is also pointed out that when NMR multiplets have been properly interpreted in terms of these empirical quantities, it is then possible to predict theoretically relative intensities of multiplets to the same degree of precision as that involved in the measurement of multiplet frequency separations.As an example the multiplet splittings of the H1 and F19 resonances in 1,1‐difluoroethylene are analyzed using the procedure proposed in the present paper.

The Extended Huckel Theory (EHT) has been applied to a series of nitrogen heterocyclic molecules, and their anions and mono- and di-protonated derivatives. In particular, pyrrole and the pyrrole anion, imidazole anion, neutral molecule and cation, pyridine and its protonated cation, and the diazines and their protonated and diprotonated cations are discussed in this paper. A considerable polarization of the sigma-bond framework is observed in all cases. The total electron densities are not changed appreciably by use of a hydrogen Slater exponent of 1·3, rather than 1·0, or by the use of real, rather than ideal, geometries. The general effect of protonation of a nitrogen atom is calculated to be an increase in the total electron density at the adjacent carbon atom(s), but a slight decrease in electron density at the ortho hydrogen atoms. These results are shown to be in accord with experimental data, since good correlations are obtained between the total carbon electron densities and (a) proton chemical shifts and (b) carbon-13 chemical shifts.

New microwave results confirm Brown and Hollis' trans-cis assignment for alkyl nitrites. In the present paper, the experimental material is widened by investigating compounds of the type XCH2CH2ONO where X = F, Cl, Br, I, CN. The barrier to trans-cis conversion is fixed to ca. 10 kcalmole−1 in all cases. Likewise, Ecis - Etrans is close to 1 kcalmole−1, and Scis - Strans ∼ 2 gcalmole−1 deg−1. Rotation about the C,C bond generates 3 isomers, 2 in which X is gauche, and 1 in which X is trans to the ONO group. By measuring proton chemical shifts and proton spin-spin couplings at room temperature where effective averaging over rotations about the C, O single bond and the ON single bond takes place, it is shown that the gauche forms are more abundant than statistics would indicate ( 2 3 ). Since the same gauche:trans ratio is observed in the case X = F for the pure trans (O,N) form at −70°C, we conclude that gauche preference also applies to the cis isomer. This rules out the idea of some intramolecular bond between non-neighbouring atoms, stabilizing the cis isomer. The new compounds X = F, Br, I, CN are characterized by their infrared spectra.

Correlations of excess chemical shift of coalesced hydroxy proton resonance signals with reinterpreted thermodynamic data for methanol-water, ethanolwater, propanol-l-water, and propanol-2-water systems were consistent with those reported for the tert-butanol-water system (Paper I of this series). In all cases there was evidence that the greatest degree of solution structuring occurred at low concentrations of alcohol. It was proposed that phase separation at low alcohol concentrations in other aqueous systems of monohydric alcohols may be associated with a molecular geometry which interferes with this solution structuring factor.

Using the assumption that the valence orbital hybridization in compounds of the type PZ5 is such that all five fluorines in PF5 are instantaneously magnetically equivalent even though the two axial bond lengths are longer than the three equatorial ones in this trigonal bipyramidal structure, an ASP LCAO MO quantum‐mechanical calculation has been made for the 31P chemical shifts of molecules of the form PZ5. As in the two previous papers of this series, π bonding to the phosphorus is included. On the assumption that the π orbitals of the phosphorus are vacant in the compound P (C6H5)5, the amount of π bonding is estimated for the symmetrically substituted compounds of the type PZ5 on which chemical‐shift data are available.

The present paper examines the origin of the 19F NMR chemical shift increase in metal fluorides with cation d10- and f14-configurations as compared to isostructural fluorides with a p6- configuration. It was shown that this effect may be explained qualitatively on the basis of the Kondo-Yamashita model. An expression was obtained allowing calculation of the input of the fluorine p-shell with the cation d-and f-shell overlap into the magnetic screening tensor for any environment of the fluoride ion. Calculations were made for the overlap integrals and screening tensors for mercury and silver fluorides, as well as for CaF2 and NaF isostructural fluorides. A CaF2-and HgF2-based discussion on the influence of partial covalency upon the 19F NMR chemical shift follows below.

This paper is a critical review of the literature on the problem of the nature of carbon–halogen bonds. It examines the various physical properties of halogen-containing organic compounds which are useful in discussing the problem of the chemical bond (infrared spectra, dipole moments, interatomic distances, nuclear quadrupole interaction constants, nuclear magnetic resonance). Special attention is paid to results from nuclear magnetic resonance, which show the uselessness of treating the properties of organohalogen compounds from the position of mesomerism–resonance theory. The correlation between the chemical shifts of nuclear magnetic resonance and the σ-constants of the substituents in various organohalogen compounds is considered. Attention is paid to the hybridisation of the orbitals of the carbon and halogen atoms and to the associated electronic displacements in unsaturated and aromatic systems. 85 references.

In unsaturated heterocyclic compounds, the relative chemical shifts of the protons bonded to the ring are strongly dependent on solvent and concentration. In 6‐membered ring compounds, as for example 4‐picoline, the β hydrogens show a pronounced shift to low field in acetone solutions and to high field in benzene solutions. This behavior is similar to the behavior found for p‐substituted toluenes (preceding paper). In the 5‐membered heterocyclic compounds, for example pyrrole, the behavior of α and β hydrogens is reversed, the proton signals of α hydrogens being displaced selectively in acetone and benzene. The results can be interpreted in terms of a preferential hydrogen bonding of the α protons with the donor solvent molecules.

Publisher Summary The years 1966 to 1969 have seen a continuous increase in the interest of NMR studies of phosphorus compounds both from the practical, for the solution of structural and conformational problems, and the theoretical aspects, for a better understanding of the nature of the bonding in phosphorus compounds. About one thousand five hundred papers appeared during those four years and it is clear that the moment was ripe for an up-dated account of the NMR achievements in this field. This chapter covers most of the aspects of NMR in phosphorus chemistry, especially stressing those aspects directly related to electronic and structural factors. Some of the issues such as resonances in solid compounds, in metal complexes and biological applications are briefly reviewed. All the compounds reviewed are tabulated in either Formula Index I (inorganics) or Formula Index II (organics), the whole comprising of more than four thousand five hundred entries. These indices list all available chemical shifts for phosphorus and fluorine and those for other nuclei (except protons) are reported in the text.

Publisher Summary This chapter presents a general review of proton magnetic resonance (PMR). The chapter explores two significant papers on the theory and correlation of coupling constants that have used a theoretical valence bond description of contact nuclear spin-spin coupling. Perturbation theory and Penney-Dirac bond orders are used to obtain a simple form for the average energy valence-bond model of the contact contribution to proton coupling constants. For the most common molecular systems, in which there are only small deviations from a localized bond description, the vicinal and long-range coupling constants are expressed in terms of the bond orders for four-electron fragments. Geminal, vicinal and long-range couplings, and couplings in aromatic and heteroaromatic systems are discussed in the chapter. A linear relationship between the proton chemical shifts for substituted aliphatic derivatives and the positive charge density on hydrogen, as determined by a M.O.-L.C.A.O. method, is obtained. The procedure, whereby the magnitude of the magnetic anisotropy of bonds is calculated from a study of relative chemical shifts, has been employed to estimate the magnetic anisotropy of the acetylenic, nitrile, and isonitrile triple bonds. Conformational analysis now ranks amongst the most important branches of organic stereochemistry, and the derivation of information about the conformation and configuration of molecules from coupling constant and chemical shift data is well documented in this chapter. The recent advent of high field superconducting magnet spectrometers has greatly increased the number of studies of biological systems that have employed NMR spectroscopy.

In addition to the traditional spectroscopic methods in chemical physics [1–3] nuclear magnetic resonance (NMR) experiments provide a powerful tool for the research of molecular motion and reorientation in any sample with nuclear magnetic dipoles. It has been shown in many earlier papers and monographs (see for instance [4–13]) that few other spectroscopic techniques offer such a direct and detailed insight into events at molecular level as magnetic resonance, although one of the most promising possibilities of NMR, namely the investigation of the Larmor frequency or magnetic field dependence of the magnetic relaxation rates, has only rarely been used compared with high-resolution and broad-line spectroscopy. This article summarizes the theoretical background and typical experimental results of this new technique, which we shall call “Nuclear magnetic relaxation spectroscopy”. The emphasis will be on liquids, mainly for experimental reasons.

Correction of an error in the paper of the above title reduces the calculated difference of chemical shift between μ + and proton by 2√2. The possibility of reducing the chemical-correction uncertainty in muon moment measurements is discussed.

Interactions of oxygen with iron, nickel and copper at room temperature have been investigated by means of an ultrahigh vacuum type X-ray photoelectron spectrometer designed by authors. Behaviors of peak heights and chemical shifts in O ls and Fe 2p spectra caused by oxygen chemi-sorption and oxidation are reported. Similar results on copper and nickel are also reported in this paper.

The configurations of the two secondary and the two tertiary alcohols whose synthesis is described in the preceding paper have been established unambiguously by analysis of n.m.r. spectra. Four techniques were used : (i) treatment of chemical shifts by the additivity relationship; (ii) study of degree to fit to the relationship between europium-induced shift and intramolecular distance; (iii) comparison between sensitivities of shifts to europium concentration; and (iv) investigation of the behaviour of the previously assigned protons of adamantan-2-ol, and spin decoupling in the europium-expanded spectrum. All results led to the same conclusions, and justify interchange of the configurations previously assigned to the secondary alcohols. The reliability of these methods is assessed.

A procedure used to calculate chemical shifts in some fluorocarbon compounds (see preceding paper) is extended to include fluorine bonded to tin(IV). In this case secondary interactions, responsible for deviations from additivity of substituent effects in fluorocarbons, are negligible.

Amino-14N chemical shifts have been measured in some substituted anilines by use of the heteronuclear double resonance method. The shifts are shown to correlate linearly with the Hammett σ values of the ring substituents and to be related directly to electron densities at the nitrogen nucleus found by other workers. This supports arguments that we have used qualitatively in previous papers. For four compounds where 15N data are also available, the relative 14N and 15N chemical shifts are found to be identical within experimental error.

The study of molecules in the gas phase by ESCA offers several advantages. Particularly, the opportunity to make direct comparisons between theoretical and experimental results is of importance. From such comparisons a more complete understanding of several fundamental phenomena in ESCA has been gained. The present paper reviews some recent work in Uppsala along this line. The effect of electron reorganization on core binding energies in atoms and molecules is analyzed. Chemical shifts in ESCA and n.m.r. are discussed. The existence of a general relation involving these chemical shifts and nuclear spin-rotation constants is pointed out. A model for analyzing ESCA intensities of the valence electrons in molecules is presented. It is shown that the analysis may be useful in identifying the molecular orbitals.For most applications of ESCA it is highly desirable to improve the resolution and the intensity. An instrument, particularly designed to achieve this for gases, is discussed. It can also handle solid samples. It makes use of a high-emission, fine-focus electron gun, a rotating anode and a double focusing quartz crystal. The first electron spectrum recorded with this new instrument is presented.

In this paper, the methods outlined in Part I are used to estimate the electron distribution from the proton chemical shifts in a series of five-membered ring heteroaromatic compounds. The systems studied are pyrrole and furan, their benzo and dibenzo derivatives, indazole, indolizine, the azaindolizines, and purine. It is found that the estimated excess charges are not as closely represented by the BJ VESCF method as was the case for the azine derivatives and that the role of the σ-electrons is in urgent need of closer investigation.

Theoretical considerations indicate that the electron distribution in 3,4,-dimethylenecyclobutene is non-uniform and a dipole moment of 0.71 D has been predicted by inclusion of non-neighbour core resonance integrals. Preliminary studies of the microwave spectrum of this compound provide a dipole moment of 0.618 � 0.011 D. The term "pseudo-alternant" is proposed to describe this phenomenon. In the present paper additional physical and chemical properties of 3,4,-dimethylene- cyclobutene are described. The observed low-field proton chemical shifts for 3,4-dimethylenecyclobutene are not accounted for using a ring current model and a small calculated paramagnetic current indicates properties usually associated with H�ckel 4n-hydrocarbons. A local anisotropy model provides a better account of the observed shift. The carbon-13- proton satellite spectrum of 3,4-dimethylenecyclobutene indicates similarities in the geometry of the four-membered ring to that in cyclobutene. In addition, infrared and ultraviolet spectra support the conclusion that this hydrocarbon be regarded as a cross-conjugated diene. A detailed discussion of the products arising from the bromination of 3,4-dimethylenecyclobutene under a variety of conditions indicates consecutive 1,4-addition of bromine across the four-membered ring, a property which has been associated with cross-conjugation. Hydrogenolysis, chlorination, iodination, and attempted Diels-Alder addition reactions are also described. 3,4-Dimethylenecyclobutene was prepared by the thermal rearrangement of hexa-1,5-diyne. The mechanisms of thermal and photolytic rearrangement of hexa-1,5-diyne are discussed using Woodward-Hoffmann postulates. 1,2-Dideutero-,1-ethyl-, and 1-n-propyl-3,4-dimethylenecyclobutene were also prepared by the thermal rearrangement of the corresponding diyne. In addition, the thermal rearrangement of hexa-1,5-diyne over the temperature range 290-700� to give variable quantities of 3,4-dimethylenecyclobutene, fulvene, and benzene is described. 3,4- Dimethylenecyclobutene is thermally rearranged to benzene at 680�.