Equivalent Protons Research Articles

Free Radicals derived from Amines and Amino-acids in some Reactions of Ninhydrin

ALLOXAN and dialuric acid form free radicals in alkaline solution1,2. Ninhydrin, a chemical analogue of alloxan, has been shown to form a free radical on reaction with glycine3. The electron spin resonance (ESR) spectrum of this radical consists of 9 lines and is attributed to the two pairs of equivalent benzenoid protons of ninhydrin.

NMR Studies on steroids—VII : Substituent effects due to sulfur-containing groups in ring a of 5α-steroids

The PMR spectra of one hundred and five 5α-steroids of known structures including a large number of thiosteroids have been recorded in order to examine the effects of various substituents attached to the A-ring. Shift values of signals of the angular methyl groups and of protons attached to ring A due to the various substituents were evaluated and listed in the Tables. Relative chemical shifts of an axial to an equatorial proton on the substituent-bearing C-3 atom and signal shifts of protons on a hydroxyl- and a mercapto-bearing carbon atom due to acetylation are also examined. The behaviour of a mercapto and an acetylthio group was found to resemble that of a hydroxyl and and acetoxyl group, respectively. Distortion of ring A due to a 2β- and a 4β-sulfur atom is discussed by inspecting signal shapes of protons attached to the substituent-bearing carbon atoms.

Study of Molecular Orbital Degeneracy in C7H7

The paramagnetic resonance of the cycloheptatrienyl radical (C7H7) has been observed in single crystals of thiourea and naphthalene and in polycrystalline thiourea, naphthalene, cycloheptatriene, and argon at temperatures ranging from 4.2° to 300°K. The spectra are of two types: (a) high-temperature spectra—eight equally spaced lines with splittings in the range 3.5–4.1 G; (b) low-temperature spectra—highly anisotropic spectra which are markedly different for each crystalline environment. The transitions from (a) to (b) occur within 5°K, and the transition temperatures are 40°, 20°, and around 13°K in thiourea, naphthalene, and cycloheptatriene, respectively. The high-temperature spectra are readily accounted for in terms of seven equivalent protons and a uniform electron spin distribution about the ring. The high-temperature spectra thus provide evidence that there is no significant static (Jahn—Teller) distortion of C7H7. The uniform spin distribution around the molecular ring is brought about by the combined effects of rapid molecular reorientation about the seven-fold axis, plus the crystalline electric-field splitting of the orbital degeneracy. That is, in a sense, the crystal field splitting ``locks'' the spin distribution to the lattice, and molecular reorientation moves the nuclei relative to a fixed spin distribution. The low-temperature spectra correspond to the electronic ground state of (nonreorienting) C7H7, as determined by the crystalline electric field. The observed low-temperature spectra of C7H7 in naphthalene are compared with spectra calculated using the Hückel, valence-bond, approximate unrestricted Hartree—Fock LCAO—MO, and Pariser—Parr approximations to the molecular electronic structure of C7H7. The observed spectra appear to be in semiquantitative agreement with calculations based on the Hartree—Fock and Pariser—Parr approximations. However, detailed comparisons between these theoretical calculations and experiment are uncertain since both vibronic interactions as well as torsional molecular oscillations have an effect on the low-temperature spin distribution.

Long-Range Effect of an Asymmetric Grouping on the Magnetic Equivalence of Methylene Group Protons

Long-Range Effect of an Asymmetric Grouping on the Magnetic Equivalence of Methylene Group Protons

A note on the intensities of N.M.R. absorption lines

A proof is given of the proposition that the intensity of the N.M.R. absorption line from a group of n equivalent protons is proportional to n. To do this, it has been necessary to satisfy the Pauli exclusion principle by classifying states according to the irreducible representations of the symmetric group. As far as spin is concerned, this classification is equivalent to one according to the value of I, the total spin. Degeneracy with respect to I, which would otherwise occur, is prohibited by the exclusion principle, and a correlation (not one-to-one) is established between I and the symmetries of the rotational states.

The EPR spectrum of δ-irradiated polymethyl methacrylate specifically deuterated in the methylene group

Polymethyl methacrylate (PMMA) on exposure to ionizing nadiations gives an EPR spectrum identical to the one obtained on polymerizing methyl methacrylate MMA) and trapping free radicals in the polymer gel. To clarify the nonequivalence of interaction of protons with the unpaired electron in the free radical concerned, MMA was synthesized, specifically deuterated in the methylene group. The infrared spectra of normal and deuterated MMA show the specificity and the practically quantitative degree of deuteration. The absorption band at 3010 cm/sup -1/, assigned to the stretching vibration C-- H of = CH/sub 2/ group, and other bands due to deformation vibrations C-- H of the same group in the regions 1410, 680, and 800 cm/sup -1/, disappear in the spectrum of deuterated MMA and a new band due to C-- D stretching vibration appears at 2230 cm/sup -1/. Absorption bands of stretching and deformation vibrations C-- H of --CH/sub 3/ groups remain unchanged. The monomer thus obtained was block polymerized at 60 deg C during 400 min with dibenzoyl peroxide as initiator (36 mmole/l) and then gamma irradiated with a dose of 2.64 x 10/sup 18/ ev/ml at a rate of 11.7 x 10/ sup 16/ ev/min/ml by a Co/sup 60/more » source. The EPR spectra of normal and deuterated PMMA, polymerized and irradiated at identical conditions, show unequivocally the interaction equivalence of the methyl protons, that gives evidence of the correctness of the Ingram hypothesis of free rotation of the methyl group around the C-- C bond with a frequency higher than 10/sup 7/ rev/sec. The interaction with one deuteron broadens the spectral lines; the broadening at max slope amounts to 4 plus or minus 2 gauss. The quartet in the EPR spectrum of normal PMMA arises from the interaction with the methyl protons only. Should this quartet originate from an interaction with two protons of the methyl group and one proton of the methylene group, there would have to be a weaker triplet superimposed upon the quartet in the EPR spectrum of deuterated PMMA; this is, however, not the case. Therefore, the quartet of normal PMMA probably arises in such a conformation of the macroradical where the axis of the unpaired electron orbital just halves the angle between the methylene C-- H bonds. (BBB)« less

EPR Observation of Steady-State Ethyl Radical Concentration in Radiolysis of Liquid Ethane

EPR observations of radicals produced during photolysis and radiolysis have been reported but the second-order rate constants used were considerably less than steady-state. The present study is focused on the steady-state concentration of reactive radicals produced in liquid systems. The EPR spectrum of liquid ethane was examined during irradiation of the sample with 2.5-Mev electrons. The spacing and intensity of the lines indicate that the electron is coupled to one of two groups of equivalert protons and a second group of three equivalent protons. The resulting spectrum consists of four sets of triplets. The secondorder rate constant for the recombination of ethyl radicals in ethane is estimated to be 4 x 10/sup 9/ liters mole/sup -1/ sec/sup -1/. (B.O.G.)

THE ELECTRON SPIN RESONANCE SPECTRA OF THE POSITIVE AND NEGATIVE IONS OF DIPHENYLENE

The electron spin resonance spectra of the positive and negative ions of diphenylene have been measured. It has been found that these spectra consist of five lines showing that the observed hyperfine interaction is caused by four equivalent protons. The over-all extent of the positive ion spectrum is 18 gauss compared with that of 12.9 gauss for the negative ion. The hyperfine splittings observed are 4.0 gauss and 2.75 gauss respectively.

Electron Spin Resonance Spectrum of Dibenzene Chromium Cation

The electron spin paramagnetic resonance of dibenzene chromium cation h a s been observed. I t s c e n t e r is a t a valhe of g = 1.98. I t shows eleven hyperfine components s e p a r a t e d by 3.5 gauss. These a r e i n t e r p r e t e d to b e eleven of the thirteen components expected to r e s u l t f r o m the interaction of the twelve equivalent protons with the unpaired electron.

Equivalence of Protons and Neutrons in Nuclei

Equivalence of Protons and Neutrons in Nuclei

The Structure of the Nucleus and its Total Moment of Momentum

The known values of the nuclear moment are classified in four divisions according to even and odd nuclear number and even and odd atomic number. All of the 31 cases are consistent with, and 12 cases in two divisions definitely support the hypotheses that: 1st, The electrons in the nucleus have no spin; 2nd, The protons have a spin of 1/2 in units of $\frac{h}{2\ensuremath{\pi}}$. These hypotheses are applied to the building up of the nuclei of equivalent protons, and the results indicate that: (1). There is an analogy between the construction of the nucleus of equivalent protons and the construction of the extranuclear portion of the atom of equivalent electrons. (2). Five quantum numbers are associated with the proton, corresponding to the five quantum numbers of the electron. (3). The rules of Pauli and Hund may be applied to the protons. (4). ($\mathrm{ii}$) coupling predominates for the protons. (5). The nuclear moment is to be identified with the inner protonic quantum number of the normal nuclear state. (6). The nuclear moment $I$ is in general the smallest $I$ of the lowest $I$-group. (7). The order of filling of the protonic subgroups is somewhat similar, especially for small nuclear numbers, to the order of filling of the electronic subgroups of an atom.