Elliot Charney

Optical activity of non-planar conjugated dienes—I : Homoannular cisoid dienes

Abstract A review is given of the results obtained so far in the investigation of the optical rotatory dispersion or circular dichroism of a number of non-planar homoannular cisoid dienes. The findings agree in every instance with the predictions of a theoretical rule connecting the sign of the Cotton effect with the chirality of the diene; two seeming exceptions can be explained through detailed conformational analysis. The rule can therefore serve as a reliable basis for stereochemical studies on this class of dienes. As expected theoretically, the amplitudes of the Cotton effects produced by these inherently dissymmetric chromophores are very high, values up to 100,000 deg mol−1 having been found. However, steroidal 1,3-dienes form a separate group characterized by comparatively low amplitudes, in many instances associated with a distinctive shape of the curve.

Far‐Ultraviolet Spectrum of Ethylene and Ethylene‐d4

The ultraviolet absorptions of the V←N transitions of C2H4 and C2D4 have been reinvestigated. The strongest observed bands are found to fit the empirical expressions: C2H4, ν (cm−1)=46 697+807ν; C2D4, ν (cm−1)=46 948+547ν. From the ratio 807/547 of the corresponding term differences of the two isotopic species, geometric considerations and group theoretical arguments, the frequencies 807 (C2H4) and 547 (C2D4) cm−1 are concluded to be the torsional frequencies in the V state. In the V state the two CH2 groups are consequently deduced to be skewed. Another frequency, 150 cm−1 in C2D4 has been observed but not interpreted.An analysis of the torsional progression shows the torsional potential of the V state to be parabolic. If a parabolic potential is also assumed for the ground state, the experimental and theoretical energy‐level diagrams are shown to be in reasonable agreement.

Optical activity of non-planar conjugated dienes—III : HMO calculation of the skew angle dependence

Abstract In two previous communications, 1,2 the results of an investigation of the rotational contribution of a dienic system which is constrained to be non-planar (skewed) have demonstrated that the sign of the rotational strength, and of the resulting Cotton effect, associated with the longest wavelength electronic transition of the system is determined by the skew or helical sense of the four carbon system of which it is composed. The theoretical basis of this conclusion is discussed here and calculations are reported of the intensity of the absorption bands, and of the rotational strength of this transition, as well as that of the transition of next higher energy as a function of the skew angle. In addition, making use of experimentally observed band widths, the contributions of these two transitions to the optical rotatory dispersion have been calculated, also as a function of skew angle, and it is demonstrated that for the one case for which X-ray data are available to determine the skew angle, the shape of the experimentally observed ORD curve is in excellent qualitative agreement with the calculation.

Optical activity of non-planar conjugated dienes—II : Transoid dienes

Abstract Earlier work1 has demonstrated that the sign of the Cotton effect associated with the longest wavelength electronic trnsition of a non-planar cisoid diene is determined by the helical sense of the diene system. The theoretical treatment has now been extended to non-planar transoid dienes and experimentally verified by determining the sign of the Cotton effect associated with a transoid diene (3-acetoxy-Δ8,14-cholestadiene) of unequivocal absolute configuration and skew sense. The optical rotatory dispersion of seven other transoid dienes has been determined and in all cases but one the sign of the measured Cotton effect agrees with the prediction.

Molecular Vibrations of Quinones. II. Infrared Spectra (Solution and Vapor) of p‐Benzoquinone and p‐Benzoquinone‐d4

Infrared spectra of quinone and quinone‐d4 have been obtained for both vapor phase (4000–650 cm−1) and solution (4000–75 cm−1). The vapor spectra are analyzed in terms of the band contours expected for transitions polarized along the three axes corresponding to the principal moments of inertia.

The spectral dependence of scattering from a spherical alga and its implications for the state of organization of the light-accepting pigments.

Abstract The cause of the spectral displacement of the 660-mμ band of extracted chlorophyll in organic solvents to about 680 mμ in vivo , as measured directly in algae suspensions, is of importance with respect to the role which energy transfer between the chlorophyll molecules plays in photosynthesis. The enhanced scattering on the long wavelength side of an absorption band in large particles, originally discussed by Price and Tetlow and invoked by Latimer and Rabinowitch to help explain this bathochromic shift, has been experimentally examined. A semiempirical theory has been developed which satisfactorily characterizes the effect. It is demonstrated that only a small part of the spectral shift arises from this selective scattering; the in vivo absorption band is established to occur at 674–675 mμ, some 10–15 mμ further to the red than the extracted pigments, indicating that a change in the environment of the chlorophyll molecules is responsible for the shift.

Polarization of the ion atmosphere of a charged cylinder.

The dipole moment is calculated for an electric-field-induced polarization of a Debye-Hückel ion atmosphere surrounding a charged rod. If L is the length of a thin rod. Q is its linear charge density, Z is charge of the salt ion in solution, and k is the Debye-Hückel shielding parameter, then for KL less, similar 10, the calculated polarizability is proportional to Z(2)Q(2)L(1.8)/K(1.2). Comparison with experimental data for DNA shows that the ion atmosphere dipole is of the correct magnitude and is consistent with observed variations with Z, Q, L and k.

Molecular vibrations of quinones—I. Fermi resonance involving the carbonyl stretch in p-benzoquinone and its isotopic derivatives

Abstract Infrared spectra in the region 1550–1700 cm −1 are reported for p -benzoquinone, four of its deuterated derivatives and two derivatives containing O 18 . Changes in the spectra with isotopic substitution and with solvent demonstrate conclusively the presence of Fermi resonance in quinone, quinone- d 4 and quinone-2,5- d 2 . A “hot band”, suggested recently as accounting for one of the three bands in this region in ordinary quinone, does not appear in the isotopic species.

Electric dichroism of DNA in aqueous solutions: electric field dependence

: The ionic strength and molecular weight dependence of the electric field dichroism of DNA, using native and sonicated calf thymus DNA, has been examined in the range of 0.09-1.0 mM NaCl solutions for molecular weights ranging from 1.24 x 10(5) to 44 x 10(5). The application of a classical theoretical analysis implies that the orientation results from an induced moment which appears to saturate at moderate fields of several killivolts per centimeter and that the induced moment is at least partly characteristic of that expected of a polyion whose charge is partially counterion compensated. The orientation leads to dichroism values which are in accord with other observations and are lower than expected for a B-form rod of DNA. These values, however, are not uniquely interpretable as resulting from base tilting.

Near‐Infrared Absorption and Circular Dichroism Spectra of Ferrocytochrome c: d→d Transitions

Transitions to the lowest crystal field singlet states of horse heart ferrocytochrome c have been identified from absorption and circular dichroism spectra in the wavelength region 5700–10 000 A. The results are correlated with crystal field and molecular orbital theoretical predictions. The Dq value for the porphyrin ring of ferrocytochrome c is found to be between 1700 and 1900 cm−1, in excellent agreement with the extended Huckel calculations of Zerner, Gouterman, and Kobayashi.