The native anomalous phasing method will have greatest application to cases where poor occupancy or multiple substitution occurs, making direct interpretation of isomorphous difference Pattersons difficult. Alternatively, this method may be useful for locating relative origins for the binding sites from several derivatives in unfavorable space groups, such as P1. The major reasons for the success of the method are that full occupancy of the native anomalous scatterer always occurs, the number and types of binding sites are chemically defined, and the X-ray data are inherently more accurate, since no scaling is needed for anomalous pairs and lack of isomorphism never occurs.The authors wish to thank Drs B. Matthews and G. Kartha for helpful discussions. This work has been supported by NSF Grant No. GB27683 and Life Insurance Medical Research Fund No. G-70-28 Crystals of 1,8-bis(dimethylamino)naphthalene, C14HIsN2, are orthorhombic, space group P212~21, with a= 12.855 (1), b= 10.110 (1), c=9"664 (1)~ and Z=4. A complete structure determination, including refinement of the positions of the hydrogen atoms, led to an R index of 0-053 and a goodness-offit of 2.02 for 1477 reflections. The molecule adopts a conformation in which one carbon atom of each of the dimethylamino groups is eclipsed with respect to the naphthalene ring. Hindrance between the dimethylamino groups and/or resonance interactions between the dimethylamino groups and the aromatic ring are sufficiently great to distort the ring in several ways, the most conspicuous being a sizable increase in the non-bonded C(1)-.. C(8) distance (2.56 ~) compared to the C(4)-.-C(5) distance (2"44 A) and a twisting of the naphthalene ring into a considerably nonplanar conformation. IntroductionThe title compound, N,N,N',N'-tetramethyl-l,8-di- usual basic properties ('the proton sponge'; Alder, Bowman, Steele & Winterman, 1968) and for the steric effects which are expected to be encountered and their influence on the conformation that the molecule will find most favorable. Normally, there is strong resonance interaction between a dimethylamino group and an aromatic ring, so that one might expect a planar conformation to be favored (cf., e.g. Wheland, 1955). However, because of the steric difficulties for compounds such as (I), there is no reasonable possibility of bringing even one of the dimethylamino groups into the plane of the ring. Alternative possibilities include (II), where 1612 PERI INTERACTIONS the methyl groups are out of one another's way but the nitrogen lone pairs are brought face to face; (III), where the lone pairs are favorably situated relative to one another but one pair of methyl groups interferes strongly with a nitrogen atom ; and (IV), a compromise achieved at the expense of some interference between one methyl group on each nitrogen atom and the hydrogens at positions 2 and 7. A further question concerns the amount of ~z character in the C(ring)-N bonds, and whether it might be sufficient to force the nitrogen atoms into planar configurations....

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In achiral conditions, a difference in the NMR spectra of the d, I forms of a chiral molecule should be a manifestation of the never observed parity nonconservation in molecules. The involved NMR parameters depend on the never measured nuclear-spin-dependent PNC potential. Calculations performed with a relativistically parameterized extended Huckel method show a difference of a few mHz in the metal resonance frequency of enantiomers, containing Pt or Pb. A discussion of the various possible limiting factors shows that such a difference could be observed.

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The possibility of observing a difference in the high-resolution NMR spectra of two enantiomers as due to parity nonconservation is discussed. Proposals to minimize the NMR linewidths are presented. It is concluded that, using the ultra- high-resolution technique, a difference could be observed with high Z value spin one- half nuclei such as Pt, T1, Xe. Other nuclei can also be considered.

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