1740 I. zyxwvutsrqponml B. zyxwv Goldberg, H. R. Crowe, and R. W. Franck Peri Interactions in the 1,3,6,8-Tetra-terf-butyl- and 1,3,8-Tri-tert-butylnaphthalene Anions. An Electron Spin Resonance Study Ira zyxwvutsrq B. Goidberg," Harry R. Crowe zyxwvuts Science Center, Rockweil International, Thousand Oaks, California 9 1360 and Richard W. Franck Chemistry Department, Fordham University, New York, New York 10458 (ReceivedJanuary 20, 1975) Publication costs assisted by Rockwell International The radical anions of 1,3,8-tri-tert-butylnaphthalene and 1,3,6,8-tetra-tert-butylnaphthalene in dime- thoxyethane were studied by electron spin resonance. Proton and carbon-13 hyperfine splittings and the g factors show a significant deviation from those of sterically noninteracting alkyl-substituted naphthalenes. These data were used to estimate that the 1 and 8 positions are displaced from the average molecular plane by about 20-25' due to steric interaction between the tert-butyl groups in the peri positions. No structural assignment could be made concerning the orientation of the tert- butyl groups which are also restricted from free rotation. Preliminary results of ion pairing between Na+ or K+ ions suggest that the cation oscil- lates from above to below the average plane of the naphthalene. Introduction The synthesis of naphthalene substituted in the 1 and 8' positions by tertiary butyl groups was recently rep0rted.l Structures of 1,8-di-tert- butylnaphthalene compounds are expected to have a geometry in which the 1 and 8 positions are forced on opposite sides of the average plane of the naphthalene as shown in Figure 1. In these molecules, the tertiary butyl groups were also found to be restricted from free rotation. Activation energies for the inversion of the 1 and zyxwvutsrqp 8 positions (to the mirror image of Figure 1) were esti- mated to be about 24 kcal/mol and the activation energy for rotation of the tert-butyl groups were determined to be 6.3 kcal/mol from NMR measurements.2 At present, there is no information on the strain angle (4) of the bonds of the 1 and 8 positions, or the lowest energy conformation of the tertiary butyl groups. Recent X-ray crystallographic studies of l&bis(dimeth- ylamin~)naphthalene,~ 1,8-di(br0momethyl)naphthalene,~ and 1,8-dinitr~naphthalene~ indicate that strain can be re- lieved by splaying apart of the substituent groups or by dis- placing the 1 and 8 positions from the plane of the naph- thalene. Both cause additional separation of the substitu- ent groups. The dominant release of strain in di(bromo- methy1)naphthalene and dinitronaphthalene occurs by splaying, while the dominant release of strain in bis(di- methy1amino)naphthalene occurs by displacement of the 1 and 8 groups. In each of these cases, the entire molecule is affected by the steric interaction at the 1 and 8 positions, but to a lesser degreee6 We report here the results of ESR investigations of anion radicals of 1,3,6,8-tetra-tert- butylnaphthalene (TB4N) and 1,3,8-tri-tert-butylnaphthalene (TB3N) in dimethoxyeth- ane (DME) solvent. These data are used to determine the angle (4) of the intersection of the planes of the 1,2 and 9 (or 7,8 and 9) carbon atoms with the mean plane of the naphthalene. The orientation of the tertiary butyl groups with respect to the axis of the 2p, orbital of the adjacent carbon atom could not be determined. In addition, prelimi- nary results of ion association of sodium and potassium with these anions are discussed. A difficulty encountered in this study is that the anion radicals generated from the 1,8-disubstituted tert-butylna- phthalenes are not stable over -30' for more than a few minutes in DME or above zyxw 0' in THF. In order to obtain the temperature dependence of the ESR spectrum of these materials, a high-resolution signal averaging technique was employed, where the time required to sweep each spectrum was much smaller than the half-life. Experimental Section The materials TB3N and TB4N were prepared as de- scribed in the 1iterature.l Anion radicals were prepared by reduction in dry purified DME with sodium or potassium. ESR spectra were recorded on a modified Varian V-4502 ESR spectrometer. Due to the instability of these radical ions, at temperatures above -30°, it was necessary to use computer control methods so that the intensity of the spec- tra did not decrease significantly during the time required to record each spectrum. This apparatus and the programs used are described el~ewhere.~ The time to scan each spec- trum was between 400 and 800 msec which required sweep rates of up to 2000 G/min. Between 32 and 256 scans were averaged each time. Molecular orbital calculations and spectrum simulations were carried out on a CDC 6600 computer. Some of the data analysis programs including line width measurements, amplitude measurements, and single and double integra- tionBof the ESR spectra were carried out on the PDP 8/m computer associated with the ESR spectrometer. Results Hyperfine splittings (hfs) of the ESR spectra of TB3N.- and TB4N.- given in Table I exhibit large deviations from corresponding hfs of the unsubstituted anion of naphtha- lene. Anion radicals of naphthalene substituted with zy tert- butyl groups in noninteracting positions exhibit proton hfs which are typically within 5 to 15% of the corresponding hfs of the anion radical of unsubstituted na~htha1ene.l~ The Journal of Physical Chemistry, Vol, zyxwvutsrqp 79, No. 16, 1975