17573. Die relative Luftfeuchtigkeit, berechnet nach der Formel (3), weicht z. T. ganz erheblich von den drei anderen Grossen ab, besonders wenn der Gesamtdruck sich dem Teildruck des Wasserdampfes nahert (fur reinen Wasserdampf hat sie naturlich keinen Sinn). Von der Benutzung dieser Grosse in Sorptionsmessungen wird daher abgeraten.4. Der relative Wasserdampfdruck, die Aktivitat des Wassers und die relative Partialdichte des Wasserdampfes konnen in Sorptionsmessungen abwechslungsweise benutzt werden, wenn ein Fehler der obengenannten Grossenordnung ausser acht gelassen werden kann. Sonst wird die ausschliessliche Benutzung des relativen Wasserdampfdruckes empfohlen.bin ich fur die vielen Anregungen wahrcnd des Entstehens dieser Arbeit zu Dank verpflichtet. Die Arbeit wurde durch einen Forschungskredit derSummary. The ESCA spectrum of protonatcd 1, S-bis-(dimethy1amino)naphthalene ("proton sponge") (I) has been recorded in the region of Nls binding energies. The results indicate that IH+ possesses an znnsymmetricul N--H. .. N hydrogen bridge.The remarkable basicity of 1, 8-his-(dimethylaminojnaphthalene (I) has been attributed to relief of steric strain upon protonation [l]. Evidence for a reduction of the severe hindrance of the N-methyl groups in (I) by rotating the -N(CH,), groups out of their optimal conjugating position has been obtained by NMR-studies [l] of I as well as by ESR-studies [a] of its radical anion. However, this distortion alone would lead to an unfavorable N-lone pair interaction, which can be rationalized on the basis of Pauli's principle [ 3 ] . Reduction of this destabilizing effect could be achieved by increasing the N -. . N distance. An X-ray cristallographic analysis of I [4] has indicated that the nitrogen atoms of the rotated -N(CH,), groups are situated -0.42 A above and below the naphthalene ring plane, which results in an N * . . N distance of -2.6 A or -0.15 k larger than that expected for a structure with parallel Car-N bonds. Clearly, protonation of I will favorably decrease the lone pair interaction,
The electrostatic potential (EP.) for aceheptylene (I) is calculated using a b -i d i o wavefunctions. I n addition, the EP. around I is approximated by a monopolc cxpression, using wavefunctions from various semiempirical procedures as a basis. It is found that the prcviously noted discrepancy between the theoretical prediction of differential nuclophilicity of the individual unsaturated C-atoms in 3,5,8,10-tetramethyl-accheptylene(II) and the experimental results of protonation is removed, if instead of local atomic charges, the EP. around 11, approximated by that of I is considered.
Publication costs assisted by the National Science FoundationThe previously described technique has been used in thermodynamic studies of disproportionation of radical anions of perylene and tetracene. The pertinent heats and entropies of disproportionation were determined for the Li' , Na+, K+, and Cs+ salts in tetrahydrofuran (THF) and in dimethoxyethane (DME). The peculiar behavior of the sodium salts in THF was confirmed and attributed to the desolvation of Na+ ions which retain their solvation in the radical-anion-cation pairs, but lose it on aggregation with dianions. In DME both the sodium and the potassium salts behave like the sodium salt in THF. The higher solvating power of the bidentate DME allows even the K+ ion to retain its solvation shell in the pair but not in the dianion aggregate. The above technique was applied in thermodynamic studies of electron transfer process, sodium trans-stilbenide + anthracene F! trans-stilbene + sodium anthracenide. Heat and entropy of this reaction were determined.A simple technique described' in a previous publication from this laboratory allows us to study thermodynamics of disproportionation of radical anions and the effect of cations on the respective AH"'s and AS"'s. The effect of cation's nature on AS" is particularly illuminating and thought provoking.This work was expanded now to two systems, perylene and tetracene in two solvents tetrahydrofuran and dimethoxyethane. The results and their interpretation are reported in this communication. They refer to reactions described by the equation Experimental SectionThe details of the technique used in this investigation are given in the earlier publication.' In essence, it is a potentiometric technique. One measures the potential difference between two electrodes, one immersed in a 50:50 solution of the parent hydrocarbon and its radical anion and the other in a 50:50 solution of the radical anion and its dianion. Bulbs containing these solutions are linked through a liquid junction and the whole unit is placed in a thermostat that allows one to vary up and down the temperature from -55 to -25 "C. The potential difference between the electrodes is measured with voltmeter of infinite resistance, its scale allowing us to read its value to 0.1 mV. The resistance of the apparatus is in the range of 50 Mohm. The measured potential is reproducible; the same reading is recorded when after changing the temperature we return to its original value. Moreover, the potential remains constant a t any fixed temperature a t least for 1 h.The purification of tetrahydrofuran (THF) and dimethoxyethane (DME) was performed on a high-vacuum line using the procedure2 well known by now. Perylene, tetracene, anthracene, and trans-stilbene acquired from Aldrich Co. were crystallized and vacuum sublimed before being used. Alkali metals (mirrors for Na, K, and Cs) were used as reducing agents.The solutions of radical-anion pairs or dianion aggregates were kept a t concentrations of lo-* to M. The fraction of free radical anions in those solutio...
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