The N1s ESCA Spectrum of Protonated 1,8‐Bis‐(Dimethylamino) Naphthalene (“proton sponge”)

Abstract

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,

Localization of hydrogen bond deuterons in proton sponges by dipolar solid state 15N NMR spectroscopy

“…Assuming a harmonic deuteron motion we calculate the average from the dipolar coupling constants obtained, using Eq. (2). These values are consistent with the crystallographic values.…”

“…For the most prominent system, i.e. 1, 8-bis(dirnethylamino) naphthalene-H+ (DMANH+, Scheme 1) two non-equivalent nitrogen atoms were observed by ESCA-spectroscopy in the gas phase [2]. This asymmetry is supported by ab initio uantum chemical calculations [3].…”

Naphthalene 'proton sponges'

“…According to Hasselbach et al, 105 neither NMR nor X-ray diffraction analysis can give an unequivocal answer to the question about the IHB symmetry in the `proton sponge' cation. This can be done only with the help of `faster' methods, such as electron spectroscopy for chemical analysis (ESCA).…”

Proton transfer from intramolecularly hydrogen-bonded acids

“…Hydrogen isotope effects on the chemical shift indicate that the proton is located in a double minimum potential well14 and the ESCA spectrum shows that the hydrogen bond is unsymmetrical. 15 It is unlikely that the hydrogen bond alone could lead to the enhanced basicities that are observed. Destabilization of the amines by steric interactions between the nitrogen lone pairs and between the alkyl substituents may also contribute.…”