780. Interaction of polynitro-compounds with aromatic hydrocarbons and bases. Part XI. A new method for determining the association constants for certain interactions between nitro-compounds and bases in solution

Po CHEONG WONG and DONALD R. ARNOLD. Can. J. Chem. 59,982 (1981). In paper number 111 of this series (2) ab initio and PCILO molecular orbital calculations for the four x-x* charge-transfer (ct) complexes formed between maleonitrile (MN) and fumaronitrile (FN), and cis (CS) and trans-l,2-dimethoxyethylene (TR) were reported. This paper reports the ct transition absorption characteristics and association constants of these complexes as a function of temperature. From this data the heats of formation of the complexes are determined and these experimental results are then compared with the theoretical values; good agreement is obtained. The order of complex stability (-A@ (kcal mol)) measured in chloroform solution is: MN-TR (0.55)< FN-TR (0.65) < MN-CS (0.78) < FN-CS (1.25).We reach the conclusion that, for these complexes, orientation effects of the substituents are quite small in magnitude and that the dominant factor influencing complex stability follows the redox potential difference. The structures of the complexes are discussed in view of these results.Po CHEONG WONG et DONALD R. ARNOLD. Can. J. Chem. 59,982 (1981). Dans la troisieme publication de cette serie (2) Nous avons conclu dans le cas de ces complexes que les effets d'orientation des substituants sont negligeables et que le facteur principal influen~ant la stabilitt du complexe suit la difference de potentiel redox. On discute de la structure de ces complexes ? i la lumiere de ces rtsultats.[Traduit par le journal] IntroductionWe have recently reported a potentially useful photochromic system based upon the irradiation of charge-transfer (ct) complexes of olefins in solution (1). For example, the ct absorption band of the trans-stilbene -fumaronitrile (t-ST-FN) complex extends out to longer wavelengths than the ct absorption band of the cis-stilbene -fumaronitrile (c-ST-FN) complex. Irradiation of the t-ST-FN complex results in up to an 86% enrichment in cis-stilbene (la). The position and absorption intensity of the ct absorption band is related to the strength of the complex. For structurally similar compounds, Mulliken has demonstrated that the strength of the complex depends mainly on the ionization potential (or oxidation potential Ey,", (D)) of the donor and electron affinity (or reduction potential E;$ (A)) of the acceptor. Therefore, the differences in the ct equilibrium constants (K) between the t-ST-FN complex and the c-ST-FN complex can be explained in terms of the difference between Ep;, (D) of c and t-ST. However, the

Section: Molecular Orbital Calculationsmentioning

confidence: 99%

Photochemical reactions of charge-transfer complexes. IV. The orientation effects of charge-transfer complexes: theory and experiment

Wong¹,

Arnold²

1981

“…( 9 ) , corrected by a least-squares procedure and also by the Rose and Drago method (10). The details of these equations and their significance for evaluation of K and E have been discussed in a previous report (1).…”

Section: A4etllodsmentioning

confidence: 99%

Donor–acceptor interactions in biomolecules. II. Spectroscopic and molecular orbital studies of amino acid – nicotinamide adenine dinucleotide complexes

Nagchaudhuri¹,

Suri²

1976

JAYANTI NAGCHAUDHURI and RASHMI SURI. Can. J. Chern. 54, 59 (1976).The nature of complex formation between aromatic amino acids and some of their components with NADi (nicotinamide adenine dinucleotide) have been studied by spectropliotometric methods. A comparison of the stability of these complexes with that of the complexes of the same donors with a model compound of NAD+ i.e. N-metl~yl-3-carboxamide pyridinium chloride (MCP) has been carried out by examining the type of complexes formed and their geometry. Simple molecular orbital calculations have been done to determine the quantity of charge transfer 6Q and stabilization energy 6E and to show the significance of mutual orientation of donor and acceptor in determining the stability. The enhanced stability of tryptophanNADi complex in comparison to indole-NADi complex Iias also been explained.

“…Solutions were made up and measured as described previously (3,12) with a n Optica CF4 spectrophotometer. 'The spectra of complexes referred to in Fig.…”

Section: E S P E R I M E N T a L Annlyticalmentioning

confidence: 99%

Charge-Transfer Complexes of Biphenylene

Emslie¹,

Foster²,

Pickles³

1966

Self Cite

An attempt has been made to redetermine the enthalpy and entropy of formation of the charge-transfer complex bet\veen tetracyanoethylene and biphenylene in dichloromethane solution from measurements of the equilibrium constant a t different temperatures. T h e results obtained under conditions where biphenylene is in excess differ from those previously published in which tetracyanoethylene was in excess. I t is argued that the optimum condition for determining equilibrium constants of a 1 : l cornplex is when the reactants are mixed in solution in this ratio. Determinations under this condition yield A H = -2.6 ltcal mole-' and AS = -4.1 e.u.'The energies of the irltermolec~~lar charge-transfer transitions of biphenylene with several different acceptors suggest that the ionization potential of biphenylene is -7.4 eV. K, was calculated on the assumption that E is temperature independent. From van't I-Ioff plots, A H = -2.8 kcal mole-' and A S = -1.0 e.u., the pure complex being used as the standard state. An attenlpt has been made to redetermine these constants by using the condition For personal use only.