Concerning the Conformation of Isolated Benzylideneaniline

Abstract

IX. 75)Sumvnavy. From PE.-spectroscopical studies the torsional angle p, of the N-phcnyl ring in isolated benzylideneaniline 1 has been found t o be dcfinitely srnallcr than p, = 90'. An approximate value q~ = 36" has been estimated which is e w n sniallcr than t h e one observed in the crystal (p, = 55") and suggested to prevail also in solutions of 1. 11 reevaluation of the gas phase optical spectrum of isolated 1 supports a torsional angle similar to that found in the other phases.Calculations of the most stable conformation of 1 as \re11 as of stilbene and azobenzene by the MINDO/3-tcchnique lead to torsional angles p, = 90" for both phenyl rings in all cases. These results are at variance with the experimental results ant1 suggcst t?iat MiND0/3-like its less advanced precursor MINDO/2 or likc CND0/2-is unreliable lor low cncrgy 12rocesscs involving rotation of n-systems connected by esscntial singlc bonds.I t is concluded that the n-energy of benzylideneaniline, likc that of stilhenti or azobenzene, \\auld favor a planar conformation. The increased torsional aiiglc: in 1 as compared to thc other two iso-conjugatc systems arises from a larger steric interaction between phenyland bridgcprotons.Introduction. -Crystalline benzylideneaniline (1) exhibitsin contrast to its iso-electronic and essentially planar analogues trans-stilbene (2) ~ 21 and tvans-azobenzene (3) [3] -an angle of twist cp = 5.5' of the S-plienyl-ring about the C-N essential single bond [4]. This deviation from planarity was already postulated on the basis of the marked differences between the optical spectra of 1 arid 2 or 3 [5] and by the resemblance of the optical absorption spectrum of 4, wliere planarity is enforced by bridging, to those of 2 and 3 [6]. That the angle of twist for 1 in solution is not too different from that in the solid is suggested by the similarity between its solution and its crystal reflectance spectrum i7]. A recent illuminating study employing deri\.atives of 1 and of the planar reference system 4 has indicated that the angle of twist varies markedly for different substituents in tlie $,$'-positions, 91 rn 0" being presumably realized for 'push-pull' substitution wliicli increases tlie bond order of the relevant C S p 2 --N s p~ bond ~ 81. -~~ -

Preparation and fate of carbon monosulfide (CS). Ultraviolet photoelectron spectroscopic study of the thermolysis of 5,5-dimethyl-1-phenyl-Δ3-1,3,4-triazoline-2-thione

“…l a shows 18.73 eV) are the major volatile products from the gas phase thermolysis of 1 that pass through the -100°C trap. A small quantity of CS is indicated by the weak band at 11.28 + 0.05 eV (13).…”

“…As usual, the a, MO remains unperturbed since there is a node at the point of substitution and the b, MO is destabilized. The bands at 10.04 and 10.57 eV we assign to the C=N .rr MO and the nitrogen lone pair, respectively, on the basis of a comparison with other alkylidene alkyl and aryl amines (17,18) and isoelectronic styrenes (19). This ordering could be reversed depending on the magnitude of the torsional angle about the phenyl-nitrogen single bond which determines the magnitude of the n-n separation (17).…”

Photoelectron spectroscopy of biologically active molecules. XVI. Benzophenone derivatives

“…As indicated by PE spectra of the series benzaldehyde [ 151, N-benzylidenemethylamine [21] and styrene [22] (Fig. 3), the splitting of the benzene elg orbitals amounts to 0.3, 0.7, and 0.8 eV, respectively.…”

The π-molecular complexes trans-azobenzene–(sym-trinitrobenezene)2 and N-benzylideneaniline–(sym-trinitrobenzene)2

“…Interest in this compound arose from its anomalous solution spectral properties compared with its isoelectronic analogues trans-azobenzene (AB) and trans-stilbene (S) (Jaffe, Yeh & Gardiner, 1958;Wiegand & Merkel, 1942). Through a wide variety of experimental and theoretical investigations the dissimilarity in spectral response has been shown to be due to conformational differences, AB and S being essentially planar, while BA is non-planar (Bally, Haselbach, Lanyiova, Marschner & Rossi, 1976, and references therein; Eckhardt & * In partial fulfilment of the requirements for the PhD degree, Ben-Gurion University of the Negev.…”