The optical rotatory dispersion and circular dichroism of azomethinies

Bonnett, Raymond

doi:10.1002/9780470771204.ch4

Cited by 5 publications

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General and theoretical aspects

Treinin

1971

PATAI'S Chemistry of Functional Groups

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Orbitals . 1. Slater-type atomic orbitals 2. Gaussian lobe functions representation G. Other than LCAO Methods . H. Conclusion . IV. REFERENCES . . . F. LCAO Self-consistent Field (Hartrec-Fock) Molecular . 44 45 45 47 48 48 50 50 52 52 c For discussion of the elFcctive radius of Ns7 in crystals see scction 1I.A.f For discussion of the chargc-transfer-to-solvent spectrum of h'c scc scction 1I.G. 9 The electroncgativity of N, is bctwecn that of Br a n d I (2.5). Thc h~lulliken scale is used herea. h En = E" + 2.60, where Eo is the clcctrodc potential; scc J. 0. Edwards, J. Am. Chcnr. SOL, 76, 1540 (1954). 4A. Treinin also capable of conjugation through their non-bonding electrons and thus can act as electron-donors, i.e. they exert a positive resonance efect ( -I-R). When this m-interaction is strong the pseudohalide group may become colinear with the atom to which it is bound6. This resonance effect is responsible for the effect of the azido group on a benzene ring, its ortho-para orienting character and its activating influence on electrophilic substitutbn. A significant difference between halides and pseudohalides lies in the 'unsaturation' of the latter; they contain low-lying, unfilled 7r orbitals which can accept electrons. This puts them higher than halides in the spectrochemical seriesfo.The reducing power of the halide and pseudohalide ions increases in the following orderff: F-, NCO-, C1-, Ng, Br-, SCN-, I-. In this and other respects the azido group shows close resemb!ance to bromine ( Table 1). The data recorded in Table 1 describe the behaviour of the azido group in its equilibrium nuclear configuration. However the main interest in this group lies in those properties which depend on changes in its geometry, its bending to form cyclic compounds7 and its dissociation to -N +N,. Obviously this has no parallel in the halogen series. B. Electronic Structure (Simplified Model)The general shape of covalent azides is shown in Figure 1. X I t L FIGURE I . The geometry of covalent azidcs (L is the atom to which N, is bound; all the nuclei lie in the xz plane).As late as 1944 azides were considered to have the classical structure RN=NdV, namely with pentavalent nitrogen ,l. This picture has been completely abandoned as it is now generally accepted that nitro-1. General and theoretical aspects 5 gen obeys the octet rule. keeping with the octet rule and the ' adjacent charge rule' 22 : One can write two canonical structures in Resonance of I and 11, with equal contributions, leads to bond order 1.5 and 2-5 for the bonds N,-N, and Nb-N, respectively, in agreement with the values derived from force constants (section 1I.E). The formal charges on N,, Nb and N, corresponding to the resonance hybrid 1-11 are -0.5, + 1 and -0-5 respectively. In both structures * For a recent discussion of hybridization and valence states of nitrogen see reference 27. General and theoretical aspects* Not to be confused with 'self-consistcnt-ficld'. t In this case the total energy of the T system is smaller than the sum of the orbital en...

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General and theoretical aspects

Treinin

1971

PATAI'S Chemistry of Functional Groups

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Diastereoselektive thermische oder säurekatalysierte Umlagerung von N,N′S‐Dibenzyliden‐1,2‐cyclopropandiaminen in cis‐2,3‐Diaryl‐2,3‐dihydro‐1H‐1,4‐diazepine

1983

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Aus den trans-l,2-Cyclopropandiaminen t4 und t5 und aromatischen Aldehyden erhalt man die frons-N,N'-Dibenzyliden-l,2-~ycIopropandiamine t l a -g bzw. t6a, b. Dagegen lassen sich bei der Umsetzung aromatischer Aldehyde mit den cis-l,2-Cyclopropandiaminen c 4 und c5 nur die cis-N,N'-Disalicyliden-l,2-~yclopropandiamine c l b bzw. c6 b isolieren. In den anderen Fallen isomerisieren sich die intermediaren cis-Bisimine in situ zu den cis-2,3-Diaryl-2,3-dihydro-lH-l,4-diazepinen c3a-d bzw. 7a. Die isolierten Bisimine t1a.c-e,g und c6b,t6a lassen sich in [D5]Brombenzol erst bei 90°C. in der Schmelze oberhalb 120"C, in die entsprechenden Dihydrodiazepine c3a, c -e,g bzw. -diazepinesThe truns-N,N'-dibenzylidene-l,2-~yclopropanediamines t 1 a -g and 16a, b are obtained in the reaction of the fruns-l,2-~yclopropanediamines 14 and 15, respectively, with aromatic aldehydes. In contrast, only the cis-N,N'-disalicyIidene-l,2-~yclopropanediamines c l b and c6b can be isolated when the aromatic aldehydes are allowed to react with the cis-l,2-cyclopropanediamines c4 and c5, respectively. In the other cases, the intermediate cis-bisimines isomerize in situ to yield the cis-2,3-diaryl-2,3-dihydro-lH-i J-diazepines c3a -d and 7a, respectively. In [DJbromobenzene solution, the isolated bisimines t l a , c-e, g and c6b. t6a rearrange above 90°C to give the corresponding dihydrodiazepines c3a. c-e. g and 7a, b. in the neat, molten state above 120°C. Surprisingly, in acetate-buffered methanol solution the dihydrodiazepines c3a, d, are also formed in the reaction of truns-l,2-cyclopropanediammonium bromide (14.2 HBr) with aldehydes at 0 Verlag Chemie GmbH, D

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