Three adjacent ring hydrogen atoms

A preliminary study of the acridone alkaloids of the roots of Boenninghausenia albiflora resulted in the identification of 1-hydroxy-N-methylacridone (41 R = Me) now the Ruta alkaloid rutacridone (42) (c/. Vol. 8, p. 84) and noracrony-cine (43) have been isolated from this species. Of two new alkaloids obtained from B. albiflora, one was shown to be 1-hydroxyacridone (41 R = H) by methylation to (41 R = Me). The n.m.r. spectrum of the other new alkaloid suggested that it was a dihydroxy-N-methyl-acridone in which ring B contained a 1-hydroxy-group and three adjacent aromatic hydrogen atoms structure (44) was proposed. 

The structures of PMs are trimeric, consisting of three molecules of PS and two molecules of methylamine that are condensed together (Table 9.5). In the structures of PMs, however, the bonds created by the condensation lack adjacent hydrogen atoms, making the connectivity assignment in 1H-NMR studies virtually impossible (see the 9-membered rings in Fig. 9.11). To circumvent this problem, a model compound of panal, K-l, having 13C-labeles at the C12 and C13 positions, has been synthesized at Kishi s laboratory (Harvard University) to make a model compound of PM (Stojanovic, 1995). 

Carbonium Ions as Reaction Intermediates.—The properties of electron-deficient substances may be expected to be of great importance in the theory of chemical reactions. For example, a positively charged (and hence electron-deficient) carbon atom in a complex carbonium ion would be expected to cause adjacent atoms to increase their ligancies, as by the formation of a three-membered ring and by the use of bridging hydrogen atoms. The analysis of the mechanisms of chemical reactions may in the course of time permit much more precise principles to be formulated than are now at hand. 

In the spectra of a-substituted naphthalenes, the bands for the isolated hydrogen and the two adjacent hydrogen atoms of /3-naphthalenes are replaced by a band for three adjacent hydrogen atoms. This band is near 810-785 cm 1. Additional bands may appear because of ring bending vibrations (see Table 2.3). The position of absorption bands for more highly substituted naphthalenes and other polynuclear aromatics are summarized by Colthup et al. (1990) and by Conley (1972). 

BINAP is one of a small number of molecules that is chiral even though it has no tetrahedral stereogenic centers. Its shape makes it a chiral molecule. The two naphthalene rings of the BINAP molecule are oriented at almost 90° to each other to minimize steric interactions between the hydrogen atoms on adjacent rings. This rigid three-dimensional shape makes BINAP non-superimposable on its mirror image, and thus it is a chiral compound. 

Cyclopropylmethyl radicals 2 are readily generated by abstraction of hydrogen atoms from sites adjacent to three-membered rings (a-hydrogens) in alkylcyclopropanes 1. 

The IR spectra of thienopyridines are apparently unremarkable, since no detailed discussion of them has appeared. In the [cj-fused systems the two adjacent hydrogen atoms and the isolated hydrogen atom of the pyridine ring give rise to out-of-plane deformation absorptions near 820 and 890 cm-1, respectively,48 and in thieno[3,4-6]pyridine it is reported that the three vicinal hydrogen atoms give bands at 775 and 800 cm-1.40... 

---