Strained heterocyclic systems. II. Acenaphtho[1,2-]quinoline

Strained heterocyclic systems. VI. Basicities of some quinoxalines

“…It has recently been established that a fused strained ring adjacent to the nitrogen atom in a quinoline ring causes a marked decrease in the basicity of such heterocyclic compounds.2-4 These observations are in accord with the concept of orbital rehybridization developed by Streitwieser and coworkers to account for the changes in kinetic acidity and reactivity toward electrophilic substitution observed With strained carbocyclic systems.8 This interpretation has gained support from a variety of studies: J (18C-H) nmr data,6•7 esr data,8•9 rates of protodesilylation,10 polarographie reduction potentials,11 and molecular orbital calculations. 12 In our earlier studies of 1,2-dihydrocyclobuta [b ]quinoline (1) and acenaphtho [1,[2][3][4][5][6]quinoline (2) decreases in basicity of ten-and fivefold, respectively, were observed relative to model compounds. Since there is greater strain in biphenylene than in benzocyclobutene,13 it was anticipated that pKa data for an azabiphenylene would exhibit a further substantial decrease in basicity.…”

“…Since there is greater strain in biphenylene than in benzocyclobutene,13 it was anticipated that pKa data for an azabiphenylene would exhibit a further substantial decrease in basicity. Although no monoazabiphenylenes have been reported in the literature, the diazabiphenylene, benzo [3,4 [cyciobuta [1,[2][3][4][5][6] [quinoxaline (3), has 3 been known for some time.14 This report, therefore, presents the synthesis and basicity measurements of a series of strained quinoxaline derivatives.…”

Ring strain effects. III. Reduction and oxidation potential shifts

“…Markgraf, et al, have recently reported that the basicity of the nonbonding electrons of a nitrogen a to a fused, strained ring decreases as the strain in the ring is increased. 3 It has also been reported that the acidity of protons a to a strained ring increases as the strain is increased.4-5 We have found that the spin densities in radical anions of aromatic hydrocarbons are substantially perturbed upon the introduction of a strained ring.6-8 The changes in spin densities were readily correlated within the Hückel framework by simply making the carbon atoms a to the strained ring more electronegative as the fused ring became more strained. Finally, several articles have appeared reporting marked changes in relative reactivities of various positions in a series of hydrocarbons toward electrophilic substitution as ring strain is introduced.9- 13 Various arguments have been presented to explain these observations.5-9-10 The only explanation presented to date which accounts for the changes in chemical as well as physical properties is that of Streitwieser.5 Streitwieser's generalization rests on an orbital electronegativity argument.…”

Dipole moments of some diazaarenes

“…In Table I are presented data for pyridine, quinoline, and 1-3. Previous reports from this laboratory have established that strained rings fused adjacent to the nitrogen atom decrease the basicity of heterocycles (10)(11)(12), but do not significantly affect the dipole moment (/). Although the data for 1-3 are broadly consistent with these relationships, the larger value for 2 prompts two observations.…”

“…Diffusivities were measured by the laminar-jet technique. The experimental setup was similar to the apparatus described by Scriven and Pigford (11). The laminar-jet chamber consists of a 36 cm long, 4 cm i.d.…”