3- Methyl-3//-azepine, ring inversion

Apparently, the 1H NMR spectra of 1 //-azepines are invariant over substantial temperature ranges.61 However, temperature dependence has been noted69 in the 13CNMR spectra of some 1 -acyl-1 //-azepines, and is attributed to hindered rotation about the N-CO bond rather than to ring-inversion phenomena AG free enthalpies of activation for hindered rotation of 62-66 kJ moP1 have been calculated. E/Z-rotamcr ratios for l-aroyl-l//-azepines have been assessed and show a slight preference for the -rotamer 22 however, an X-ray structural analysis of l-(4-bromobenzoyl)-2-methyl-3.5,7-triphenyl-l//-azepine demonstrates that in the crystal state it is exclusively in the E configuration.22... 

Fully unsaturated seven-membered heterocyclics have alternating bond lengths and are normally in boat conformations. Ring inversion barriers are 42.7 kJ mol-1 for 3-methyl-3ff-azepine and 35.6 kJ mol-1 for 3//-azepin-2-one (CHEC 5.16.2.3). The barriers for oxepin and thiepin are somewhat lower. Annulation can introduce large conformational barriers, to the extent of making possible the resolution into enantiomers of a tribenzoxepin (71CB2923). 

H-Azepine, 2-(o-hydroxyphenyl)-synthesis, 7, 538 3H-Azepine, methyl- H NMR, 7, 495 3H-Azepine, 3-methyl-ring inversion barrier, 7, 14 3H-Azepine, 2-methylene-isomerization, 7, 505 3H-Azepine, 7-(N-phthalimido) synthesis, 7, 538 4H-Azepine, 4,5-dihydro-cyclization, 7, 524... 

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