✍ Scribed by Torbjörn Drakenberg; Jan Sandström; José Seita
No coin nor oath required. For personal study only.
Proton‐coupled and noise‐decoupled ^13^C NMR spectra of 1‐azulenecarbaldehyde, 1‐acetylazulene and 1,3‐azulenedicarbaldehyde have been studied, and complete assignments have been made based on the ^13^C^1^H coupling constants, additivity of substituent effects (SIS), and previous assignment for the parent hydrocarbon. The barriers to rotation of the aldehyde group in the above azulenecarbaldehydes and in some naphthaldehydes have been determined by ^13^C dynamic NMR, (DNMR), resulting in free energies of activation of 42.7, 26.8 and 34.4 kJ mol^−1^ for 1‐azulenecarbaldehyde, 1‐naphthaldehyde and 2‐naphthaldehyde respectively. The same order of barriers is obtained by CNDO/2 calculations. A 4‐methoxy substituent in 1‐naphthaldehyde and a 6‐methoxy substituent in 2‐naphthaldehyde increases the rotational barrier by 4.6 and 2.9 kJ mol^−1^, respectively, whereas a 3‐methoxy substituent in 2‐naphthaldehyde reduces the barrier by 6.7 kJ mol^−1^. The conformations of the dominant rotamers are deduced from ^13^C chemical shifts to be Z for 1‐azulenecarbaldehyde and 1‐naphthaldehyde, and E for 2‐naphthaldehyde.
📜 SIMILAR VOLUMES
## Abstract The ^13^C NMR spectra of several 2‐substituted imidazoles and benzimidazoles have been measured. The substituent was CH~3~, COOH and CONHR, where R = H, __n__‐Bu, __p__‐tolyl or __m__‐chlorophenyl. Carbons 4 and 5 in the imidazoles and the carbon pairs 8/9, 4/7 and 5/6 become equivalent
## Abstract The rotational barrier in the __N__,__N__‐dimethylamide group is studied by proton NMR for __N__,__N__‐dimethylnicotinamide and two quaternary salts in aqueous solution. The carbon‐13 NMR spectra of a number of aromatic __N__,__N__‐dimethylamides are discussed. A roughly linear correlat