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Ring‐chain tautomerism of aldehyde n‐methylated semicarbazones
Author(s) -
Uda Masayuki,
Kubota Seiju
Publication year - 1978
Publication title -
journal of heterocyclic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.321
H-Index - 59
eISSN - 1943-5193
pISSN - 0022-152X
DOI - 10.1002/jhet.5570150519
Subject(s) - chemistry , tautomer , aldehyde , ring (chemistry) , steric effects , benzaldehyde , semicarbazide , medicinal chemistry , stereochemistry , carbon atom , nitrogen atom , organic chemistry , catalysis
Ring‐chain tautomerism of thirty‐six aldehyde semicarbazones was studied by nmr spectro‐scopy. The 2,4‐dimethylsemicarbazones of benzaldehyde, p ‐tolualdehyde, p ‐anisaldehyde, and P ‐chlorobenzaldehyde exist as chain forms in DMSO‐d 6 , but as both ring and chain forms in deuteriotriiluoroacetic acid. Unlike these semicarbazones, the aldehyde semicarbazones of N ‐unsubstituted semicarbazide, 2‐methylsemicarbazide, and 4‐methylsemicarbazide did not cyclo‐isomerize in either DMSO‐ d 6 or deuteriotrifluoroacetic acid. These results indicate that protona‐tion of the C=N nitrogen atom and steric hindrance of the 2‐methyl group with an aromatic group at the C=N carbon atom in the chain form cause cycloisomerization to ring isomers.