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Effects of methyl substituents on the proton chemical shifts in the NMR spectra of the twenty methyl and ethyl substituted hydrazines. Electronegativity values for hydrazyl groups
Author(s) -
Condon F. E.
Publication year - 1974
Publication title -
organic magnetic resonance
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.483
H-Index - 72
eISSN - 1097-458X
pISSN - 0030-4921
DOI - 10.1002/mrc.1270061002
Subject(s) - electronegativity , chemistry , chemical shift , substituent , alkyl , hydrogen , proton , methyl group , hydrogen bond , medicinal chemistry , proton nmr , stereochemistry , organic chemistry , molecule , physics , quantum mechanics
The CH proton NMR spectra of the twenty conceivable methyl and ethyl substituted hydrazines are presented and analyzed with respect to effects on chemical shifts of the CH protons caused by replacement of hydrogen by methyl and ethyl groups on the CNNC chain. Thirteen different methyl substituent effects and six different ethyl substituent effects are identified and evaluated. Most of the effects are shielding and in accordance with an electron‐releasing inductive effect of alkyl groups. A deshielding effect (the ‘CC bond effect’) is observed when a methyl group replaces the hydrogen on the carbon bearing the hydrogen in focus and primary hydrogen on the carbon bearing the hydrogen in focus and primary hydrogens become secondary, as observed in other systems. On the basis of their effects on the chemical shifts of methyl protons in CH 3 X, eighteen different hydrazyl groups (× = NR 1 NR 2 R 3 ) fall into three classes: I (R 1 = H; R 2 , R 3 = H or alkyl); II (R 1 = alkyl; R 2 and/or R 3 = H); III (R 1 , R 2 and R 3 = alkyl), with slightly different electronegativities: 2·94, 2·83 and 2·74, respectively.